Endoscopic and interstitial Nd:YAG laser therapy to control duodenal and periampullary carcinoma

NASA Astrophysics Data System (ADS)

Barr, Hugh; Fowler, Aiden L.

1996-12-01

Duodenal and periampullary cancer present with jaundice, bleeding and obstruction. Many patients are unsuitable for radical surgery. Endoscopic palliation of jaundice can be achieved using endoscopic sphincterotomy or stent insertion. However, the problems of bleeding and obstruction can be difficult to manage. Ten patients were treated using superficial Nd:YAG laser ablation and lower power interstitial laser therapy. After initial outpatient endoscopic therapy, treatment was repeated at 4 monthly intervals to prevent recurrent symptoms. Bleeding was controlled in all patients and only one patient developed obstructive symptoms between treatment sessions. This responded to further endoscopic laser therapy. The median survival was 21 months. Laser treated patients were compared with a historical series of 22 patients treated with endoscopic sphincterotomy or stent insertion. The complication rate was less in patients treated with the laser.

Interstitial laser photochemotherapy with new anthrapyrazole drugs for the treatment of xenograft tumors.

PubMed

Paiva, M B; Saxton, R E; Letts, G A; Chung, P S; Soudant, J; Vanderwerf, Q; Castro, D J

1995-10-01

Photodynamic therapy (PDT) with lasers and new dyes has gained popularity in recent years as a minimally invasive technique with high tumoricidal effects in vitro and in some cancer patients. However, because new laser dyes are not FDA approved at present, the clinical evaluation of PDT may be years away. During the past 6 years we have used laser alone for photothermal ablation in both preclinical studies and in a large number of patients with an observed 60% tumor response rate. The 40% treatment failure led us to explore the possibility of combined therapy with lasers and standard chemotherapeutic drugs. We have recently tested a promising preclinical alternative using implantation of a bare 600-microns KTP 532 laser fiberoptic in multiple tumor sites 30 min after intratumor injection of the anthrapyrazole DUP-941. As a control, this drug was injected in 3 sites of P3 human squamous cell tumor transplants in nude mice, which led to tumor stasis without regression. Similar 400-600 mm3 tumors exposed to laser illumination alone (0.8 W for 5 sec) at multiple sites resulted in tumor regrowth after 10 weeks in 80% of the animals. However, combining interstitial laser illumination with intratumor DUP-941 injections led to complete tumor regression in 85% of the mice. We propose that intratumor drug injection followed by interstitial laser fiberoptic treatment represents a potentially useful new method for tumor ablation in advanced cancer patients.

Diffusion and interactions of interstitials in hard-sphere interstitial solid solutions

NASA Astrophysics Data System (ADS)

van der Meer, Berend; Lathouwers, Emma; Smallenburg, Frank; Filion, Laura

2017-12-01

Using computer simulations, we study the dynamics and interactions of interstitial particles in hard-sphere interstitial solid solutions. We calculate the free-energy barriers associated with their diffusion for a range of size ratios and densities. By applying classical transition state theory to these free-energy barriers, we predict the diffusion coefficients, which we find to be in good agreement with diffusion coefficients as measured using event-driven molecular dynamics simulations. These results highlight that transition state theory can capture the interstitial dynamics in the hard-sphere model system. Additionally, we quantify the interactions between the interstitials. We find that, apart from excluded volume interactions, the interstitial-interstitial interactions are almost ideal in our system. Lastly, we show that the interstitial diffusivity can be inferred from the large-particle fluctuations alone, thus providing an empirical relationship between the large-particle fluctuations and the interstitial diffusivity.

Comparison of laser- and RF-based interstitial coagulation systems for the treatment of liver tumors (Invited Paper)

NASA Astrophysics Data System (ADS)

de Jager, Arjan A.; van Trier, Bart N.; Veenendaal, Liesbeth M.; van Hillegersberg, Richard; Verdaasdonk, Rudolf M.

2005-04-01

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world. Surgical treatments, including hepatic resection and liver transplantation are considered as the most effective treatment of HCC. However, less than 20% of HCC patients can be treated surgically because of: multi-focal diseases, proximity of tumor to key vascular or biliary structures and inadequate functional hepatic reserve related coexistent cirrhosis. In this unfortunate groups of patients various palliative treatments modalities are being performed to extend the time of survival and quality of life. These techniques include trans-catheter arterial chemoembolization (TACE), percutaneous ethanol injection (PEI) and Interstitial Thermal Therapy: laser-induced interstitial thermotherapy (LITT) and radio-frequency ablation (RFA).

Laser Interstitial Thermal Therapy Technology, Physics of Magnetic Resonance Imaging Thermometry, and Technical Considerations for Proper Catheter Placement During Magnetic Resonance Imaging-Guided Laser Interstitial Thermal Therapy.

PubMed

Patel, Nitesh V; Mian, Matthew; Stafford, R Jason; Nahed, Brian V; Willie, Jon T; Gross, Robert E; Danish, Shabbar F

2016-12-01

Laser-induced thermal therapy has become a powerful tool in the neurosurgical armamentarium. The physics of laser therapy are complex, but a sound understanding of this topic is clinically relevant, as many centers have incorporated it into their treatment algorithm, and educated patients are demanding consideration of its use for their disease. Laser ablation has been used for a wide array of intracranial lesions. Laser catheter placement is guided by stereotactic planning; however, as the procedure has popularized, the number of ways in which the catheter can be inserted has also increased. There are many technical nuances for laser placement, and, to date, there is not a clear understanding of whether any one technique is better than the other. In this review, we describe the basic physics of magnetic resonance-guided laser-induced thermal therapy and describe the several common techniques for accurate Visualase laser catheter placement in a stepwise fashion. MRg-LITT, magnetic resonance-guided laser-induced thermal therapyPAD, precision aiming device.

"Artificial lymphatic system": a new approach to reduce interstitial hypertension and increase blood flow, pH and pO2 in solid tumors.

PubMed

DiResta, G R; Lee, J; Healey, J H; Levchenko, A; Larson, S M; Arbit, E

2000-05-01

A mechanical drainage system, the "artificial lymphatic system" (ALS), consisting of a vacuum source and drain, is evaluated for its ability to aspirate the interstitial fluids responsible for the elevated interstitial fluid pressure (IFP) observed in solid tumors. IFP, pH, and pO2 radial profiles were measured before and after aspiration using wick-in-needle (WIN) probes, needle pH and oxygen electrodes, respectively. Laser Doppler flowmetry measured temporal changes in blood flow rate (BFR) at the tumor surface during aspiration. The WIN probe and IFP profile data were analyzed using numerical simulation and distributed mathematical models, respectively. The model parameter, P(E), reflecting central tumor IFP, was reduced from 15.3 to 5.7 mm Hg in neuroblastoma and from 13.3 to 12.1 mm Hg in Walker 256, respectively, following aspiration. The simulation demonstrated that spatial averaging inherent in WIN measurements reduced the calculated magnitude of the model parameter changes. IFP was significantly lower (p<0.05), especially in regions surrounding the drain, and BFR was significantly higher (p<0.05) following 25 and 45 min of aspiration, respectively; pH and pO2 profiles increased following aspiration. The experimental and mathematical findings suggest that ALS aspiration may be a viable way of reducing IFP and increasing BFR, pO2, and pH and should enhance solid tumor chemo and radiation therapy.

MR-guided laser-induced interstitial thermotherapy of recurrent glioblastoma multiforme: preliminary results in 16 patients.

PubMed

Schwarzmaier, Hans-Joachim; Eickmeyer, Frank; von Tempelhoff, Wernholt; Fiedler, Volkhard Ulrich; Niehoff, Hendrik; Ulrich, Slif Dagobert; Yang, Qin; Ulrich, Frank

2006-08-01

We investigated the survival after laser-induced interstitial thermotherapy in 16 patients suffering from recurrent glioblastoma multiforme. The concept underlying the intervention is the cytoreduction of the tumor tissue by local thermocoagulation. All patients received standard chemotherapy (temozolomide). The median overall survival time after the first relapse was 9.4 months, corresponding to a median overall survival time after laser irradiation of 6.9 months. During the study, however, the median survival after laser coagulation increased to 11.2 months. This survival time is substantially longer than those reported for the natural history (<5 months) or after chemotherapy (temozolomide: 5.4-7.1 months). We conclude that cytoreduction by laser irradiation might be a promising option for patients suffering from recurrent glioblastoma multiforme. In addition, the data indicate the presence of a substantial learning curve. Future work should optimize the therapeutic regimen and evaluate this treatment approach in controlled clinical trials.

Coagulative interstitial laser-induced thermotherapy of benign prostatic hyperplasia: online imaging with a T2-weighted fast spin-echo MR sequence--experience in six patients.

PubMed

Mueller-Lisse, U G; Thoma, M; Faber, S; Heuck, A F; Muschter, R; Schneede, P; Weninger, E; Hofstetter, A G; Reiser, M F

1999-02-01

To determine if hypointense lesions clearly outline on T2-weighted fast spin-echo (SE) magnetic resonance (MR) images obtained during coagulative interstitial laser-induced thermotherapy (LITT) of a prostate with benign hyperplasia. In six patients with benign prostatic hyperplasia (BPH), 12 LITT treatments were followed online with repetitive axial T2-weighted fast SE imaging (repetition time, 3,700 msec; echo time, 138 msec; acquisition time, 19 seconds). Development, time course, correlation with interstitial tissue temperature, and diameters of hypointense lesions around the laser diffusor tip were investigated. Lesion diameters on T2-weighted images acquired during LITT were compared with diameters of final lesions on T2-weighted images and unperfused lesions on enhanced T1-weighted SE images obtained at the end of therapy. Hypointense lesions developed within 20-40 seconds of LITT. Average correlation coefficients between interstitial temperature development and signal intensity development were 0.92 during LITT and 0.90 after LITT. Regression slopes were significantly steeper during LITT (0.67% signal intensity change per degree Celsius) than after LITT (0.47% per degree Celsius; P = .038). Lesions remained visible after LITT for all procedures. Average maximum diameters of lesions were 1-3 mm larger during LITT than after LITT (P = .0006-.019). Repetitive T2-weighted fast SE MR imaging during interstitial coagulative LITT of BPH demonstrates the development of permanent hypointense prostate lesions. However, posttherapeutic lesion diameters tend to be overestimated during LITT.

Near "real" time magnetic resonance images as a monitoring system for interstitial laser therapy: experimental protocols

NASA Astrophysics Data System (ADS)

Castro, Dan J.; Farahani, Keyvan; Soudant, Jacques; Zwarun, Andrew A.; Lufkin, Robert B.

1992-06-01

The failure rate of cancer treatment remains unacceptably high, still being a leading cause of mortality in adults and children despite major advances over the past 50 years in the fields of surgery, radiation therapy and, more recently, chemo and immunotherapy. Surgical access to some deep tumors of the head and neck and other areas often require extensive dissections with residual functional and cosmetic deformities. Repeated treatment is not possible after maximum dose radiotherapy and chemotherapy is still limited by its systemic toxicity. An attractive solution to these problems would be the development of a new adjunctive method combining the best features of interstitial laser therapy for selective tumor destruction via minimally invasive techniques for access and 3-D magnetic resonance imaging (MRI) as a monitoring system for laser-tissue interactions. Interstitial laser therapy (ILT) via fiberoptics allow laser energy to be delivered directly into deeper tissues. However, this concept will become clinically useful only when noninvasive, accurate, and reproducible monitoring methods are developed to measure energy delivery to tissues. MRI has numerous advantages in evaluating the irreversible effects of laser treatment in tissues, since laser energy includes changes not only in the thermal motions of hydrogen protons within the tissue, but also in the distribution and mobility of water and lipids. These techniques should greatly improve the use of ILT in combination with MRI to allow treatment of deeper, more difficult to reach tumors of head and neck and other anatomical areas with a single needle stick.

A finite element method model to simulate laser interstitial thermo therapy in anatomical inhomogeneous regions

PubMed Central

Mohammed, Yassene; Verhey, Janko F

2005-01-01

Background Laser Interstitial ThermoTherapy (LITT) is a well established surgical method. The use of LITT is so far limited to homogeneous tissues, e.g. the liver. One of the reasons is the limited capability of existing treatment planning models to calculate accurately the damage zone. The treatment planning in inhomogeneous tissues, especially of regions near main vessels, poses still a challenge. In order to extend the application of LITT to a wider range of anatomical regions new simulation methods are needed. The model described with this article enables efficient simulation for predicting damaged tissue as a basis for a future laser-surgical planning system. Previously we described the dependency of the model on geometry. With the presented paper including two video files we focus on the methodological, physical and mathematical background of the model. Methods In contrast to previous simulation attempts, our model is based on finite element method (FEM). We propose the use of LITT, in sensitive areas such as the neck region to treat tumours in lymph node with dimensions of 0.5 cm – 2 cm in diameter near the carotid artery. Our model is based on calculations describing the light distribution using the diffusion approximation of the transport theory; the temperature rise using the bioheat equation, including the effect of microperfusion in tissue to determine the extent of thermal damage; and the dependency of thermal and optical properties on the temperature and the injury. Injury is estimated using a damage integral. To check our model we performed a first in vitro experiment on porcine muscle tissue. Results We performed the derivation of the geometry from 3D ultrasound data and show for this proposed geometry the energy distribution, the heat elevation, and the damage zone. Further on, we perform a comparison with the in-vitro experiment. The calculation shows an error of 5% in the x-axis parallel to the blood vessel. Conclusions The FEM technique proposed can overcome limitations of other methods and enables an efficient simulation for predicting the damage zone induced using LITT. Our calculations show clearly that major vessels would not be damaged. The area/volume of the damaged zone calculated from both simulation and in-vitro experiment fits well and the deviation is small. One of the main reasons for the deviation is the lack of accurate values of the tissue optical properties. In further experiments this needs to be validated. PMID:15631630

Ab-initio study of dilute nitride substitutional and split-interstitial impurities in gallium antimonide (N-GaSb)

NASA Astrophysics Data System (ADS)

Jadaun, Priyamvada; Nair, Hari P.; Bank, Seth R.; Banerjee, Sanjay K.

2012-02-01

We present an ab-initio density functinal theory study of dilute-nitride GaSb. Adding dilute quantities of nitrogen causes rapid reduction in bandgap of GaSb (˜300 meV for 2% N). Due to this rapid reduction in bandgap, dilute-nitrides provide a pathway for extending the emission of GaSb based type-I diode lasers into the mid-infrared wavelength region (3-5 micron). In this study we look at the effect of substitutional N impurity on the electronic properties of our system and compare it with the band-anticrossing model, a phenomenological model, which has been used to explain giant band bowing observed in dilute-nitride alloys. We also study the effect of Sb-N split interstitials which are known to be non-radiative recombination centers. Furthermore we also discuss the stability of the Sb-N split interstitial relative to substitutional nitrogen to determine if the split interstitials can be annihilated using post-growth annealing to improve the radiative lifetime of the material which essential for laser operation.

Monte Carlo simulation of non-invasive glucose measurement based on FMCW LIDAR

NASA Astrophysics Data System (ADS)

Xiong, Bing; Wei, Wenxiong; Liu, Nan; He, Jian-Jun

2010-11-01

Continuous non-invasive glucose monitoring is a powerful tool for the treatment and management of diabetes. A glucose measurement method, with the potential advantage of miniaturizability with no moving parts, based on the frequency modulated continuous wave (FMCW) LIDAR technology is proposed and investigated. The system mainly consists of an integrated near-infrared tunable semiconductor laser and a detector, using heterodyne technology to convert the signal from time-domain to frequency-domain. To investigate the feasibility of the method, Monte Carlo simulations have been performed on tissue phantoms with optical parameters similar to those of human interstitial fluid. The simulation showed that the sensitivity of the FMCW LIDAR system to glucose concentration can reach 0.2mM. Our analysis suggests that the FMCW LIDAR technique has good potential for noninvasive blood glucose monitoring.

Kinetic Monte Carlo (kMC) simulation of carbon co-implant on pre-amorphization process.

PubMed

Park, Soonyeol; Cho, Bumgoo; Yang, Seungsu; Won, Taeyoung

2010-05-01

We report our kinetic Monte Carlo (kMC) study of the effect of carbon co-implant on the pre-amorphization implant (PAL) process. We employed BCA (Binary Collision Approximation) approach for the acquisition of the initial as-implant dopant profile and kMC method for the simulation of diffusion process during the annealing process. The simulation results implied that carbon co-implant suppresses the boron diffusion due to the recombination with interstitials. Also, we could compare the boron diffusion with carbon diffusion by calculating carbon reaction with interstitial. And we can find that boron diffusion is affected from the carbon co-implant energy by enhancing the trapping of interstitial between boron and interstitial.

Near-infrared fiber delivery systems for interstitial photothermal therapy

NASA Astrophysics Data System (ADS)

Slatkine, Michael; Mead, Douglass S.; Konwitz, Eli; Rosenberg, Zvi

1995-05-01

Interstitial photothermal coagulation has long been recognized as a potential important, minimally invasive modality for treating a variety of pathologic conditions. We present two different technologies for interstitial photothermal coagulation of tissue with infrared lasers: An optical fiber with a radially symmetric diffusing tip for deep coagulation, and a flat bare fiber for the coagulation of thin and long lesions by longitudinally moving the fiber while lasing in concert. Urology and Gynecology Fibers: The fibers are 600 microns diameter with 20 - 40 mm frosted distal tips protected by a smooth transparent cover. When used with a Neodymium:YAG (Nd:YAG) laser, the active fiber surface diffuses optical radiation in a radial pattern, delivering up to 40 W power, and thus providing consistent and uniform interstitial photothermal therapy. Coagulation depth ranges from 4 to 15 mm. Animal studies in the United States and clinical studies in Europe have demonstrated the feasibility of using these fibers to treat benign prostatic hyperplasia and endometrial coagulation. Rhinology Fiber: The fiber is an 800 micron diameter flat fiber operated at 8 W power level while being interstitially pushed and pulled along its axis. A long and thin coagulated zone is produced. The fiber is routinely used for the shrinking of hypertrophic turbinates without surrounding and bone mucusal damage in ambulatory environments.

Interstitial laser coagulation of benign prostatic hyperplasia: a minimally invasive treatment alternative

NASA Astrophysics Data System (ADS)

Ordonez, Robert F.; Mittemeyer, Bernhard T.; Aronoff, David R.; de Riese, Werner T. W.

2003-06-01

The use of minimally invasive treatments for benign prostatic hyperplasia (BPH) have been introduced into the medical community. Over the last decade several minimally invasive treatment techniques have been approved for use. In particular, interstitial laser coagulation (ILC) has shown pomise as an alternative to the current gold standard, transurethral resection of prostate (TURP). Studies show ILC to have equal efficacy as TURP while causing less side effects. Future technical advances as well as increased physician experience with ILC could lead to the replacement of TURP as the gold standard in trestment of BPH.

Stability and migration of large oxygen clusters in UO(2+x): density functional theory calculations.

PubMed

Andersson, D A; Espinosa-Faller, F J; Uberuaga, B P; Conradson, S D

2012-06-21

Using ab initio molecular dynamics simulations and nudged elastic band calculations we examine the finite temperature stability, transition pathways, and migration mechanisms of large oxygen clusters in UO(2+x). Here we specifically consider the recently proposed split quad-interstitial and cuboctahedral oxygen clusters. It is shown that isolated cuboctahedral clusters may transform into more stable configurations that are closely linked to the split quad-interstitial. The split quad-interstitial is stable with respect to single interstitials occupying the empty octahedral holes of the UO(2) lattice. In order to better understand discrepancies between theory and experiments, the simulated atomic pair distribution functions for the split quad-interstitial structures are analyzed with respect to the distribution function for U(4)O(9) previously obtained from neutron diffraction data. Our nudged elastic band calculations suggest that the split quad-interstitial may migrate by translating one of its constituent di-interstitial clusters via a barrier that is lower than the corresponding barrier for individual interstitials, but higher than the barrier for the most stable di-interstitial cluster.

Influence of Carbon interstitials to Ti1-xMexN (Me = Zr, Al, Cr) coatings by pulsed laser ablation on wear resistance

NASA Astrophysics Data System (ADS)

Jeon, Seol; Hong, Eunpyo; Kwon, Se-Hun; Lee, Heesoo

2018-06-01

The wear resistance of Ti1-xMexN (Me = Zr, Al, Cr) coatings by the laser carburization process was investigated in terms of local atomic structural changes. The repeated pulsed laser ablation was performed to the Ti1-xMexN coating surfaces after Graphite paste was covered. The friction coefficients of the coating specimens were decreased from ∼0.7 to 0.2, and the formation of cracks and debris was suppressed by implementing the laser ablation process. ToF-SIMS depth profiles showed that the laser carburization helps Carbon penetrate into the coating layer as deep as ∼20 nm below its surface. XPS and XAFS analyses revealed that the improvement of the wear resistance of the coatings was achieved not by formation of TiC or ZrC lattices on the coatings surfaces but by Carbon interstitials to the Ti1-xMexN lattices.

Development of transrectal diffuse optical tomography combined with 3D-transrectal ultrasound imaging to monitor the photocoagulation front during interstitial photothermal therapy of primary focal prostate cancer

NASA Astrophysics Data System (ADS)

He, Jie; Weersink, Robert; Veilleux, Israel; Mayo, Kenwrick; Zhang, Anqi; Piao, Daqing; Alam, Adeel; Trachtenberg, John; Wilson, Brian C.

2013-03-01

Interstitial near-infrared laser thermal therapy (LITT) is currently undergoing clinical trials as an alternative to watchful waiting or radical surgery in patients with low-risk focal prostate cancer. Currently, we use magnetic resonance image (MRI)-based thermography to monitor treatment delivery and determine indirectly the completeness of the target tissue destruction while avoiding damage to adjacent normal tissues, particularly the rectal wall. However, incomplete tumor destruction has occurred in a significant fraction of patients due to premature termination of treatment, since the photocoagulation zone is not directly observed. Hence, we are developing transrectal diffuse optical tomography (TRDOT), in combination with transrectal 3D ultrasound (3D-TRUS), to address his limitation. This is based on the large changes in optical scattering expected upon tissue coagulation. Here, we present forward simulations of a growing coagulated lesion with optical scattering contrast, using an established finite element analysis software platform (NIRFAST). The simulations were validated in tissue-simulating phantoms, with measurements acquired by a state-of-the-art continuous wave (CW) TRDOT system and a recently assembled bench-top CW-DOT system, with specific source-detector configurations. Two image reconstruction schemes were investigated and evaluated, specifically for the accurate delineation of the posterior boundary of the coagulation zone as the critical parameter for treatment guidance in this clinical application.

Phase transformation pathways of ultrafast-laser-irradiated Ln2O3 (Ln =Er -Lu )

NASA Astrophysics Data System (ADS)

Rittman, Dylan R.; Tracy, Cameron L.; Chen, Chien-Hung; Solomon, Jonathan M.; Asta, Mark; Mao, Wendy L.; Yalisove, Steven M.; Ewing, Rodney C.

2018-01-01

Ultrafast laser irradiation causes intense electronic excitations in materials, leading to transient high temperatures and pressures. Here, we show that ultrafast laser irradiation drives an irreversible cubic-to-monoclinic phase transformation in Ln2O3 (Ln =Er -Lu ), and explore the mechanism by which the phase transformation occurs. A combination of grazing incidence x-ray diffraction and transmission electron microscopy are used to determine the magnitude and depth-dependence of the phase transformation, respectively. Although all compositions undergo the same transformation, their transformation mechanisms differ. The transformation is pressure-driven for Ln =Tm -Lu , consistent with the material's phase behavior under equilibrium conditions. However, the transformation is thermally driven for Ln =Er , revealing that the nonequilibrium conditions of ultrafast laser irradiation can lead to novel transformation pathways. Ab initio molecular-dynamics simulations are used to examine the atomic-scale effects of electronic excitation, showing the production of oxygen Frenkel pairs and the migration of interstitial oxygen to tetrahedrally coordinated constitutional vacancy sites, the first step in a defect-driven phase transformation.

Phase transformation pathways of ultrafast-laser-irradiated Ln 2 O 3 ( Ln = Er – Lu )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rittman, Dylan R.; Tracy, Cameron L.; Chen, Chien-Hung

Ultrafast laser irradiation causes intense electronic excitations in materials, leading to transient high temperatures and pressures. Here, we show that ultrafast laser irradiation drives an irreversible cubic-to-monoclinic phase transformation in Ln 2O 3 ( Ln = Er – Lu ) , and explore the mechanism by which the phase transformation occurs. A combination of grazing incidence x-ray diffraction and transmission electron microscopy are used to determine the magnitude and depth-dependence of the phase transformation, respectively. Although all compositions undergo the same transformation, their transformation mechanisms differ. The transformation is pressure-driven for Ln = Tm – Lu , consistent with themore » material's phase behavior under equilibrium conditions. However, the transformation is thermally driven for Ln = Er , revealing that the nonequilibrium conditions of ultrafast laser irradiation can lead to novel transformation pathways. Ab initio molecular-dynamics simulations are used to examine the atomic-scale effects of electronic excitation, showing the production of oxygen Frenkel pairs and the migration of interstitial oxygen to tetrahedrally coordinated constitutional vacancy sites, the first step in a defect-driven phase transformation.« less

Phase transformation pathways of ultrafast-laser-irradiated Ln 2 O 3 ( Ln = Er – Lu )

DOE PAGES

Rittman, Dylan R.; Tracy, Cameron L.; Chen, Chien-Hung; ...

2018-01-10

Ultrafast laser irradiation causes intense electronic excitations in materials, leading to transient high temperatures and pressures. Here, we show that ultrafast laser irradiation drives an irreversible cubic-to-monoclinic phase transformation in Ln 2O 3 ( Ln = Er – Lu ) , and explore the mechanism by which the phase transformation occurs. A combination of grazing incidence x-ray diffraction and transmission electron microscopy are used to determine the magnitude and depth-dependence of the phase transformation, respectively. Although all compositions undergo the same transformation, their transformation mechanisms differ. The transformation is pressure-driven for Ln = Tm – Lu , consistent with themore » material's phase behavior under equilibrium conditions. However, the transformation is thermally driven for Ln = Er , revealing that the nonequilibrium conditions of ultrafast laser irradiation can lead to novel transformation pathways. Ab initio molecular-dynamics simulations are used to examine the atomic-scale effects of electronic excitation, showing the production of oxygen Frenkel pairs and the migration of interstitial oxygen to tetrahedrally coordinated constitutional vacancy sites, the first step in a defect-driven phase transformation.« less

Microprocessor-controlled Nd:YAG laser for hyperthermia induction in the RIF-1 tumor.

PubMed

Waldow, S M; Russell, G E; Wallner, P E

1992-01-01

Near-infrared radiation from a Nd:YAG laser at 1,064 nm was used interstitially or superficially to induce hyperthermia in RIF-1 tumors in C3H male mice. A single 600-microns quartz fiber with a 0.5-cm cylindrical diffusor or a weakly diverging microlens at its distal end was used to deliver laser energy to tumors in the hind leg (mean volume = 100 mm3). Two thermocouples were inserted into each tumor. One thermocouple controlled a microprocessor-driven hyperthermia program (maximum output of 3.5 Watts) to maintain the desired temperature. Tumors were exposed to various temperature-time combinations (42-45 degrees C/30 min). Our initial results indicated that excellent temperature control to within 0.2 degrees C of the desired temperature at the feedback thermocouple was achievable during both superficial and interstitial heat treatments. Temperatures at the second thermocouple, however, were found to be lower by as much as 2.3 degrees C (using the cylindrical diffusor) or higher by up to 4.6 degrees C (using the microlens) when compared to the feedback thermocouple temperature. Several correlations were seen between total dose, tumor growth delay, percent skin necrosis, and temperature at the second thermocouple after several superficial and interstitial treatments. Statistically significant improvements in tumor growth delay (at 42 and 45 degrees C) and increased percent skin necrosis at all temperatures were observed after superficial versus interstitial treatment.

Prenatal Therapy of Large Placental Chorioangiomas: Case Report and Review of the Literature

PubMed Central

Hosseinzadeh, Pardis; Shamshirsaz, Alireza A.; Javadian, Pouya; Espinoza, Jimmy; Gandhi, Manisha; Ruano, Rodrigo; Cass, Darrell L.; Olutoye, Oluyinka A.; Belfort, Michael A.

2015-01-01

Objective To review techniques and outcomes of different prenatal treatments for large placental chorioangiomas. Study Design Presentation of a case of laparoscopic-assisted laser coagulation and a systematic review of the literature for articles related to intervention for placental chorioangioma. Results A total of 37 cases of definitive (n = 23) and supportive therapy (n = 14) were evaluated, including one case treated in our center. Approximately 35% of the patients had a spontaneous preterm delivery in definitive treatment group versus 36% in the supportive group. The infant survival rates were 65 and 71% in the two groups, respectively. We further compared the two types of laser ablation (fetoscopic [n = 10] and interstitial [n = 4]). Approximately 30% of the patients in the fetoscopic and 25% in interstitial group, had a spontaneous preterm delivery. Survival rates were 60 and 100% in fetoscopic and interstitial groups, respectively. Conclusion Laser ablation and embolization of chorioangiomas via minimally invasive approach may prevent or reverse fetal hydrops due to high cardiac states. However, further studies are needed to refine the appropriate selection criteria that will justify the risk of this invasive in utero therapy for chorioangiomas. PMID:26495184

Hi-tech of the prostate: interstitial laser coagulation of benign prostatic hypertrophy

NASA Astrophysics Data System (ADS)

Muschter, Rolf; Hofstetter, Alfons G.; Hessel, Stefan F. F.; Keiditsch, Ernst; Rothenberger, Karl-Heinz; Schneede, Peter; Frank, Klaus H.

1992-06-01

We report on the new technique of interstitial laser coagulation of the prostate (ILCP) in the treatment of benign prostatic hyperplasia (BPH). Basic experiments by use of a Nd:YAG laser in combination with a newly designed fiber tip homogeneously distributing the laser irradiation have been performed in potato, muscle, liver, and surgically removed human BPH-tissue to determine the volume of coagulation. The coagulation zone surrounding the probe was well defined and homogeneous. The size was dependent on laser power and irradiation time. Carbonization was never present except in darker tissues irradiated with high energy. Volume and time resolved measurements correlated well with the size of coagulation. 10 W and 5 minutes, for example, resulted in a coagulation zone of 17 X 15 mm. Comparable results have been seen in in-vivo experiments in surgically exposed canine prostates. Specimen for macroscopic and microscopic examination were taken immediately after treatment and after 5 and 35 days. The well demarked coagulation necrosis of the early stage resulted in cystic degeneration and fibrosis in the later stages. This was combined with shrinkage and reduction in volume. The urothelium of the urethra, the external sphincter and the rectum showed no damage. Until now, 15 patients suffering from obstructive symptoms due to BPH have been treated with interstitial laser coagulation. The probes were inserted from the perineum into the center of each lateral lobe of the prostate by transrectal ultrasound guidance, while the median lobe was treated by urethroscopic guidance, while the median lobe was treated by urethroscopic control. Dependent on the size of the prostate irradiation, time was 5 to 10 minutes per lobe at a power setting of 5 to 10 W.

Studies On Endoscopic Local Hyperthermia Using Nd-YAG Laser

NASA Astrophysics Data System (ADS)

Tsunekawa, H.; Kanemaki, N.; Furusawa, A.; Hotta, M.; Kuroiwa, A.; Nishida, M.; Mori, N.; Watanabe, Y.; Morise, K.; Iizuka, A.

1987-03-01

Attempting a new method of laser irradiation for depressed gastric carcinoma, using a newly developed interstitial probe and laser attenuator, we applied local hyperthermia with prolonged low watt contact irradiation. Experimental studies were performed with this probe, using BDF1 mice injected hypodermically with Lewis lung carcinoma. A laser power of 2.0 w at the tip of fiber produced the most desirable temperature curve, about 43 - 60°C at the irradiation site. Clinical applications were carried out on 15 patients with early gastric carcinoma (mainly depressed), 10 preoperative pilot cases and 5 inoperable cases. In follow-up operations and biopsies gastric carcinoma was found to have completely dis-appeared in 2 of the preoperative and 4 of the inoperable cases. In the remaining 8 preoperative cases residual traces of carcinoma were found at the margin of the laser ulcer, but not at the bottom of it. We propose that endoscopic local hyperthermia using interstitial probe and low power irradiation (2.0 W) is the safest and most suitable method of dealing with depressed carcinoma.

Temperature-sensitive junction transformations for mid-wavelength HgCdTe photovoltaic infrared detector arrays by laser beam induced current microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiu, Weicheng; National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083; Hu, Weida, E-mail: wdhu@mail.sitp.ac.cn

2014-11-10

In this paper, we report on the disappearance of the photosensitive area extension effect and the unusual temperature dependence of junction transformation for mid-wavelength, n-on-p HgCdTe photovoltaic infrared detector arrays. The n-type region is formed by B{sup +} ion implantation on Hg-vacancy-doped p-type HgCdTe. Junction transformations under different temperatures are visually captured by a laser beam induced current microscope. A physical model of temperature dependence on junction transformation is proposed and demonstrated by using numerical simulations. It is shown that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation dependence on temperature, and the weaker mixedmore » conduction compared with long-wavelength HgCdTe photodiode contributes to the disappearance of the photosensitive area extension effect in mid-wavelength HgCdTe infrared detector arrays.« less

Primary radiation damage of Zr-0.5%Nb binary alloy: atomistic simulation by molecular dynamics method

NASA Astrophysics Data System (ADS)

Tikhonchev, M.; Svetukhin, V.; Kapustin, P.

2017-09-01

Ab initio calculations predict high positive binding energy (˜1 eV) between niobium atoms and self-interstitial configurations in hcp zirconium. It allows the expectation of increased niobium fraction in self-interstitials formed under neutron irradiation in atomic displacement cascades. In this paper, we report the results of molecular dynamics simulation of atomic displacement cascades in Zr-0.5%Nb binary alloy and pure Zr at the temperature of 300 K. Two sets of n-body interatomic potentials have been used for the Zr-Nb system. We consider a cascade energy range of 2-20 keV. Calculations show close estimations of the average number of produced Frenkel pairs in the alloy and pure Zr. A high fraction of Nb is observed in the self-interstitial configurations. Nb is mainly detected in single self-interstitial configurations, where its fraction reaches tens of percent, i.e. more than its tenfold concentration in the matrix. The basic mechanism of this phenomenon is the trapping of mobile self-interstitial configurations by niobium. The diffusion of pure zirconium and mixed zirconium-niobium self-interstitial configurations in the zirconium matrix at 300 K has been simulated. We observe a strong dependence of the estimated diffusion coefficients and fractions of Nb in self-interstitials produced in displacement cascades on the potential.

MR-guided interstitial laser thermotherapy of colorectal liver metastases: efficiency, safety and patient survival.

PubMed

Pech, M; Wieners, G; Freund, T; Dudeck, O; Fischbach, F; Ricke, J; Seemann, M D

2007-04-26

Evaluation of MR-guided interstitial laser thermotherapy (ILT) of colorectal liver metastases under consideration of efficacy, safety and patient survival. Sixty-six inoperable patients with a total of 117 colorectal liver metastases were treated with MR-guided laser therapy in 96 sessions. 40.9% of patients presented metastases from rectum carcinoma, 30.3% from sigmoid carcinoma and 28.8% from colon carcinoma. Inclusion criteria were < or =5 metastases < or =5 cm in greatest diameter and no extrahepatic tumor spread. Internally water-cooled 9F power-laser-applicators were placed under CT-fluoroscopy. For MR-guided ILT, a 1064 nm Nd-YAG-lasers with a beam divider with multi applicator technique was used. The energy applied was 10 watt per centimeter diffusor length, with the diffusor length ranging from 20 to 40 mm. The mean duration of the energy application was 23 minutes (range: 15 - 37 minutes). The endpoint of the laser ablation was defined as the absence of hyperintense tumor tissue in the continuously monitored T2-w fat saturated gradient-echo sequences. Follow-up included contrast-enhanced MRI using T1- and T2-weighted spin-echo and gradient-echo sequences every three months after treatment. Survival times were calculated using the Kaplan-Meier method. The median follow-up was 8.7 months (mean 11.8; standard deviation 9.9; range 1 to 36). The overall median progression free survival was 6.1 months (range, 0.3 to 27+ months). Median survival was 23 months (95% CI, 17-29 months). The rate of major complications was 2.1% (n = 2) and peri-procedural mortality (30 days) was 3% (n = 2). After 3, 6, 9, and 12 months, local tumor control was 98.3%, 91.4%, 76.1%, and 69.4%, respectively. In no patient metastatic deposits along the catheter access route were found. In patients with colorectal liver metastases, interstitial laser thermotherapy is an effective and safe therapeutic option and therefore suitable not only in palliative situations.

Laser Assisted Cancer Immunotherapy: An Experimental Theraputic Approach in Balb/c Mice

NASA Astrophysics Data System (ADS)

Gray, John

2005-03-01

Among the different therapeutic approaches to treat superficial malignant tumors, Laser Assisted Cancer Immunotherapy (LACI) shows promise. Experiments are in progress in our laboratory based on the concept of LACI which utilizes a light absorbing dye (Indocyanine Green, ICG), an immunoadjuvant (Glycated Chitosan, GC), and an infrared diode laser (1-15w) operating at 804 nm. Superficial tumors (5 to 7 mm in diameter) of the T4 cell line are grown in an animal model (Balb/C mice). The tumors are injected with ICG and GC prior to interstitial/surface irradiation of the tumor. The tumors' internal temperatures are monitored during the irradiation by invasive (microthermocouples) as well as noninvasive (infrared detector) modes. Along with the various experimental parameters, only the laser delivery (interstitial/surface) and laser intensity are varied in this initial stage so that the tumor temperature is in the range of 55 degrees C to 65 degrees C to ensure hyperthermic cell killing. The goal of the project is to determine the precise temperature range through which primary tumor necrosis and a vigorous immune response will end in tumor elimination. Experimental results coupled with a theoretical framework of laser-tissue interactions will be presented in the context of this therapeutic approach.

Role of laser therapy in benign prostate hyperplasia (BPH)

NASA Astrophysics Data System (ADS)

de Riese, Werner T.; Sharpe, Brent A.; Aronoff, David B.; Mittemeyer, Bernhard T.

2001-05-01

Benign prostatic hyperplasia (BPH) is a common disease in males older than 50 years of age. 75-80% of this population is considered to have some degree of BPH causing clinical symptoms and requiring urological treatment. Transurethral resection of the prostate (TUR-P) is currently the standard surgical treatment modality for BPH. In an attempt to minimize the need for hospitalization and the associated perioperative and postoperative morbidity, alternatives have been sought. Various types of laser techniques such as interstitial laser coagulation and side-firing technology have been proposed. Numerous studies have shown that laser procedures safely and effectively reduce the volume of the prostate. Intra- and postoperative bleeding are nearly unknown complications for laser procedures, whereas this is the most relevant complication for the TUR-P. Due to significant tissue edema after laser treatment, patients commonly show delayed time to void adequately and, therefore, catheter drainage is often necessary for 3 to 21 days. Retrograde ejaculation is reported to occur less (0- 10%) compared to TUR-P (greater than 60%). Urinary tract infections are very common after interstitial laser coagulation. Although not many long-term clinical data are available, various studies have shown that BPH patients improve in symptom score, flow rate and post-void residual up to 3 years after laser treatment. This paper presents a concise review of efficacy, advantages and disadvantages of the most frequently used laser techniques as well as the long-term clinical data compared to TUR-P.

Fiber optic laser rod

DOEpatents

Erickson, G.F.

1988-04-13

A laser rod is formed from a plurality of optical fibers, each forming an individual laser. Synchronization of the individual fiber lasers is obtained by evanescent wave coupling between adjacent optical fiber cores. The fiber cores are dye-doped and spaced at a distance appropriate for evanescent wave coupling at the wavelength of the selected dye. An interstitial material having an index of refraction lower than that of the fiber core provides the optical isolation for effective lasing action while maintaining the cores at the appropriate coupling distance. 2 figs.

Laser Ablatin of Dental Hard Tissue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seka, W.; Rechmann, P.; Featherstone, J.D.B.

This paper discusses ablation of dental hard tissue using pulsed lasers. It focuses particularly on the relevant tissue and laser parameters and some of the basic ablation processes that are likely to occur. The importance of interstitial water and its phase transitions is discussed in some detail along with the ablation processes that may or may not directly involve water. The interplay between tissue parameters and laser parameters in the outcome of the removal of dental hard tissue is discussed in detail.

Kinetics of self-interstitial migration in bcc and fcc transition metals

NASA Astrophysics Data System (ADS)

Bukkuru, S.; Bhardwaj, U.; Srinivasa Rao, K.; Rao, A. D. P.; Warrier, M.; Valsakumar, M. C.

2018-03-01

Radiation damage is a multi-scale phenomenon. A thorough understanding of diffusivities and the migration energies of defects is a pre-requisite to quantify the after-effects of irradiation. We investigate the thermally activated mobility of self-interstitial atom (SIA) in bcc transition metals Fe, Mo, Nb and fcc transition metals Ag, Cu, Ni, Pt using molecular dynamics (MD) simulations. The self-interstitial diffusion involves various mechanisms such as interstitialcy, dumbbell or crowdion mechanisms. Max-Space Clustering (MSC) method has been employed to identify the interstitial and its configuration over a wide range of temperature. The self-interstitial diffusion is Arrhenius like, however, there is a slight deviation at high temperatures. The migration energies, pre-exponential factors of diffusion and jump-correlation factors, obtained from these simulations can be used as inputs to Monte Carlo simulations of defect transport. The jump-correlation factor shows the degree of preference of rectilinear or rotational jumps. We obtain the average jump-correlation factor of 1.4 for bcc metals and 0.44 for fcc metals. It indicates that rectilinear jumps are preferred in bcc metals and rotational jumps are preferred in fcc metals.

Long-term effects of laser-imiquimod combination in the treatment of late-stage melanoma patients

NASA Astrophysics Data System (ADS)

Naylor, Mark F.; Le, Henry; Li, Xiaosong; Nordquist, Robert E.; Hode, Tomas; Liu, Hong; Chen, Wei R.

2012-03-01

Topical application of a potent immunological modulator, imiquimod, followed by laser irradiation has been used for the treatment of late-stage melanoma patients. This novel approach, laser-assisted laser immunotherapy (LIT), targets the root course of melanoma, a highly metastatic cancer. We started a phase I clinical trial in 2006 with promising initial outcomes. The laser-imiquimod combination showed significant palliative effects for these patients with multiple treatment cycles. For the returning patients, we found that the recurrent tumors were less aggressive than usually seen in untreated patients. The current protocol uses a light-absorbing dye for selective laser photothermal interaction with a non-invasive treatment mode. It has limitations for patient treatment, particularly for large, deeper tumors, and for patients with dark pigmented skins. This study provides some information on the treated patients (both stage IV and stage IV) during the past several years. We also discuss the future directions of LIT, particularly in the area of photothermal treatment mode with a new approach of interstitial irradiation. The current results in melanoma treatment using LIT indicate that the combination of photothermal therapy and immunological stimulation may hold the key for the treatment of late-stage, metastatic cancers, not only for cutaneous cancers such as melanoma and breast cancer, but also for deep and internal tumors using different operations modes such as interstitial laser irradiation.

Application research of rail transit safety protection based on laser detection

NASA Astrophysics Data System (ADS)

Wang, Zhifei

2016-10-01

Platform screen door can not only prevent the passengers fell or jumped the track danger, to passengers bring comfortable waiting environment, but also has the function of environmental protection and energy saving. But platform screen door and train the full-length gap region is insecure in the system design of a hidden, such as passengers for some reason (grab the train) in the interstitial region retention, is sandwiched between the intercity safety door and the door, and such as the region lacks security detection and alarm system, once the passengers in the gap region retention (caught), bring more serious threat to the safety of passengers and traffic safety. This paper from the point of view of the design presents the physical, infrared, laser three safety protection device setting schemes. Domestic intelligence of between rail transit shield door and train security clearance processing used is screen door system standard configuration, the obstacle detection function for avoid passengers stranded in the clearance has strong prevention function. Laser detection research and development projects can access to prevent shield door and train gap clamp safety measures. Rail safety protection method are studied applying laser detection technique. According to the laser reflection equation of foreign body, the characteristics of laser detection of foreign bodies are given in theory. By using statistical analysis method, the workflow of laser detection system is established. On this basis, protection methods is proposed. Finally the simulation and test results show that the laser detection technology in the rail traffic safety protection reliability and stability, And the future laser detection technology in is discussed the development of rail transit.

Fiber 1.56-1.9 μm lasers in treatment of vascular malformations in children and adults

NASA Astrophysics Data System (ADS)

Abushkin, Ivan A.; Privalov, Valeriy A.; Lappa, Alexander V.; Minaev, Vladimir P.

2013-03-01

A few new low invasive fiber laser technologies for treatment of 1) capillary malformations (port-wine stains), 2) venous, arterial, and arteriovenous malformations, 3) lymphatic malformations of 3 types: micro, small and large-cystic lymphangiomas are presented in this work. There were applied 1.56 μm laser distant photocoagulation, 1.56 μm laser endovascular thermotherapy, 1.9 μm laser instant ablation, 1.9 μm laser interstitial thermotherapy, and 1.9 μm laser excision. The technologies were applied to about 300 patients. Good clinical and esthetic results have been achieved in great majority cases.

Interstitial photodynamic therapy in combination with Cetuximab for recurrent head and neck squamous cell carcinoma

NASA Astrophysics Data System (ADS)

Rigual, Nestor; Dildeep, Ambujakshan; Shafirstein, Gal

2013-03-01

Background and Purpose: Combination therapy of interstitial photodynamic therapy (iPDT) with Cetuximab to attain symptomatic control of recurrent head and neck cancer. Methods: Two patients with Unresectable recurrent Head and Neck SCC were treated with iPDT alone and iPDT and cetuximab. Treatments were administered in an outpatient setting. A single dose of Photofrin at 2 mg per kilogram of body weight was administered intravenously two days prior to laser illumination. The iPDT was accomplished by delivering 630-nm laser light through two laser fibers with 2.5 and 5 cm long diffusive ends. Light irradiance of 400 mW/cm for 250 seconds was used to deliver a total of 100 J/cm, during the iPDT. Light applications were conducted, twice, at 3-4 days interval. One of the patients was treated with cetuximab along with iPDT. Results: Near total resolution of tumor was observed in the patient treated with iPDT and cetuximab, and partial resolution was seen in the patient treated with iPDT alone. Conclusion: Interstitial photodynamic therapy may be used to treat patients with recurrent unresectable head and neck cancer. The combination of iPDT with Cetuximab has the potential to improve tumor response in the patient population for whom there is no effective therapies. This observation merits further studies.

New surgical treatment options in patients with benign prostate hyperplasia (BPH)

NASA Astrophysics Data System (ADS)

de Riese, Werner T. W.; Nelius, Thomas; Aronoff, David R.; Mittemeyer, Bernhard T.

2003-06-01

Benign prostatic hyperplasia (BPH) is a common disease in males older than 50 years of age. 75-80% of this population is considered to have some degree of BPH causing clinical symptoms and requiring urological treatment. Transurethral resection of the prostate (TUR-P) is currently the standard surgical treatment modality for BPH. In an attempt to minimize the need for hospitalization and the associated perioperative and postoperative morbidity, alternatives have been sought. Various types of Laser techniques such as interstitial Laser cogaulation and side-firing technology have been proposed. Numerous studies have shown that Laser procedures safely and effectively reduce the volume of the prostate. Intra- and postoperative bleeding are nearly unknown complications for Laser procedures, whereas this is the most relevant complication for the TUR-P. Due to significant tissue edema after Laser treatment, patients commonly show delayed time to void adequately, and therefore, catheter drainage is often necessary for 3 to 21 days. Retrograde ejaculation is reported to occur less (0 - 10%) compared to TUR-P (> 60%). Urinary tract infections are very common after interstitial laser coagulation. Although not many long-term clinical data are available, various studies have shown that BPH patients improve in symptom score, flow rate and post-void residual up to 3 years after Laser treatment. This paper presents a concise review of efficacy, advantages and disadvantages of the most frequently used Laser techniques as well as the long-term clinical data compared to TUR-P.

Molecular dynamics and quasidynamics simulations of the annealing of bulk and near-surface interstitials formed in molecular-beam epitaxial Si due to low-energy particle bombardment during deposition

NASA Technical Reports Server (NTRS)

Kitabatake, M.; Fons, P.; Greene, J. E.

1991-01-01

The relaxation, diffusion, and annihilation of split and hexagonal interstitials resulting from 10 eV Si irradiation of (2x1)-terminated Si(100) are investigated. Molecular dynamics and quasidynamics simulations, utilizing the Tersoff many-body potential are used in the investigation. The interstitials are created in layers two through six, and stable atomic configurations and total potential energies are derived as a function of site symmetry and layer depth. The interstitial Si atoms are allowed to diffuse, and the total potential energy changes are calculated. Lattice configurations along each path, as well as the starting configurations, are relaxed, and minimum energy diffusion paths are derived. The results show that the minimum energy paths are toward the surface and generally involved tetrahedral sites. The calculated interstitial migration activation energies are always less than 1.4 eV and are much lower in the near-surface region than in the bulk.

Comparison of different laser systems in the treatment of hypertrophic and atrophic scars and keloids

NASA Astrophysics Data System (ADS)

Scharschmidt, D.; Algermissen, Bernd; Willms-Jones, J.-C.; Philipp, Carsten M.; Berlien, Hans-Peter

1997-12-01

Different laser systems and techniques are used for the treatment of hypertrophic scars, keloids and acne scars. Significant criteria in selecting a suitable laser system are the scar's vascularization, age and diameter. Flashlamp- pumped dye-lasers, CO2-lasers with scanner, Argon and Nd:YAG-lasers are used. Telangiectatic scars respond well to argon lasers, erythematous scars and keloids to dye-laser treatment. Using interstitial Nd:YAG-laser vaporization, scars with a cross-section over 1 cm can generally be reduced. For the treatment of atrophic and acne scars good cosmetic results are achieved with a CO2-laser/scanner system, which allows a precise ablation of the upper dermis with low risk of side-effects.

Interstitial solute transport in 3D reconstructed neuropil occurs by diffusion rather than bulk flow.

PubMed

Holter, Karl Erik; Kehlet, Benjamin; Devor, Anna; Sejnowski, Terrence J; Dale, Anders M; Omholt, Stig W; Ottersen, Ole Petter; Nagelhus, Erlend Arnulf; Mardal, Kent-André; Pettersen, Klas H

2017-09-12

The brain lacks lymph vessels and must rely on other mechanisms for clearance of waste products, including amyloid [Formula: see text] that may form pathological aggregates if not effectively cleared. It has been proposed that flow of interstitial fluid through the brain's interstitial space provides a mechanism for waste clearance. Here we compute the permeability and simulate pressure-mediated bulk flow through 3D electron microscope (EM) reconstructions of interstitial space. The space was divided into sheets (i.e., space between two parallel membranes) and tunnels (where three or more membranes meet). Simulation results indicate that even for larger extracellular volume fractions than what is reported for sleep and for geometries with a high tunnel volume fraction, the permeability was too low to allow for any substantial bulk flow at physiological hydrostatic pressure gradients. For two different geometries with the same extracellular volume fraction the geometry with the most tunnel volume had [Formula: see text] higher permeability, but the bulk flow was still insignificant. These simulation results suggest that even large molecule solutes would be more easily cleared from the brain interstitium by diffusion than by bulk flow. Thus, diffusion within the interstitial space combined with advection along vessels is likely to substitute for the lymphatic drainage system in other organs.

Vanadium supersaturated silicon system: a theoretical and experimental approach

NASA Astrophysics Data System (ADS)

Garcia-Hemme, Eric; García, Gregorio; Palacios, Pablo; Montero, Daniel; García-Hernansanz, Rodrigo; Gonzalez-Diaz, Germán; Wahnon, Perla

2017-12-01

The effect of high dose vanadium ion implantation and pulsed laser annealing on the crystal structure and sub-bandgap optical absorption features of V-supersaturated silicon samples has been studied through the combination of experimental and theoretical approaches. Interest in V-supersaturated Si focusses on its potential as a material having a new band within the Si bandgap. Rutherford backscattering spectrometry measurements and formation energies computed through quantum calculations provide evidence that V atoms are mainly located at interstitial positions. The response of sub-bandgap spectral photoconductance is extended far into the infrared region of the spectrum. Theoretical simulations (based on density functional theory and many-body perturbation in GW approximation) bring to light that, in addition to V atoms at interstitial positions, Si defects should also be taken into account in explaining the experimental profile of the spectral photoconductance. The combination of experimental and theoretical methods provides evidence that the improved spectral photoconductance up to 6.2 µm (0.2 eV) is due to new sub-bandgap transitions, for which the new band due to V atoms within the Si bandgap plays an essential role. This enables the use of V-supersaturated silicon in the third generation of photovoltaic devices.

Dissociative diffusion mechanism in vacancy-rich materials according to mass action kinetics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biderman, N. J.; Sundaramoorthy, R.; Haldar, Pradeep

We conducted two sets of diffusion-reaction numerical simulations using a finite difference method (FDM) in order to investigate fast impurity diffusion via interstitial sites in vacancy-rich materials such as Cu(In,Ga)Se 2 (CIGS) and Cu 2ZnSn(S, Se) 4 (CZTSSe or CZTS) via the dissociative diffusion mechanism where the interstitial diffuser ultimately reacts with a vacancy to produce a substitutional. The first set of simulations extends the standard interstitial-limited dissociative diffusion theory to vacancy-rich material conditions where vacancies are annihilated in large amounts, introducing non-equilibrium vacancy concentration profiles. The second simulation set explores the vacancy-limited dissociative diffusion where impurity incorporation increases themore » equilibrium vacancy concentration. In addition to diffusion profiles of varying concentrations and shapes that were obtained in all simulations, some of the profiles can be fitted with the constant- and limited-source solutions of Fick’s second law despite the non-equilibrium condition induced by the interstitial-vacancy reaction. The first set of simulations reveals that the dissociative diffusion coefficient in vacancy-rich materials is inversely proportional to the initial vacancy concentration. In the second set of numerical simulations, impurity-induced changes in the vacancy concentration lead to distinctive diffusion profile shapes. The simulation results are also compared with published data of impurity diffusion in CIGS. And according to the characteristic properties of diffusion profiles from the two set of simulations, experimental detection of the dissociative diffusion mechanism in vacancy-rich materials may be possible.« less

Dissociative diffusion mechanism in vacancy-rich materials according to mass action kinetics

DOE PAGES

Biderman, N. J.; Sundaramoorthy, R.; Haldar, Pradeep; ...

2016-05-13

We conducted two sets of diffusion-reaction numerical simulations using a finite difference method (FDM) in order to investigate fast impurity diffusion via interstitial sites in vacancy-rich materials such as Cu(In,Ga)Se 2 (CIGS) and Cu 2ZnSn(S, Se) 4 (CZTSSe or CZTS) via the dissociative diffusion mechanism where the interstitial diffuser ultimately reacts with a vacancy to produce a substitutional. The first set of simulations extends the standard interstitial-limited dissociative diffusion theory to vacancy-rich material conditions where vacancies are annihilated in large amounts, introducing non-equilibrium vacancy concentration profiles. The second simulation set explores the vacancy-limited dissociative diffusion where impurity incorporation increases themore » equilibrium vacancy concentration. In addition to diffusion profiles of varying concentrations and shapes that were obtained in all simulations, some of the profiles can be fitted with the constant- and limited-source solutions of Fick’s second law despite the non-equilibrium condition induced by the interstitial-vacancy reaction. The first set of simulations reveals that the dissociative diffusion coefficient in vacancy-rich materials is inversely proportional to the initial vacancy concentration. In the second set of numerical simulations, impurity-induced changes in the vacancy concentration lead to distinctive diffusion profile shapes. The simulation results are also compared with published data of impurity diffusion in CIGS. And according to the characteristic properties of diffusion profiles from the two set of simulations, experimental detection of the dissociative diffusion mechanism in vacancy-rich materials may be possible.« less

Computational Modeling of 3D Tumor Growth and Angiogenesis for Chemotherapy Evaluation

PubMed Central

Tang, Lei; van de Ven, Anne L.; Guo, Dongmin; Andasari, Vivi; Cristini, Vittorio; Li, King C.; Zhou, Xiaobo

2014-01-01

Solid tumors develop abnormally at spatial and temporal scales, giving rise to biophysical barriers that impact anti-tumor chemotherapy. This may increase the expenditure and time for conventional drug pharmacokinetic and pharmacodynamic studies. In order to facilitate drug discovery, we propose a mathematical model that couples three-dimensional tumor growth and angiogenesis to simulate tumor progression for chemotherapy evaluation. This application-oriented model incorporates complex dynamical processes including cell- and vascular-mediated interstitial pressure, mass transport, angiogenesis, cell proliferation, and vessel maturation to model tumor progression through multiple stages including tumor initiation, avascular growth, and transition from avascular to vascular growth. Compared to pure mechanistic models, the proposed empirical methods are not only easy to conduct but can provide realistic predictions and calculations. A series of computational simulations were conducted to demonstrate the advantages of the proposed comprehensive model. The computational simulation results suggest that solid tumor geometry is related to the interstitial pressure, such that tumors with high interstitial pressure are more likely to develop dendritic structures than those with low interstitial pressure. PMID:24404145

Dynamics of Helium-Loaded Grain Boundaries under Shear Deformation in α-Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Fei; Yang, Li; Heinisch, Howard L.

2014-03-30

The defects produced in collision cascades will interact with microstructural features in materials, such as GBs and dislocations. The coupled motion of GBs under stress has been widely observed in simulations and experiments. Two symmetric tilt GBs with a common <110> tilt axis (Σ3 and Σ11) in bcc iron are used to investigate the coupled motion of GBs under shear deformation. Also, we have explored the effect of self-interstitial atoms (SIAs) loading on the GB motion, with different concentrations of interstitials randomly inserted around the GB plane. The simulation results show that the interstitial loading reduces the critical stress ofmore » the GB coupled motion for the Σ3 GB. Furthermore, the interstitials and vacancies are inserted randomly at the GB plane and at a distance of 1 nm away from the GB plane, respectively, to understand the self-healing mechanism of GBs under stress. The behavior of the defect-loaded GBs depends on the GB structure. The loaded interstitials in the Σ3 GB easily form <111> interstitial clusters that do not move along with the GB. The vacancies in the Σ3 GB impede the GB motion. However, the interstitials move along with the Σ11 GB and annihilate with vacancies when the GB moves into the vacancy-rich region, leading to the self-healing and damage recovery of the Σ11 GB.« less

Resistance to tumour challenge after tumour laser thermotherapy is associated with a cellular immune response

PubMed Central

Ivarsson, K; Myllymäki, L; Jansner, K; Stenram, U; Tranberg, K-G

2005-01-01

Previous studies in our laboratory have shown that interstitial laser thermotherapy (ILT) of an experimental liver tumour is superior to surgical excision, at least partly due to a laser-induced immunological effect. The aim of the present study was to investigate the time–response relationship of the ILT-induced immunisation and the cellular response of macrophages and lymphocytes. A dimethylhydrazine-induced adenocarcinoma was transplanted into the liver of syngeneic rats. Rats with tumour were treated 6–8 days later (tumour size 0.25–0.40 cm3) with ILT of tumour or resection of the tumour-bearing lobe. Two groups of rats without tumour were treated with resection of a normal liver lobe or ILT of normal liver. A challenging tumour was implanted into the liver of each rat 2, 5 or 10 weeks after primary treatment. Rats were killed 6, 12 and 48 days (or earlier due to their condition) after challenge (n=8 in all groups). Immunohistochemical techniques were used to determine lymphocytes (CD8, CD4) and macrophages (ED1, ED2) in rats having had treatment of a primary tumour. Interstitial laser thermotherapy of the first tumour was followed by eradication of challenging tumour and absence of tumour spread. This contrasted with rapid growth and spread of challenging tumour in the other groups. In the challenging vital tumour tissue and in the interface between the tumour and surroundings, the number of ED1 macrophages and CD8 lymphocytes was higher in rats having been treated with the ILT of tumour than in those having undergone resection of the tumour-bearing lobe. The number of ED2 macrophages and CD4 lymphocytes was low and did not vary between these two groups. Interstitial laser thermotherapy elicited an immune response that eradicated a challenging tumour and was associated with increased numbers of tumour-infiltrating macrophages and CD8 lymphocytes. PMID:16091763

Laser induced thermal therapy (LITT) for pediatric brain tumors: case-based review

PubMed Central

Riordan, Margaret

2014-01-01

Integration of Laser induced thermal therapy (LITT) to magnetic resonance imaging (MRI) have created new options for treating surgically challenging tumors in locations that would otherwise have represented an intrinsic comorbidity by the approach itself. As new applications and variations of the use are discussed, we present a case-based review of the history, development, and subsequent updates of minimally invasive MRI-guided laser interstitial thermal therapy (MRgLITT) ablation in pediatric brain tumors. PMID:26835340

Kinetic Monte Carlo Simulation of Oxygen Diffusion in Ytterbium Disilicate

NASA Technical Reports Server (NTRS)

Good, Brian S.

2015-01-01

Ytterbium disilicate is of interest as a potential environmental barrier coating for aerospace applications, notably for use in next generation jet turbine engines. In such applications, the transport of oxygen and water vapor through these coatings to the ceramic substrate is undesirable if high temperature oxidation is to be avoided. In an effort to understand the diffusion process in these materials, we have performed kinetic Monte Carlo simulations of vacancy-mediated and interstitial oxygen diffusion in Ytterbium disilicate. Oxygen vacancy and interstitial site energies, vacancy and interstitial formation energies, and migration barrier energies were computed using Density Functional Theory. We have found that, in the case of vacancy-mediated diffusion, many potential diffusion paths involve large barrier energies, but some paths have barrier energies smaller than one electron volt. However, computed vacancy formation energies suggest that the intrinsic vacancy concentration is small. In the case of interstitial diffusion, migration barrier energies are typically around one electron volt, but the interstitial defect formation energies are positive, with the result that the disilicate is unlikely to exhibit experience significant oxygen permeability except at very high temperature.

Average structure and local configuration of excess oxygen in UO(2+x).

PubMed

Wang, Jianwei; Ewing, Rodney C; Becker, Udo

2014-03-19

Determination of the local configuration of interacting defects in a crystalline, periodic solid is problematic because defects typically do not have a long-range periodicity. Uranium dioxide, the primary fuel for fission reactors, exists in hyperstoichiometric form, UO(2+x). Those excess oxygen atoms occur as interstitial defects, and these defects are not random but rather partially ordered. The widely-accepted model to date, the Willis cluster based on neutron diffraction, cannot be reconciled with the first-principles molecular dynamics simulations present here. We demonstrate that the Willis cluster is a fair representation of the numerical ratio of different interstitial O atoms; however, the model does not represent the actual local configuration. The simulations show that the average structure of UO(2+x) involves a combination of defect structures including split di-interstitial, di-interstitial, mono-interstitial, and the Willis cluster, and the latter is a transition state that provides for the fast diffusion of the defect cluster. The results provide new insights in differentiating the average structure from the local configuration of defects in a solid and the transport properties of UO(2+x).

Effects of interstitial heating on the RIF-1 tumor using an Nd:YAG laser with multiple fibers.

PubMed

Tobin, K M; Waldow, S M

1996-01-01

Hyperthermia was induced in tumor-bearing C3H mice using a Nd:YAG laser emitting near-infrared radiation at 1,064 nm. The efficacy of multiple implanted fiberoptics in the control of the RIF-1 tumor was investigated. RIF-1 tumors in the right hind leg were heated interstitially at 42, 44, or 46 degrees C for 30 or 60 minutes. Two, three, or four 400-microns quartz fibers terminating in a 1.0-cm cylindrical diffusor were inserted into each tumor, as were five microthermocouples to monitor temperature during treatment. Laser Doppler Flow (LDF) was also recorded pre- and post-treatment to determine changes in red blood cell flux in overlying skin (42, 44, or 46 degrees C) and the center of the tumor (46 degrees C). These experiments indicated that interstitial heating at 42, 44, and 46 degrees C resulted in tumor growth delay, although long-term control of tumors was not achieved. Treatment using four fibers resulted in the greatest tumor growth delay at 42 and 44 degrees C, increasing tumor doubling time by 50% or greater compared to control tumors; tumor growth delay following 46 degrees C treatments was seven times greater than that in control tumors. Significant changes (decreases) in LDF (P < .05) were seen in four treatment groups, using two fibers at 42 degrees C for 30 minutes, four fibers at 44 and 46 degrees C for 60 minutes on the overlying skin, and 46 degrees C for 60 minutes in the center of the tumor. Initial data indicate that interstitial heating with multiple fibers increases tumor growth delay compared to previous single fiber treatments, with tumor growth delay increasing with increasing treatment temperature; however, long-term tumor control was not achieved under the conditions investigated. Follow-up studies will explore the use of higher temperatures and/or longer treatment times in order to optimize tumor response.

Phase-field Model for Interstitial Loop Growth Kinetics and Thermodynamic and Kinetic Models of Irradiated Fe-Cr Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yulan; Hu, Shenyang Y.; Sun, Xin

2011-06-15

Microstructure evolution kinetics in irradiated materials has strongly spatial correlation. For example, void and second phases prefer to nucleate and grow at pre-existing defects such as dislocations, grain boundaries, and cracks. Inhomogeneous microstructure evolution results in inhomogeneity of microstructure and thermo-mechanical properties. Therefore, the simulation capability for predicting three dimensional (3-D) microstructure evolution kinetics and its subsequent impact on material properties and performance is crucial for scientific design of advanced nuclear materials and optimal operation conditions in order to reduce uncertainty in operational and safety margins. Very recently the meso-scale phase-field (PF) method has been used to predict gas bubblemore » evolution, void swelling, void lattice formation and void migration in irradiated materials,. Although most results of phase-field simulations are qualitative due to the lake of accurate thermodynamic and kinetic properties of defects, possible missing of important kinetic properties and processes, and the capability of current codes and computers for large time and length scale modeling, the simulations demonstrate that PF method is a promising simulation tool for predicting 3-D heterogeneous microstructure and property evolution, and providing microstructure evolution kinetics for higher scale level simulations of microstructure and property evolution such as mean field methods. This report consists of two parts. In part I, we will present a new phase-field model for predicting interstitial loop growth kinetics in irradiated materials. The effect of defect (vacancy/interstitial) generation, diffusion and recombination, sink strength, long-range elastic interaction, inhomogeneous and anisotropic mobility on microstructure evolution kinetics is taken into account in the model. The model is used to study the effect of elastic interaction on interstitial loop growth kinetics, the interstitial flux, and sink strength of interstitial loop for interstitials. In part II, we present a generic phase field model and discuss the thermodynamic and kinetic properties in phase-field models including the reaction kinetics of radiation defects and local free energy of irradiated materials. In particular, a two-sublattice thermodynamic model is suggested to describe the local free energy of alloys with irradiated defects. Fe-Cr alloy is taken as an example to explain the required thermodynamic and kinetic properties for quantitative phase-field modeling. Finally the great challenges in phase-field modeling will be discussed.« less

EFFECTS OF LASER RADIATION ON MATTER. LASER PLASMA Annealing of induced absorption in quartz glasses by ArF laser radiation

NASA Astrophysics Data System (ADS)

Sergeev, P. B.; Sergeev, A. P.

2010-11-01

Annealing of individual bands of electron-beam-induced absorption (IA) in the region of 150 — 400 nm in KS-4V, KU-1, and Corning 7980 (ArF Grade) quartz glasses by ArF laser radiation is studied. It is shown that the phototransformation of the IA spectra occurs mainly due to a significant decrease in the amplitudes of bands at λ = 183.5, 213, and 260 nm. The role played by interstitial oxygen, hydrogen, and chlorine in the formation and relaxation of glass defects is considered.

Effect of interstitial and substitution alloying elements on the intrinsic stacking fault energy of nanocrystalline fcc-iron by atomistic simulation study

NASA Astrophysics Data System (ADS)

Mohammadzadeh, Mina; Mohammadzadeh, Roghayeh

2017-11-01

The stacking fault energy (SFE) is an important parameter in the deformation mechanism of face centered cubic (fcc) iron-based alloy. In this study, the effect of interstitial (C and N) and substitution (Nb and Ti) alloying elements on the intrinsic SFE (ISFE) of nanocrystalline iron were investigated via molecular dynamics (MD) simulation. The modified embedded atom method (MEAM) inter-atomic potential was used in the MD simulations. The results demonstrate a strong dependence of ISFE with addition of interstitial alloying elements but only a mild increase in ISFE with addition of substitution alloying elements in the composition range of 0 < {CNb, CTi} < 3 (at%). Moreover, it is shown that alloying of fcc iron with N decreases ISFE, whereas it increases significantly by addition of carbon element [0 < {CC, CN} < 3.5 (at%)]. The simulation method employed in this work shows reasonable agreement with some published experimental/calculated data.

W and X Photoluminescence Centers in Crystalline Si: Chasing Candidates at Atomic Level Through Multiscale Simulations

NASA Astrophysics Data System (ADS)

Aboy, María; Santos, Iván; López, Pedro; Marqués, Luis A.; Pelaz, Lourdes

2018-04-01

Several atomistic techniques have been combined to identify the structure of defects responsible for X and W photoluminescence lines in crystalline Si. We used kinetic Monte Carlo simulations to reproduce irradiation and annealing conditions used in photoluminescence experiments. We found that W and X radiative centers are related to small Si self-interstitial clusters but coexist with larger Si self-interstitials clusters that can act as nonradiative centers. We used molecular dynamics simulations to explore the many different configurations of small Si self-interstitial clusters, and selected those having symmetry compatible with W and X photoluminescence centers. Using ab initio simulations, we calculated their formation energy, donor levels, and energy of local vibrational modes. On the basis of photoluminescence experiments and our multiscale theoretical calculations, we discuss the possible atomic configurations responsible for W and X photoluminescence centers in Si. Our simulations also reveal that the intensity of photoluminescence lines is the result of competition between radiative centers and nonradiative competitors, which can explain the experimental quenching of W and X lines even in the presence of the photoluminescence centers.

Numerical Modeling of Fluid Flow in Solid Tumors

PubMed Central

Soltani, M.; Chen, P.

2011-01-01

A mathematical model of interstitial fluid flow is developed, based on the application of the governing equations for fluid flow, i.e., the conservation laws for mass and momentum, to physiological systems containing solid tumors. The discretized form of the governing equations, with appropriate boundary conditions, is developed for a predefined tumor geometry. The interstitial fluid pressure and velocity are calculated using a numerical method, element based finite volume. Simulations of interstitial fluid transport in a homogeneous solid tumor demonstrate that, in a uniformly perfused tumor, i.e., one with no necrotic region, because of the interstitial pressure distribution, the distribution of drug particles is non-uniform. Pressure distribution for different values of necrotic radii is examined and two new parameters, the critical tumor radius and critical necrotic radius, are defined. Simulation results show that: 1) tumor radii have a critical size. Below this size, the maximum interstitial fluid pressure is less than what is generally considered to be effective pressure (a parameter determined by vascular pressure, plasma osmotic pressure, and interstitial osmotic pressure). Above this size, the maximum interstitial fluid pressure is equal to effective pressure. As a consequence, drugs transport to the center of smaller tumors is much easier than transport to the center of a tumor whose radius is greater than the critical tumor radius; 2) there is a critical necrotic radius, below which the interstitial fluid pressure at the tumor center is at its maximum value. If the tumor radius is greater than the critical tumor radius, this maximum pressure is equal to effective pressure. Above this critical necrotic radius, the interstitial fluid pressure at the tumor center is below effective pressure. In specific ranges of these critical sizes, drug amount and therefore therapeutic effects are higher because the opposing force, interstitial fluid pressure, is low in these ranges. PMID:21673952

[Progress in laser neurosurgery].

PubMed

Majchrzak, H; Kopera, M; Idzik, M

1991-01-01

Nd:YAG lasers with different wavelengths are used in neurosurgery. Their great advantage is the ability of coagulation of blood vessels and delivery through flexible fiber optics . Nd:YAG laser with wavelength 1.318 microns is used, besides, to connect blood vessels and nerves. CO2 laser is the best cutting tool but requires, for delivery rigid cable. Both types of lasers cause shrinkage and vaporisation of the tumors what facilitates its removing without greater traumatisation of surrounding tissues. The introduction of sapphire contact tips to Nd:YAG and argon lasers enables application of small laser powers and diminish the area of damage in surrounding structures. Contact laser is used for destroying of tumours, coagulation of blood vessels, restoration of patency of the main arteries, interstitial denaturation of gliomas and denaturation of the nucleus pulposus in lumbar vertebral column.

Raman study of the thermal stability of HgBa 2CaCu 2O 6+δ and HgBa 2Ca 2Cu 3O 8+δ

NASA Astrophysics Data System (ADS)

Chang, H.; He, Z. H.; Meng, R. L.; Xue, Y. Y.; Chu, C. W.

1995-02-01

We studied the thermal stability of HgBa 2CaCu 2O 6+δ and HgBa 2Ca 2Cu 3O 8+δ at varying laser irradiation power. Each compound has two Raman bands around 570 and 590 cm -1 which are assigned to the vibrations of the interstitial oxygen in HgO δ layers and the apical oxygen in BaO layers, respectively. The 590 cm -1 band shifts position slightly with irradiation, and both the intensity and position of the 570 cm -1 band vary significantly with the laser power. The occupation factor of the interstitial oxygen is sensitive to the annealing temperature. At higher temperatures (550-600°C), both compounds decompose into various (Ba,Cu)-oxides such as Ba 1- xCa xCuO 2.

[Current view and critic of alternatives to transurethral surgery of prostatic benign prostate].

PubMed

Rodríguez, José Vicente

2003-11-01

Critical update of transurethral surgery options based on the last decade most relevant bibliography. Comparative study between Incision/TUR of the prostate and alternative techniques, accordingly to data from 30 randomized studies and 28 clinical studies. We evaluate efficiency, retreatment index, morbidity, post operative number of days with catheter, anesthetic requirements, and cost. Data are expressed as percentages resulting from a differential formula in randomized studies and simple percentages or numeric expression for relevant clinical data. Efficiency: all alternative treatments show a symptomatic improvement (> 50%) similar to that achieved by transurethral surgery; post treatment flowmetry percentage increase is inferior in all alternatives except vaporization, holmium laser and prosthesis. Re-Treatment requirements: they were higher in all alternatives except the ablative ones (vaporization and holmium laser). Morbidity: all of them had an operative estimated blood loss inferior to TUR and similar to prostatic incision; contact laser and vaporization had more irritative symptoms than incision, and VLAP and TUMT more than TUR; TUMT and interstitial laser have a higher rate of post operative infection; all alternatives except the ablative ones had lower percentages of urethral stenosis and retrograde ejaculation. Number of days of catheter post operative: it was comparatively longer after vaporization and very long after VLAP, interstitial laser and TUMT. All treatments except TUNA and TUMT require the same anesthesia than transurethral surgery. The cost/benefit has not been sufficiently evaluated, but it is superior with holmium laser, contact laser and vaporization than with transurethral surgery. Based on study data we can accept holmium laser as a real alternative, TUMT in cases when surgery is questioned and intraprostatic prosthesis when it is not possible.

A high-accuracy measurement method of glucose concentration in interstitial fluid based on microdialysis

NASA Astrophysics Data System (ADS)

Li, Dachao; Xu, Qingmei; Liu, Yu; Wang, Ridong; Xu, Kexin; Yu, Haixia

2017-11-01

A high-accuracy microdialysis method that can provide the reference values of glucose concentration in interstitial fluid for the accurate evaluation of non-invasive and minimally invasive continuous glucose monitoring is reported in this study. The parameters of the microdialysis process were firstly optimized by testing and analyzing three main factors that impact microdialysis recovery, including the perfusion rate, temperature, and glucose concentration in the area surrounding the microdialysis probe. The precision of the optimized microdialysis method was then determined in a simulation system that was designed and established in this study to simulate variations in continuous glucose concentration in the human body. Finally, the microdialysis method was tested for in vivo interstitial glucose concentration measurement.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS Fibreoptic diffuse-light irradiators of biological tissues

NASA Astrophysics Data System (ADS)

Volkov, Vladimir V.; Loshchenov, V. B.; Konov, Vitalii I.; Kononenko, Vitalii V.

2010-10-01

We report techniques for the fabrication of laser radiation diffusers for interstitial photodynamic therapy. Using chemical etching of the distal end of silica fibre with a core diameter of 200 — 600 μm, we have obtained long (up to 40 mm) diffusers with good scattering uniformity. Laser ablation has been used to produce cylindrical diffusers with high emission contrast and a scattering uniformity no worse than ~10 % in their middle part. The maximum length of the diffusers produced by this method is 20 — 25 mm.

Formation and Migration Energies of Interstitials in Silicon Under Strain Conditions

NASA Technical Reports Server (NTRS)

Halicioglu, Timur; Barnett, David M.

1999-01-01

Simulation calculations are conducted for Si substrates to analyze formation and diffusion energies of interstitials under strain condition using statics methods .based on a Stillinger-Weber type potential function. Defects in the vicinity of the surface region and in the bulk are examined, and the role played by compressive and tensile strains on the energetics of interstitials is investigated. Results indicate that strain alters defect energetics which, in turn, modifies their diffusion characteristics.

Evaluation of gravimetric techniques to estimate the microvascular filtration coefficient

PubMed Central

Dongaonkar, R. M.; Laine, G. A.; Stewart, R. H.

2011-01-01

Microvascular permeability to water is characterized by the microvascular filtration coefficient (Kf). Conventional gravimetric techniques to estimate Kf rely on data obtained from either transient or steady-state increases in organ weight in response to increases in microvascular pressure. Both techniques result in considerably different estimates and neither account for interstitial fluid storage and lymphatic return. We therefore developed a theoretical framework to evaluate Kf estimation techniques by 1) comparing conventional techniques to a novel technique that includes effects of interstitial fluid storage and lymphatic return, 2) evaluating the ability of conventional techniques to reproduce Kf from simulated gravimetric data generated by a realistic interstitial fluid balance model, 3) analyzing new data collected from rat intestine, and 4) analyzing previously reported data. These approaches revealed that the steady-state gravimetric technique yields estimates that are not directly related to Kf and are in some cases directly proportional to interstitial compliance. However, the transient gravimetric technique yields accurate estimates in some organs, because the typical experimental duration minimizes the effects of interstitial fluid storage and lymphatic return. Furthermore, our analytical framework reveals that the supposed requirement of tying off all draining lymphatic vessels for the transient technique is unnecessary. Finally, our numerical simulations indicate that our comprehensive technique accurately reproduces the value of Kf in all organs, is not confounded by interstitial storage and lymphatic return, and provides corroboration of the estimate from the transient technique. PMID:21346245

Diffusion of oxygen interstitials in UO2+x using kinetic Monte Carlo simulations: Role of O/M ratio and sensitivity analysis

NASA Astrophysics Data System (ADS)

Behera, Rakesh K.; Watanabe, Taku; Andersson, David A.; Uberuaga, Blas P.; Deo, Chaitanya S.

2016-04-01

Oxygen interstitials in UO2+x significantly affect the thermophysical properties and microstructural evolution of the oxide nuclear fuel. In hyperstoichiometric Urania (UO2+x), these oxygen interstitials form different types of defect clusters, which have different migration behavior. In this study we have used kinetic Monte Carlo (kMC) to evaluate diffusivities of oxygen interstitials accounting for mono- and di-interstitial clusters. Our results indicate that the predicted diffusivities increase significantly at higher non-stoichiometry (x > 0.01) for di-interstitial clusters compared to a mono-interstitial only model. The diffusivities calculated at higher temperatures compare better with experimental values than at lower temperatures (< 973 K). We have discussed the resulting activation energies achieved for diffusion with all the mono- and di-interstitial models. We have carefully performed sensitivity analysis to estimate the effect of input di-interstitial binding energies on the predicted diffusivities and activation energies. While this article only discusses mono- and di-interstitials in evaluating oxygen diffusion response in UO2+x, future improvements to the model will primarily focus on including energetic definitions of larger stable interstitial clusters reported in the literature. The addition of larger clusters to the kMC model is expected to improve the comparison of oxygen transport in UO2+x with experiment.

Doxorubicin-loaded Zein in situ gel for interstitial chemotherapy.

PubMed

Cao, Xiaoying; Geng, Jianning; Su, Suwen; Zhang, Linan; Xu, Qian; Zhang, Li; Xie, Yinghua; Wu, Shaomei; Sun, Yongjun; Gao, Zibin

2012-01-01

A novel drug delivery system of doxorubicin (DOX)-loaded Zein in situ gel for interstitial chemotherapy was investigated in this study. The possible mechanisms of drug release were described according to morphological analysis by optical microscopy and scanning electronic microscope (SEM). In vitro and in vivo anti-tumor activity studies showed that DOX-loaded Zein in situ gel was superior to DOX solution. Local pharmacokinetics in tumor tissue was studied by quantitative analysis with confocal laser scanning microscopy (CLSM) combined with microdialysis technology. A pharmacokinetics mathematical model of DOX-loaded Zein in situ gel in tumors was then built.

The accumulation of femtosecond laser radiation energy in crystals of lithium fluoride

NASA Astrophysics Data System (ADS)

Dresvyanskiy, V. P.; Glazunov, D. S.; Alekseev, S. V.; Losev, V. F.; Chadraa, B.; Bukhtsooj, O.; Baasankhuu, N.; Zandan, B.; Martynovich, E. F.

2015-12-01

We present the results of studies of energy accumulation during the non-destructive interaction of extremely intense near infrared laser radiation with model wide band gap dielectric crystals of lithium fluoride, when the intensity of pulses is sufficient for effective highly nonlinear absorption of light and for the excitation of the electron subsystem of matter and the energy of pulses is still not sufficient for significant heating, evaporation, laser breakdown or other destruction to occur. We studied the emission of energy in the form of light sum of thermally stimulated luminescence accumulated under conditions of self-focusing and multiple filamentation of femtosecond laser radiation. It was established that it's the F2 and F3+ color centers and supplementary to them centers of interstitial type which accumulate energy under the action of a single femtosecond laser pulses. When irradiated by series of pulses the F3, F3- and F4 centers additionally appear. F2 centers are the main centers of emission in the process of thermally stimulated luminescence of accumulated energy. The interstitial fluoride ions (I-centers) are the kinetic particles. They split off from the X3- centers in the result of thermal decomposition of latter on the I-centers and molecules X20. I-centers recombine with F3+ centers and form F2 centers in excited state. The latter produce the characteristic emission spectrum emitted in the form of thermally stimulated luminescence.

Low-power interstitial photocoagulation of uterine leiomyomas by KTP/YAG laser: a review of 50 consecutive cases

NASA Astrophysics Data System (ADS)

Chapman, Roxana

1994-12-01

Interstitial laser photocoagulation (ILP), which is a new method of low power laser destruction of tumors, has been used to treat laparoscopically 50 consecutive patients with symptomatic uterine leiomyomas which were difficult or impossible to remove via laparoscopy. The KTP/YAG laser, with wavelengths of 532 and 1064 nm respectively, was employed. Holes 2 cm apart were drilled with a 600 micrometers quartz laser fiber employing the KTP component at 8 W and subsequent coagulation of the surrounding myoma tissue was accomplished during the withdrawal of the fiber over the course of 10 - 30 s but using the YAG component at 8 W until the whole myoma had been treated. Thirty seven became symptom free and have remained so. Six were lost to follow up. Of 10 complaining of subfertility 4, in whom uterine myomas were the only etiological factor, have become pregnant. Seven patients required further treatment: Two were retreated because their myomas were excessively large and did not completely disappear with the initial ILP, 2 received further ILP because of the development of new myomas and 3 were subjected to laparoscopically assisted vaginal hysterectomy at patients' request (2 because of the development of new myomas and 1 because of the development of further endometriosis). Finally, in 7 cases, residual tumor or scar tissue was biopsied and examined for the presence of oestrogen and progesterone receptors. None was discovered and in 2 subsequent pregnancy did not cause further growth of residual myoma tissue.

Primary damage formation in bcc iron

NASA Astrophysics Data System (ADS)

Stoller, R. E.; Odette, G. R.; Wirth, B. D.

1997-11-01

Primary defect formation in bee iron has been extensively investigated using the methods of molecular dynamics (MD) and Monte Carlo (MC) simulation. This research has employed a modified version of the Finnis-Sinclair interatomic potential. MD was used in the simulation of displacement cascades with energies up to 40 keV and to examine the migration of the interstitial clusters that were observed to form in the cascade simulations. Interstitial cluster binding energies and the stable cluster configurations were determined by structural relaxation and energy minimization using a MC method with simulated annealing. Clusters containing up to 19 interstitials were examined. Taken together with the previous work, these new simulations provide a reasonably complete description of primary defect formation in iron. The results of the displacement cascade simulations have been used to characterize the energy and temperature dependence of primary defect formation in terms of two parameters: (1) the number of surviving point defects and (2) the fraction of the surviving defects that are contained in clusters. The number of surviving point defects is expressed as a fraction of the atomic displacements calculated using the secondary displacement model of Norgett-Robinson-Torrens (NRT). Although the results of the high energy simulations are generally consistent with those obtained at lower energies, two notable exceptions were observed. The first is that extensive subcascade formation at 40 keV leads to a higher defect survival fraction than would be predicted from extrapolation of the results obtained for energies up to 20 keV. The stable defect fraction obtained from the MD simulations is a smoothly decreasing function up to 20 keV. Subcascade formation leads to a slight increase in this ratio at 40 keV, where the value is about the same as at 10 keV. Secondly, the potential for a significant level of in-cascade vacancy clustering was observed. Previous cascade studies employing this potential have reported extensive interstitial clustering, but little evidence of vacancy clustering. Interstitial clusters were found to be strongly bound, with binding energies in excess of 1 eV. The larger clusters exhibited a complex, 3D structure and were composed of <111> crowdions. These clusters were observed to migrate by collective <111> translations with an activation energy on the order of 0.1 eV.

External and intralesional photocoagulation of hemangioma in children with infrared diode laser

NASA Astrophysics Data System (ADS)

Abushkin, Ivan A.; Privalov, Valery A.; Lappa, Alexander V.; Besshtanko, Evgeny L.

2005-08-01

Infra-red diode laser with wavelength 1060 nm was used for combined treatment of 163 children aged from 21 days to 13 years with 221 hemangiomas. For interstitial coagulation a power of 1.8-2 W and a power density of 5-90 J/cm3 were used in continuous mode. For distant coagulation pulse mode was applied with pulse/pause duration 30-50/200-250 ms, average power 1.3-2 W, and power density 65-450 J/cm2. 197 (89.1 %) hemangiomas were capillary, 7 (3.2 %) cavernous, and 17 (7.7 %) combined (combination of capillary and cavernous hemangiomas). The area of hemangiomas ranged from 6 mm2 to 48 cm2. For the majority (193, 87.3 %) of hemangiomas one session of photocoagulation was enough to achieve a good cosmetic effect. However, 28 (12.7 %) hemangiomas were treated repeatedly, 11 (5%) of them needed 4-7 sessions. In 8 children with cavernous and combined hemangiomas both distant and interstitial laser coagulation were used. In all, good or excellent results were obtained in 96,3 % of the patients. In 6 (3.7%) patients with extensive combined hematomas the considerable improvement was achieved.

Advanced technology in neurosurgery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pluchino, F.; Broggi, G.

1987-01-01

Technological improvements in neurosurgery are discussed. The use of surgical lasers, ultrasound aspirators, bipolar coagulator and operative microscopes for surgery of deep-seated neoplasms and vascular malformations is discussed. Intraoperative monitoring, chronotherapy, chronic neurostimulation and stereotactic interstitial irradiation are covered and indications for interventional neuroradiology are reviewed.

A Wsbnd Ne interatomic potential for simulation of neon implantation in tungsten

NASA Astrophysics Data System (ADS)

Backman, Marie; Juslin, Niklas; Huang, Guiyang; Wirth, Brian D.

2016-08-01

An interatomic pair potential for Wsbnd Ne is developed for atomistic molecular dynamics simulations of neon implantation in tungsten. The new potential predicts point defect energies and binding energies of small clusters that are in good agreement with electronic structure calculations. Molecular dynamics simulations of small neon clusters in tungsten show that trap mutation, in which an interstitial neon cluster displaces a tungsten atom from its lattice site, occurs for clusters of three or more neon atoms. However, near a free surface, trap mutation can occur at smaller sizes, including even a single neon interstitial in close proximity to a (100) or (110) surface.

Magnetic Resonance Imaging-Guided Focused Laser Interstitial Thermal Therapy for Intracranial Lesions: Single-Institution Series

PubMed Central

Hawasli, Ammar H.; Bagade, Swapnil; Shimony, Joshua S.; Miller-Thomas, Michelle

2013-01-01

BACKGROUND: Surgical treatments for deep-seated intracranial lesions have been limited by morbidities associated with resection. Real-time magnetic resonance imaging–guided focused laser interstitial thermal therapy (LITT) offers a minimally invasive surgical treatment option for such lesions. OBJECTIVE: To review treatments and results of patients treated with LITT for intracranial lesions at Washington University School of Medicine. METHODS: In a review of 17 prospectively recruited LITT patients (34-78 years of age; mean, 59 years), we report demographics, treatment details, postoperative imaging characteristics, and peri- and postoperative clinical courses. RESULTS: Targets included 11 gliomas, 5 brain metastases, and 1 epilepsy focus. Lesions were lobar (n = 8), thalamic/basal ganglia (n = 5), insular (n = 3), and corpus callosum (n = 1). Mean target volume was 11.6 cm3, and LITT produced 93% target ablation. Patients with superficial lesions had shorter intensive care unit stays. Ten patients experienced no perioperative morbidities. Morbidities included transient aphasia, hemiparesis, hyponatremia, deep venous thrombosis, and fatal meningitis. Postoperative magnetic resonance imaging showed blood products within the lesion surrounded by new thin uniform rim of contrast enhancement and diffusion restriction. In conjunction with other therapies, LITT targets often showed stable or reduced local disease. Epilepsy focus LITT produced seizure freedom at 8 months. Preliminary overall median progression-free survival and survival from LITT in tumor patients were 7.6 and 10.9 months, respectively. However, this small cohort has not been followed for a sufficient length of time, necessitating future outcomes studies. CONCLUSION: Early peri- and postoperative clinical data demonstrate that LITT is a safe and viable ablative treatment option for intracranial lesions, and may be considered for select patients. ABBREVIATION: LITT, laser interstitial thermal therapy PMID:24056317

Effect of interstitial low level laser therapy on tibial defect

NASA Astrophysics Data System (ADS)

Lee, Sangyeob; Ha, Myungjin; Hwang, Donghyun; Yu, Sungkon; Jang, Seulki; Park, Jihoon; Radfar, Edalat; Kim, Hansung; Jung, Byungjo

2016-03-01

Tibial defect is very common musculoskeletal disorder which makes patient painful and uncomfortable. Many studies about bone regeneration tried to figure out fast bone healing on early phase. It is already known that low level laser therapy (LLLT) is very convenient and good for beginning of bone disorder. However, light scattering and absorption obstruct musculoskeletal therapy which need optimal photon energy delivery. This study has used an interstitial laser probe (ILP) to overcome the limitations of light penetration depth and scattering. Animals (mouse, C57BL/6) were divided into three groups: laser treated test group 1 (660 nm; power 10 mW; total energy 5 J) and test group 2 (660 nm; power 20 mW; total energy 10 J); and untreated control group. All animals were taken surgical operation to make tibial defect on right crest of tibia. The test groups were treated every 48 hours with ILP. Bone volume and X-ray attenuation coefficient were measured on 0, 14th and 28th day with u-CT after treatment and were used to evaluate effect of LLLT. Results show that bone volume of test groups has been improved more than control group. X-ray attenuation coefficients of each groups have slightly different. The results suggest that LLLT combined with ILP may affect on early phase of bone regeneration and may be used in various musculoskeletal disease in deep tissue layer.

Stochastic annealing simulations of defect interactions among subcascades

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heinisch, H.L.; Singh, B.N.

1997-04-01

The effects of the subcascade structure of high energy cascades on the temperature dependencies of annihilation, clustering and free defect production are investigated. The subcascade structure is simulated by closely spaced groups of lower energy MD cascades. The simulation results illustrate the strong influence of the defect configuration existing in the primary damage state on subsequent intracascade evolution. Other significant factors affecting the evolution of the defect distribution are the large differences in mobility and stability of vacancy and interstitial defects and the rapid one-dimensional diffusion of small, glissile interstitial loops produced directly in cascades. Annealing simulations are also performedmore » on high-energy, subcascade-producing cascades generated with the binary collision approximation and calibrated to MD results.« less

Biodegradable magnesium nanoparticle-enhanced laser hyperthermia therapy

PubMed Central

Wang, Qian; Xie, Liping; He, Zhizhu; Di, Derui; Liu, Jing

2012-01-01

Background Recently, nanoparticles have been demonstrated to have tremendous merit in terms of improving the treatment specificity and thermal ablation effect on tumors. However, the potential toxicity and long-term side effects caused by the introduced nanoparticles and by expelling them out of the body following surgery remain a significant challenge. Here, we propose for the first time to directly adopt magnesium nanoparticles as the heating enhancer in laser thermal ablation to avoid these problems by making full use of the perfect biodegradable properties of this specific material. Methods To better understand the new nano “green” hyperthermia modality, we evaluated the effects of magnesium nanoparticles on the temperature transients inside the human body subject to laser interstitial heating. Further, we experimentally investigated the heating enhancement effects of magnesium nanoparticles on a group of biological samples: oil, egg white, egg yolk, in vitro pig tissues, and the in vivo hind leg of rabbit when subjected to laser irradiation. Results Both the theoretical simulations and experimental measurements demonstrated that the target tissues injected with magnesium nanoparticles reached much higher temperatures than tissues without magnesium nanoparticles. This revealed the enhancing behavior of the new nanohyperthermia method. Conclusion Given the unique features of magnesium nanoparticles – their complete biological safety and ability to enhance heating – which most other advanced metal nanoparticles do not possess, the use of magnesium nanoparticles in hyperthermia therapy offers an important “green” nanomedicine modality for treating tumors. This method has the potential to be used in clinics in the near future. PMID:22956872

Laser bioengineering of glass-titanium implants surface

NASA Astrophysics Data System (ADS)

Lusquiños, F.; Arias-González, F.; Penide, J.; del Val, J.; Comesaña, R.; Quintero, F.; Riveiro, A.; Boutinguiza, M.; Pascual, M. J.; Durán, A.; Pou, J.

2013-11-01

Osseointegration is the mean challenge when surgical treatments fight against load-bearing bone diseases. Absolute bone replacement by a synthetic implant has to be completed not only from the mechanics point of view, but also from a biological approach. Suitable strength, resilience and stress distribution of titanium alloy implants are spoiled by the lack of optimal biological characteristics. The inert quality of extra low interstitial titanium alloy, which make it the most attractive metallic alloy for biomedical applications, oppose to an ideal surface with bone cell affinity, and capable to stimulate bone attachment bone growth. Diverse laser treatments have been proven as effective tools to modify surface properties, such as wettability in contact to physiological fluids, or osteoblast guided and slightly enhanced attachment. The laser surface cladding can go beyond by providing titanium alloy surfaces with osteoconduction and osteoinduction properties. In this research work, the laser radiation is used to produce bioactive glass coatings on Ti6Al4V alloy substrates. Specific silicate bioactive glass compositions has been investigated to achieve suitable surface tension and viscosity temperature behavior during processing, and to provide with the required release of bone growth gene up regulation agents in the course of resorption mediated by physiological fluids. The produced coatings and interfaces, the surface osteoconduction properties, and the chemical species release in simulated physiological fluid were characterized by scanning electron microscopy (SEM), hot stage microscopy (HSM), X-ray diffraction (XRD), X ray fluorescence (XRF), and Fourier transform infrared spectroscopy (FTIR).

In situ temperature measurements with thermocouple probes during laser interstitial thermotherapy (LITT): quantification and correction of a measurement artifact.

PubMed

Manns, F; Milne, P J; Gonzalez-Cirre, X; Denham, D B; Parel, J M; Robinson, D S

1998-01-01

The purpose of this work was to quantify the magnitude of an artifact induced by stainless steel thermocouple probes in temperature measurements made in situ during experimental laser interstitial thermo-therapy (LITT). A procedure for correction of this observational error is outlined. A CW Nd:YAG laser system emitting 20W for 25-30 s delivered through a fiber-optic probe was used to create localized heating. The temperature field around the fiber-optic probe during laser irradiation was measured every 0.3 s in air, water, 0.4% intralipid solution, and fatty cadaver pig tissue, with a field of up to fifteen needle thermocouple probes. Direct absorption of Nd:YAG laser radiation by the thermocouple probes induced an overestimation of the temperature, ranging from 1.8 degrees C to 118.6 degrees C in air, 2.2 degrees C to 9.9 degrees C in water, 0.7 C to 4.7 C in intralipid and 0.3 C to 17.9 C in porcine tissue after irradiation at 20W for 30 s and depending on the thermocouple location. The artifact in porcine tissue was removed by applying exponential and linear fits to the measured temperature curves. Light absorption by thermocouple probes can induce a significant artifact in the measurement of laser-induced temperature increases. When the time constant of the thermocouple effect is much smaller than the thermal relaxation time of the surrounding tissue, the artifact can be accurately quantified. During LITT experiments where temperature differences of a few degrees are significant, the thermocouple artifact must be removed in order to be able accurately to predict the treatment outcome.

Formation of prismatic loops from C15 Laves phase interstitial clusters in body-centered cubic iron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yongfeng; Bai, Xian-Ming; Tonks, Michael R.

2015-03-01

This Letter reports the transition of C15 phase self-interstitial clusters to loops in body-centered-cubic Iron. Molecular dynamics simulations are performed to evaluate the relative stabilities of difference interstitial cluster configurations including C15 phase structure and <100> and <111>/2 loops. Within a certain size range, C15 cluster are found more stable than loops, and the relative stabilities are reversed beyond that range. In accordance to the crossover in relative stabilities, C15 clusters may grow by absorbing individual interstitials at small sizes and transitions into loops eventually. The transition takes place by nucleation and reaction of <111>/2 loop segments. These observations explainmore » the absence of C15 phase interstitial clusters predicted by density-functional-theory calculations in previous experimental observations. More importantly, the current results provide a new formation mechanism of <100> loops which requires no interaction of loops.« less

Endoscopic Photodynamic Therapy: Fiber Optic Delivery For The Treatment Of Esophageal And Bronchial Cancer

NASA Astrophysics Data System (ADS)

Mang, Thomas S.; Nava, Hector R.; Regal, Anne-Marie

1989-06-01

Clinical studies in photodynamic therapy (PDT) have utilized lasers to take advantage of coupling efficiencies to optical fibers allowing light to be delivered to many areas of the body. This is particularly true in endoscopic PDT. Both interstitial and superficial delivery techniques can be applied using one of a variety of delivery fibers available. A fiber with an optically flat end with a lens to produce a spot with a homogeneous intensity is used for superficial applications. Diffusers of various lengths, at the tip of a fiber, produce a cylindrical isotropic pattern and are suited for either intraluminal or interstitial illuminations.

Impact of Laser Radiation on Microhardness of a Semiconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medvid', A.; Onufrijevs, P.; Chiradze, G.

2011-12-23

It was found that strongly absorbed Nd:YAG laser radiation leads to a non-monotonous dependence of microhardness of p- and n-type Si crystals on laser radiation. This dependence is characterized by two maxima for p-Si and one maximum for n-Si crystals. In both cases the increase of microhardness at higher laser intensity is explained by formation of mechanically compressed layer at the irradiated surface due to concentration of the interstitial atoms of Si at the surface in temperature gradient field. The decrease of the microhardness is explained by formation of nano-cones as a result of plastic deformation of the mechanically stressedmore » layer. The additional maximum at lower laser intensity for p-Si crystal is explained by p-n type inversion of Si conductivity.« less

Experimental and numerical investigation of dual phase steels formability during laser-assisted hole-flanging

NASA Astrophysics Data System (ADS)

Motaman, S. A. H.; Komerla, K.; Storms, T.; Prahl, U.; Brecher, C.; Bleck, W.

2018-05-01

Today, in the automotive industry dual phase (DP) steels are extensively used in the production of various structural parts due to their superior mechanical properties. Hole-flanging of such steels due to simultaneous bending and stretching of sheet metal, is complex and associated with some issues such as strain and strain rate localization, development of micro-cracks, inhomogeneous sheet thinning, etc. In this study an attempt is made to improve the formability of DP sheets, by localized Laser heating. The Laser beam was oscillated in circular pattern rapidly around the pre-hole, blanked prior to the flanging process. In order to investigate formability of DP steel (DP1000), several uniaxial tensile tests were conducted from quasi to intermediate strain rates at different temperatures in warm regime. Additionally, experimentally acquired temperature and strain rate-dependent flow curves were fed into thermomechanical finite element (FE) simulation of the hole-flanging process using the commercial FE software ABAQUS/Explicit. Several FE simulations were performed in order to evaluate the effect of blank's initial temperature and punch speed on deformation localization, stress evolution and temperature distribution in DP1000 sheets during warm hole-flanging process. The experimental and numerical analyses revealed that prescribing a distribution of initial temperature between 300 to 400 °C to the blank and setting a punch speed that accommodates strain rate range of 1 to 5 s-1 in the blank, provides the highest strain hardening capacity in the considered rate and temperature regimes for DP1000. This is in fact largely due to the dynamic strain aging (DSA) effect which occurs due to pinning of mobile dislocations by interstitial solute atoms, particularly at elevated temperatures.

Asymmetry of radiation damage properties in Al-Ti nanolayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Setyawan, Wahyu; Gerboth, Matthew D.; Yao, Bo

2014-02-01

Molecular dynamics (MD) simulations were employed with empirical potentials to study the effects of multilayer interfaces and interface spacing in Al-Ti nanolayers. Several model interfaces derived from stacking of close-packed layers or face-centered cubic \\{100\\} layers were investigated. The simulations reveal significant and important asymmetries in defect production withmore » $$\\sim$$60\\% of vacancies created in Al layers compared to Ti layers within the Al-Ti multilayer system. The asymmetry in the creation of interstitials is even more pronounced. The asymmetries cause an imbalance in the ratio of vacancies and interstitials in films of dissimilar materials leading to $>$$90\\% of the surviving interstitials located in the Al layers. While in the close-packed nanolayers the interstitials migrate to the atomic layers adjacent to the interface of the Al layers, in the \\{100\\} nanolayers the interstitials migrate to the center of the Al layers and away from the interfaces. The degree of asymmetry and defect ratio imbalance increases as the layer spacing decreases in the multilayer films. Underlying physical processes are discussed including the interfacial strain fields and the individual elemental layer stopping power in nanolayered systems. In addition, experimental work was performed on low-dose (10$$^{16}$ atoms/cm$^2$) helium (He) irradiation on Al/Ti nanolayers (5 nm per film), resulting in He bubble formation $$\\sim$$1 nm in diameter in the Ti film near the interface. The correlation between the preferential flux of displaced atoms from Ti films to Al films during the defect production that is revealed in the simulations and the morphology and location of He bubbles from the experiments is discussed.« less

Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shenyang; Burkes, Douglas E.; Lavender, Curt A.

2016-07-08

Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the for- mation mechanism of gas bubble superlattices is not well understood. A number of physical processes may affect the gas bubble nucleation and growth; hence, the morphology of gas bubble microstructures including size and spatial distributions. In this work, a phase-field model integrating a first-passage Monte Carlo method to investigate the formation mechanism of gas bubble superlattices was devel- oped. Six physical processes are taken into account in the model: 1) heterogeneous generation of gas atoms, vacancies, and interstitials informed from atomistic simulations; 2) one-dimensional (1-D) migration of interstitials; 3) irradiation-induced dissolution of gas atoms; 4) recombination between vacancies and interstitials; 5) elastic interaction; and 6) heterogeneous nucleation of gas bubbles. We found that the elastic interaction doesn’t cause the gas bubble alignment, and fast 1-D migration of interstitials alongmore » $$\\langle$$110$$\\rangle$$ directions in the body-centered cubic U matrix causes the gas bubble alignment along $$\\langle$$110$$\\rangle$$ directions. It implies that 1-D interstitial migration along [110] direction should be the primary mechanism of a fcc gas bubble superlattice which is observed in bcc UMo alloys. Simulations also show that fission rates, saturated gas concentration, and elastic interaction all affect the morphology of gas bubble microstructures.« less

Interstitial ablation and imaging of soft tissue using miniaturized ultrasound arrays

NASA Astrophysics Data System (ADS)

Makin, Inder R. S.; Gallagher, Laura A.; Mast, T. Douglas; Runk, Megan M.; Faidi, Waseem; Barthe, Peter G.; Slayton, Michael H.

2004-05-01

A potential alternative to extracorporeal, noninvasive HIFU therapy is minimally invasive, interstitial ultrasound ablation that can be performed laparoscopically or percutaneously. Research in this area at Guided Therapy Systems and Ethicon Endo-Surgery has included development of miniaturized (~3 mm diameter) linear ultrasound arrays capable of high power for bulk tissue ablation as well as broad bandwidth for imaging. An integrated control system allows therapy planning and automated treatment guided by real-time interstitial B-scan imaging. Image quality, challenging because of limited probe dimensions and channel count, is aided by signal processing techniques that improve image definition and contrast. Simulations of ultrasonic heat deposition, bio-heat transfer, and tissue modification provide understanding and guidance for development of treatment strategies. Results from in vitro and in vivo ablation experiments, together with corresponding simulations, will be described. Using methods of rotational scanning, this approach is shown to be capable of clinically relevant ablation rates and volumes.

New laser treatment approaches for benign prostatic hyperplasia.

PubMed

Fried, Nathaniel M

2007-01-01

The recent introduction of higher power 100 W holmium:yttrium-aluminum-garnet (Ho:YAG) and 80 W potassium titanyl phosphate lasers for rapid incision and vaporization of the prostate has resulted in renewed interest in the use of lasers for treatment of benign prostatic hyperplasia (BPH). Although long-term studies are still lacking, short-term results demonstrate that these procedures are at least as safe and effective in relieving BPH symptoms as transurethral resection of the prostate and may provide reduced morbidity. Other laser techniques, such as interstitial laser coagulation and contact laser vaporization of the prostate, have lost popularity due to complications with increased catheterization time, irritative symptoms, and infection rates. Although Ho:YAG laser enucleation of the prostate is more difficult to learn and a slower procedure than potassium titanyl phosphate laser vaporization, the Ho:YAG laser is currently the most proven laser technique for BPH treatment. This article reviews the latest developments in laser treatment of BPH over the past 2 years and provides a view toward the future of lasers in the treatment of BPH.

Atomistic Simulation of Displacement Cascades in Zircon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devanathan, Ram; Weber, William J.; Corrales, Louis R.

2002-05-06

Low energy displacement cascades in zircon (ZrSiO4) initiated by a Zr primary knock-on atom have been investigated by molecular dynamics simulations using a Coulombic model for long-range interactions, Buckingham potential for short-range interactions and Ziegler-Biersack potentials for close pair interactions. Displacements were found to occur mainly in the O sublattice, and O replacements by a ring mechanism were predominant. Clusters containing Si interstitials bridged by O interstitials, vacancy clusters and anti-site defects were found to occur. This Si-O-Si bridging is considerable in quenched liquid ZrSiO4.

Interstitial micelles in binary blends of A B A triblock copolymers and homopolymers

NASA Astrophysics Data System (ADS)

Wołoszczuk, S.; Banaszak, M.

2018-01-01

We investigate triblock-homopolymer blends of types A1BA2/A and A1BA2/B, using a lattice Monte Carlo method. While the simulated triblock chains are compositionally symmetric in terms of the A-to-B volume ratio, the A1 block is significantly shorter than the A2 block. For the pure A1BA2 melt and the A1BA2 solutions in selective solvent the phase behavior is relatively well known, including existence and stability of the interstitial micelles which were discovered in previous Monte Carlo simulations. In this paper we study the stability of the interstitial micelles as a function of triblock volume fraction in selective homopolymers of either type A or type B, using two significantly different homopolymer chain lengths. We found that adding selective homopolymer of type A shifts the stability of the interstitial micelles into significantly higher temperatures. We also obtained, via self-assembly, intriguing new nanostructures which can be identified as ordered truncated octahedra. Finally, we established that the phase behavior of the triblock-homopolymer blends depends relatively weakly on the chain length of the added homopolymer.

Effects of applied strain on nanoscale self-interstitial cluster formation in BCC iron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Ning; Setyawan, Wahyu; Kurtz, Richard J.

2017-09-01

The effect of applied strains on the configurational evolution of self-interstitial clusters in BCC iron (Fe) is explored with atomistic simulations. A novel cluster configuration is discovered at low temperatures (<600 K), which consists of <110> dumbbells and <111> crowdions in a specific configuration, resulting in an immobile defect. The stability and diffusion of this cluster at higher temperatures is explored. In addition, an anisotropy distribution factor of a particular [hkl] interstitial loop within the family of loops is calculated as a function of strain. The results show that loop anisotropy is governed by the angle between the stress directionmore » and the orientation of the <111> crowdions in the loop, and directly linked to the stress induced preferred nucleation of self-interstitial atoms.« less

Effects of cyclophosphamide on laser immunotherapy for the treatment of metastatic cancer

NASA Astrophysics Data System (ADS)

Bahavar, Cody F.; Acquaviva, Joseph T.; Rabei, Sheyla; Sikes, Allie; Nordquist, Robert E.; Hode, Tomas; Liu, Hong; Chen, Wei R.

2014-02-01

Laser immunotherapy (LIT) is an innovative cancer modality that uses laser irradiation and immunological stimulation to treat late-stage, metastatic cancers. The current mode of operation in LIT is through interstitial laser irradiation. Although LIT is still in development, recent clinical trials have shown that it can be used to successfully treat patients with late-stage breast cancer and melanoma. Cyclophosphamide is a chemotherapy drug that suppresses regulatory T cells when used in low doses. In this study tumor-bearing rats were treated with LIT using an 805-nm laser with a power of 2.0 W and low-dose cyclophosphamide. Glycated chitosan was used as an immunological stimulant. The goal was to observe the effects of different doses of cyclophosphamide in addition to LIT on the survival of the tumor-bearing rats.

Coupling of atom-by-atom calculations of extended defects with B kick-out equations: application to the simulation of boron ted

NASA Astrophysics Data System (ADS)

Lampin, E.; Cristiano, F.; Lamrani, Y.; Colombeau, B.

2004-02-01

We present simulations of B TED based on a complete calculation of the extended defect growth/shrinkage during annealing. The Si self-interstitial supersaturation calculated at the extended defect depth is coupled to the set of equations for the B kick-out diffusion through a generation/recombination term in the diffusion equation of the Si self-interstitials. The simulations are compared to the measurements performed on a Si wafer containing several B marker layers, where the amount of TED varies from one peak to the other. The good agreement obtained on this experiment is very promising for the application of these calculations to the case of ultra-shallow B + implants.

Raman spectra of Hg-based superconductors: Effect of oxygen defects

NASA Astrophysics Data System (ADS)

Zhou, Xingjiang; Cardona, M.; Chu, C. W.; Lin, Q. M.; Loureiro, S. M.; Marezio, M.

1996-09-01

Polarized micro-Raman scattering measurements have been performed on the five members of the HgBa2Can-1CunO2n+2+δ (n=1, 2, 3, 4, and 5) high-Tc superconductor family. A systematic evolution of the spectrum, which mainly involves oxygen-related phonons around 590, 570, 540, and 470 cm-1, with an increasing number of CuO2 layers, has been observed. Local laser annealing measurements clearly demonstrate that all these phonons are closely related to interstitial oxygen in the HgOδ planes. The origin of the spectrum evolution with the number of CuO2 layers lies in the variation of interstitial oxygen content.

In-vitro analysis of early calcification in aortic valvular interstitial cells using Laser-Induced Breakdown Spectroscopy (LIBS).

PubMed

Davari, Seyyed Ali; Masjedi, Shirin; Ferdous, Zannatul; Mukherjee, Dibyendu

2018-01-01

Calcific aortic valve disease (CAVD) is a major cardiovascular disorder caused by osteogenic differentiation of valvular interstitial cells (VICs) within aortic valves. Conventional methods like colorimetric assays and histology fail to detect small calcium depositions during in-vitro VIC cultures. Laser-induced breakdown spectroscopy (LIBS) is a robust analytical tool used for inorganic materials characterizations, but relatively new to biomedical applications. We employ LIBS, for the first time, for quantitative in-vitro detection of calcium depositions in VICs at various osteogenic differentiation stages. VICs isolated from porcine aortic valves were cultured in osteogenic media over various days. Colorimetric calcium assays based on arsenazo dye and Von Kossa staining measured the calcium depositions within VICs. Simultaneously, LIBS signatures for Ca I (422.67 nm) atomic emission lines were collected for estimating calcium depositions in lyophilized VIC samples. Our results indicate excellent linear correlation between the calcium assay and our LIBS measurements. Furthermore, unlike the assay results, the LIBS results could resolve calcium signals from cell samples with as early as 2 days of osteogenic culture. Quantitatively, the LIBS measurements establish the limit of detection for calcium content in VICs to be ∼0.17±0.04 μg which indicates a 5-fold improvement over calcium assay. Picture: Quantitative LIBS enables in-vitro analysis for early stage detection of calcium deposition within aortic valvular interstitial cells (VICs). © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modeling the suppression of boron transient enhanced diffusion in silicon by substitutional carbon incorporation

NASA Astrophysics Data System (ADS)

Ngau, Julie L.; Griffin, Peter B.; Plummer, James D.

2001-08-01

Recent work has indicated that the suppression of boron transient enhanced diffusion (TED) in carbon-rich Si is caused by nonequilibrium Si point defect concentrations, specifically the undersaturation of Si self-interstitials, that result from the coupled out-diffusion of carbon interstitials via the kick-out and Frank-Turnbull reactions. This study of boron TED reduction in Si1-x-yGexCy during 750 °C inert anneals has revealed that the use of an additional reaction that further reduces the Si self-interstitial concentration is necessary to describe accurately the time evolved diffusion behavior of boron. In this article, we present a comprehensive model which includes {311} defects, boron-interstitial clusters, a carbon kick-out reaction, a carbon Frank-Turnbull reaction, and a carbon interstitial-carbon substitutional (CiCs) pairing reaction that successfully simulates carbon suppression of boron TED at 750 °C for anneal times ranging from 10 s to 60 min.

Effects of applied strain on nanoscale self-interstitial cluster formation in BCC iron

NASA Astrophysics Data System (ADS)

Gao, Ning; Setyawan, Wahyu; Kurtz, Richard J.; Wang, Zhiguang

2017-09-01

The effect of applied strains on the configurational evolution of self-interstitial clusters in BCC iron (Fe) is explored with atomistic simulations. A novel cluster configuration is discovered at low temperatures (<600 K), which consists of 〈 110 〉 dumbbells and 〈 111 〉 crowdions in a specific configuration, resulting in an immobile defect. The stability and diffusion of this cluster at higher temperatures is explored. In addition, an anisotropy distribution factor of a particular [ hkl ] interstitial loop within the family of 〈 hkl 〉 loops is calculated as a function of strain. The results show that loop anisotropy is governed by the angle between the stress direction and the orientation of the 〈 111 〉 crowdions in the loop, and directly linked to the stress induced preferred nucleation of self-interstitial atoms.

Periodic surface structure bifurcation induced by ultrafast laser generated point defect diffusion in GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abere, Michael J.; Yalisove, Steven M.; Torralva, Ben

2016-04-11

The formation of high spatial frequency laser induced periodic surface structures (HSFL) with period <0.3 λ in GaAs after irradiation with femtosecond laser pulses in air is studied. We have identified a point defect generation mechanism that operates in a specific range of fluences in semiconductors between the band-gap closure and ultrafast-melt thresholds that produces vacancy/interstitial pairs. Stress relaxation, via diffusing defects, forms the 350–400 nm tall and ∼90 nm wide structures through a bifurcation process of lower spatial frequency surface structures. The resulting HSFL are predominately epitaxial single crystals and retain the original GaAs stoichiometry.

Computer Simulations of the Tumor Vasculature: Applications to Interstitial Fluid Flow, Drug Delivery, and Oxygen Supply.

PubMed

Welter, Michael; Rieger, Heiko

2016-01-01

Tumor vasculature, the blood vessel network supplying a growing tumor with nutrients such as oxygen or glucose, is in many respects different from the hierarchically organized arterio-venous blood vessel network in normal tissues. Angiogenesis (the formation of new blood vessels), vessel cooption (the integration of existing blood vessels into the tumor vasculature), and vessel regression remodel the healthy vascular network into a tumor-specific vasculature. Integrative models, based on detailed experimental data and physical laws, implement, in silico, the complex interplay of molecular pathways, cell proliferation, migration, and death, tissue microenvironment, mechanical and hydrodynamic forces, and the fine structure of the host tissue vasculature. With the help of computer simulations high-precision information about blood flow patterns, interstitial fluid flow, drug distribution, oxygen and nutrient distribution can be obtained and a plethora of therapeutic protocols can be tested before clinical trials. This chapter provides an overview over the current status of computer simulations of vascular remodeling during tumor growth including interstitial fluid flow, drug delivery, and oxygen supply within the tumor. The model predictions are compared with experimental and clinical data and a number of longstanding physiological paradigms about tumor vasculature and intratumoral solute transport are critically scrutinized.

Effect of Strain Field on Threshold Displacement Energy of Tungsten Studied by Molecular Dynamics Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Dong; Gao, Ning; Setyawan, W.

The influence of strain field on defect formation energy and threshold displacement energy (Ed) in body-centered cubic (BCC) tungsten (W) has been studied with molecular dynamics simulations. Two different W potentials (Fikar and Juslin) were compared and the results indicate that the connection distance and selected function linking the short-range and long-range portions of the potentials affects the threshold displacement energy and its direction-specific values. The minimum Ed direction calculated with the Fikar-potential is <100> and with the Juslin-potential is <111>. Nevertheless, the most stable self-interstitial configuration is found to be a <111>-crowdion for both potentials. This stable configuration doesmore » not change with applied strain. Varying the strain from compression to tension increases the vacancy formation energy but decreases the self-interstitial formation energy. The formation energy of a self-interstitial changes more significantly than a vacancy such that Ed decreases with applied hydrostatic strain from compression to tension.« less

N vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in TiN studied by ab-initio and classical molecular dynamics

NASA Astrophysics Data System (ADS)

Sangiovanni, Davide G.; Alling, Björn; Hultman, Lars; Abrikosov, Igor A.

2015-03-01

We use ab-initio and classical molecular dynamics (AIMD, CMD) to simulate diffusion of N vacancy and N self-interstitial point-defects in B1 TiN. The physical properties of TiN, important material system for thin film and coatings applications, are largely dictated by concentration and mobility of point defects. We determine N dilute-point-defect diffusion pathways, activation energies, attempt frequencies, and diffusion coefficients as a function of temperature. In addition, MD simulations reveal an unanticipated atomistic process, which controls the spontaneous formation of N-self-interstitial/N-vacancy pairs (Frenkel pairs) in defect-free TiN. This entails that a N lattice atom leaves its bulk position and bonds to a neighboring N lattice atom. In most cases, Frenkel-pair NI and NV recombine within a fraction of ns; 50% of these processes result in the exchange of two nitrogen lattice atoms. Occasionally, however, Frenkel-pair N-interstitial atoms permanently escape from the anion vacancy site, thus producing unpaired NI and NV point defects. The Knut and Alice Wallenberg foundation (Isotope Project, 2011.0094), the Swedish Research Council (VR) Linköping Linnaeus Initiative LiLi-NFM (Grant 2008-6572), and the Swedish Government Strategic Research (Grant MatLiU 2009-00971).

Nitrogen vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in B 1 TiN studied by ab initio and classical molecular dynamics with optimized potentials

NASA Astrophysics Data System (ADS)

Sangiovanni, D. G.; Alling, B.; Steneteg, P.; Hultman, L.; Abrikosov, I. A.

2015-02-01

We use ab initio and classical molecular dynamics (AIMD and CMD) based on the modified embedded-atom method (MEAM) potential to simulate diffusion of N vacancy and N self-interstitial point defects in B 1 TiN. TiN MEAM parameters are optimized to obtain CMD nitrogen point-defect jump rates in agreement with AIMD predictions, as well as an excellent description of Ti Nx(˜0.7

Estimates of point defect production in α-quartz using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Cowen, Benjamin J.; El-Genk, Mohamed S.

2017-07-01

Molecular dynamics (MD) simulations are performed to investigate the production of point defects in α-quartz by oxygen and silicon primary knock-on atoms (PKAs) of 0.25-2 keV. The Wigner-Seitz (WS) defect analysis is used to identify the produced vacancies, interstitials, and antisites, and the coordination defect analysis is used to identify the under and over-coordinated oxygen and silicon atoms. The defects at the end of the ballistic phase and the residual defects, after annealing, increase with increased PKA energy, and are statistically the same for the oxygen and silicon PKAs. The WS defect analysis results show that the numbers of the oxygen vacancies and interstitials (VO, Oi) at the end of the ballistic phase is the highest, followed closely by those of the silicon vacancies and interstitials (VSi, Sii). The number of the residual oxygen and silicon vacancies and interstitials are statistically the same. In addition, the under-coordinated OI and SiIII, which are the primary defects during the ballistic phase, have high annealing efficiencies (>89%). The over-coordinated defects of OIII and SiV, which are not nearly as abundant in the ballistic phase, have much lower annealing efficiencies (<63%) that decrease with increased PKA energy.

Real-time temperature monitoring with fiber Bragg grating sensor during diffuser-assisted laser-induced interstitial thermotherapy.

PubMed

Pham, Ngot Thi; Lee, Seul Lee; Park, Suhyun; Lee, Yong Wook; Kang, Hyun Wook

2017-04-01

High-sensitivity temperature sensors have been used to validate real-time thermal responses in tissue during photothermal treatment. The objective of the current study was to evaluate the feasible application of a fiber Bragg grating (FBG) sensor for diffuser-assisted laser-induced interstitial thermotherapy (LITT) particularly to treat tubular tissue disease. A 600 - ? m core-diameter diffuser was employed to deliver 980-nm laser light for coagulation treatment. Both a thermocouple and a FBG were comparatively tested to evaluate temperature measurements in ex vivo liver tissue. The degree of tissue denaturation was estimated as a function of irradiation times and quantitatively compared with light distribution as well as temperature development. At the closer distance to a heat source, the thermocouple measured up to 41% higher maximum temperature than the FBG sensor did after 120-s irradiation (i.e., 98.7 ° C ± 6.1 ° C for FBG versus 131.0 ° C ± 5.1 ° C for thermocouple; p < 0.001 ). Ex vivo porcine urethra tests confirmed the real-time temperature measurements of the FBG sensor as well as consistently circumferential tissue denaturation after 72-s irradiation ( coagulation thickness = 2.2 ± 0.3 ?? mm ). The implementation of FBG can be a feasible sensing technique to instantaneously monitor the temperature developments during diffuser-assisted LITT for treatment of tubular tissue structure.

Magnetic resonance imaging-guided focused laser interstitial thermal therapy for subinsular metastatic adenocarcinoma: technical case report.

PubMed

Hawasli, Ammar H; Ray, Wilson Z; Murphy, Rory K J; Dacey, Ralph G; Leuthardt, Eric C

2012-06-01

To describe the novel use of the AutoLITT System (Monteris Medical, Winnipeg, Manitoba, Canada) for focused laser interstitial thermal therapy (LITT) with intraoperative magnetic resonance imaging (MRI) and stereotactic image guidance for the treatment of metastatic adenocarcinoma in the left insula. The patient was a 61-year-old right-handed man with a history of metastatic adenocarcinoma of the colon. He had previously undergone resection of multiple lesions, Gamma Knife radiosurgery, and whole-brain radiation. Despite treatment of a left insular tumor, serial imaging revealed that the lesion continued to enlarge. Given the refractory nature of this tumor to radiation and the deep-seated location, the patient elected to undergo LITT treatment. The center of the lesion and entry point on the scalp were identified with STEALTH (Medtronic, Memphis, Tennessee) image-guided navigation. The AXiiiS Stereotactic Miniframe (Monteris Medical) for the LITT system was secured onto the skull, and a trajectory was defined to achieve access to the centroid of the tumor. After a burr hole was made, a gadolinium template probe was inserted into the AXiiiS base. The trajectory was confirmed via an intraoperative MRI, and the LITT probe driver was attached to the base and CO2-cooled, side-firing laser LITT probe. The laser was activated and thermometry images were obtained. Two trajectories, posteromedial and anterolateral, produced satisfactory tumor ablation. LITT with intraoperative MRI and stereotactic image guidance is a newly available, minimally invasive, and therapeutically viable technique for the treatment of deep seated brain tumors.

High-power diffusing-tip fibers for interstitial photocoagulation

NASA Astrophysics Data System (ADS)

Sinofsky, Edward L.; Farr, Norman; Baxter, Lincoln; Weiler, William

1997-05-01

A line of optical fiber based diffusing tips has been designed, developed, and tested that are capable of distributing tens of watts of cw laser power over lengths ranging from two millimeters to over 10 cm. The result is a flexible non-stick diffuser capable of coagulating large volumes of tissue in reasonably short exposures of 3 - 5 minutes. Sub-millimeter diameter devices have a distinct effect on reducing the force needed to insert the applicator interstitially into tissue. Utilizing our design approach, we have produced diffusers based on 200 micrometer core fiber that has delivered over 35 watts of Nd:YAG energy over diffusion lengths as short as 4 mm. These applicators are being tested for applications in oncology, cardiology, electrophysiology, urology and gynecology.

Effects of Oxygen Content on Tensile and Fatigue Performance of Ti-6Al-4 V Manufactured by Selective Laser Melting

NASA Astrophysics Data System (ADS)

Quintana, Oscar A.; Tong, Weidong

2017-12-01

We investigated the selective laser melting (SLM) process for development of Ti-6Al-4 V solid material with oxygen content corresponding to the extra low interstitial (ELI) and non-ELI conditions. The microstructure, chemistry, and tensile properties of samples in as-built and hot isostatically pressed (HIPed) condition were evaluated for both material types, while fatigue performance was evaluated by rotating bending fatigue tests on both smooth and notched SLM ELI and non-ELI Ti-6Al-4 V samples in HIPed condition.

The effects of self-interstitial clusters on cascade defect evolution beyond the primary damage state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heinisch, H.L.

1997-04-01

The intracascade evolution of the defect distributions of cascades in copper is investigated using stochastic annealing simulations applied to cascades generated with molecular dynamics (MD). The temperature and energy dependencies of annihilation, clustering and free defect production are determined for individual cascades. The annealing simulation results illustrate the strong influence on intracascade evolution of the defect configuration existing in the primary damage state. Another factor significantly affecting the evolution of the defect distribution is the rapid one-dimensional diffusion of small, glissile interstitial loops produced directly in cascades. This phenomenon introduces a cascade energy dependence of defect evolution that is apparentmore » only beyond the primary damage state, amplifying the need for further study of the annealing phase of cascade evolution and for performing many more MD cascade simulations at higher energies.« less

The relevance of light diffusion profiles for interstitial PDT using light-diffusing optical fibers

NASA Astrophysics Data System (ADS)

Stringasci, Mirian D.; Fortunato, Thereza C.; Moriyama, Lilian T.; Vollet Filho, José Dirceu; Bagnato, Vanderlei S.; Kurachi, Cristina

2017-02-01

Photodynamic therapy (PDT) is a technique used for several tumor types treatment. Light penetration on biological tissue is one limiting factor for PDT applied to large tumors. An alternative is using interstitial PDT, in which optical fibers are inserted into tumors. Cylindrical diffusers have been used in interstitial PDT. Light emission of different diffusers depends on the manufacturing process, size and optical properties of fibers, which make difficult to establish an adequate light dosimetry, since usually light profile is not designed for direct tissue-fiber contact. This study discusses the relevance of light distribution by a cylindrical diffuser into a turbid lipid emulsion solution, and how parts of a single diffuser contribute to illumination. A 2 cm-long cylindrical diffuser optical fiber was connected to a diode laser (630 nm), and the light spatial distribution was measured by scanning the solution with a collection probe. From the light field profile generated by a 1 mm-long intermediary element of a 20 mm-long cylindrical diffuser, recovery of light distribution for the entire diffuser was obtained. PDT was performed in rat healthy liver for a real treatment outcome analysis. By using computational tools, a typical necrosis profile generated by the irradiation with such a diffuser fiber was reconstructed. The results showed that it was possible predicting theoretically the shape of a necrosis profile in a healthy, homogeneous tissue with reasonable accuracy. The ability to predict the necrosis profile obtained from an interstitial illumination by optical diffusers has the potential improve light dosimetry for interstitial PDT.

Paramagnetic dysprosium-doped zinc oxide thin films grown by pulsed-laser deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lo, Fang-Yuh, E-mail: fangyuhlo@ntnu.edu.tw; Ting, Yi-Chieh; Chou, Kai-Chieh

2015-06-07

Dysprosium(Dy)-doped zinc oxide (Dy:ZnO) thin films were fabricated on c-oriented sapphire substrate by pulsed-laser deposition with doping concentration ranging from 1 to 10 at. %. X-ray diffraction (XRD), Raman-scattering, optical transmission spectroscopy, and spectroscopic ellipsometry revealed incorporation of Dy into ZnO host matrix without secondary phase. Solubility limit of Dy in ZnO under our deposition condition was between 5 and 10 at. % according to XRD and Raman-scattering characteristics. Optical transmission spectroscopy and spectroscopic ellipsometry also showed increase in both transmittance in ultraviolet regime and band gap of Dy:ZnO with increasing Dy density. Zinc vacancies and zinc interstitials were identified by photoluminescencemore » spectroscopy as the defects accompanied with Dy incorporation. Magnetic investigations with a superconducting quantum interference device showed paramagnetism without long-range order for all Dy:ZnO thin films, and a hint of antiferromagnetic alignment of Dy impurities was observed at highest doping concentration—indicating the overall contribution of zinc vacancies and zinc interstitials to magnetic interaction was either neutral or toward antiferromagnetic. From our investigations, Dy:ZnO thin films could be useful for spin alignment and magneto-optical applications.« less

Development of ex vivo model for determining temperature distribution in tumor tissue during photothermal therapy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Doughty, Austin; Liu, Shaojie; Zhou, Feifan; Liu, Hong; Chen, Wei R.

2017-02-01

We have recently developed Laser Immunotherapy (LIT), a targeted cancer treatment modality using synergistic application of near-infrared laser irradiation and in situ immunological stimulation. This study further investigates the principles underlying the immune response to LIT treatment by studying immunological impact of the laser photothermal effect in vivo, in vitro, and ex vivo. Tumor cells were stressed in vitro, and samples were collected to analyze protein expression with a Western Blot. Additionally, a tumor model was designed using bovine liver tissue suspended in agarose gel which was treated using laser interstitially and monitored with both proton-resonance frequency shift MR thermometry and thermocouples. From the bovine liver tumor model, we were able to develop the correlation between tissue temperature elevation and laser power and distance from the fiber tip. Similar data was collected by monitoring the temperature of a metastatic mammary tumor in a rat during laser irradiation. Ultimately, these results show that the laser irradiation of LIT leads to clear immunological effects for an effective combination therapy to treat metastatic cancers.

Mathematical modeling of laser lipolysis

PubMed Central

Mordon, Serge R; Wassmer, Benjamin; Reynaud, Jean Pascal; Zemmouri, Jaouad

2008-01-01

Background and Objectives Liposuction continues to be one of the most popular procedures performed in cosmetic surgery. As the public's demand for body contouring continues, laser lipolysis has been proposed to improve results, minimize risk, optimize patient comfort, and reduce the recovery period. Mathematical modeling of laser lipolysis could provide a better understanding of the laser lipolysis process and could determine the optimal dosage as a function of fat volume to be removed. Study design/Materials and Methods An Optical-Thermal-Damage Model was formulated using finite-element modeling software (Femlab 3.1, Comsol Inc). The general model simulated light distribution using the diffusion approximation of the transport theory, temperature rise using the bioheat equation and laser-induced injury using the Arrhenius damage model. Biological tissue was represented by two homogenous regions (dermis and fat layer) with a nonlinear air-tissue boundary condition including free convection. Video recordings were used to gain a better understanding of the back and forth movement of the cannula during laser lipolysis in order to consider them in our mathematical model. Infrared video recordings were also performed in order to compare the actual surface temperatures to our calculations. The reduction in fat volume was determined as a function of the total applied energy and subsequently compared to clinical data reported in the literature. Results In patients, when using cooled tumescent anesthesia, 1064 nm Nd:YAG laser or 980 nm diode laser: (6 W, back and forth motion: 100 mm/s) give similar skin surface temperature (max: 41°C). These measurements are in accordance with those obtained by mathematical modeling performed with a 1 mm cannula inserted inside the hypodermis layer at 0.8 cm below the surface. Similarly, the fat volume reduction observed in patients at 6-month follow up can be determined by mathematical modeling. This fat reduction depends on the applied energy, typically 5 cm3 for 3000 J. At last, skin retraction was observed in patients at 6-month follow up. This observation can be easily explained by mathematical modeling showing that the temperature increase inside the lower dermis is sufficient (48–50°C) to induce skin tightening Discussion and Conclusion Laser lipolysis can be described by a theoretical model. Fat volume reduction observed in patients is in accordance with model calculations. Due to heat diffusion, temperature elevation is also produced inside the lower reticular dermis. This interesting observation can explain remodeling of the collagenous tissue, with clinically evident skin tightening. In conclusion, while the heat generated by interstitial laser irradiation provides stimulate lipolysis of the fat cells, the collagen and elastin are also stimulated resulting in a tightening in the skin. This mathematical model should serve as a useful tool to simulate and better understand the mechanism of action of the laser lipolysis PMID:18312643

Interstitial ultrasound ablation of tumors within or adjacent to bone: Contributions of preferential heating at the bone surface

NASA Astrophysics Data System (ADS)

Scott, Serena J.; Prakash, Punit; Salgaonkar, Vasant; Jones, Peter D.; Cam, Richard N.; Han, Misung; Rieke, Viola; Burdette, E. Clif; Diederich, Chris J.

2013-02-01

Preferential heating of bone due to high ultrasound attenuation may enhance thermal ablation performed with cathetercooled interstitial ultrasound applicators in or near bone. At the same time, thermally and acoustically insulating cortical bone may protect sensitive structures nearby. 3D acoustic and biothermal transient finite element models were developed to simulate temperature and thermal dose distributions during catheter-cooled interstitial ultrasound ablation near bone. Experiments in ex vivo tissues and tissue-mimicking phantoms were performed to validate the models and to quantify the temperature profiles and ablated volumes for various distances between the interstitial applicator and the bone surface. 3D patient-specific models selected to bracket the range of clinical usage were developed to investigate what types of tumors could be treated, applicator configurations, insertion paths, safety margins, and other parameters. Experiments show that preferential heating at the bone surface decreases treatment times compared to when bone is absent and that all tissue between an applicator and bone can be ablated when they are up to 2 cm apart. Simulations indicate that a 5-7 mm safety margin of normal bone is needed to protect (thermal dose < 6 CEM43°C and T < 45°C) sensitive structures behind ablated bone. In 3D patient-specific simulations, tumors 1.0-3.8 cm (L) and 1.3-3.0 cm (D) near or within bone were ablated (thermal dose > 240 CEM43°C) within 10 min without damaging the nearby spinal cord, lungs, esophagus, trachea, or major vasculature. Preferential absorption of ultrasound by bone may provide improved localization, faster treatment times, and larger treatment zones in tumors in and near bone compared to other heating modalities.

A distinct type of cell in myocardium: interstitial Cajal-like cells (ICLCs)

PubMed Central

Kostin, S; Popescu, L M

2009-01-01

Abstract The existence of a novel type of interstitial cells in the heart, interstitial Cajal-like cells (ICLCs), had been described for the first time in 2005. Their identification was mainly based on ultrastructural criteria: very long (tens up to hundreds of micrometres) and moniliform prolongations, which are extremely thin (less than 0.2 μm), below the resolving power of light microscopy. Myocardial ICLCs were also identified by methylene-blue vital staining, silver impregnation, and immunoreactivity for CD 34, vimentin, CD117/c-kit, etc. Although a series of studies provided evidence for the existence of ICLCs in human atria and rat ventricles, further investigations in other laboratories, using additional techniques, are required to substantiate the consistency of these findings. Here we provide further evidence for the existence of ICLCs in human and mammalian hearts (by transmission and scanning electron microscopy, as well as confocal laser scanning microscopy). Noteworthy, we confirm that ICLCs communicate with neighbouring cells via shedding (micro)vesicles. Although these so-called ICLCs represent a distinct type of cells, different from classical interstitial cells of Cajal, or fibroblasts, their role(s) in myocardium remain(s) to be established. Several hypotheses are proposed: (i) adult stromal (mesenchymal) stem cells, which might participate in cardiac repair/remodelling; (ii) intercellular signalling (e.g. via shedding microvesicles); (iii) chemo-mechanical transducers and (iv) players in pacemaking and/or arrhytmogenesis, and so on. PMID:19183408

High-intensity intermittent exercise increases pulmonary interstitial edema at altitude but not at simulated altitude.

PubMed

Edsell, Mark E; Wimalasena, Yashvi H; Malein, William L; Ashdown, Kimberly M; Gallagher, Carla A; Imray, Chris H; Wright, Alex D; Myers, Stephen D

2014-12-01

Ascent to high altitude leads to a reduction in ambient pressure and a subsequent fall in available oxygen. The resulting hypoxia can lead to elevated pulmonary artery (PA) pressure, capillary stress, and an increase in interstitial fluid. This fluid can be assessed on lung ultrasound (LUS) by the presence of B-lines. We undertook a chamber and field study to assess the impact of high-intensity exercise in hypoxia on the development of pulmonary interstitial edema in healthy lowlanders. Thirteen volunteers completed a high-intensity intermittent exercise (HIIE) test at sea level, in acute normobaric hypoxia (12% O2, approximately 4090 m equivalent altitude), and in hypobaric hypoxia during a field study at 4090 m after 6 days of acclimatization. Pulmonary interstitial edema was assessed by the evaluation of LUS B-lines. After HIIE, no increase in B-lines was seen in normoxia, and a small increase was seen in acute normobaric hypoxia (2 ± 2; P < .05). During the field study at 4090 m, 12 participants (92%) demonstrated 7 ± 4 B-lines at rest, which increased to 17 ± 5 immediately after the exercise test (P < .001). An increase was evident in all participants. There was a reciprocal fall in peripheral arterial oxygen saturations (Spo2) after exercise from 88% ± 4% to 80% ± 8% (P < .01). B-lines and Spo2 in all participants returned to baseline levels within 4 hours. HIIE led to an increase in B-lines at altitude after subacute exposure but not during acute exposure at equivalent simulated altitude. This may indicate pulmonary interstitial edema. Copyright © 2014 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.

Interstitial ultrasound ablation of vertebral and paraspinal tumours: Parametric and patient-specific simulations

PubMed Central

Scott, Serena J.; Salgaonkar, Vasant; Prakash, Punit; Burdette, E. Clif; Diederich, Chris J.

2015-01-01

Purpose Theoretical parametric and patient-specific models are applied to assess the feasibility of interstitial ultrasound ablation of tumours in and near the spine and to identify potential treatment delivery strategies. Methods 3D patient-specific finite element models (n=11) of interstitial ultrasound ablation of tumours associated with spine were generated. Gaseous nerve insulation and various applicator configurations, frequencies (3 and 7 MHz), placement trajectories, and tumour locations were simulated. Parametric studies with multilayered models investigated the impacts of tumour attenuation, tumour dimension, and the thickness of bone insulating critical structures. Temperature and thermal dose were calculated to define ablation (>240 equivalent minutes at 43°C (EM43°C)) and safety margins (<45°C & <6 EM43°C), and to determine performance and required delivery parameters. Results Osteolytic tumours (≤44 mm) encapsulated by bone could be successfully ablated with 7 MHz interstitial ultrasound (8.1-16.6 W/cm2, 120-5900 J, 0.4-15 min). Ablation of tumours (94.6-100% volumetric) 0-14.5 mm from the spinal canal was achieved within 3-15 min without damaging critical nerves. 3 MHz devices provided faster ablation (390 versus 930 s) of an 18 mm diameter osteoblastic (high bone content) volume than 7 MHz devices. Critical anatomy in proximity to the tumour could be protected by selection of appropriate applicator configurations, active sectors, and applied power schemas, and through gaseous insulation. Preferential ultrasound absorption at bone surfaces facilitated faster, more effective ablations in osteolytic tumours and provided isolation of ablative energies and temperatures. Conclusions Parametric and patient-specific studies demonstrated the feasibility and potential advantages of interstitial ultrasound ablation treatment of paraspinal and osteolytic vertebral tumours. PMID:25017322

Interstitial and Interlayer Ion Diffusion Geometry Extraction in Graphitic Nanosphere Battery Materials.

PubMed

Gyulassy, Attila; Knoll, Aaron; Lau, Kah Chun; Wang, Bei; Bremer, Peer-Timo; Papka, Michael E; Curtiss, Larry A; Pascucci, Valerio

2016-01-01

Large-scale molecular dynamics (MD) simulations are commonly used for simulating the synthesis and ion diffusion of battery materials. A good battery anode material is determined by its capacity to store ion or other diffusers. However, modeling of ion diffusion dynamics and transport properties at large length and long time scales would be impossible with current MD codes. To analyze the fundamental properties of these materials, therefore, we turn to geometric and topological analysis of their structure. In this paper, we apply a novel technique inspired by discrete Morse theory to the Delaunay triangulation of the simulated geometry of a thermally annealed carbon nanosphere. We utilize our computed structures to drive further geometric analysis to extract the interstitial diffusion structure as a single mesh. Our results provide a new approach to analyze the geometry of the simulated carbon nanosphere, and new insights into the role of carbon defect size and distribution in determining the charge capacity and charge dynamics of these carbon based battery materials.

Interstitial and Interlayer Ion Diffusion Geometry Extraction in Graphitic Nanosphere Battery Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gyulassy, Attila; Knoll, Aaron; Lau, Kah Chun

2016-01-01

Large-scale molecular dynamics (MD) simulations are commonly used for simulating the synthesis and ion diffusion of battery materials. A good battery anode material is determined by its capacity to store ion or other diffusers. However, modeling of ion diffusion dynamics and transport properties at large length and long time scales would be impossible with current MD codes. To analyze the fundamental properties of these materials, therefore, we turn to geometric and topological analysis of their structure. In this paper, we apply a novel technique inspired by discrete Morse theory to the Delaunay triangulation of the simulated geometry of a thermallymore » annealed carbon nanosphere. We utilize our computed structures to drive further geometric analysis to extract the interstitial diffusion structure as a single mesh. Our results provide a new approach to analyze the geometry of the simulated carbon nanosphere, and new insights into the role of carbon defect size and distribution in determining the charge capacity and charge dynamics of these carbon based battery materials.« less

Interstitial and interlayer ion diffusion geometry extraction in graphitic nanosphere battery materials

DOE PAGES

Gyulassy, Attila; Knoll, Aaron; Lau, Kah Chun; ...

2016-01-31

Large-scale molecular dynamics (MD) simulations are commonly used for simulating the synthesis and ion diffusion of battery materials. A good battery anode material is determined by its capacity to store ion or other diffusers. However, modeling of ion diffusion dynamics and transport properties at large length and long time scales would be impossible with current MD codes. To analyze the fundamental properties of these materials, therefore, we turn to geometric and topological analysis of their structure. In this paper, we apply a novel technique inspired by discrete Morse theory to the Delaunay triangulation of the simulated geometry of a thermallymore » annealed carbon nanosphere. We utilize our computed structures to drive further geometric analysis to extract the interstitial diffusion structure as a single mesh. Lastly, our results provide a new approach to analyze the geometry of the simulated carbon nanosphere, and new insights into the role of carbon defect size and distribution in determining the charge capacity and charge dynamics of these carbon based battery materials.« less

Approaches toward a blue semiconductor laser

NASA Technical Reports Server (NTRS)

Ladany, I.

1989-01-01

Possible approaches for obtaining semiconductor diode laser action in the blue region of the spectrum are surveyed. A discussion of diode lasers is included along with a review of the current status of visible emitters, presently limited to 670 nm. Methods are discussed for shifting laser emission toward shorter wavelengths, including the use of II-IV materials, the increase in the bandgap of III-V materials by addition of nitrogen, and changing the bandstructure from indirect to direct by incorporating interstitial atoms or by constructing superlattices. Non-pn-junction injection methods are surveyed, including avalanche breakdown, Langmuir-Blodgett diodes, heterostructures, carrier accumulation, and Berglund diodes. Prospects of inventing new multinary semiconducting materials are discussed, and a number of novel materials described in the literature are tabulated. New approaches available through the development of quantum wells and superlattices are described, including resonant tunneling and the synthesis of arbitrary bandgap materials through multiple quantum wells.

Effect of interstitial low level laser stimulation in skin density

NASA Astrophysics Data System (ADS)

Jang, Seulki; Ha, Myungjin; Lee, Sangyeob; Yu, Sungkon; Park, Jihoon; Radfar, Edalat; Hwang, Dong Hyun; Lee, Han A.; Kim, Hansung; Jung, Byungjo

2016-03-01

As the interest in skin was increased, number of studies on skin care also have been increased. The reduction of skin density is one of the symptoms of skin aging. It reduces elasticity of skin and becomes the reason of wrinkle formation. Low level laser therapy (LLLT) has been suggested as one of the effective therapeutic methods for skin aging as in hasten to change skin density. This study presents the effect of a minimally invasive laser needle system (MILNS) (wavelength: 660nm, power: 20mW) in skin density. Rabbits were divided into three groups. Group 1 didn't receive any laser stimulation as a control group. Group 2 and 3 as test groups were exposed to MILNS with energy of 8J and 6J on rabbits' dorsal side once a week, respectively. Skin density of rabbits was measured every 12 hours by using an ultrasound skin scanner.

Hydrodynamic effects in laser cutting of biological tissue phantoms

NASA Astrophysics Data System (ADS)

Zhigarkov, V. S.; Yusupov, V. I.; Tsypina, S. I.; Bagratashvili, V. N.

2017-11-01

We study the thermal and transport processes that occur in the course of incision formation at the surface of a biological tissue phantom under the action of near-IR, moderate-power, continuous-wave laser radiation (λ = 1.94 μm) delivered by means of an optical fibre with an absorbing coating on its exit face. It is shown that in addition to the thermal effect, the laser-induced hydrodynamic effects caused by the explosive boiling of the interstitial water make a large contribution to the phantom destruction mechanism. These effects lead to the tissue rupture accompanied by the ejection of part of the fragmented substance from the site of laser impact and the formation of highly porous structure near the incision surface. We have found that the depth, the width and the relief of the laser incision wall in the case of using the optical fibre moving with a constant velocity, depend on the fibre tilt angle with respect to the phantom surface, as well as the direction of the fibre motion.

Nitrogen diffusion in hafnia and the impact of nitridation on oxygen and hydrogen diffusion: A first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sathiyanarayanan, Rajesh, E-mail: rajessat@in.ibm.com, E-mail: rajesh.sathiyanarayanan@gmail.com; Pandey, R. K.; Murali, K. V. R. M.

2015-01-21

Using first-principles simulations, we have computed incorporation energies and diffusion barriers of ammonia, the nitrogen molecule and atomic nitrogen in monoclinic hafnia (m-HfO{sub 2}). Our calculations show that ammonia is likely to dissociate into an NH{sub 2} molecular unit, whereas the nitrogen molecule remains as a molecule either in the interstitial space or at an oxygen lattice site. The lowest energy pathway for the diffusion of atomic nitrogen interstitials consists of the hopping of the nitrogen interstitial between neighboring three-coordinated lattice oxygen atoms that share a single Hf atom, and the barrier for such hops is determined by a switchingmore » mechanism. The substitutional nitrogen atom shows a preference for diffusion through the doubly positive oxygen vacancy-mediated mechanism. Furthermore, we have investigated the impact of nitrogen atoms on the diffusion barriers of oxygen and hydrogen interstitials in m-HfO{sub 2}. Our results show that nitrogen incorporation has a significant impact on the barriers for oxygen and hydrogen diffusion: nitrogen atoms attract oxygen and hydrogen interstitials diffusing in the vicinity, thereby slowing down (reducing) their diffusion (diffusion length)« less

Radiation-enhanced self- and boron diffusion in germanium

NASA Astrophysics Data System (ADS)

Schneider, S.; Bracht, H.; Klug, J. N.; Hansen, J. Lundsgaard; Larsen, A. Nylandsted; Bougeard, D.; Haller, E. E.

2013-03-01

We report experiments on proton radiation-enhanced self- and boron (B) diffusion in germanium (Ge) for temperatures between 515 ∘C and 720 ∘C. Modeling of the experimental diffusion profiles measured by means of secondary ion mass spectrometry is achieved on the basis of the Frenkel pair reaction and the interstitialcy and dissociative diffusion mechanisms. The numerical simulations ascertain concentrations of Ge interstitials and B-interstitial pairs that deviate by several orders of magnitude from their thermal equilibrium values. The dominance of self-interstitial related defects under irradiation leads to an enhanced self- and B diffusion in Ge. Analysis of the experimental profiles yields data for the diffusion of self-interstitials (I) and the thermal equilibrium concentration of BI pairs in Ge. The temperature dependence of these quantities provides the migration enthalpy of I and formation enthalpy of BI that are compared with recent results of atomistic calculations. The behavior of self- and B diffusion in Ge under concurrent annealing and irradiation is strongly affected by the property of the Ge surface to hinder the annihilation of self-interstitials. The limited annihilation efficiency of the Ge surface can be caused by donor-type surface states favored under vacuum annealing, but the physical origin remains unsolved.

HELIUM EFFECTS ON DISPLACEMENT CASCADE IN TUNGSTEN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Setyawan, Wahyu; Nandipati, Giridhar; Roche, Kenneth J.

2013-09-30

Molecular dynamics (MD) simulations were performed to investigate He effects on displacement cascades in W. Helium content, proportion of interstitial and substitutional He and temperature were varied to reveal the various effects. The effect of interstitial He on the number of self-interstitial atoms (SIAs) produced during cascade damage appears to be insignificant. However, interstitial He tends to fill a vacancy (V). Nevertheless, this process is less favorable than SIA-V recombination particularly when excess SIAs are present before a cascade. The efficiency of He filling and SIA-V recombination increases as temperature increases due to increased point defect mobility. Likewise, substitutional Hemore » is more susceptible to displacement during a collision cascade than W. This susceptibility increases towards higher temperatures. Consequently, the number of surviving V is governed by the interplay between displaced substitutional He and SIA-V recombination. The temperature dependence of these processes results in a minimum number of V reached at an intermediate temperature.« less

Intralayer magnetic ordering in Ge/Mn digital alloys

NASA Astrophysics Data System (ADS)

Otrokov, M. M.; Ernst, A.; Ostanin, S.; Fischer, G.; Buczek, P.; Sandratskii, L. M.; Hergert, W.; Mertig, I.; Kuznetsov, V. M.; Chulkov, E. V.

2011-04-01

We present a first-principles investigation of the electronic properties of Ge/Mn digital alloys obtained by the insertion of Mn monolayers in the Ge host. The main attention is devoted to the study of the magnetic properties of the Mn layers for various types of ordering of the Mn atoms. Depending on the type of Mn position three different structures are considered: substitutional, interstitial, and combined substitutional-interstitial. In all three cases numerical structural relaxation of the atomic positions has been performed. We find that the intralayer exchange parameters depend strongly on the crystal structure. For the substitutional and interstitial types of structure the stable magnetic order was found to be ferromagnetic. For the mixed substitutional-interstitial structure the ferromagnetic configuration appears unstable and a complex ferrimagnetic structure forms. The spin-wave excitations are calculated within the Heisenberg model. The critical temperatures of the magnetic phase transitions are determined using Monte Carlo simulations with interatomic exchange parameters obtained for two different magnetic reference states: a ferromagnetic and a disordered local moment state.

New World Vistas: Air and Space Power for the 21st Century, Materials Volume.

DTIC Science & Technology

1996-06-01

derivatives from niche (non-silicon) materials: IR sensors, radars, lasers, and high - temperature , adverse-environment electronics. Investment in these...Develop metastable interstitial composites to create extremely high temperatures for destroying chemical biological warfare agents. " Explosives: 1...synthesize of high temperature materials that will be tailored for specific applications/ components. These materials will tend to have microstructures on

Role for Lower Extremity Interstitial Fluid Volume Changes in the Development of Orthostasis after Simulated Microgravity

NASA Technical Reports Server (NTRS)

Platts, Steven H.; Summers, Richard L.; Martin, David S.; Meck, Janice V.; Coleman, Thomas G.

2007-01-01

Reentry orthostasis after exposure to the conditions of spaceflight is a persistent problem among astronauts. In a previous study, a computer model systems analysis was used to examine the physiologic mechanisms involved in this phenomenon. In this analysis, it was determined that an augmented capacitance of lower extremity veins due to a fluid volume contracture of the surrounding interstitial spaces during spaceflight results in an increase in sequestered blood volume upon standing and appears to be the initiating mechanism responsible for reentry orthostasis. In this study, we attempt to validate the central premise of this hypothesis using a ground-based spaceflight analog. 10 healthy subjects were placed at bed rest in a 6 head down tilt position for 60 days of bed rest. The impact of adaptations in interstitial fluid volume and venous capacitance in the lower extremities were then observed during a standard tilt test protocol performed before and after the confinement period. The interstitial thickness superficial to the calcaneous immediately below the lateral malleolus was measured using ultrasound with a 17-5 MHz linear array transducer. Measurements of the changes in anterior tibial vein diameter during tilt were obtained by similar methods. The measurements were taken while the subjects were supine and then during upright tilt (80') for thirty minutes, or until the subject had signs of presyncope. Additional measurements of the superficial left tibia interstitial thickness and stroke volume by standard echocardiographic methods were also recorded. In addition, calf compliance was measured over a pressure range of 10-60 mmHg, using plethysmography, in a subset of these subjects (n = 5). There was a average of 6% diminution in the size of the lower extremity interstitial space as compared to measurements acquired prior to bed rest. This contracture of the interstitial space coincided with a subsequent relative increase in the percentage change in tibial vein diameter and stroke volume upon tilting in contrast to the observations made before bed rest (54 vs 23% respectively). Compliance in the calf increased by an average of 36% by day 27 of bedrest. A systems analysis using a computer model of cardiovascular physiology suggests that microgravity induced interstitial volume depletion results in an accentuation of venous blood volume sequestration and is the initiating event in reentry orthostasis. This hypothesis was tested in volunteer subjects using a ground-based spaceflight analog model that simulated the body fluid redistribution induced by microgravity exposure. Measurements of changes in the interstitial spaces and observed responses of the anterior tibial vein with tilt, together with the increase in calf compliance, were consistent with our proposed mechanism for the initiation of postflight orthostasis often seen in astronauts.

Phosphorus-defect interactions during thermal annealing of ion implanted silicon

NASA Astrophysics Data System (ADS)

Keys, Patrick Henry

Ion implantation of dopant atoms into silicon generates nonequilibrium levels of crystal defects that can lead to the detrimental effects of transient enhanced diffusion (TED), incomplete dopant activation, and p-n junction leakage. In order to control these effects, it is vital to have a clear understanding of dopant-defect interactions and develop models that account for these interactions. This research focuses on experimentally investigating and modeling the clustering of phosphorus dopant atoms with silicon interstitials. Damage recovery of 40keV Si+ implants in phosphorus doped wells is experimentally analyzed. The effects of background phosphorus concentration, self implant dose, and anneal temperature are investigated. Phosphorus concentrations ranging from 2.0 x 1017 to 4.0 x 1019 cm-3 and Si+ doses ranging from 5.0 x 1013 cm-2 to 2.0 x 1014 cm-2 are studied during 650-800°C anneals. A dramatic reduction in the number of interstitials bound in {311} defects with increasing phosphorus background concentration is observed. It is suggested that the reduction of interstitials in {311} defects at high phosphorus concentrations is due to the formation of phosphorus-interstitial clusters (PICs). The critical concentration for clustering (approximately 1.0 x 1019 cm-3 at 750°C) is strongly temperature dependent and in close agreement with the kink concentration of phosphorus diffusion. Information gained from these "well experiments" is applied to the study of direct phosphorus implantation. An experimental study is conducted on 40keV phosphorus implanted to a dose of 1.0 x 1014 cm-2 during 650-800°C anneals. Electrically inactive PICs are shown to form at concentrations below the solid solubility limit due to high interstitial supersaturations. Data useful for developing a model to accurately predict phosphorus diffusion under nonequilibrium conditions are extracted from the experimental results. A cluster-mediated diffusion model is developed using the Florida Object Oriented Process Simulator (FLOOPS). The nucleation of defects is controlled by the diffusion-limited competition for excess interstitials between PICs and {311} clusters. The release of interstitials is driven by cluster dissolution. Modeling results show a strong correlation to those experimentally observed over a wide temporal and thermal domain using a single set of parameters. Improvements in process simulator accuracy are demonstrated with respect to dopant activation, TED, and dose loss.

Identifying self-interstitials of bcc and fcc crystals in molecular dynamics

NASA Astrophysics Data System (ADS)

Bukkuru, S.; Bhardwaj, U.; Warrier, M.; Rao, A. D. P.; Valsakumar, M. C.

2017-02-01

Identification of self-interstitials in molecular dynamics (MD) simulations is of critical importance. There exist several criteria for identifying the self-interstitial. Most of the existing methods use an assumed cut-off value for the displacement of an atom from its lattice position to identify the self-interstitial. The results obtained are affected by the chosen cut-off value. Moreover, these chosen cut-off values are independent of temperature. We have developed a novel unsupervised learning algorithm called Max-Space Clustering (MSC) to identify an appropriate cut-off value and its dependence on temperature. This method is compared with some widely used methods such as effective sphere (ES) method and nearest neighbor sphere (NNS) method. The cut-off radius obtained using our method shows a linear variation with temperature. The value of cut-off radius and its temperature dependence is derived for five bcc (Cr, Fe, Mo, Nb, W) and six fcc (Ag, Au, Cu, Ni, Pd, Pt) crystals. It is seen that the ratio of the cut-off values "r" to the lattice constant "a" lies between 0.23 and 0.3 at 300 K and this ratio is on an average smaller for the fcc crystals. Collision cascade simulations are carried out for Primary knock-on Atom (PKA) energies of 5 keV in Fe (at 300 K and 1000 K) and W (at 300 K and 2500 K) and the results are compared using the various methods.

Radiologists' confidence in detecting abnormalities on chest images and their subjective judgments of image quality

NASA Astrophysics Data System (ADS)

King, Jill L.; Gur, David; Rockette, Howard E.; Curtin, Hugh D.; Obuchowski, Nancy A.; Thaete, F. Leland; Britton, Cynthia A.; Metz, Charles E.

1991-07-01

The relationship between subjective judgments of image quality for the performance of specific detection tasks and radiologists' confidence level in arriving at correct diagnoses was investigated in two studies in which 12 readers, using a total of three different display environments, interpreted a series of 300 PA chest images. The modalities used were conventional films, laser-printed films, and high-resolution CRT display of digitized images. For the detection of interstitial disease, nodules, and pneumothoraces, there was no statistically significant correlation (Spearman rho) between subjective ratings of quality and radiologists' confidence in detecting these abnormalities. However, in each study, for all modalities and all readers but one, a small but statistically significant correlation was found between the radiologists' ability to correctly and confidently rule out interstitial disease and their subjective ratings of image quality.

Online dosimetry for temoporfin-mediated interstitial photodynamic therapy using the canine prostate as model

NASA Astrophysics Data System (ADS)

Swartling, Johannes; Höglund, Odd V.; Hansson, Kerstin; Södersten, Fredrik; Axelsson, Johan; Lagerstedt, Anne-Sofie

2016-02-01

Online light dosimetry with real-time feedback was applied for temoporfin-mediated interstitial photodynamic therapy (PDT) of dog prostate. The aim was to investigate the performance of online dosimetry by studying the correlation between light dose plans and the tissue response, i.e., extent of induced tissue necrosis and damage to surrounding organs at risk. Light-dose planning software provided dose plans, including light source positions and light doses, based on ultrasound images. A laser instrument provided therapeutic light and dosimetric measurements. The procedure was designed to closely emulate the procedure for whole-prostate PDT in humans with prostate cancer. Nine healthy dogs were subjected to the procedure according to a light-dose escalation plan. About 0.15 mg/kg temoporfin was administered 72 h before the procedure. The results of the procedure were assessed by magnetic resonance imaging, and gross pathology and histopathology of excised tissue. Light dose planning and online dosimetry clearly resulted in more focused effect and less damage to surrounding tissue than interstitial PDT without dosimetry. A light energy dose-response relationship was established where the threshold dose to induce prostate gland necrosis was estimated from 20 to 30 J/cm2.

Simulation of defects in fusion plasma first wall materials

NASA Astrophysics Data System (ADS)

T, Troev; N, Nankov; T, Yoshiie

2014-06-01

Numerical calculations of radiation damages in beryllium, alpha-iron and tungsten irradiated by fusion neutrons were performed using molecular dynamics (MD) simulations. The displacement cascades efficiency has been calculated using the Norgett-Robinson-Torrens (NRT) formula, the universal pair-potential of Ziegler-Biersack-Littmark (ZBL) and the EAM inter-atomic potential. The pair potential overestimates the defects production by a factor of 2. The ZBL pair potential results and the EAM are comparable at higher primary knock-on atom (PKA) energies (E > 100 keV). We found that the most common types of defects are single vacancies, di-vacancies, interstitials and small number of interstitial clusters. On the bases of calculated results, the behavior of vacancies, empty nano-voids and nano-voids with hydrogen and helium were discussed.

Finesse of transparent tissue cutting by ultrafast lasers at various wavelengths.

PubMed

Wang, Jenny; Schuele, Georg; Palanker, Daniel

2015-01-01

Transparent ocular tissues, such as the cornea and crystalline lens, can be ablated or dissected using short-pulse lasers. In refractive and cataract surgeries, the cornea, lens, and lens capsule can be cut by producing dielectric breakdown in the focus of a near-infrared (IR) femtosecond laser, which results in explosive vaporization of the interstitial water, causing mechanical rupture of the surrounding tissue. Here, we compare the texture of edges of lens capsule cut by femtosecond lasers with IR and ultraviolet (UV) wavelengths and explore differences in interactions of these lasers with biological molecules. Scanning electron microscopy indicates that a 400-nm laser is capable of producing very smooth cut edges compared to 800 or 1030 nm at a similar focusing angle. Using gel electrophoresis and liquid chromatography/mass spectrometry, we observe laser-induced nonlinear breakdown of proteins and polypeptides by 400-nm femtosecond pulses above and below the dielectric breakdown threshold. On the other hand, 800-nm femtosecond lasers do not produce significant dissociation even above the threshold of dielectric breakdown. However, despite this additional interaction of UV femtosecond laser with proteins, we determine that efficient cutting requires plasma-mediated bubble formation and that remarkably smooth edges are the result of reduced thresholds and smaller focal volume.

DISPLACEMENT CASCADE SIMULATION IN TUNGSTEN UP TO 200 KEV OF DAMAGE ENERGY AT 300, 1025, AND 2050 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Setyawan, Wahyu; Nandipati, Giridhar; Roche, Kenneth J.

2015-09-22

We generated molecular dynamics database of primary defects that adequately covers the range of tungsten recoil energy imparted by 14-MeV neutrons. During this semi annual period, cascades at 150 and 200 keV at 300 and 1025 K were simulated. Overall, we included damage energy up to 200 keV at 300 and 1025 K, and up to 100 keV at 2050 K. We report the number of surviving Frenkel pairs (NF) and the size distribution of defect clusters. The slope of the NF curve versus cascade damage energy (EMD), on a log-log scale, changes at a transition energy (μ). For EMDmore » > μ, the cascade forms interconnected damage regions that facilitate the formation of large clusters of defects. At 300 K and EMD = 200 keV, the largest size of interstitial cluster and vacancy cluster is 266 and 335, respectively. Similarly, at 1025 K and EMD = 200 keV, the largest size of interstitial cluster and vacancy cluster is 296 and 338, respectively. At 2050 K, large interstitial clusters also routinely form, but practically no large vacancy clusters do« less

Could transvaginal, ultrasound-guided ovarian interstitial laser treatment replace laparoscopic ovarian drilling in women with polycystic ovary syndrome resistant to clomiphene citrate?

PubMed

Api, Murat

2009-12-01

A number of novel surgical modalities that destroy or remove some ovarian tissue to restore ovarian function in patients with polycystic ovary syndrome have been described in the most recent literature. Although these modalities were reported to have easy applicability and low cost with shorter hospital stay, the efficacy and safety concerns need to be discussed extensively.

Zinc Vacancy Formation and its Effect on the Conductivity of ZnO

NASA Astrophysics Data System (ADS)

Khan, Enamul; Weber, Marc; Langford, Steve; Dickinson, Tom

2010-03-01

Exposing single crystal ZnO to 193-nm ArF excimer laser radiation can produce metallic zinc nanoparticles along the surface. The particle production mechanism appears to involve interstitial-vacancy pair formation in the near-surface bulk. Conductivity measurements made with one probe inside the laser spot and the other outside show evidence for rectifying behavior. Positron annihilation spectroscopy confirms the presence of Zn vacancies. We suggest that Zn vacancies are a possible source of p-type behavior in irradiated ZnO. Quadrupole mass spectroscopy shows that both oxygen and zinc are emitted during irradiation. Electron-hole pair production has previously been invoked to account for particle desorption from ZnO during UV illumination. Our results suggest that preexisting and laser-generated defects play a critical role in particle desorption and Zn vacancy formation.

Safety of Laser Interstitial Thermal Therapy in Patients With Pacemakers.

PubMed

Grewal, Sanjeet S; Gorny, Krzysztof R; Favazza, Christopher P; Watson, Robert E; Kaufmann, Timothy J; Van Gompel, Jamie J

2018-02-10

Laser interstitial thermal therapy (LiTT) has increasingly been used as a treatment option for medically refractory epilepsy, tumors, and radiation necrosis. The use of LiTT requires intraoperative magnetic resonance (MR) thermography. This can become an issue in patients with other implanted therapeutic devices such as pacemakers and vagal nerve stimulators due to concerns regarding increases in the specific absorption rate (SAR). This is a technical case report demonstrating a successfully and safely performed LiTT in a 1.5-T magnetic resonance imaging (MRI) in a patient with a pacemaker for mesial temporal sclerosis. An 83-yr-old gentleman who had an implanted cardiac pacemaker presented with medically intractable epilepsy and was confirmed to have mesial temporal sclerosis on imaging. Video electroencephalography demonstrated concordant ipsilateral seizures and semiology. He underwent LiTT for ablation of the mesial temporal lobe. This was performed with the below described protocol with a cardiology nurse monitoring the patient's cardiac condition and a physicist monitoring SAR, and MR imaging quality without any adverse events. This study reports on a protocol of cardiac and MR SAR to safely perform MR-guided LiTT in the setting of traditional pacemakers in patients who are not pacemaker dependent. Copyright © 2018 by the Congress of Neurological Surgeons

Consistency analysis on laser signal in laser guided weapon simulation

NASA Astrophysics Data System (ADS)

Yin, Ruiguang; Zhang, Wenpan; Guo, Hao; Gan, Lin

2015-10-01

The hardware-in-the-loop simulation is widely used in laser semi-active guidance weapon experiments, the authenticity of the laser guidance signal is the key problem of reliability. In order to evaluate the consistency of the laser guidance signal, this paper analyzes the angle of sight, laser energy density, laser spot size, atmospheric back scattering, sun radiation and SNR by comparing the different working state between actual condition and hardware-in-the-loop simulation. Based on measured data, mathematical simulation and optical simulation result, laser guidance signal effects on laser seeker are determined. By using Monte Carlo method, the laser guided weapon trajectory and impact point distribution are obtained, the influence of the systematic error are analyzed. In conclusion it is pointed out that the difference between simulation system and actual system has little influence in normal guidance, has great effect on laser jamming. The research is helpful to design and evaluation of laser guided weapon simulation.

Predicting vacancy-mediated diffusion of interstitial solutes in α -Fe

NASA Astrophysics Data System (ADS)

Barouh, Caroline; Schuler, Thomas; Fu, Chu-Chun; Jourdan, Thomas

2015-09-01

Based on a systematic first-principles study, the lowest-energy migration mechanisms and barriers for small vacancy-solute clusters (VnXm ) are determined in α -Fe for carbon, nitrogen, and oxygen, which are the most frequent interstitial solutes in several transition metals. We show that the dominant clusters present at thermal equilibrium (V X and V X2 ) have very reduced mobility compared to isolated solutes, while clusters composed of a solute bound to a small vacancy cluster may be significantly more mobile. In particular, V3X is found to be the fastest cluster for all three solutes. This result relies on the large diffusivity of the most compact trivacancy in a bcc lattice. Therefore, it may also be expected for interstitial solutes in other bcc metals. In the case of iron, we find that V3X may be as fast as or even more mobile than an interstitial solute. At variance with common assumptions, the trapping of interstitial solutes by vacancies does not necessarily decrease the mobility of the solute. Additionally, cluster dynamics simulations are performed considering a simple iron system with supersaturation of vacancies, in order to investigate the impacts of small mobile vacancy-solute clusters on properties such as the transport of solute and the cluster size distributions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shenyang; Joshi, Vineet; Lavender, Curt A.

Experiments showed that recrystallization dramatically speeds up the gas bubble swelling kinetics in metallic UMo fuels. In this work a recrystallization model is developed to study the effect of microstructures and radiation conditions on recrystallization kinetics. The model integrates the rate theory of intra-granular gas bubble and interstitial loop evolution and a phase field model of recrystallization zone evolution. A fast passage method is employed to describe one dimensional diffusion of interstitials which have diffusivity several order magnitude larger than that of the fission gas Xe. With the model, the effect of grain sizes on recrystallization kinetics is simulated.

The role of inducible nitric oxide synthase for interstitial remodeling of alveolar septa in surfactant protein D-deficient mice

PubMed Central

Atochina-Vasserman, Elena N.; Massa, Christopher B.; Birkelbach, Bastian; Guo, Chang-Jiang; Scott, Pamela; Haenni, Beat; Beers, Michael F.; Ochs, Matthias; Gow, Andrew J.

2015-01-01

Surfactant protein D (SP-D) modulates the lung's immune system. Its absence leads to NOS2-independent alveolar lipoproteinosis and NOS2-dependent chronic inflammation, which is critical for early emphysematous remodeling. With aging, SP-D knockout mice develop an additional interstitial fibrotic component. We hypothesize that this age-related interstitial septal wall remodeling is mediated by NOS2. Using invasive pulmonary function testing such as the forced oscillation technique and quasistatic pressure-volume perturbation and design-based stereology, we compared 29-wk-old SP-D knockout (Sftpd−/−) mice, SP-D/NOS2 double-knockout (DiNOS) mice, and wild-type mice (WT). Structural changes, including alveolar epithelial surface area, distribution of septal wall thickness, and volumes of septal wall components (alveolar epithelium, interstitial tissue, and endothelium) were quantified. Twenty-nine-week-old Sftpd−/− mice had preserved lung mechanics at the organ level, whereas elastance was increased in DiNOS. Airspace enlargement and loss of surface area of alveolar epithelium coexist with increased septal wall thickness in Sftpd−/− mice. These changes were reduced in DiNOS, and compared with Sftpd−/− mice a decrease in volumes of interstitial tissue and alveolar epithelium was found. To understand the effects of lung pathology on measured lung mechanics, structural data were used to inform a computational model, simulating lung mechanics as a function of airspace derecruitment, septal wall destruction (loss of surface area), and septal wall thickening. In conclusion, NOS2 mediates remodeling of septal walls, resulting in deposition of interstitial tissue in Sftpd−/−. Forward modeling linking structure and lung mechanics describes the complex mechanical properties by parenchymatous destruction (emphysema), interstitial remodeling (septal wall thickening), and altered recruitability of acinar airspaces. PMID:26320150

Comparative study of displacement cascades simulated with 'magnetic' potentials and Mendelev-type potential in α-Fe

NASA Astrophysics Data System (ADS)

Gao, Chan; Tian, Dongfeng; Li, Maosheng; Qian, Dazhi

2017-04-01

Different interatomic potentials produce displacement cascades with different features, and hence they significantly influence the results obtained from the displacement cascade simulations. The displacement cascade simulations in α-Fe have been carried out by molecular dynamics with three 'magnetic' potentials (MP) and Mendelev-type potential in this paper. Prior to the cascade simulations, the 'magnetic' potentials are hardened to suit for cascade simulations. We find that the peak time, maximum of defects, cascade volume and cascade density with 'magnetic' potentials are smaller than those with Mendelev-type potential. There is no significant difference within statistical uncertainty in the defect production efficiency with Mendelev-type potential and the second 'magnetic' potential at the same cascade energy, but remarkably smaller than those with the first and third 'magnetic' potential. Self interstitial atom (SIA) clustered fractions with 'magnetic' potentials are smaller than that with Mendelev-type potential, especially at the higher energy, due to the larger interstitial formation energies which result from the 'magnetic' potentials. The defect clustered fractions, which are input data for radiation damage accumulation models, may influence the prediction of microstructural evolution under radiation.

The thermodynamic and kinetic interactions of He interstitial clusters with bubbles in W

DOE PAGES

Perez, Danny; Sandoval, Luis; Uberuaga, Blas P.; ...

2016-05-26

Due to its enviable properties, tungsten is a leading candidate plasma facing material in nuclear fusion reactors. But, like many other metals, tungsten is known to be affected by the high doses of helium atoms incoming from the plasma. Indeed, the implanted interstitial helium atoms cluster together and, upon reaching a critical cluster size, convert into substitutional nanoscale He bubbles. These bubbles then grow by absorbing further interstitial clusters from the matrix. This process can lead to deleterious changes in microstructure, degradation of mechanical properties, and contamination of the plasma. In order to better understand the growth process, we usemore » traditional and accelerated molecular dynamics simulations to investigate the interactions between interstitial He clusters and pre-existing bubbles. These interactions are characterized in terms of thermodynamics and kinetics. We also show that the proximity of the bubble leads to an enhancement of the trap mutation rate and, consequently, to the nucleation of satellite bubbles in the neighborhood of existing ones. Finally, we uncover a number of mechanisms that can lead to the subsequent annihilation of such satellite nanobubbles.« less

The thermodynamic and kinetic interactions of He interstitial clusters with bubbles in W

NASA Astrophysics Data System (ADS)

Perez, Danny; Sandoval, Luis; Uberuaga, Blas P.; Voter, Arthur F.

2016-05-01

Due to its enviable properties, tungsten is a leading candidate plasma facing material in nuclear fusion reactors. However, like many other metals, tungsten is known to be affected by the high doses of helium atoms incoming from the plasma. Indeed, the implanted interstitial helium atoms cluster together and, upon reaching a critical cluster size, convert into substitutional nanoscale He bubbles. These bubbles then grow by absorbing further interstitial clusters from the matrix. This process can lead to deleterious changes in microstructure, degradation of mechanical properties, and contamination of the plasma. In order to better understand the growth process, we use traditional and accelerated molecular dynamics simulations to investigate the interactions between interstitial He clusters and pre-existing bubbles. These interactions are characterized in terms of thermodynamics and kinetics. We show that the proximity of the bubble leads to an enhancement of the trap mutation rate and, consequently, to the nucleation of satellite bubbles in the neighborhood of existing ones. We also uncover a number of mechanisms that can lead to the subsequent annihilation of such satellite nanobubbles.

Atomistic understanding of cation exchange in PbS nanocrystals using simulations with pseudoligands

PubMed Central

Fan, Zhaochuan; Lin, Li-Chiang; Buijs, Wim; Vlugt, Thijs J. H.; van Huis, Marijn A.

2016-01-01

Cation exchange is a powerful tool for the synthesis of nanostructures such as core–shell nanocrystals, however, the underlying mechanism is poorly understood. Interactions of cations with ligands and solvent molecules are systematically ignored in simulations. Here, we introduce the concept of pseudoligands to incorporate cation-ligand-solvent interactions in molecular dynamics. This leads to excellent agreement with experimental data on cation exchange of PbS nanocrystals, whereby Pb ions are partially replaced by Cd ions from solution. The temperature and the ligand-type control the exchange rate and equilibrium composition of cations in the nanocrystal. Our simulations reveal that Pb ions are kicked out by exchanged Cd interstitials and migrate through interstitial sites, aided by local relaxations at core–shell interfaces and point defects. We also predict that high-pressure conditions facilitate strongly enhanced cation exchange reactions at elevated temperatures. Our approach is easily extendable to other semiconductor compounds and to other families of nanocrystals. PMID:27160371

Ab initio simulations of the structure, energetics and mobility of radiation-induced point defects in bcc Nb

NASA Astrophysics Data System (ADS)

Cerdeira, M. A.; Palacios, S. L.; González, C.; Fernández-Pello, D.; Iglesias, R.

2016-09-01

The formation, binding and migration energetics of helium clusters inside a niobium crystal have been analysed via ab initio simulations. The effect of placing several He atoms within an n-vacancy previously formed or as interstitials inside the initial perfect bulk matrix has been studied. DFT-based results show that He atoms prefer to aggregate forming small clusters at n-vacancy sites rather than at interstitial positions in the perfect crystal. The minimum formation energy is found when NHe is equal to the number of vacancies, n. It follows that vacancies act as almost perfect traps for He atoms, as is well known for other metals. The migration barriers of He atoms inside vacancies increase considerably when compared to what happens for vacancies alone. A secondary consequence is that the full set of energies obtained will be highly relevant as an input for new approaches to KMC simulations of defects in Nb.

The evolution of interaction between grain boundary and irradiation-induced point defects: Symmetric tilt GB in tungsten

NASA Astrophysics Data System (ADS)

Li, Hong; Qin, Yuan; Yang, Yingying; Yao, Man; Wang, Xudong; Xu, Haixuan; Phillpot, Simon R.

2018-03-01

Molecular dynamics method is used and scheme of calculational tests is designed. The atomic evolution view of the interaction between grain boundary (GB) and irradiation-induced point defects is given in six symmetric tilt GB structures of bcc tungsten with the energy of the primary knock-on atom (PKA) EPKA of 3 and 5 keV and the simulated temperature of 300 K. During the collision cascade with GB structure there are synergistic mechanisms to reduce the number of point defects: one is vacancies recombine with interstitials, and another is interstitials diffuse towards the GB with vacancies almost not move. The larger the ratio of the peak defect zone of the cascades overlaps with the GB region, the statistically relative smaller the number of surviving point defects in the grain interior (GI); and when the two almost do not overlap, vacancy-intensive area generally exists nearby GBs, and has a tendency to move toward GB with the increase of EPKA. In contrast, the distribution of interstitials is relatively uniform nearby GBs and is affected by the EPKA far less than the vacancy. The GB has a bias-absorption effect on the interstitials compared with vacancies. It shows that the number of surviving vacancies statistically has increasing trend with the increase of the distance between PKA and GB. While the number of surviving interstitials does not change much, and is less than the number of interstitials in the single crystal at the same conditions. The number of surviving vacancies in the GI is always larger than that of interstitials. The GB local extension after irradiation is observed for which the interstitials absorbed by the GB may be responsible. The designed scheme of calculational tests in the paper is completely applicable to the investigation of the interaction between other types of GBs and irradiation-induced point defects.

Low-level lasers: their role in the mechanisms of the stimulation of the reparative processes

NASA Astrophysics Data System (ADS)

Yeliseenko, Vladimir I.

1994-08-01

The transformation of light energy into thermal energy with extremely high temperatures, the evaporation of interstitial and intracellular fluids, and the cytoplasmic proteins coagulation are the most important factors in the mechanism of high-power lasers effect on biological tissues. A set of dystrophic disorders develops in tissues as a result, up to the coagulative necrosis, which lays in the basis of the laser thermal crust at incised edges. With CO2 laser the damage is evident from the first cell layers. Its size is in the linear correlation with exposure time. The Nd:YAG and argon lasers' light penetrates the superficial cell layers without damage practically and realizes in deeper well vascularized tissue layers, the submucous layer of the gastrointestinal hollow organs, in particular. It depends on the closeness of the irradiation spectrum of absorption of hemoglobin and result in blood coagulation in the vascular lumine with formation of the `coagulative laser thrombi.' That explains a wide use of laser irradiation in urgent endoscopy for arresting acute gastrointestinal hemorrhages. For these reasons Nd:YAG laser `contact scalpel' technique with sapphire tips is used for incisions on parenchymatous organs with simultaneous blood coagulation in vessels lumina with good hemostasis and holestasis (hepatobiliar surgery), and for pancreas and thyroid surgery, in gynecology and other surgical areas.

Hyperthermia treatment of spontaneously occurring oral cavity tumors using a computer-controlled Nd:YAG laser system

NASA Astrophysics Data System (ADS)

Panjehpour, Masoud; Overholt, Bergein F.; Frazier, Donita L.; Klebanow, Edward R.

1991-05-01

Conventional hyperthermia treatment of superficial tumors in the oral cavity is difficult due to inability in accessing the lesion. A new hyperthermia technique employing near infrared Nd:YAG irradiation delivered through an optical fiber is introduced for heating oral and nasal tumors in animals. This system consisted of an Nd:YAG laser, a He-Ne laser, a computer controlled optical shutter, an interstitial thermometer, computer and a printer. The tumors were heated via surface illumination of the lesion. A thermocouple implanted in the base of the tumor provided temperature feedback for laser energy regulation. Three spontaneously occurring canine (two squamous cell carcinoma on the gum, one pigmented melanoma on the hard palate) and one feline tumor (squamous cell carcinoma on the nose) have been treated with the Nd:YAG laser-induced hyperthermia delivered following radiation therapy. The tumor temperature was maintained between 43.2-43.5 degree(s)C for one hour. Nd:YAG hyperthermia allowed efficient delivery of heat to veterinary oral and nasal lesions otherwise impossible to treat with conventional heating techniques.

Atomistic simulations to characterize the influence of applied strain and PKA energy on radiation damage evolution in pure aluminum

NASA Astrophysics Data System (ADS)

Sahi, Qurat-ul-ain; Kim, Yong-Soo

2018-05-01

Knowledge of defects generation, their mobility, growth rate, and spatial distribution is the cornerstone for understanding the surface and structural evolution of a material used under irradiation conditions. In this study, molecular dynamics simulations were used to investigate the coupled effect of primary knock-on atom (PKA) energy and applied strain (uniaxial and hydrostatic) fields on primary radiation damage evolution in pure aluminum. Cascade damage simulations were carried out for PKA energy ranging between 1 and 20 keV and for applied strain values ranging between -2% and 2% at the fixed temperature of 300 K. Simulation results showed that as the atomic displacement cascade proceeds under uniaxial and hydrostatic strains, the peak and surviving number of Frenkel point defects increases with increasing tension; however, these increments were more prominent under larger volume changing deformations (hydrostatic strain). The percentage fraction of point defects that aggregate into clusters increases under tension conditions; compared to the reference conditions with no strain, these increases are around 13% and 7% for interstitials and vacancies, respectively (under 2% uniaxial strain), and 19% and 11% for interstitials and vacancies, respectively (under 2% hydrostatic strain). Clusters formed of vacancies and interstitials were both larger under tensile strain conditions, with increases in both the average and maximum cluster sizes. The rate of increase/decrease in the number of Frenkel pairs, their clustering, and their size distributions under expansion/compression strain conditions were higher for higher PKA energies. Overall, the present results suggest that strain effects should be considered carefully in radiation damage environments, specifically for conditions of low temperature and high radiation energy. Compressive strain conditions could be beneficial for materials used in nuclear reactor power systems.

SU-F-19A-12: Split-Ring Applicator with Interstitial Needle for Improved Volumetric Coverage in HDR Brachytherapy for Cervical Cancer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sherertz, T; Ellis, R; Colussi, V

2014-06-15

Purpose: To evaluate volumetric coverage of a Mick Radionuclear titanium Split-Ring applicator (SRA) with/without interstitial needle compared to an intracavitary Vienna applicator (VA), interstitial-intracavitary VA, and intracavitary ring and tandem applicator (RTA). Methods: A 57 year-old female with FIGO stage IIB cervical carcinoma was treated following chemoradiotherapy (45Gy pelvic and 5.4Gy parametrial boost) with highdose- rate (HDR) brachytherapy to 30Gy in 5 fractions using a SRA. A single interstitial needle was placed using the Ellis Interstitial Cap for the final three fractions to increase coverage of left-sided gross residual disease identified on 3T-MRI. High-risk (HR) clinical target volume (CTV) andmore » intermediate-risk (IR) CTV were defined using axial T2-weighted 2D and 3D MRI sequences (Philips PET/MRI unit). Organs-at-risks (OARs) were delineated on CT. Oncentra planning system was used for treatment optimization satisfying GEC-ESTRO guidelines for target coverage and OAR constraints. Retrospectively, treatment plans (additional 20 plans) were simulated using intracavitary SRA (without needle), intracavitary VA (without needle), interstitial-intracavitary VA, and intracavitary RTA with this same patient case. Plans were optimized for each fraction to maintain coverage to HR-CTV. Results: Interstitial-intracavitary SRA achieved the following combined coverage for external radiation and brachytherapy (EQD2): D90 HR-CTV =94.6Gy; Bladder-2cc =88.9Gy; Rectum-2cc =65.1Gy; Sigmoid-2cc =48.9Gy; Left vaginal wall (VW) =103Gy, Right VW =99.2Gy. Interstitial-intracavitary VA was able to achieve identical D90 HR-CTV =94.6Gy, yet Bladder-2cc =91.9Gy (exceeding GEC-ESTRO recommendations of 2cc<90Gy) and Left VW =120.8Gy and Right VW =115.5Gy. Neither the SRA nor VA without interstitial needle could cover HR-CTV adequately without exceeding dose to Bladder-2cc. Conventional RTA was unable to achieve target coverage for the HR-CTV >80Gy without severely overdosing OARs. Conclusion: The Ellis Interstitial Cap for the SRA offered superior dosimetric coverage as compared to the interstitialintracavitary VA. This represents the first reported use for this devise, and further investigation is warranted.« less

Photo-acoustic sensor based on an inexpensive piezoelectric film transducer and an amplitude-stabilized single-mode external cavity diode laser for in vitro measurements of glucose concentration

NASA Astrophysics Data System (ADS)

Bayrakli, Ismail; Erdogan, Yasar Kemal

2018-06-01

The present paper focuses on development of a compact photo-acoustic sensor using inexpensive components for glucose analysis. An amplitude-stabilized wavelength-tunable single-mode external cavity diode laser operating around 1050 nm was realized and characterized for the use of laser beam as an excitation light source. In the established setup, a fine tuning range of 9 GHz was achieved. The glucose solution was obtained by diluting D-glucose in sterile water. The acoustic signal generated by the optical excitation was detected via a chip piezoelectric film transducer. A detection limit of 50 mM (900 mg/dl) was achieved. The device may be of great interest for its applications in medicine and health monitoring. The sensor is promising for non-invasive in vivo glucose measurements from interstitial fluid.

Successful Nd:Yag Laser Photocoagulation Of Arrhythmogenic Myocardium: Potential Limitations Of Current Optical Delivery Systems.

NASA Astrophysics Data System (ADS)

Svenson, Robert H.; Marroum, Marie-Claire; Frank, Frank; Selle, Jay G.; Gallagher, John J.; Bou-Saba, George; Seifert, Kathleen T.; Linder, Kathy; Tatsis, George P.

1987-04-01

Canine myocardial lesions of predictable dimensions can be achieved with Nd:YAG laser photocoagulation. These lesions are well demarcated from surrounding normal tissue and heal with homogeneous scar formation. Intraoperative Nd:YAG laser photocoagulation successfully ablated 52 of 55 ventricular tachycardias in 17 patients. Histologic examination of tissues from these arrhythmogenic areas showed differences from lesions produced on canine epicardium. Lesions from the human cases were less predictable and not well circumscribed. These differences are felt to be due to optical inhomogeneities present in diseased, scarred human myocardium, geometric irregularities of the endocardial surface, anatomical constraints on tissue-fiber distance, and the angle of incidence of the beam with the tissue. Modifications of current delivery systems may overcome some of these limitations. Ablation of ventricular tachycardia arising deeper than 4.0 to 6.0 mm. from the irradiated surface may require interstitial probes coupled to the fiberoptic.

Energetics analysis of interstitial loops in single-phase concentrated solid-solution alloys

NASA Astrophysics Data System (ADS)

Wang, Xin-Xin; Niu, Liang-Liang; Wang, Shaoqing

2018-04-01

Systematic energetics analysis on the shape preference, relative stability and radiation-induced segregation of interstitial loops in nickel-containing single-phase concentrated solid-solution alloys have been conducted using atomistic simulations. It is shown that the perfect loops prefer rhombus shape for its low potential energy, while the Frank faulted loops favor ellipse for its low potential energy and the possible large configurational entropy. The decrease of stacking fault energy with increasing compositional complexity provides the energetic driving force for the formation of faulted loops, which, in conjunction with the kinetic factors, explains the experimental observation that the fraction of faulted loops rises with increasing compositional complexity. Notably, the kinetics is primarily responsible for the absence of faulted loops in nickel-cobalt with a very low stacking fault energy. We further demonstrate that the simultaneous nickel enrichment and iron/chromium depletion on interstitial loops can be fully accounted for by their energetics.

DISPLACEMENT CASCADE SIMULATION IN TUNGSTEN AT 1025 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Setyawan, Wahyu; Nandipati, Giridhar; Roche, Kenneth J.

2013-09-30

Molecular dynamics simulation was employed to investigate the irradiation damage properties of bulk tungsten at 1025 K (0.25 melting temperature). A comprehensive data set of primary cascade damage was generated up to primary knock-on atom (PKA) energies 100 keV. The dependence of the number of surviving Frenkel pairs (NFP) on the PKA energy (E) exhibits three different characteristic domains presumably related to the different cascade morphologies that form. The low-energy regime < 0.2 keV is characterized by a hit-or-miss type of Frenkel pair (FP) production near the displacement threshold energy of 128 eV. The middle regime 0.3 – 30 keVmore » exhibits a sublinear dependence of log(NFP) vs log(E) associated with compact cascade morphology with a slope of 0.73. Above 30 keV, the cascade morphology consists of complex branches or interconnected damage regions. In this extended morphology, large interstitial clusters form from superposition of interstitials from nearby damage regions. Strong clustering above 30 keV results in a superlinear dependence of log(NFP) vs log(E) with a slope of 1.365. At 100 keV, an interstitial cluster of size 92 and a vacancy cluster of size 114 were observed.« less

A new airborne laser rangefinder dynamic target simulator for non-stationary environment

NASA Astrophysics Data System (ADS)

Ma, Pengge; Pang, Dongdong; Yi, Yang

2017-11-01

For the non-stationary environment simulation in laser range finder product testing, a new dynamic target simulation system is studied. First of all, the three-pulsed laser ranging principle, laser target signal composition and mathematical representation are introduced. Then, the actual nonstationary working environment of laser range finder is analyzed, and points out that the real sunshine background light clutter and target shielding effect in laser echo become the main influencing factors. After that, the dynamic laser target signal simulation method is given. Eventlly, the implementation of automatic test system based on arbitrary waveform generator is described. Practical application shows that the new echo signal automatic test system can simulate the real laser ranging environment of laser range finder, and is suitable for performance test of products.

Laser Capture Microdissection and Multiplex-Tandem PCR Analysis of Proximal Tubular Epithelial Cell Signaling in Human Kidney Disease

PubMed Central

Wilkinson, Ray; Wang, Xiangju; Kassianos, Andrew J.; Zuryn, Steven; Roper, Kathrein E.; Osborne, Andrew; Sampangi, Sandeep; Francis, Leo; Raghunath, Vishwas; Healy, Helen

2014-01-01

Interstitial fibrosis, a histological process common to many kidney diseases, is the precursor state to end stage kidney disease, a devastating and costly outcome for the patient and the health system. Fibrosis is historically associated with chronic kidney disease (CKD) but emerging evidence is now linking many forms of acute kidney disease (AKD) with the development of CKD. Indeed, we and others have observed at least some degree of fibrosis in up to 50% of clinically defined cases of AKD. Epithelial cells of the proximal tubule (PTEC) are central in the development of kidney interstitial fibrosis. We combine the novel techniques of laser capture microdissection and multiplex-tandem PCR to identify and quantitate “real time” gene transcription profiles of purified PTEC isolated from human kidney biopsies that describe signaling pathways associated with this pathological fibrotic process. Our results: (i) confirm previous in-vitro and animal model studies; kidney injury molecule-1 is up-regulated in patients with acute tubular injury, inflammation, neutrophil infiltration and a range of chronic disease diagnoses, (ii) provide data to inform treatment; complement component 3 expression correlates with inflammation and acute tubular injury, (iii) identify potential new biomarkers; proline 4-hydroxylase transcription is down-regulated and vimentin is up-regulated across kidney diseases, (iv) describe previously unrecognized feedback mechanisms within PTEC; Smad-3 is down-regulated in many kidney diseases suggesting a possible negative feedback loop for TGF-β in the disease state, whilst tight junction protein-1 is up-regulated in many kidney diseases, suggesting feedback interactions with vimentin expression. These data demonstrate that the combined techniques of laser capture microdissection and multiplex-tandem PCR have the power to study molecular signaling within single cell populations derived from clinically sourced tissue. PMID:24475278

Interstitial laser immunotherapy for treatment of metastatic mammary tumors in rats

NASA Astrophysics Data System (ADS)

Figueroa, Daniel; Joshi, Chet; Wolf, Roman F.; Walla, Jonny; Goddard, Jessica; Martin, Mallory; Kosanke, Stanley D.; Broach, Fred S.; Pontius, Sean; Brown, Destiny; Li, Xiaosong; Howard, Eric; Nordquist, Robert E.; Hode, Tomas; Chen, Wei R.

2011-03-01

Thermal therapy has been used for cancer treatment for more than a century. While thermal effect can be direct, immediate, and controllable, it is not sufficient to completely eradicate tumors, particularly when tumors have metastasized locally or to the distant sites. Metastases are the major cause of treatment failure and cancer deaths. Current available therapies, such as surgery, radiation, and chemotherapy, only have limited curative effects in patients with late-stage, metastatic cancers. Immunotherapy has been considered as the ultimate approach for cancer treatment since a systemic, anti-tumor, immunological response can be induced. Using the combination of photothermal therapy and immunotherapy, laser immunotherapy (LIT),a novel immunotherapy modality for late-stage cancer treatment, has been developed. LIT has shown great promise in pre-clinical studies and clinical breast cancer and melanoma pilot trials. However, the skin color and the depth of the tumor have been challenges for effective treatment with LIT. To induce a thermal destruction zone of appropriate size without causing thermal damage on the skin, we have developed interstitial laser immunotherapy (ILIT) using a cylindrical diffuser. To determine the effectiveness of ILIT, we treated the DMBA-4 metastatic tumors in rats. The thermal damage in tumor tissue was studied using TTC immersion and hematoxolin and eosin (H & E) staining. Also observed was the overall survival of the treated animals. Our results demonstrated that the ILIT could impact a much larger tumor area, and it significantly reduced the surface damage compared with the early version of non-invasive LIT. The survival data also indicate that ILIT has the potential to become an effective tool for the treatment of deeper, larger, and metastatic tumors, with reduced side effects.

Interstitial photodynamic therapy of canine prostate with meso-tetra-(m-hydroxyphenyl) chlorin and 5-aminolevulinic acid: a preliminary study

NASA Astrophysics Data System (ADS)

Chang, Shi-Chung; Buonaccorsi, Giovanni A.; MacRobert, Alexander J.; Bown, Stephen G.

1996-01-01

Photodynamic therapy (PDT) is proved to have potential for managing various malignancies. We investigated tissue biodistribution and photodynamic effects on a canine model in vivo using second generation photosensitizers, meso-tetra(m-hydroxyphenyl)chlorin (mTHPC) and 5-aminolaevulinic acid (ALA) to evaluate the feasibility and possible future application of PDT on the prostate. Using fluorescence microscopy, the optimal sensitization time of the prostate was between 24 - 72 hours with mTHPC and, 3 hours with ALA. After optimum time of sensitization, prostates of mature beagle were treated with laser at various sites by placing fiber interstitially under the guidance of transrectal ultrasound. The light dose for each treatment site was 100 J (100 mW for 1,000 seconds at the wavelength of 650 and 630 nm, respectively). With mTHPC, single laser fiber was able to induce organ confined PDT lesion as large as 20 by 18 by 18 mm in size. However, the PDT lesion with ALA was negligible 3 days after treatment. Physical distress manifested as urinary retention, poor appetite and body weigh loss, was more prominent with increasing number of treatment sites as a result of extensive prostatic swelling and urethral damages. However, these problems usually alleviated spontaneously 7 to 10 days after PDT. The characteristic histological changes were hemorrhagic necrosis and glandular destruction with preservation of interlobular collagen fibers. Urethral damage seen at the early stage healed by regeneration of urothelium in 4 weeks. We conclude that interstitial PDT with mTHPC is technically possible to produce extensive glandular necrosis in the normal prostate which heals safely and does not change the prostatic architecture. ALA, although it seems promising for bladder tumors, is much less effective than mTHPC on the prostate. With mTHPC, it might have the potential for treating prostate cancers localized in the periphery of the gland.

Separation of ice crystals from interstitial aerosol particles using virtual impaction at the Fifth International Ice Nucleation Workshop FIN-3

NASA Astrophysics Data System (ADS)

Roesch, M.; Garimella, S.; Roesch, C.; Zawadowicz, M. A.; Katich, J. M.; Froyd, K. D.; Cziczo, D. J.

2016-12-01

In this study, a parallel-plate ice chamber, the SPectrometer for Ice Nuclei (SPIN, DMT Inc.) was combined with a pumped counterflow virtual impactor (PCVI, BMI Inc.) to separate ice crystals from interstitial aerosol particles by their aerodynamic size. These measurements were part of the FIN-3 workshop, which took place in fall 2015 at Storm Peak Laboratory (SPL), a high altitude mountain top facility (3220 m m.s.l.) in the Rocky Mountains. The investigated particles were sampled from ambient air and were exposed to cirrus-like conditions inside SPIN (-40°C, 130% RHice). Previous SPIN experiments under these conditions showed that ice crystals were found to be in the super-micron range. Connected to the outlet of the ice chamber, the PCVI was adjusted to separate all particulates aerodynamically larger than 3.5 micrometer to the sample flow while smaller ones were rejected and removed by a pump flow. Using this technique reduces the number of interstitial aerosol particles, which could bias subsequent ice nucleating particle (INP) analysis. Downstream of the PCVI, the separated ice crystals were evaporated and the flow with the remaining INPs was split up to a particle analysis by laser mass spectrometry (PALMS) instrument a laser aerosol spectrometer (LAS, TSI Inc.) and a single particle soot photometer (SP2, DMT Inc.). Based on the sample flow and the resolution of the measured particle data, the lowest concentration threshold for the SP2 instrument was 294 INP L-1 and for the LAS instrument 60 INP L-1. Applying these thresholds as filters to the measured PALMS time series 944 valid INP spectra using the SP2 threshold and 445 valid INP spectra using the LAS threshold were identified. A sensitivity study determining the number of good INP spectra as a function of the filter threshold concentration showed a two-phase linear growth when increasing the threshold concentration showing a breakpoint around 100 INP L-1.

Microdefects and self-interstitial diffusion in crystalline silicon

NASA Astrophysics Data System (ADS)

Knowlton, William Barthelemy

In this thesis, a study is presented of D-defects and self-interstitial diffusion in silicon using Li ion (Lisp+) drifting in an electric field and transmission electron microscopy (TEM). Obstruction of Lisp+ drifting has been found in wafers from certain but not all FZ p-type Si. Incomplete Lisp+ drifting always occurs in the central region of the wafers. This work established that interstitial oxygen is not responsible for hindering Lisp+ drifting. The Osb i concentration was measured ({˜}2× 10sp{15}\\ cmsp{-3}) by local vibrational mode Fourier transform infrared spectroscopy and did not vary radially across the wafer. TEM was performed on a samples from the partially Lisp+ drifted area and compared to regions without D-defects. Precipitates were found only in the region containing D-defects that had partially Lisp+ drifted. This result indicates D-defects are responsible for the precipitation that halts the Lisp+ drift process. The precipitates were characterized using selected area diffraction (SAD) and image contrast analysis. The results suggested that the precipitates may cause stacking faults and their identity may be lithium silicides such as Lisb{21}Sisb5\\ and\\ Lisb{13}Sisb4. TEM revealed a decreasing distribution of Li precipitates as a function of Lisp+ drift depth along the growth direction. A preliminary model is presented that simulates Lisp+ drifting. The objective of the model is to incorporate the Li precipitate density distribution and Lisp+ drift depth to extract the size and capture cross-section of the D-defects. Nitrogen (N) doping has been shown to eliminate D-defects as measured by conventional techniques. However, Lisp+ drifting has shown that D-defects are indeed still present. Lisp+ drifting is able to detect D-defects at concentrations lower than conventional techniques. Lisp+ drifting and D-defects provide a useful means to study Si self-interstitial diffusion. The process modeling program SUPREM-IV was used to simulate the results of Si self-interstitial diffusion obtained from Lisp+ drifting experiments. Anomalous results from the Si self-interstitial diffusion experiments forced a re-examination of the possibility of thermal dissociation of D-defects. Thermal annealing experiments that were performed support this possibility. A review of the current literature illustrates the need for more research on the effects of thermal processing on FZ Si to understand the dissolution kinetics of D-defects.

Atomic-scale investigation of point defects and hydrogen-solute atmospheres on the edge dislocation mobility in alpha iron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhatia, M. A.; Solanki, K. N., E-mail: kiran.solanki@asu.edu; Groh, S.

2014-08-14

In this study, we present atomistic mechanisms of 1/2 [111](11{sup ¯}0) edge dislocation interactions with point defects (hydrogen and vacancies) and hydrogen solute atmospheres in body centered cubic (bcc) iron. In metals such as iron, increases in hydrogen concentration can increase dislocation mobility and/or cleavage-type decohesion. Here, we first investigate the dislocation mobility in the presence of various point defects, i.e., change in the frictional stress as the edge dislocation interacts with (a) vacancy, (b) substitutional hydrogen, (c) one substitutional and one interstitial hydrogen, (d) interstitial hydrogen, (e) vacancy and interstitial hydrogen, and (f) two interstitial hydrogen. Second, we examinemore » the role of a hydrogen-solute atmosphere on the rate of local dislocation velocity. The edge dislocation simulation with a vacancy in the compression side of the dislocation and an interstitial hydrogen atom at the tension side exhibit the strongest mechanical response, suggesting a higher potential barrier and hence, the higher frictional stress (i.e., ∼83% higher than the pure iron Peierls stress). In the case of a dislocation interacting with a vacancy on the compressive side, the vacancy binds with the edge dislocation, resulting in an increase in the friction stress of about 28% when compared with the Peierls stress of an edge dislocation in pure iron. Furthermore, as the applied strain increases, the vacancy migrates through a dislocation transportation mechanism by attaining a velocity of the same order as the dislocation velocity. For the case of the edge dislocation interacting with interstitial hydrogen on the tension side, the hydrogen atom jumps through one layer perpendicular to the glide plane during the pinning-unpinning process. Finally, our simulation of dislocation interactions with hydrogen show first an increase in the local dislocation velocity followed by a pinning of the dislocation core in the atmosphere, resulting in resistance to dislocation motion as the dislocation moves though the hydrogen-solute atmospheres. With this systematic, atomistic study of the edge dislocation with various point defects, we show significant increase in obstacle strengths in addition to an increase in the local dislocation velocity during interaction with solute atmospheres. The results have implications for constitutive development and modeling of the hydrogen effect on dislocation mobility and deformation in metals.« less

Numerical modeling of fluid and oxygen exchanges through microcirculation for the assessment of microcirculation alterations caused by type 2 diabetes.

PubMed

Tang, Yuanliang; He, Ying

2018-05-01

Type 2 diabetes mellitus (DM2) is frequently accompanied by microcirculation complications, including structural and functional alterations, which may have serious effects on substance exchanges between blood and interstitial tissue and the health of organs. In this paper, we aim to study the influence of microcirculation alterations in DM2 patients on fluid and oxygen exchanges through a model analysis. A fluid flow and oxygen transport model were developed by considering the interplay between blood in capillary network and interstitial tissue. The two regions were separately represented by 1D network model and 3D volume model, and the immersed boundary method (IBM) was adopted to solve fluid and mass transfer between these two regions. By using the model, the steady flow field and the distributions of oxygen in capillary network and surrounding tissue were firstly simulated. In the interstitial volume, fluid pressure and oxygen tension decreased with the increase of distance from the network; in the network, oxygen tension in blood plasma dropped from 100 mm Hg at the entrance to about 40 mm Hg at the exit. We further tested several structural and functional disorders related to diabetic pathological conditions. Simulated results show that the impaired connectivity of the network could result in poor robustness in maintaining blood flow and perfused surface; under high fluid permeability conditions of capillary walls, the pressure gradient was much larger around the capillary bed, and this alteration led to a saturation level of the interstitial pressure when lymphatic flow drainage can't work effectively; the variations in network connectivity and permeability of capillary wall also had unfavorable influence on oxygen distributions in interstitial tissue. In addition, when the oxygen releasing capacity of hemoglobin was confined by glycosylated hemoglobin (HbA1) in the case of diabetes, the plasma could not be complemented with adequate oxygen and thus the hypoxic tissue range will be extended. This study illustrates that when microcirculation disturbances, including the structure of capillary network, the wall osmosis property and the capacity of blood binding oxygen occur in DM2, some negative impacts are raised on microvascular hemodynamics and metabolism circumstance of interstitial tissue. Copyright © 2018 Elsevier Inc. All rights reserved.

Ablative therapy for liver tumours

PubMed Central

Dick, E A; Taylor-Robinson, S D; Thomas, H C; Gedroyc, W M W

2002-01-01

Established ablative therapies for the treatment of primary and secondary liver tumours, including percutaneous ethanol injection, cryotherapy, and radiofrequency ablation, are discussed. Newer techniques such as magnetic resonance imaging guided laser interstitial thermal therapy of liver tumours has produced a median survival rate of 40.8 months after treatment. The merits of this newly emerging technique are discussed, together with future developments, such as focused ultrasound therapy, which holds the promise of non-invasive thermoablation treatment on an outpatient basis. PMID:11950826

Carbon diffusion in bulk hcp zirconium: A multi-scale approach

NASA Astrophysics Data System (ADS)

Xu, Y.; Roques, J.; Domain, C.; Simoni, E.

2016-05-01

In the framework of the geological repository of the used fuel claddings of pressurized water reactor, carbon behavior in bulk zirconium is studied by periodic Density Functional Theory calculations. The C interstitial sites were investigated and it was found that there are two possible carbon interstitial sites: a distorted basal tetragonal site and an octahedral site. There are four types of possible atomic jumps between them. After calculating the migration energies, the attempt frequencies and the jump probabilities for each possible migration path, kinetic Monte Carlo (KMC) simulations were performed to simulate carbon diffusion at the macroscopic scale. The results show that carbon diffusion in pure Zr bulk is extremely limited at the storage temperature (50 °C). Since there are defects in Zr bulk, in a second step, the effect of atomic vacancy was studied and it was proved that vacancies cannot increase carbon diffusion.

Carbide and nitride precipitation during laser cladding of Inconel 718 alloy coatings

NASA Astrophysics Data System (ADS)

Zhang, Yaocheng; Li, Zhuguo; Nie, Pulin; Wu, Yixiong

2013-11-01

The microstructure of the laser clad Inconel 718 alloy coating was observed by scanning electron microscope (SEM). The chemical composition of precipitation phases was investigated by energy dispersive spectrometer (EDS) and solid phase microextraction (SPME). The crystal structure and lattice constants of precipitation are determined by transmission electron microscope (TEM). Vickers hardness of the coatings and the nanohardness of the interstitial phases were measured. The insular carbide (MC) and the tetragonal nitride (MN) with face-centered cubic (FCC) structure are rich in Ti and Nb but depleted in Ni, Fe and Cr due to the interdiffusion and redistribution of alloying elements between MC and MN and supersaturated matrix. MC and MN were precipitated in the forms of (Nb0.12Ti0.88)C1.5 and (Nb0.88Ti0.12)N1.5, and the Gibbs free energies of formation can be expressed as Δ G [ (Nb0.12Ti0.88)C1.5 ] 0 = - 122.654 - 3.1332 T (kJ /mol) and Δ G [ (Nb0.88Ti0.12)N1.5 ] 0 = - 157.814 - 3.0251 T (kJ /mol). The nanohardness and Young's modulus of the MC and MN were much higher than the matrix, and the plastic deformation energy of interstitial phases was lower than the matrix. The precipitation of MC and MN is beneficial to the mechanical properties of coating.

Modeling and Measurement of Correlation between Blood and Interstitial Glucose Changes

PubMed Central

Shi, Ting; Li, Dachao; Li, Guoqing; Zhang, Yiming; Xu, Kexin; Lu, Luo

2016-01-01

One of the most effective methods for continuous blood glucose monitoring is to continuously measure glucose in the interstitial fluid (ISF). However, multiple physiological factors can modulate glucose concentrations and affect the lag phase between blood and ISF glucose changes. This study aims to develop a compensatory tool for measuring the delay in ISF glucose variations in reference to blood glucose changes. A theoretical model was developed based on biophysics and physiology of glucose transport in the microcirculation system. Blood and interstitial fluid glucose changes were measured in mice and rats by fluorescent and isotope methods, respectively. Computer simulation mimicked curves were fitted with data resulting from fluorescent measurements of mice and isotope measurements of rats, indicating that there were lag times for ISF glucose changes. It also showed that there was a required diffusion distance for glucose to travel from center of capillaries to interstitial space in both mouse and rat models. We conclude that it is feasible with the developed model to continuously monitor dynamic changes of blood glucose concentration through measuring glucose changes in ISF with high accuracy, which requires correct parameters for determining and compensating for the delay time of glucose changes in ISF. PMID:27239479

Simulation of laser beam reflection at the sea surface modeling and validation

NASA Astrophysics Data System (ADS)

Schwenger, Frédéric; Repasi, Endre

2013-06-01

A 3D simulation of the reflection of a Gaussian shaped laser beam on the dynamic sea surface is presented. The simulation is suitable for the pre-calculation of images for cameras operating in different spectral wavebands (visible, short wave infrared) for a bistatic configuration of laser source and receiver for different atmospheric conditions. In the visible waveband the calculated detected total power of reflected laser light from a 660nm laser source is compared with data collected in a field trial. Our computer simulation comprises the 3D simulation of a maritime scene (open sea/clear sky) and the simulation of laser beam reflected at the sea surface. The basic sea surface geometry is modeled by a composition of smooth wind driven gravity waves. To predict the view of a camera the sea surface radiance must be calculated for the specific waveband. Additionally, the radiances of laser light specularly reflected at the wind-roughened sea surface are modeled considering an analytical statistical sea surface BRDF (bidirectional reflectance distribution function). Validation of simulation results is prerequisite before applying the computer simulation to maritime laser applications. For validation purposes data (images and meteorological data) were selected from field measurements, using a 660nm cw-laser diode to produce laser beam reflection at the water surface and recording images by a TV camera. The validation is done by numerical comparison of measured total laser power extracted from recorded images with the corresponding simulation results. The results of the comparison are presented for different incident (zenith/azimuth) angles of the laser beam.

Temperature field simulation on Ti6Al4V and Inconel718 heated by continuous infrared laser

NASA Astrophysics Data System (ADS)

Wang, Yanshen; Zhang, Zheng; Feng, Weiwei; Wang, Bo; Gai, Yuxian

2014-08-01

Laser assisted machining technology can heat and soften metals, which can be used for improving the machinability of superalloys such as Ti6Al4V and Inconel718. Researches on temperature field simulation of Ti6Al4V and Inconel718 are conducted in this paper. A thermal differential equation is established based on Fourier's law and energy conservation law. Then, a model using ABAQUS for simulating heat transfer process is brought out, which is then experimentally validated. Using the simulation model, detailed investigations on temperature field simulation are carried out in Ti6Al4V and Inconel718. According to simulation, surface temperature of the two superalloys eventually reaches their peak values, and the peak temperature of Ti6Al4V is much higher than that of Inconel718. To further investigate temperature heated by laser, laser parameters such as power, scanning velocity, laser spot radius and inclination angle are set to be variables separately for simulation. Simulation results show that laser power and laser spot radius are predominant factors in heating process compared with the influence of scanning velocity and inclination angle. Simulations in this paper provide valuable references for parameter optimization in the following laser heating experiments, which plays an important role in laser assisted machining.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Haixuan; Osetskiy, Yury N; Stoller, Roger E

The fundamentals of the framework and the details of each component of the self-evolving atomistic kinetic Monte Carlo (SEAKMC) are presented. The strength of this new technique is the ability to simulate dynamic processes with atomistic fidelity that is comparable to molecular dynamics (MD) but on a much longer time scale. The observation that the dimer method preferentially finds the saddle point (SP) with the lowest energy is investigated and found to be true only for defects with high symmetry. In order to estimate the fidelity of dynamics and accuracy of the simulation time, a general criterion is proposed andmore » applied to two representative problems. Applications of SEAKMC for investigating the diffusion of interstitials and vacancies in bcc iron are presented and compared directly with MD simulations, demonstrating that SEAKMC provides results that formerly could be obtained only through MD. The correlation factor for interstitial diffusion in the dumbbell configuration, which is extremely difficult to obtain using MD, is predicted using SEAKMC. The limitations of SEAKMC are also discussed. The paper presents a comprehensive picture of the SEAKMC method in both its unique predictive capabilities and technically important details.« less

The simulation study on optical target laser active detection performance

NASA Astrophysics Data System (ADS)

Li, Ying-chun; Hou, Zhao-fei; Fan, Youchen

2014-12-01

According to the working principle of laser active detection system, the paper establishes the optical target laser active detection simulation system, carry out the simulation study on the detection process and detection performance of the system. For instance, the performance model such as the laser emitting, the laser propagation in the atmosphere, the reflection of optical target, the receiver detection system, the signal processing and recognition. We focus on the analysis and modeling the relationship between the laser emitting angle and defocus amount and "cat eye" effect echo laser in the reflection of optical target. Further, in the paper some performance index such as operating range, SNR and the probability of the system have been simulated. The parameters including laser emitting parameters, the reflection of the optical target and the laser propagation in the atmosphere which make a great influence on the performance of the optical target laser active detection system. Finally, using the object-oriented software design methods, the laser active detection system with the opening type, complete function and operating platform, realizes the process simulation that the detection system detect and recognize the optical target, complete the performance simulation of each subsystem, and generate the data report and the graph. It can make the laser active detection system performance models more intuitive because of the visible simulation process. The simulation data obtained from the system provide a reference to adjust the structure of the system parameters. And it provides theoretical and technical support for the top level design of the optical target laser active detection system and performance index optimization.

Water Dynamics at Protein-Protein Interfaces: Molecular Dynamics Study of Virus-Host Receptor Complexes.

PubMed

Dutta, Priyanka; Botlani, Mohsen; Varma, Sameer

2014-12-26

The dynamical properties of water at protein-water interfaces are unlike those in the bulk. Here we utilize molecular dynamics simulations to study water dynamics in interstitial regions between two proteins. We consider two natural protein-protein complexes, one in which the Nipah virus G protein binds to cellular ephrin B2 and the other in which the same G protein binds to ephrin B3. While the two complexes are structurally similar, the two ephrins share only a modest sequence identity of ∼50%. X-ray crystallography also suggests that these interfaces are fairly extensive and contain exceptionally large amounts of waters. We find that while the interstitial waters tend to occupy crystallographic sites, almost all waters exhibit residence times of less than hundred picoseconds in the interstitial region. We also find that while the differences in the sequence of the two ephrins result in quantitative differences in the dynamics of interstitial waters, the trends in the shifts with respect to bulk values are similar. Despite the high wetness of the protein-protein interfaces, the dynamics of interstitial waters are considerably slower compared to the bulk-the interstitial waters diffuse an order of magnitude slower and have 2-3 fold longer hydrogen bond lifetimes and 2-1000 fold slower dipole relaxation rates. To understand the role of interstitial waters, we examine how implicit solvent models compare against explicit solvent models in producing ephrin-induced shifts in the G conformational density. Ephrin-induced shifts in the G conformational density are critical to the allosteric activation of another viral protein that mediates fusion. We find that in comparison with the explicit solvent model, the implicit solvent model predicts a more compact G-B2 interface, presumably because of the absence of discrete waters at the G-B2 interface. Simultaneously, we find that the two models yield strikingly different induced changes in the G conformational density, even for those residues whose conformational densities in the apo state are unaffected by the treatment of the bulk solvent. Together, these results show that the explicit treatment of interstitial water molecules is necessary for a proper description of allosteric transitions.

Laser surgery for selected small animal soft-tissue conditions

NASA Astrophysics Data System (ADS)

Bartels, Kenneth E.

1991-05-01

With the acquisition of a Nd:YAG and a CO2 laser in the College of Veterinary Medicine at Oklahoma State University in 1989, over 100 small animal clinical cases have been managed with these modern modalities for surgical excision and tissue vaporization. Most procedures have been for oncologic problems, but inflammatory, infectious, or congenital conditions including vaporization of acral lick 'granulomas,' excision/vaporization of foreign body induced, infected draining tracts, and resection of elongated soft palates have been successfully accomplished. Laser excision or vaporization of both benign and malignant neoplasms have effectively been performed and include feline nasal squamous cell carcinoma, mast cell tumors, and rectal/anal neoplasms. Results to date have been excellent with animals exhibiting little postoperative pain, swelling, and inflammation. Investigations involving application of laser energy for tissue welding of esophageal lacerations and hepatitic interstitial hyperthermia for metastatic colorectal cancer have also shown potential. A review of cases with an emphasis on survival time and postoperative morbidity suggests that carefully planned laser surgical procedures in clinical veterinary practice done with standardized protocols and techniques offer an acceptable means of treating conditions that were previously considered extremely difficult or virtually impossible to perform.

Laser-induced interstitial thermotherapy (LITT) with the KTP 532 laser for the treatment of uterine adenomyosis

NASA Astrophysics Data System (ADS)

Chapman, Roxana; Chapman, Kenneth

1997-05-01

Adenomyosis is a condition in which the myometrium is infiltrated by endometrial glands and stroma. This results in myometrial hyperplasia, uterine enlargement and causes menorrhagia, dysmenorrhoea and dyspareunia for which there is no known cure other than hysterectomy. The success of LITT in the treatment of uterine leiomyomata suggested that this might also be effective for the treatment of adenomyosis. Initially LITT was carried out on patients with adenomyosis prior to hysterectomy, then on patients who had completed child-bearing and finally on those who desired a family. Not only were symptoms relieved but pregnancies occurred spontaneously. The KTP 532 nm component of the KTP/YAG laser, which is absorbed by red pigment, was used with a 600 micrometer fiber with a bare tip via a needle microstat at laparoscopy. Holes were drilled in the abnormal tissue 3 cm apart and the laser fiber then slowly withdrawn, the object being to coagulate the surrounding blood vessels and adenomyotic tissue. The number of joules required depended on the volume of tissue treated.

Bioeffect of lipohemia rabbits irradiated in oral mucosa with 650-nm diode-laser-accompanied oxygen inspiration and clinical application

NASA Astrophysics Data System (ADS)

Yang, Fu-Shou; Tang, Jin-Xian; Liu, Cheng; Yang, Xi-Cheng; Pang, Hi-Xiu

1998-11-01

The study on irradiating in oral mucosa of rabbits with 650 nm diode laser and clinical application has been reported in this paper. The result of animal experiment showed: the obvious decrease of cholesterin and triglyceride has been found among those highly lipohemia rabbits in the experiments of 650nm diode laser irradiating accompanying with oxygen, as well as the parameters of hemorheology obviously being improved, as compared with highly lipohemia rabbits un-irradiating, the statistical analysis showing P < 0.01. In the meantime, the observation of histopathology shows, the lipide decreasing in aorta wall, intramyocardinal membranous layer,and renal interstitial in the group of rabbits which are irradiated with laser and accompanying with oxygen inspiration, and even the perfectly recovered tissue in some rabbits has been seen. This experimental result is significantly for clinical application. The results of clinic application showed, that the patients employed this method which treatment cerebral infarction, lipohemia, the total effective ratio achieved 91.7 percent, perfect effect 30.6 percent.

Cleveland Clinic experience with interstitial laser coagulation of the prostate

NASA Astrophysics Data System (ADS)

Ulchaker, James C.; Ng, Christopher S.; Palone, David; Angie, Michelle; Kursh, Elroy D.

2000-05-01

Transurethral resection of the prostate (TURP) has long been considered the gold standard therapy for benign prostatic hyperplasia (BPH). The problems associated with the TURP, which have been extensively described, include significant bleeding, TUR syndrome, incontinence, stricture, bladder neck contracture, and sexual dysfunction. The desire for simpler, less morbid alternative therapies to TURP has led to an eruption of research and development in the last decade. This is fueled by the continued research for more economical alternatives in our current high cost health care system.

Oxygen-induced recombination centers in as-grown Czochralski silicon crystals

NASA Technical Reports Server (NTRS)

Nauka, K.; Gatos, H. C.; Lagowski, J.

1983-01-01

Simultaneous quantitative microprofiles of the interstitial oxygen concentration and of the excess carrier lifetime are obtained in Czochralski-grown Si crystals employing double laser absorption scanning. It is found that oxygen concentration maxima and minima along the crystal growth direction coincide with lifetime minima and maxima, respectively. Another finding is that the magnitude of oxygen-induced lifetime changes increases dramatically in going from the center to the periphery of the crystal. The findings discussed imply that 'as-grown' oxygen precipitates figure in lifetime-limiting processes.

Miniaturization of Microwave Ablation Antennas

NASA Astrophysics Data System (ADS)

Luyen, Hung

Microwave ablation (MWA) is a promising minimally invasive technique for the treatment of various types of cancers as well as non-oncological diseases. In MWA, an interstitial antenna is typically used to deliver microwave energy to the diseased tissue and heat it up to lethal temperature levels that induce cell death. The desired characteristics of the interstitial antenna include a narrow diameter to minimize invasiveness of the treatment, a low input reflection coefficient at the operating frequency, and a localized heating zone. Most interstitial MWA antennas are fed by coaxial cables and designed for operation at either 915 MHz or 2.45 GHz. Coax-fed MWA antennas are commonly equipped with coaxial baluns to achieve localized heating. However, the conventional implementation of coaxial baluns increases the overall diameters of the antennas and therefore make them more invasive. It is highly desirable to develop less invasive antennas with shorter active lengths and smaller diameters for MWA applications. In this work, we demonstrate the feasibility of using higher frequency microwaves for tissue ablation and present several techniques for decreasing diameters of MWA antennas. First, we investigated MWA at higher frequencies by conducting numerical and experimental studies to compare ablation performance at 10 GHz and 1.9 GHz. Simulation and ex vivo ablation experiment results demonstrate comparable ablation zone dimensions achieved at these two frequencies. Operating at higher frequencies enables interstitial antennas with shorter active lengths. This can be combined with smaller-diameter antenna designs to create less invasive applicators or allow integration of multiple radiating elements on a single applicator to have better control and customization of the heating patterns. Additionally, we present three different coax-fed antenna designs and a non-coaxial-based balanced antenna that have smaller-diameter configurations than conventional coax-fed balun-equipped antennas. The antennas were evaluated and optimized in electromagnetic and thermal simulations. Then prototypes of these antennas were fabricated and experimentally characterized in ex vivo ablation experiments. Simulation and experimental results are in good agreement and demonstrate that the proposed antennas provide good impedance matching and localized heating patterns at their operating frequencies while having about 30% smaller diameters compared to conventional coax-fed balun-equipped MWA antennas.

Application of acoustical thermometry to noninvasive monitoring of internal temperature during laser hyperthermia

NASA Astrophysics Data System (ADS)

Krotov, Eugene V.; Yakovlev, Ivan V.; Zhadobov, Maxim; Reyman, Alexander M.; Zharov, Vladimir P.

2002-06-01

This work present the results of experimental study of applicability of acoustical brightness thermometry (ABT) in monitoring of internal temperature during laser hyperthermia and interstitial therapy. In these experiments the radiation of pulse repetition Nd:YAG laser (1064 nm) and continuous diode laser (800 nm) were used as heating sources. Experiments were performed in vitro by insertion of optical fiber inside the objects - optically transparent gelatin with incorporated light absorbing heterogeneities and samples of biological tissues (e.g. liver). During laser heating, internal temperature in absorbing heterogeneity and at fiber end were monitored by means of multi-channel ABT. The independent temperature control was performed with tiny electronic thermometer incorporated in heated zones. The results of experiments demonstrated reasonable sensitivity and accuracy of ABT for real-time temperature control during different kind of laser thermal therapies. According to preliminary data, ABT allow to measure temperature in depth up to 3-5 cm (depends on tissue properties) with spatial resolution some mm. Obtained data show that ABT is a very promising tool to give quantitative measure for different types of energy deposition (laser, microwave, focused ultrasound etc) at the depth commonly encountered in tumors of vital organs. Besides, ABT could give information about diffusion effects in heated zones or optical absorption. This work was supported by Russian Foundation for Basic Research and 6th competition-expertise of young scientists of Russian Academy of Sciences.

Multi-Phonon Relaxation of H^- Local Modes in CaF_2

NASA Astrophysics Data System (ADS)

Davison, C. P.; Happek, U.; Campbell, J. A.; Engholm, J. R.; Schwettman, H. A.

1998-03-01

Local modes play an important role in the relaxation of vibrational modes of small molecules in solids (J.R. Engholm, C.W. Rella, H.A. Schwettman, and U. Happek; Phys. Rev. Lett. 77), 1302 (1996)., but only few attempts have been reported to study the relaxation of these local modes. Here we report on experiments to investigate the non-radiative relaxation of H^- local modes in CaF_2. Using a pump-probe technique, saturation experiments on the H^- local modes, both interstitial and substitutional, were performed at the Stanford Free Electron Laser Center. At low temperature we find a relaxation time T1 of 45 psec for the substitutional H^- local mode, and a more rapid relaxation for the interstitial H^- local modes next to La^3+ and Lu^3+ impurities. Information on the decay channels of the local modes are obtained from the characteristic temperature dependence of the relaxation rates. This work is supported in part by the ONR, Grant No. N00014-94-1024.

A near infrared holographic glucose sensor.

PubMed

Vezouviou, Evangelia; Lowe, Christopher R

2015-06-15

Real-time glucose monitoring has been beneficial in reducing health complications associated with diabetes as well as a decrease in mortality. This report describes a novel holographic platform, fabricated via laser ablation on chitosan hydrogel with gold nanoparticles with a replaying in visible and near IR. The sensor responded with a 12 nm and 7 nm shift in wavelength at glucose concentrations in the 0-70 mM range and in the visible and near IR, respectively, at pH 7.4 and an ionic strength of 154 mM. The sensor did not respond to potential interferences found in the interstitial fluid, such as fructose, vitamin C and lactate, at their respective normal concentrations and was stable to fluctuations in temperature, pH and ionic strength. The characteristics of this sensor suggests that it may be applicable for use as an implanted device for the real time monitoring of glucose concentrations in the interstitial fluid using near IR as the interrogating medium. Copyright © 2015 Elsevier B.V. All rights reserved.

Observation of interstitial molecular hydrogen in clathrate hydrates.

PubMed

Grim, R Gary; Barnes, Brian C; Lafond, Patrick G; Kockelmann, Winfred A; Keen, David A; Soper, Alan K; Hiratsuka, Masaki; Yasuoka, Kenji; Koh, Carolyn A; Sum, Amadeu K

2014-09-26

The current knowledge and description of guest molecules within clathrate hydrates only accounts for occupancy within regular polyhedral water cages. Experimental measurements and simulations, examining the tert-butylamine + H2 + H2O hydrate system, now suggest that H2 can also be incorporated within hydrate crystal structures by occupying interstitial sites, that is, locations other than the interior of regular polyhedral water cages. Specifically, H2 is found within the shared heptagonal faces of the large (4(3)5(9)6(2)7(3)) cage and in cavities formed from the disruption of smaller (4(4)5(4)) water cages. The ability of H2 to occupy these interstitial sites and fluctuate position in the crystal lattice demonstrates the dynamic behavior of H2 in solids and reveals new insight into guest-guest and guest-host interactions in clathrate hydrates, with potential implications in increasing overall energy storage properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perez, Danny, E-mail: danny-perez@lanl.gov; Sandoval, Luis; Voter, Arthur F.

Due to its enviable properties, tungsten is a leading candidate plasma facing material in nuclear fusion reactors. However, like many other metals, tungsten is known to be affected by the high doses of helium atoms incoming from the plasma. Indeed, the implanted interstitial helium atoms cluster together and, upon reaching a critical cluster size, convert into substitutional nanoscale He bubbles. These bubbles then grow by absorbing further interstitial clusters from the matrix. This process can lead to deleterious changes in microstructure, degradation of mechanical properties, and contamination of the plasma. In order to better understand the growth process, we usemore » traditional and accelerated molecular dynamics simulations to investigate the interactions between interstitial He clusters and pre-existing bubbles. These interactions are characterized in terms of thermodynamics and kinetics. We show that the proximity of the bubble leads to an enhancement of the trap mutation rate and, consequently, to the nucleation of satellite bubbles in the neighborhood of existing ones. We also uncover a number of mechanisms that can lead to the subsequent annihilation of such satellite nanobubbles.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perez, Danny; Sandoval, Luis; Uberuaga, Blas P.

Due to its enviable properties, tungsten is a leading candidate plasma facing material in nuclear fusion reactors. But, like many other metals, tungsten is known to be affected by the high doses of helium atoms incoming from the plasma. Indeed, the implanted interstitial helium atoms cluster together and, upon reaching a critical cluster size, convert into substitutional nanoscale He bubbles. These bubbles then grow by absorbing further interstitial clusters from the matrix. This process can lead to deleterious changes in microstructure, degradation of mechanical properties, and contamination of the plasma. In order to better understand the growth process, we usemore » traditional and accelerated molecular dynamics simulations to investigate the interactions between interstitial He clusters and pre-existing bubbles. These interactions are characterized in terms of thermodynamics and kinetics. We also show that the proximity of the bubble leads to an enhancement of the trap mutation rate and, consequently, to the nucleation of satellite bubbles in the neighborhood of existing ones. Finally, we uncover a number of mechanisms that can lead to the subsequent annihilation of such satellite nanobubbles.« less

Anomalous dynamics of interstitial dopants in soft crystals

PubMed Central

Tauber, Justin; Higler, Ruben; Sprakel, Joris

2016-01-01

The dynamics of interstitial dopants govern the properties of a wide variety of doped crystalline materials. To describe the hopping dynamics of such interstitial impurities, classical approaches often assume that dopant particles do not interact and travel through a static potential energy landscape. Here we show, using computer simulations, how these assumptions and the resulting predictions from classical Eyring-type theories break down in entropically stabilized body-centered cubic (BCC) crystals due to the thermal excitations of the crystalline matrix. Deviations are particularly severe close to melting where the lattice becomes weak and dopant dynamics exhibit strongly localized and heterogeneous dynamics. We attribute these anomalies to the failure of both assumptions underlying the classical description: (i) The instantaneous potential field experienced by dopants becomes largely disordered due to thermal fluctuations and (ii) elastic interactions cause strong dopant–dopant interactions even at low doping fractions. These results illustrate how describing nonclassical dopant dynamics requires taking the effective disordered potential energy landscape of strongly excited crystals and dopant–dopant interactions into account. PMID:27856751

Research of laser echo signal simulator

NASA Astrophysics Data System (ADS)

Xu, Rui; Shi, Rui; Wang, Xin; Li, Zhou

2015-11-01

Laser echo signal simulator is one of the most significant components of hardware-in-the-loop (HWIL) simulation systems for LADAR. System model and time series model of laser echo signal simulator are established. Some influential factors which could induce fixed error and random error on the simulated return signals are analyzed, and then these system insertion errors are analyzed quantitatively. Using this theoretical model, the simulation system is investigated experimentally. The results corrected by subtracting fixed error indicate that the range error of the simulated laser return signal is less than 0.25m, and the distance range that the system can simulate is from 50m to 20km.

Migration of defect clusters and xenon-vacancy clusters in uranium dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Dong; Gao, Fei; Deng, Huiqiu

2014-07-01

The possible transition states, minimum energy paths and migration mechanisms of defect clusters and xenon-vacancy defect clusters in uranium dioxide have been investigated using the dimer and the nudged elastic-band methods. The nearby O atom can easily hop into the oxygen vacancy position by overcoming a small energy barrier, which is much lower than that for the migration of a uranium vacancy. A simulation for a vacancy cluster consisting of two oxygen vacancies reveals that the energy barrier of the divacancy migration tends to decrease with increasing the separation distance of divacancy. For an oxygen interstitial, the migration barrier formore » the hopping mechanism is almost three times larger than that for the exchange mechanism. Xe moving between two interstitial sites is unlikely a dominant migration mechanism considering the higher energy barrier. A net migration process of a Xe-vacancy pair containing an oxygen vacancy and a xenon interstitial is identified by the NEB method. We expect the oxygen vacancy-assisted migration mechanism to possibly lead to a long distance migration of the Xe interstitials in UO2. The migration of defect clusters involving Xe substitution indicates that Xe atom migrating away from the uranium vacancy site is difficult.« less

Effects of Ti and TiC ceramic powder on laser-cladded Ti-6Al-4V in situ intermetallic composite

NASA Astrophysics Data System (ADS)

Ochonogor, O. F.; Meacock, C.; Abdulwahab, M.; Pityana, S.; Popoola, A. P. I.

2012-12-01

Titanium metal matrix composite (MMCs) was developed on titanium alloy (Ti-6Al-4V) substrate with the aim of improving the hardness and wear properties by laser cladding technique using a Rofin Sinar 4 kW Nd: YAG laser. Wear investigations were carried out with the aid of three body abrasion tester. The resultant microstructure show homogeneous distribution of TiC particles free from cracks and pores. Multiple track deposited systems with 50% overlap revealed micro-hardness increase from 357.3 HV0.1for the substrate reaching a peak as high as 922.2 HV0.1 for 60%Ti + 40%TiC and the least 665.3 HV0.1 for 80%Ti + 20%TiC MMCs. The wear resistance of the materials improved significantly, indicating a fifteen-fold wear rate reduction due to the proper distribution of ceramic particles thereby forming interstitial carbides as revealed by the X-ray diffraction spectrum.

Quantum cascade lasers (QCLs) in biomedical spectroscopy.

PubMed

Schwaighofer, Andreas; Brandstetter, Markus; Lendl, Bernhard

2017-10-02

Quantum cascade lasers (QCL) are the first room temperature semiconductor laser source for the mid-IR spectral region, triggering substantial development for the advancement of mid-IR spectroscopy. Mid-IR spectroscopy in general provides rapid, label-free and objective analysis, particularly important in the field of biomedical analysis. Due to their unique properties, QCLs offer new possibilities for development of analytical methods to enable quantification of clinically relevant concentration levels and to support medical diagnostics. Compared to FTIR spectroscopy, novel and elaborated measurement techniques can be implemented that allow miniaturized and portable instrumentation. This review illustrates the characteristics of QCLs with a particular focus on their benefits for biomedical analysis. Recent applications of QCL-based spectroscopy for analysis of a variety of clinically relevant samples including breath, urine, blood, interstitial fluid, and biopsy samples are summarized. Further potential for technical advancements is discussed in combination with future prospects for employment of QCL-based devices in routine and point-of-care diagnostics.

Investigation of interstitial ultrasound ablation of spinal and paraspinal tumors: A patient-specific and parametric simulation study

NASA Astrophysics Data System (ADS)

Scott, Serena J.; Salgaonkar, Vasant; Prakash, Punit; Burdette, E. Clif; Diederich, Chris J.

2017-03-01

Preferential acoustic absorption and heating of bone can significantly impact interstitial ultrasound ablation of tumors within or bordering the spine. Furthermore, intervening cortical bone may provide acoustic and thermal insulation that can protect sensitive structures nearby, such as the spinal cord. The objectives of this study are firstly, to apply parametric and patient-specific models to theoretically assess the feasibility of interstitial ultrasound ablation of tumors within and near the spine, and secondly, to identify potential energy delivery strategies, safety criteria, advantages, and disadvantages of interstitial ultrasound in this setting. Transient biothermal models using previously validated approximations for power deposition within bone from interstitial sources were employed. Multilayered axisymmetric models were used to perform a parametric assessment of the impact of tumor dimensions, attenuation (dependent on residual bone content), perfusion, and maximum temperature thresholds on necessary treatment parameters and on treatment effectiveness. 3D patient-specific finite element models were generated based on segmented CT scans for nine representative patient cases selected to bracket a range of clinical interest, with tumors in or near the vertebrae, sacrum, and ilium. Tumors were 10-27 mm in diameter, 10-43 mm long, and 0-14 mm from the spinal canal. Paraspinal tumors, osteolytic vertebral tumors, and a mixed osteolytic/osteoblastic iliac bone tumor were considered. 7 MHz (1.5 mm OD) and 3.0 MHz (3.2 mm OD) applicators with an array of 1-4 tubular transducers (0.5 -1.5 cm long, 150-360° sector angles), were applied in various implant configurations. Variable thicknesses of bone insulating critical anatomy from the tumor and insulation of the spinal cord with injected carbon dioxide were also investigated for definition of safety margins and possible protection of critical structures. 6-44 mm diameter osteolytic tumors surrounded by bone and blastic (high bone content) lesions up to 20 mm in diameter could be fully ablated by 7 MHz interstitial ultrasound using 120-5,900 J and treatment durations of 0.4-15 min. 100% of the volumes of five simulated tumors located 4.3-14 mm from the spinal canal and 94.6-99.9% of the volumes of four simulated tumors 0-4.5 mm from the spinal canal were ablated (>240 EM43°C) within 15 min without damaging (<6 EM43°C) critical nerves. Preferential ultrasound absorption and concomitant heating at bone surfaces allowed for faster, more effective ablations with less delivered energy. 3-5 mm of normal cortical bone was found to provide a safety margin and reduce temperature elevations in untargeted tissues. Critical anatomy less than 3-5 mm from a tumor encapsulated by bone could be preserved by reducing the acoustic energy aimed towards these structures and/or through injection of insulating CO2. Parametric and patient-specific studies demonstrated the feasibility of interstitial ultrasound ablation of paraspinal tumors and osteolytic tumors within the spine. Preferential absorption of ultrasound by bone may provide improved localization, faster treatment times, and larger treatment zones in highly osteolytic and soft tissue tumors in and near bone compared to other heating modalities. This work was supported by the NIH grant R44CA112852.

Simulation of laser interaction with ablative plasma and hydrodynamic behavior of laser supported plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tong Huifeng; Yuan Hong; Tang Zhiping

When an intense laser beam irradiates on a solid target, ambient air ionizes and becomes plasma, while part of the target rises in temperature, melts, vaporizes, ionizes, and yet becomes plasma. A general Godunov finite difference scheme WENO (Weighted Essentially Non-Oscillatory Scheme) with fifth-order accuracy is used to simulate 2-dimensional axis symmetrical laser-supported plasma flow field in the process of laser ablation. The model of the calculation of ionization degree of plasma and the interaction between laser beam and plasma are considered in the simulation. The numerical simulations obtain the profiles of temperature, density, and velocity at different times whichmore » show the evolvement of the ablative plasma. The simulated results show that the laser energy is strongly absorbed by plasma on target surface and that the velocity of laser supported detonation (LSD) wave is half of the ideal LSD value derived from Chapman-Jouguet detonation theory.« less

Direct solar-pumped iodine laser amplifier

NASA Technical Reports Server (NTRS)

Han, K. S.

1985-01-01

This semiannual progress report covers the period from April 1, 1985 to Sept. 30, 1985 under NASA grant NAS1-441 entitled direct solar pumped iodine laser amplifier. During this period the parametric studies of the iodine laser oscillator pumped by a Vortek simulator was carried out before the amplifier studies. The amplifier studies are postponed to the extended period following completion of the parametric studies. In addition, the kinetic modeling of a solar pumped iodine laser amplifier, and the experimental work for a solar pumped dye laser amplifier are in progress. This report contains three parts: (1) the radiation characteristics of solar simulator and the parametric characteristics of photodissociation iodine laser continuously pumped by a Vortek solar simulator; (2) kinetic modeling of a solar pumped iodine laser amplifier; and (3) the study of the dye laser amplifier pumped by a Tamarack solar simulator.

Simulation of Layered Magma Chambers.

ERIC Educational Resources Information Center

Cawthorn, Richard Grant

1991-01-01

The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles…

Modeling radiation induced segregation in Iron-Chromium alloys

DOE PAGES

Senninger, Oriane; Soisson, Frederic; Martinez Saez, Enrique; ...

2015-10-16

Radiation induced segregation in ferritic Fe-Cr alloys is studied by Atomistic Kinetic Monte Carlo simulations that include di usion of chemical species by vacancy and interstitial migration, recombination, and elimination at sinks. The parameters of the di usion model are tted to DFT calculations. Transport coe cients that control the coupling between di usion of defects and chemical species are measured in dilute and concentrated alloys. Radiation induced segregation near grain boundaries is directly simulated with this model. We nd that the di usion of vacancies toward sinks leads to a Cr depletion. Meanwhile, the di usion of self-interstitials causesmore » an enrichment of Cr in the vicinity of sinks. For concentrations lower than 15%Cr, we predict that sinks will be enriched with Cr for temperatures lower than a threshold. When the temperature is above this threshold value, the sinks will be depleted in Cr. These results are compared to previous experimental studies and models. Cases of radiation induced precipitation and radiation accelerated precipitation are considered.« less

Role of pre-existing point defects on primary damage production and amorphization in silicon carbide (β-SiC)

NASA Astrophysics Data System (ADS)

Sahoo, Deepak Ranjan; Szlufarska, Izabela; Morgan, Dane; Swaminathan, Narasimhan

2018-01-01

Molecular dynamics simulations of displacement cascades were conducted to study the effect of point defects on the primary damage production in β-SiC. Although all types of point defects and Frenkel pairs were considered, Si interstitials and Si Frenkel pairs were unstable and hence excluded from the cascade studies. Si (C) vacancies had the maximum influence, enhancing C (Si) antisites and suppressing C interstitial production, when compared to the sample without any defects. The intracascade recombination mechanisms, in the presence of pre-existing defects, is explored by examining the evolution of point defects during the cascade. To ascertain the role of the unstable Si defects on amorphization, simulations involving explicit displacements of Si atoms were conducted. The dose to amorphization with only Si displacements was much lower than what was observed with only C displacements. The release of elastic energy accumulated due to Si defects, is found to be the amorphizing mechanism.

Influence of dislocation strain fields on the diffusion of interstitial iron impurities in silicon

NASA Astrophysics Data System (ADS)

Ziebarth, Benedikt; Mrovec, Matous; Elsässer, Christian; Gumbsch, Peter

2015-09-01

The efficiency of silicon (Si)-based solar cells is strongly affected by crystal defects and impurities. Metallic impurities, in particular interstitial iron (Fe) atoms, cause large electric losses because they act as recombination centers for photogenerated charge carriers. Here, we present a systematic first-principles density functional theory (DFT) study focusing on the influence of hydrostatic, uniaxial, and shear strains on the thermodynamic stability and the diffusivity of Fe impurities in crystalline Si. Our calculations show that the formation energy of neutral Fe interstitials in tetrahedral interstitial sites is almost unaffected by uniform deformations of the Si crystal up to strains of 5%. In contrast, the migration barrier varies significantly with strain, especially for hydrostatic deformation. In order to determine effective diffusion coefficients for different strain states, a kinetic Monte Carlo (kMC) model was set up based on the activation energy barriers and frequency factors obtained from the DFT simulations. By using the strain dependence of the migration barrier, we examined the migration of Fe interstitials in the vicinity of perfect 1 /2 <110 > screw and 60∘ mixed dislocations, and 1 /6 <112 > 90∘ and 30∘ partial dislocations. While the strain field of the perfect screw dislocation always enhances the local Fe diffusion, the existence of tensile and compressive regions around the 60∘ mixed dislocation results in a strong anisotropic diffusion profile with significantly faster and slower diffusivities on its tensile and compressive sides. The influences of the partial dislocations are qualitatively similar to that of the 60∘ mixed dislocation.

Phase-field modeling of void anisotropic growth behavior in irradiated zirconium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, G. M.; Wang, H.; Lin, De-Ye

2017-06-01

A three-dimensional (3D) phase field model was developed to study the effects of surface energy and diffusivity anisotropy on void growth behavior in irradiated Zr. The gamma surface energy function, which is used in the phase field model, was developed with the surface energy anisotropy calculated from the molecular dynamics (MD) simulations. It is assumed that vacancies have much larger mobility in c-axis than a- and b- axes while interstitials have much larger mobility in basal plane then that in c-axis. With the model, the equilibrium void morphology and the effect of defect concentrations and defect mobility anisotropy on voidmore » growth behavior were simulated. The simulations demonstrated that 1) The developed phase-field model can correctly reproduce the faceted void morphology predicted by the Wullf construction. 2) With isotropic diffusivity the void prefers to grow on the basal plane. 3) When the vacancy has large mobility along c-axis and interstitial has a large mobility on the basal plane of hexagonal closed packed (hcp) Zr alloys a platelet void grows in c-direction and shrinks on the basal plane, which is in agreement with the experimental observation of void growth behavior in irradiated Zr.« less

Current role of lasers in the treatment of benign prostatic hyperplasia (BPH).

PubMed

Kuntz, Rainer M

2006-06-01

Evaluate the current role of lasers in the treatment of benign prostatic hyperplasia (BPH). The results of a MEDLINE search for randomised trials and case series of the last 5 yr and published review articles were analysed for the safety and efficacy of neodymium:yttrium aluminum garnet (Nd:YAG), potassium-titanyl-phosphate (KTP), and holmium (Ho):YAG laser prostatectomy. The analysis includes 12 reports on randomised clinical trials, 2 comparative studies, 10 review articles, and a total of >5000 patients. Laser treatment of BPH has evolved from coagulation to enucleation. Blood loss is significantly reduced compared with transurethral resection and open prostatectomy. Visual laser ablation of the prostate and interstitial laser coagulation cause coagulative necrosis with secondary ablation. Long postoperative catheterisation, unpredictable outcomes, and high reoperation rates have restricted the use of these techniques. Ablative/vaporising techniques have become popular again with the marketing of new high-powered 80-W KTP and 100-W Ho lasers. Vaporisation immediately removes obstructing tissue. Short-term results are promising, but large series, long-term results, and randomised trials are lacking. Holmium laser enucleation (HoLEP) allows whole lobes of the prostate to be removed, mimicking the action of the index finger in open prostatectomy. Prostates of all sizes can be operated on. It is at least as safe and effective as transurethral resection of the prostate and open prostatectomy, with significantly lower morbidity. It is the only laser procedure that provides a specimen for histologic evaluation. HoLEP appears to be a size-independent new "gold standard" in the surgical treatment of BPH.

Effect of Heat Treatment on Borides Precipitation and Mechanical Properties of CoCrFeNiAl1.8Cu0.7B0.3Si0.1 High-Entropy Alloy Prepared by Arc-Melting and Laser-Cladding

NASA Astrophysics Data System (ADS)

Zhang, H.; Tang, H.; He, Y. Z.; Zhang, J. L.; Li, W. H.; Guo, S.

2017-11-01

Effects of heat treatment on borides precipitation and mechanical properties of arc-melted and laser-cladded CoCrNiFeAl1.8Cu0.7B0.3Si0.1 high-entropy alloys were comparatively studied. The arc-melted alloy contains lots of long strip borides distributed in the body-centered cubic phase, with a hardness about 643 HV0.5. Laser-cladding can effectively inhibit the boride precipitation and the laser-cladded alloy is mainly composed of a simple bcc solid solution, with a high hardness about 769 HV0.5, indicating the strengthening effect by interstitial boron atoms is greater than the strengthening by borides precipitation. Heat treatments between 800°C and 1200°C can simultaneously improve the hardness and fracture toughness of arc-melted alloys, owing to the boride spheroidization, dissolution, re-precipitation, and hence the increased boron solubility and nano-precipitation in the bcc solid solution. By contrast, the hardness of laser-cladded alloys reduce after heat treatments in the same temperature range, due to the decreased boron solubility in the matrix.

Human cadaver retina model for retinal heating during corneal surgery with a femtosecond laser

NASA Astrophysics Data System (ADS)

Sun, Hui; Fan, Zhongwei; Yun, Jin; Zhao, Tianzhuo; Yan, Ying; Kurtz, Ron M.; Juhasz, Tibor

2014-02-01

Femtosecond lasers are widely used in everyday clinical procedures to perform minimally invasive corneal refractive surgery. The intralase femtosecond laser (AMO Corp. Santa Ana, CA) is a common example of such a laser. In the present study a numerical simulation was developed to quantify the temperature rise in the retina during femtosecond intracorneal surgery. Also, ex-vivo retinal heating due to laser irradiation was measured with an infrared thermal camera (Fluke Corp. Everett, WA) as a validation of the simulation. A computer simulation was developed using Comsol Multiphysics to calculate the temperature rise in the cadaver retina during femtosecond laser corneal surgery. The simulation showed a temperature rise of less than 0.3 degrees for realistic pulse energies for the various repetition rates. Human cadaver retinas were irradiated with a 150 kHz Intralase femtosecond laser and the temperature rise was measured withan infrared thermal camera. Thermal camera measurements are in agreement with the simulation. During routine femtosecond laser corneal surgery with normal clinical parameters, the temperature rise is well beneath the threshold for retina damage. The simulation predictions are in agreement with thermal measurements providing a level of experimental validation.

Continuous glucose determination using fiber-based tunable mid-infrared laser spectroscopy

NASA Astrophysics Data System (ADS)

Yu, Songlin; Li, Dachao; Chong, Hao; Sun, Changyue; Xu, Kexin

2014-04-01

Wavelength-tunable laser spectroscopy in combination with a small-sized fiber-optic attenuated total reflection (ATR) sensor (fiber-based evanescent field analysis, FEFA) is reported for the continuous measurement of the glucose level. We propose a method of controlling and stabilizing the wavelength and power of laser emission and present a newly developed mid-infrared wavelength-tunable laser with a broad emission spectrum band of 9.19-9.77 μm (1024-1088 cm-1). The novel small-sized flow-through fiber-optic ATR sensor with long optical sensing length was used for glucose level determination. The experimental results indicate that the noise-equivalent concentration of this laser measurement system is as low as 3.8 mg/dL, which is among the most precise glucose measurements using mid-infrared spectroscopy. The sensitivity, which is three times that of conventional Fourier transform infrared spectrometer, was acquired because of the higher laser power and higher spectral resolution. The best prediction of the glucose concentration in phosphate buffered saline solution was achieved using the five-variable partial least-squares model, yielding a root-mean-square error of prediction as small as 3.5 mg/dL. The high sensitivity, multiple tunable wavelengths and small fiber-based sensor with long optical sensing length make glucose determination possible in blood or interstitial fluid in vivo.

Laser altimetry simulator. Version 3.0: User's guide

NASA Technical Reports Server (NTRS)

Abshire, James B.; Mcgarry, Jan F.; Pacini, Linda K.; Blair, J. Bryan; Elman, Gregory C.

1994-01-01

A numerical simulator of a pulsed, direct detection laser altimeter has been developed to investigate the performance of space-based laser altimeters operating over surfaces with various height profiles. The simulator calculates the laser's optical intensity waveform as it propagates to and is reflected from the terrain surface and is collected by the receiver telescope. It also calculates the signal and noise waveforms output from the receiver's optical detector and waveform digitizer. Both avalanche photodiode and photomultiplier detectors may be selected. Parameters of the detected signal, including energy, the 50 percent rise-time point, the mean timing point, and the centroid, can be collected into histograms and statistics calculated after a number of laser firings. The laser altimeter can be selected to be fixed over the terrain at any altitude. Alternatively, it can move between laser shots to simulate the terrain profile measured with the laser altimeter.

Refined Simulation of Satellite Laser Altimeter Full Echo Waveform

NASA Astrophysics Data System (ADS)

Men, H.; Xing, Y.; Li, G.; Gao, X.; Zhao, Y.; Gao, X.

2018-04-01

The return waveform of satellite laser altimeter plays vital role in the satellite parameters designation, data processing and application. In this paper, a method of refined full waveform simulation is proposed based on the reflectivity of the ground target, the true emission waveform and the Laser Profile Array (LPA). The ICESat/GLAS data is used as the validation data. Finally, we evaluated the simulation accuracy with the correlation coefficient. It was found that the accuracy of echo simulation could be significantly improved by considering the reflectivity of the ground target and the emission waveform. However, the laser intensity distribution recorded by the LPA has little effect on the echo simulation accuracy when compared with the distribution of the simulated laser energy. At last, we proposed a refinement idea by analyzing the experimental results, in the hope of providing references for the waveform data simulation and processing of GF-7 satellite in the future.

Flight Tasks and Metrics to Evaluate Laser Eye Protection in Flight Simulators

DTIC Science & Technology

2017-07-07

AFRL-RH-FS-TR-2017-0026 Flight Tasks and Metrics to Evaluate Laser Eye Protection in Flight Simulators Thomas K. Kuyk Peter A. Smith Solangia...34Flight Tasks and Metrics to Evaluate Laser Eye Protection in Flight Simulators" (AFRL-RH-FS-TR- 2017 - 0026 SHORTER.PATRI CK.D.1023156390 Digitally...SUBTITLE Flight Tasks and Metrics to Evaluate Laser Eye Protection in Flight Simulators 5a. CONTRACT NUMBER FA8650-14-D-6519 5b. GRANT NUMBER 5c

Molecular dynamic simulation study of plasma etching L10 FePt media in embedded mask patterning (EMP) process

NASA Astrophysics Data System (ADS)

Zhu, Jianxin; Quarterman, P.; Wang, Jian-Ping

2017-05-01

Plasma etching process of single-crystal L10-FePt media [H. Wang et al., Appl. Phys. Lett. 102(5) (2013)] is studied using molecular dynamic simulation. Embedded-Atom Method [M. S. Daw and M. I. Baskes, Phy. Rev. B 29, 6443 (1984); X. W. Zhou, R. A. Johnson and H. N. G. Wadley, Phy. Rev. B 69, 144113 (2004)] is used to calculate the interatomic potential within atoms in FePt alloy, and ZBL potential [J.F. Ziegler, J. P. Biersack and U. Littmark, "The Stopping and Range of Ions in Matter," Volume 1, Pergamon,1985] in comparison with conventional Lennard-Jones "12-6" potential is applied to interactions between etching gas ions and metal atoms. It is shown the post-etch structure defects can include amorphized surface layer and lattice interstitial point defects that caused by etchant ions passed through the surface layer. We show that the amorphized or damaged FePt lattice surface layer (or "magnetic dead-layer") thickness after etching increases with ion energy for Ar ion impacts, but significantly small for He ions at up to 250eV ion energy. However, we showed that He sputtering creates more interstitial defects at lower energy levels and defects are deeper below the surface compared to Ar sputtering. We also calculate the interstitial defect level and depth as dependence on ion energy for both Ar and He ions. Media magnetic property loss due to these defects is also discussed.

Computer simulation of a multiple-aperture coherent laser radar

NASA Astrophysics Data System (ADS)

Gamble, Kevin J.; Weeks, Arthur R.

1996-06-01

This paper presents the construction of a 2D multiple aperture coherent laser radar simulation that is capable of including the effects of the time evolution of speckle on the laser radar output. Every portion of a laser radar system is modeled in software, including quarter and half wave plates, beamsplitters (polarizing and non-polarizing), the detector, the laser source, and all necessary lenses. Free space propagation is implemented using the Rayleigh- Sommerfeld integral for both orthogonal polarizations. Atmospheric turbulence is also included in the simulation and is modeled using time correlated Kolmogorov phase screens. The simulation itself can be configured to simulate both monostatic and bistatic systems. The simulation allows the user to specify component level parameters such as extinction ratios for polarizing beam splitters, detector sizes and shapes. orientation of the slow axis for quarter/half wave plates and other components used in the system. This is useful from a standpoint of being a tool in the design of a multiple aperture laser radar system.

Simulation of laser beam reflection at the sea surface

NASA Astrophysics Data System (ADS)

Schwenger, Frédéric; Repasi, Endre

2011-05-01

A 3D simulation of the reflection of a Gaussian shaped laser beam on the dynamic sea surface is presented. The simulation is suitable for both the calculation of images of SWIR (short wave infrared) imaging sensor and for determination of total detected power of reflected laser light for a bistatic configuration of laser source and receiver at different atmospheric conditions. Our computer simulation comprises the 3D simulation of a maritime scene (open sea/clear sky) and the simulation of laser light reflected at the sea surface. The basic sea surface geometry is modeled by a composition of smooth wind driven gravity waves. The propagation model for water waves is applied for sea surface animation. To predict the view of a camera in the spectral band SWIR the sea surface radiance must be calculated. This is done by considering the emitted sea surface radiance and the reflected sky radiance, calculated by MODTRAN. Additionally, the radiances of laser light specularly reflected at the wind-roughened sea surface are modeled in the SWIR band considering an analytical statistical sea surface BRDF (bidirectional reflectance distribution function). This BRDF model considers the statistical slope statistics of waves and accounts for slope-shadowing of waves that especially occurs at flat incident angles of the laser beam and near horizontal detection angles of reflected irradiance at rough seas. Simulation results are presented showing the variation of the detected laser power dependent on the geometric configuration of laser, sensor and wind characteristics.

Results of the NeuroBlate System first-in-humans Phase I clinical trial for recurrent glioblastoma: clinical article.

PubMed

Sloan, Andrew E; Ahluwalia, Manmeet S; Valerio-Pascua, Jose; Manjila, Sunil; Torchia, Mark G; Jones, Stephen E; Sunshine, Jeffrey L; Phillips, Michael; Griswold, Mark A; Clampitt, Mark; Brewer, Cathy; Jochum, Jennifer; McGraw, Mary V; Diorio, Dawn; Ditz, Gail; Barnett, Gene H

2013-06-01

Laser interstitial thermal therapy has been used as an ablative treatment for glioma; however, its development was limited due to technical issues. The NeuroBlate System incorporates several technological advances to overcome these drawbacks. The authors report a Phase I, thermal dose-escalation trial assessing the safety and efficacy of NeuroBlate in recurrent glioblastoma multiforme (rGBM). Adults with suspected supratentorial rGBM of 15- to 40-mm dimension and a Karnofsky Performance Status score of ≥ 60 were eligible. After confirmatory biopsy, treatment was delivered using a rigid, gas-cooled, side-firing laser probe. Treatment was monitored using real-time MRI thermometry, and proprietary software providing predictive thermal damage feedback was used by the surgeon, along with control of probe rotation and depth, to tailor tissue coagulation. An external data safety monitoring board determined if toxicity at lower levels justified dose escalation. Ten patients were treated at the Case Comprehensive Cancer Center (Cleveland Clinic and University Hospitals-Case Medical Center). Their average age was 55 years (range 34-69 years) and the median preoperative Karnofsky Performance Status score was 80 (range 70-90). The mean tumor volume was 6.8 ± 5 cm(3) (range 2.6-19 cm(3)), the percentage of tumor treated was 78% ± 12% (range 57%-90%), and the conformality index was 1.21 ± 0.33 (range 1.00-2.04). Treatment-related necrosis was evident on MRI studies at 24 and 48 hours. The median survival was 316 days (range 62-767 days). Three patients improved neurologically, 6 remained stable, and 1 worsened. Steroid-responsive treatment-related edema occurred in all patients but one. Three had Grade 3 adverse events at the highest dose. NeuroBlate represents new technology for delivering laser interstitial thermal therapy, allowing controlled thermal ablation of deep hemispheric rGBM. CLINICAL TRIAL REGISTRATION NO.: NCT00747253 ( ClinicalTrials.gov ).

Performance calculation and simulation system of high energy laser weapon

NASA Astrophysics Data System (ADS)

Wang, Pei; Liu, Min; Su, Yu; Zhang, Ke

2014-12-01

High energy laser weapons are ready for some of today's most challenging military applications. Based on the analysis of the main tactical/technical index and combating process of high energy laser weapon, a performance calculation and simulation system of high energy laser weapon was established. Firstly, the index decomposition and workflow of high energy laser weapon was proposed. The entire system was composed of six parts, including classical target, platform of laser weapon, detect sensor, tracking and pointing control, laser atmosphere propagation and damage assessment module. Then, the index calculation modules were designed. Finally, anti-missile interception simulation was performed. The system can provide reference and basis for the analysis and evaluation of high energy laser weapon efficiency.

Potential energy landscape of an interstitial O2 molecule in a SiO2 film near the SiO2/Si(001) interface

NASA Astrophysics Data System (ADS)

Ohta, Hiromichi; Watanabe, Takanobu; Ohdomari, Iwao

2008-10-01

Potential energy distribution of interstitial O2 molecule in the vicinity of SiO2/Si(001) interface is investigated by means of classical molecular simulation. A 4-nm-thick SiO2 film model is built by oxidizing a Si(001) substrate, and the potential energy of an O2 molecule is calculated at Cartesian grid points with an interval of 0.05 nm in the SiO2 film region. The result shows that the potential energy of the interstitial site gradually rises with approaching the interface. The potential gradient is localized in the region within about 1 nm from the interface, which coincides with the experimental thickness of the interfacial strained layer. The potential energy is increased by about 0.62 eV at the SiO2/Si interface. The result agrees with a recently proposed kinetic model for dry oxidation of silicon [Phys. Rev. Lett. 96, 196102 (2006)], which argues that the oxidation rate is fully limited by the oxidant diffusion.

A tungsten-rhenium interatomic potential for point defect studies

DOE PAGES

Setyawan, Wahyu; Gao, Ning; Kurtz, Richard J.

2018-05-28

A tungsten-rhenium (W-Re) classical interatomic potential is developed within the embedded atom method (EAM) interaction framework. A force-matching method is employed to fit the potential to ab initio forces, energies, and stresses. Simulated annealing is combined with the conjugate gradient technique to search for an optimum potential from over 1000 initial trial sets. The potential is designed for studying point defects in W-Re systems. It gives good predictions of the formation energies of Re defects in W and the binding energies of W self-interstitial clusters with Re. The potential is further evaluated for describing the formation energy of structures inmore » the σ and χ intermetallic phases. The predicted convex-hulls of formation energy are in excellent agreement with ab initio data. In pure Re, the potential can reproduce the formation energies of vacancy and self-interstitial defects sufficiently accurately, and gives the correct ground state self-interstitial configuration. Furthermore, by including liquid structures in the fit, the potential yields a Re melting temperature (3130 K) that is close to the experimental value (3459 K).« less

A tungsten-rhenium interatomic potential for point defect studies

NASA Astrophysics Data System (ADS)

Setyawan, Wahyu; Gao, Ning; Kurtz, Richard J.

2018-05-01

A tungsten-rhenium (W-Re) classical interatomic potential is developed within the embedded atom method interaction framework. A force-matching method is employed to fit the potential to ab initio forces, energies, and stresses. Simulated annealing is combined with the conjugate gradient technique to search for an optimum potential from over 1000 initial trial sets. The potential is designed for studying point defects in W-Re systems. It gives good predictions of the formation energies of Re defects in W and the binding energies of W self-interstitial clusters with Re. The potential is further evaluated for describing the formation energy of structures in the σ and χ intermetallic phases. The predicted convex-hulls of formation energy are in excellent agreement with ab initio data. In pure Re, the potential can reproduce the formation energies of vacancies and self-interstitial defects sufficiently accurately and gives the correct ground state self-interstitial configuration. Furthermore, by including liquid structures in the fit, the potential yields a Re melting temperature (3130 K) that is close to the experimental value (3459 K).

A tungsten-rhenium interatomic potential for point defect studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Setyawan, Wahyu; Gao, Ning; Kurtz, Richard J.

A tungsten-rhenium (W-Re) classical interatomic potential is developed within the embedded atom method (EAM) interaction framework. A force-matching method is employed to fit the potential to ab initio forces, energies, and stresses. Simulated annealing is combined with the conjugate gradient technique to search for an optimum potential from over 1000 initial trial sets. The potential is designed for studying point defects in W-Re systems. It gives good predictions of the formation energies of Re defects in W and the binding energies of W self-interstitial clusters with Re. The potential is further evaluated for describing the formation energy of structures inmore » the σ and χ intermetallic phases. The predicted convex-hulls of formation energy are in excellent agreement with ab initio data. In pure Re, the potential can reproduce the formation energies of vacancy and self-interstitial defects sufficiently accurately, and gives the correct ground state self-interstitial configuration. Furthermore, by including liquid structures in the fit, the potential yields a Re melting temperature (3130 K) that is close to the experimental value (3459 K).« less

Direct solar-pumped iodine laser amplifier

NASA Technical Reports Server (NTRS)

Han, K. S.

1986-01-01

During this period the parametric studies of the iodine laser oscillator pumped by a Vortek simulator were carried out before amplifier studies. The amplifier studies are postponed to the extended period after completing the parametric studies. In addition, the kinetic modeling of a solar-pumped iodine laser amplifier, and the experimental work for a solar pumped dye laser amplifier are in progress. This report contains three parts: (1) a 10 W CW iodine laser pumped by a Vortek solar simulator; (2) kinetic modeling to predict the time to lasing threshold, lasing time, and energy output of solar-pumped iodine laser; and (3) the study of the dye laser amplifier pumped by a Tamarack solar simulator.

Simulation of a polarized laser beam reflected at the sea surface: modeling and validation

NASA Astrophysics Data System (ADS)

Schwenger, Frédéric

2015-05-01

A 3-D simulation of the polarization-dependent reflection of a Gaussian shaped laser beam on the dynamic sea surface is presented. The simulation considers polarized or unpolarized laser sources and calculates the polarization states upon reflection at the sea surface. It is suitable for the radiance calculation of the scene in different spectral wavebands (e.g. near-infrared, SWIR, etc.) not including the camera degradations. The simulation also considers a bistatic configuration of laser source and receiver as well as different atmospheric conditions. In the SWIR, the detected total power of reflected laser light is compared with data collected in a field trial. Our computer simulation combines the 3-D simulation of a maritime scene (open sea/clear sky) with the simulation of polarized or unpolarized laser light reflected at the sea surface. The basic sea surface geometry is modeled by a composition of smooth wind driven gravity waves. To predict the input of a camera equipped with a linear polarizer, the polarized sea surface radiance must be calculated for the specific waveband. The s- and p-polarization states are calculated for the emitted sea surface radiance and the specularly reflected sky radiance to determine the total polarized sea surface radiance of each component. The states of polarization and the radiance of laser light specularly reflected at the wind-roughened sea surface are calculated by considering the s- and p- components of the electric field of laser light with respect to the specular plane of incidence. This is done by using the formalism of their coherence matrices according to E. Wolf [1]. Additionally, an analytical statistical sea surface BRDF (bidirectional reflectance distribution function) is considered for the reflection of laser light radiances. Validation of the simulation results is required to ensure model credibility and applicability to maritime laser applications. For validation purposes, field measurement data (images and meteorological data) was analyzed. An infrared laser, with or without a mounted polarizer, produced laser beam reflection at the water surface and images were recorded by a camera equipped with a polarizer with horizontal or vertical alignment. The validation is done by numerical comparison of measured total laser power extracted from recorded images with the corresponding simulation results. The results of the comparison are presented for different incident (zenith/azimuth) angles of the laser beam and different alignment for the laser polarizers (vertical/horizontal/without) and the camera (vertical/horizontal).

Finite Element Analysis of Interaction of Laser Beam with Material in Laser Metal Powder Bed Fusion Process.

PubMed

Fu, Guang; Zhang, David Z; He, Allen N; Mao, Zhongfa; Zhang, Kaifei

2018-05-10

A deep understanding of the laser-material interaction mechanism, characterized by laser absorption, is very important in simulating the laser metal powder bed fusion (PBF) process. This is because the laser absorption of material affects the temperature distribution, which influences the thermal stress development and the final quality of parts. In this paper, a three-dimensional finite element analysis model of heat transfer taking into account the effect of material state and phase changes on laser absorption is presented to gain insight into the absorption mechanism, and the evolution of instantaneous absorptance in the laser metal PBF process. The results showed that the instantaneous absorptance was significantly affected by the time of laser radiation, as well as process parameters, such as hatch space, scanning velocity, and laser power, which were consistent with the experiment-based findings. The applicability of this model to temperature simulation was demonstrated by a comparative study, wherein the peak temperature in fusion process was simulated in two scenarios, with and without considering the effect of material state and phase changes on laser absorption, and the simulated results in the two scenarios were then compared with experimental data respectively.

Laser Altimeter for Flight Simulator

NASA Technical Reports Server (NTRS)

Webster, L. D.

1986-01-01

Height of flight-simulator probe above model of terrain measured by automatic laser triangulation system. Airplane simulated by probe that moves over model of terrain. Altitude of airplane scaled from height of probe above model. Height measured by triangulation of laser beam aimed at intersection of model surface with plumb line of probe.

Calculation of the fractional interstitial component of boron diffusion and segregation coefficient of boron in Si0.8Ge0.2

NASA Astrophysics Data System (ADS)

Fang, Tilden T.; Fang, Wingra T. C.; Griffin, Peter B.; Plummer, James D.

1996-02-01

Investigation of boron diffusion in strained silicon germanium buried layers reveals a fractional interstitial component of boron diffusion (fBI) in Se0.8Ge0.2 approximately equal to the fBI value in silicon. In conjunction with computer-simulated boron profiles, the results yield an absolute lower-bound of fBI in Si0.8Ge0.2 of ˜0.8. In addition, the experimental methodology provides a unique vehicle for measuring the segregation coefficient; oxidation-enhanced diffusion is used instead of an extended, inert anneal to rapidly diffuse the dopant to equilibrium levels across the interface, allowing the segregation coefficient to be measured more quickly.

Time frequency power profile of QRS complex obtained with wavelet transform in spontaneously hypertensive rats.

PubMed

Takano, Nami K; Tsutsumi, Takeshi; Suzuki, Hiroshi; Okamoto, Yoshiwo; Nakajima, Toshiaki

2012-02-01

We evaluated whether frequency analysis could detect the development of interstitial fibrosis in rats. SHR/Izm and age-matched WKY/Izm were used. Limb lead II electrocardiograms were recorded. Continuous wavelet transform (CWT) was applied for the time-frequency analysis. The integrated time-frequency power (ITFP) between QRS complexes was measured and compared between groups. The ITFP at low-frequency bands (≤125Hz) was significantly higher in SHR/Izm. The percent change of ITFP showed the different patterns between groups. Prominent interstitial fibrosis with an increase in TIMP-1 mRNA expression was also observed in SHR/Izm. These results were partly reproduced in a computer simulation. Copyright © 2011 Elsevier Ltd. All rights reserved.

MR-guided transcranial focused ultrasound safely enhances interstitial dispersion of large polymeric nanoparticles in the living brain

PubMed Central

Mohammadabadi, Ali; Nguyen, Ben A.; Guo, Sijia; Winkles, Jeffrey A.; Kim, Anthony J.; Gullapalli, Rao; Keller, Asaf; Frenkel, Victor

2018-01-01

Generating spatially controlled, non-destructive changes in the interstitial spaces of the brain has a host of potential clinical applications, including enhancing the delivery of therapeutics, modulating biological features within the tissue microenvironment, altering fluid and pressure dynamics, and increasing the clearance of toxins, such as plaques found in Alzheimer’s disease. Recently we demonstrated that ultrasound can non-destructively enlarge the interstitial spaces of the brain ex vivo. The goal of the current study was to determine whether these effects could be reproduced in the living brain using non-invasive, transcranial MRI-guided focused ultrasound (MRgFUS). The left striatum of healthy rats was treated using MRgFUS. Computer simulations facilitated treatment planning, and targeting was validated using MRI acoustic radiation force impulse imaging. Following MRgFUS treatments, Evans blue dye or nanoparticle probes were infused to assess changes in the interstitial space. In MRgFUS-treated animals, enhanced dispersion was observed compared to controls for 70 nm (12.8 ± 0.9 mm3 vs. 10.6 ± 1.0 mm3, p = 0.01), 200 nm (10.9 ± 1.4 mm3 vs. 7.4 ± 0.7 mm3, p = 0.01) and 700 nm (7.5 ± 0.4 mm3 vs. 5.4 ± 1.2 mm3, p = 0.02) nanoparticles, indicating enlargement of the interstitial spaces. No evidence of significant histological or electrophysiological injury was identified. These findings suggest that transcranial ultrasound can safely and effectively modulate the brain interstitium and increase the dispersion of large therapeutic entities such as particulate drug carriers or modified viruses. This has the potential to expand the therapeutic uses of MRgFUS. PMID:29415084

Numerical Modeling of Interstitial Fluid Flow Coupled with Blood Flow through a Remodeled Solid Tumor Microvascular Network

PubMed Central

Soltani, M.; Chen, P.

2013-01-01

Modeling of interstitial fluid flow involves processes such as fluid diffusion, convective transport in extracellular matrix, and extravasation from blood vessels. To date, majority of microvascular flow modeling has been done at different levels and scales mostly on simple tumor shapes with their capillaries. However, with our proposed numerical model, more complex and realistic tumor shapes and capillary networks can be studied. Both blood flow through a capillary network, which is induced by a solid tumor, and fluid flow in tumor’s surrounding tissue are formulated. First, governing equations of angiogenesis are implemented to specify the different domains for the network and interstitium. Then, governing equations for flow modeling are introduced for different domains. The conservation laws for mass and momentum (including continuity equation, Darcy’s law for tissue, and simplified Navier–Stokes equation for blood flow through capillaries) are used for simulating interstitial and intravascular flows and Starling’s law is used for closing this system of equations and coupling the intravascular and extravascular flows. This is the first study of flow modeling in solid tumors to naturalistically couple intravascular and extravascular flow through a network. This network is generated by sprouting angiogenesis and consisting of one parent vessel connected to the network while taking into account the non-continuous behavior of blood, adaptability of capillary diameter to hemodynamics and metabolic stimuli, non-Newtonian blood flow, and phase separation of blood flow in capillary bifurcation. The incorporation of the outlined components beyond the previous models provides a more realistic prediction of interstitial fluid flow pattern in solid tumors and surrounding tissues. Results predict higher interstitial pressure, almost two times, for realistic model compared to the simplified model. PMID:23840579

Novel doping alternatives for single-layer transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Onofrio, Nicolas; Guzman, David; Strachan, Alejandro

2017-11-01

Successful doping of single-layer transition metal dichalcogenides (TMDs) remains a formidable barrier to their incorporation into a range of technologies. We use density functional theory to study doping of molybdenum and tungsten dichalcogenides with a large fraction of the periodic table. An automated analysis of the energetics, atomic and electronic structure of thousands of calculations results in insightful trends across the periodic table and points out promising dopants to be pursued experimentally. Beyond previously studied cases, our predictions suggest promising substitutional dopants that result in p-type transport and reveal interesting physics behind the substitution of the metal site. Doping with early transition metals (TMs) leads to tensile strain and a significant reduction in the bandgap. The bandgap increases and strain is reduced as the d-states are filled into the mid TMs; these trends reverse as we move into the late TMs. Additionally, the Fermi energy increases monotonously as the d-shell is filled from the early to mid TMs and we observe few to no gap states, indicating the possibility of both p- (early TMs) and n- (mid TMs) type doping. Quite surprisingly, the simulations indicate the possibility of interstitial doping of TMDs; the energetics reveal that a significant number of dopants, increasing in number from molybdenum disulfide to diselenide and to ditelluride, favor the interstitial sites over adsorbed ones. Furthermore, calculations of the activation energy associated with capturing the dopants into the interstitial site indicate that the process is kinetically possible. This suggests that interstitial impurities in TMDs are more common than thought to date and we propose a series of potential interstitial dopants for TMDs relevant for application in nanoelectronics based on a detailed analysis of the predicted electronic structures.

Molecular Dynamics Simulations of Laser Powered Carbon Nanotube Gears

NASA Technical Reports Server (NTRS)

Srivastava, Deepak; Globus, Al; Han, Jie; Chancellor, Marisa K. (Technical Monitor)

1997-01-01

Dynamics of laser powered carbon nanotube gears is investigated by molecular dynamics simulations with Brenner's hydrocarbon potential. We find that when the frequency of the laser electric field is much less than the intrinsic frequency of the carbon nanotube, the tube exhibits an oscillatory pendulam behavior. However, a unidirectional rotation of the gear with oscillating frequency is observed under conditions of resonance between the laser field and intrinsic gear frequencies. The operating conditions for stable rotations of the nanotube gears, powered by laser electric fields are explored, in these simulations.

Research on the laser angle deception jamming technology of laser countermeasure

NASA Astrophysics Data System (ADS)

Ma, Shi-wei; Chen, Wen-jian; Gao, Wei; Duan, Yuan-yuan

2015-10-01

In recent years , laser guided weapons behave very well at destroying the military goals in the local wars, the single-shot probability, effective range and hitting precision getting better. And the semi-active laser guided weapons are the most widely used laser guided weapons. In order to improve the viability and protect important military goals, it's necessary to study the technology to against the semi-active guided weapons. This paper studies the working principle, the advantages and disadvantages of the semi-active guided weapons at first, and analyze the possibility of laser angle deception jamming system working. Then it analyzes the working principle and process of laser angle deception jamming technology. Finally it designs a half-real simulation system of laser angle deception jamming, which consists of semi-active laser guided weapons simulation system and laser angle deception jamming system. The simulation system demonstrates the working process of the laser angle deception jamming system. This paper provides fundamental base for the research on the countermeasure technology of semi-active laser guided weapons.

Computer simulation in mechanical spectroscopy

NASA Astrophysics Data System (ADS)

Blanter, M. S.

2012-09-01

Several examples are given for use of computer simulation in mechanical spectroscopy. On one hand simulation makes it possible to study relaxation mechanisms, and on the other hand to use the colossal accumulation of experimental material to study metals and alloys. The following examples are considered: the effect of Al atom ordering on the Snoek carbon peak in alloys of the system Fe - Al - C; the effect of plastic strain on Finkel'shtein - Rozin relaxation in Fe - Ni - C austenitic steel; checking the adequacy of energy interactions of interstitial atoms, calculated on the basis of a first-principle model by simulation of the concentration dependence of Snoek relaxation parameters in Nb - O.

Numerical simulation of melt ejection during the laser drilling process on aluminum alloy by millisecond pulsed laser

NASA Astrophysics Data System (ADS)

Wei, Zhang; Jin, Guangyong; Wang, Yibin

2016-01-01

In this paper, established a physical model to simulate the melt ejection induced by millisecond pulsed laser on aluminum alloy and use the finite element method to simulate the whole process. A semi-infinite axisymmetric model was established according to the experiment and the analytical solution of temperature in a solid phase was derived based on the thermal conduction equation. Mean while, by assuming that material was removed from the hole once it was melted, the function describing the hole's shape was obtained with the energy balance theory. This simulation is based on the interaction between single pulsed laser with different pulse-width and different peak energy and aluminum alloy material, the result of numerical simulation is that the hole's depth increases with the increase of laser energy and the hole's depth increases with the increase of laser pulse width, the keyhole depth is linearly increased with the increase of laser energy, respectively; the growth of the keyhole radius is in the trend to be gentle. By comparing the theoretical simulation data and the actual test data, we discover that: we discover that: the relative error between the theoretical values and the actual values is about 8.8%, the theoretical simulation curve is well consistent with the actual experimental curve. This research may provide the theoretical references to the understanding of the interaction between millisecond pulsed laser and many kinds of materials, as well as be beneficial to the application of the laser materials processing and military field.

Synthesis of Hf 8O 7, a new binary hafnium oxide, at high pressures and high temperatures

DOE PAGES

Bayarjargal, L.; Morgenroth, W.; Schrodt, N.; ...

2017-01-23

In this paper, two binary phases in the system Hf-O have been synthesized at pressures between 12 and 34 GPa and at temperatures up to 3000 K by reacting Hf with HfO 2 using a laser-heated diamond anvil cell. In situ X-ray diffraction in conjunction with density functional theory calculations has been employed to characterize a previously unreported tetragonal Hf 8O 7 phase. This phase has a structure which is based on an fcc Hf packing with oxygen atoms occupying octahedral interstitial positions. Its predicted bulk modulus is 223(1) GPa. The second phase has a composition close to Hf 6O,more » where oxygen atoms occupy octahedral interstitial sites in an hcp Hf packing. Its experimentally determined bulk modulus is 128(30) GPa. Finally, the phase diagram of Hf metal was further constrained at high pressures and temperatures, where we show that α-Hf transforms to β-Hf around 2160(150) K and 18.2 GPa and β-Hf remains stable up to at least 2800 K at this pressure.« less

Mild elevation of body temperature reduces tumor interstitial fluid pressure and hypoxia and enhances efficacy of radiotherapy in murine tumor models.

PubMed

Sen, Arindam; Capitano, Maegan L; Spernyak, Joseph A; Schueckler, John T; Thomas, Seneca; Singh, Anurag K; Evans, Sharon S; Hylander, Bonnie L; Repasky, Elizabeth A

2011-06-01

Human and rodent solid tumors often exhibit elevated interstitial fluid pressure (IFP). This condition is recognized as a prognostic indicator for reduced responses to therapy and decreased disease-free survival rate. In the present study, we tested whether induction of a thermoregulatory-mediated increase in tissue blood flow, induced by exposure of mice to mild environmental heat stress, could influence IFP and other vascular parameters within tumors. Using several murine tumor models, we found that heating results in a sustained reduction in tumor IFP correlating with increased tumor vascular perfusion (measured by fluorescent imaging of perfused vessels, laser Doppler flowmetry, and MRI) as well as a sustained reduction in tumor hypoxia. Furthermore, when radiation therapy was administered 24 hours postheating, we observed a significant improvement in efficacy that may be a result of the sustained reduction in tumor hypoxia. These data suggest, for the first time, that environmental manipulation of normal vasomotor function is capable of achieving therapeutically beneficial changes in IFP and microvascular function in the tumor microenvironment.

Research on the laser transmission characteristics simulation and comprehensive test in complex channel environment

NASA Astrophysics Data System (ADS)

Fu, Qiang; Liu, Jianhua; Wang, Xiaoman; Jiang, Huilin; Liu, Zhi

2014-12-01

The laser transmission characteristics affected in the complex channel environment, which limits the performance of laser equipment and engineering application severely. The article aim at the influence of laser transmission in atmospheric and seawater channels, summarizes the foreign researching work of the simulation and comprehensive test regarding to the laser transmission characteristics in complex environment. And researched the theory of atmospheric turbulence effect, water attenuation features, and put forward the corresponding theoretical model. And researched the simulate technology of atmospheric channel and sea water channel, put forward the analog device plan, adopt the similar theory of flowing to simulate the atmosphere turbulence .When the flowing has the same condition of geometric limits including the same Reynolds, they must be similar to each other in the motivation despite of the difference in the size, speed, and intrinsic quality. On this basis, set up a device for complex channel simulation and comprehensive testing, the overall design of the structure of the device, Hot and Cold Air Convection Simulation of Atmospheric Turbulence, mainly consists of cell body, heating systems, cooling systems, automatic control system. he simulator provides platform and method for the basic research of laser transmission characteristics in the domestic.

Finite element model of the temperature increase in excised porcine cadaver iris during direct illumination by femtosecond laser pulses

PubMed Central

Sun, Hui; Kurtz, Ronald M.

2012-01-01

Abstract. In order to model the thermal effect of laser exposure of the iris during laser corneal surgery, we simulated the temperature increase in porcine cadaver iris. The simulation data for the 60 kHz FS60 Laser showed that the temperature increased up to 1.23°C and 2.45°C (at laser pulse energy 1 and 2 µJ, respectively) by the 24 second procedure time. Calculated temperature profiles show good agreement with data obtained from ex vivo experiments using porcine cadaver iris. Simulation results of different types of femtosecond lasers indicate that the Laser in situ keratomileusis procedure does not present a safety hazard to the iris. PMID:22894525

Simulation of the temperature increase in human cadaver retina during direct illumination by 150-kHz femtosecond laser pulses

PubMed Central

Sun, Hui; Hosszufalusi, Nora; Mikula, Eric R.; Juhasz, Tibor

2011-01-01

We have developed a two-dimensional computer model to predict the temperature increase of the retina during femtosecond corneal laser flap cutting. Simulating a typical clinical setting for 150-kHz iFS advanced femtosecond laser (0.8- to 1-μJ laser pulse energy and 15-s procedure time at a laser wavelength of 1053 nm), the temperature increase is 0.2°C. Calculated temperature profiles show good agreement with data obtained from ex vivo experiments using human cadaver retina. Simulation results obtained for different commercial femtosecond lasers indicate that during the laser in situ keratomileusis procedure the temperature increase of the retina is insufficient to induce damage. PMID:22029369

The characteristics simulation of FMCW laser backscattering signals

NASA Astrophysics Data System (ADS)

Liu, Bohu; Song, Chengtian; Duan, Yabo

2018-04-01

A Monte Carlo simulation model of FMCW laser transmission in a smoke interference environment was established in this paper. The aerosol extinction coefficient and scattering coefficient changed dynamically in the simulation according to the smoke concentration variation, aerosol particle distributions and photon spatial positions. The simulation results showed that the smoke backscattering interference produced a number of amplitude peaks in the beat signal spectrum; the SNR of target echo signal to smoke interference was related to the transmitted laser wavelength and the aerosol particle size distribution; a better SNR could be obtained when the laser wavelength was in the range of 560-1660 nm. The characteristics of FMCW laser backscattering signals generated by simulation are consistent with the theoretical analysis. Therefore, this study was greatly helpful for improving the ability of identifying target and anti-interference in the further research.

Effects of laser-plasma instabilities on hydro evolution in an OMEGA-EP long-scale-length experiment

DOE PAGES

Li, J.; Hu, S. X.; Ren, C.

2017-02-28

Laser-plasma instabilities and hydro evolution of the coronal plasma in an OMEGA EP long-scale-length experiment with planar targets were studied with particle-in-cell (PIC) and hydrodynamic simulations. Plasma and laser conditions were first obtained in a two-dimensional DRACO hydro simulation with only inverse-bremsstrahlung absorption. Using these conditions, an OSIRIS PIC simulation was performed to study laser absorption and hot-electron generation caused by laser-plasma instabilities (LPIs) near the quarter-critical region. The obtained PIC information was subsequently coupled to another DRACO simulation to examine how the LPIs affect the overall hydrodynamics. Lastly, the results showed that the LPI-induced laser absorption increased the electronmore » temperature but did not significantly change the density scale length in the corona.« less

Effects of laser-plasma instabilities on hydro evolution in an OMEGA-EP long-scale-length experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J.; Hu, S. X.; Ren, C.

Laser-plasma instabilities and hydro evolution of the coronal plasma in an OMEGA EP long-scale-length experiment with planar targets were studied with particle-in-cell (PIC) and hydrodynamic simulations. Plasma and laser conditions were first obtained in a two-dimensional DRACO hydro simulation with only inverse-bremsstrahlung absorption. Using these conditions, an OSIRIS PIC simulation was performed to study laser absorption and hot-electron generation caused by laser-plasma instabilities (LPIs) near the quarter-critical region. The obtained PIC information was subsequently coupled to another DRACO simulation to examine how the LPIs affect the overall hydrodynamics. Lastly, the results showed that the LPI-induced laser absorption increased the electronmore » temperature but did not significantly change the density scale length in the corona.« less

Laser selective cutting of biological tissues by impulsive heat deposition through ultrafast vibrational excitations.

PubMed

Franjic, Kresimir; Cowan, Michael L; Kraemer, Darren; Miller, R J Dwayne

2009-12-07

Mechanical and thermodynamic responses of biomaterials after impulsive heat deposition through vibrational excitations (IHDVE) are investigated and discussed. Specifically, we demonstrate highly efficient ablation of healthy tooth enamel using 55 ps infrared laser pulses tuned to the vibrational transition of interstitial water and hydroxyapatite around 2.95 microm. The peak intensity at 13 GW/cm(2) was well below the plasma generation threshold and the applied fluence 0.75 J/cm(2) was significantly smaller than the typical ablation thresholds observed with nanosecond and microsecond pulses from Er:YAG lasers operating at the same wavelength. The ablation was performed without adding any superficial water layer at the enamel surface. The total energy deposited per ablated volume was several times smaller than previously reported for non-resonant ultrafast plasma driven ablation with similar pulse durations. No micro-cracking of the ablated surface was observed with a scanning electron microscope. The highly efficient ablation is attributed to an enhanced photomechanical effect due to ultrafast vibrational relaxation into heat and the scattering of powerful ultrafast acoustic transients with random phases off the mesoscopic heterogeneous tissue structures.

Laser-induced interstitial thermotherapy (LITT) for treatment of uterine leiomyomas: 750 myomas were treated by LITT and the results over a five-year period are analyzed

NASA Astrophysics Data System (ADS)

Chapman, Roxana

1997-05-01

Approximately 750 leiomyomas of 250 symptomatic patients were treated by LITT over a five-year period. Only 12% were lost to follow-up. Most were treated by a combination of the KTP/YAG laser, rarely by one or the other alone, and a few with the diode laser. The fiber optic was inserted 2 cm apart and, depending on the size of the tumor, 480 - 20,000 Joules were required. Most were treated laparoscopically but very large myomas were treated percutaneously under ultrasound control. Symptoms were nearly always relieved and the six failures were found to be due to unrecognized adenomyosis and other associated pathology. Half the patients complaining of infertility became pregnant and, in those whose only pathology had been leiomyomas it approached 90%. Vaginal delivery was not found to be contraindicated. Finally, oestrogen receptors and epidermal growth factor were found to be destroyed. It is concluded that LITT enables leiomyomas of all sizes and locations to be treated by a minimally invasive method with preservation of the uterus.

Suppressing Two-Plasmon Decay with Laser Frequency Detuning

DOE PAGES

Follett, R. K.; Shaw, J. G.; Myatt, J. F.; ...

2018-03-30

Three-dimensional laser-plasma interaction simulations show that laser frequency detuning by an amount achievable with current laser technology can be used to suppress the two-plasmon decay (TPD) instability and the corresponding hot-electron generation. For the plasma conditions and laser configuration in a direct-drive inertial confinement fusion implosion on the OMEGA laser, the simulations show that ~0.7% laser frequency detuning is sufficient to eliminate TPD-driven hot-electron generation in current experiments. In conclusion, this allows for higher ablation pressures in future implosion designs by using higher laser intensities.

Suppressing Two-Plasmon Decay with Laser Frequency Detuning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Follett, R. K.; Shaw, J. G.; Myatt, J. F.

Three-dimensional laser-plasma interaction simulations show that laser frequency detuning by an amount achievable with current laser technology can be used to suppress the two-plasmon decay (TPD) instability and the corresponding hot-electron generation. For the plasma conditions and laser configuration in a direct-drive inertial confinement fusion implosion on the OMEGA laser, the simulations show that ~0.7% laser frequency detuning is sufficient to eliminate TPD-driven hot-electron generation in current experiments. In conclusion, this allows for higher ablation pressures in future implosion designs by using higher laser intensities.

Suppressing Two-Plasmon Decay with Laser Frequency Detuning

NASA Astrophysics Data System (ADS)

Follett, R. K.; Shaw, J. G.; Myatt, J. F.; Palastro, J. P.; Short, R. W.; Froula, D. H.

2018-03-01

Three-dimensional laser-plasma interaction simulations show that laser frequency detuning by an amount achievable with current laser technology can be used to suppress the two-plasmon decay (TPD) instability and the corresponding hot-electron generation. For the plasma conditions and laser configuration in a direct-drive inertial confinement fusion implosion on the OMEGA laser, the simulations show that ˜0.7 % laser frequency detuning is sufficient to eliminate TPD-driven hot-electron generation in current experiments. This allows for higher ablation pressures in future implosion designs by using higher laser intensities.

Molecular dynamics study of lubricant depletion by pulsed laser heating

NASA Astrophysics Data System (ADS)

Seo, Young Woo; Rosenkranz, Andreas; Talke, Frank E.

2018-05-01

In this study, molecular dynamics simulations were performed to numerically investigate the effect of pulsed laser heating on lubricant depletion. The maximum temperature, the lubricant depletion width, the number of evaporated lubricant beads and the number of fragmented lubricant chains were studied as a function of laser peak power, pulse duration and repetition rate. A continuous-wave laser and a square pulse laser were simulated and compared to a Gaussian pulse laser. With increasing repetition rate, pulsed laser heating was found to approach continuous-wave laser heating.

Effects of a simulated microgravity model on cell structure and function in rat testis and epididymis

NASA Technical Reports Server (NTRS)

Hadley, Jill A.; Hall, Joseph C.; O'Brien, Ami; Ball, Richard

1992-01-01

The effect of simulated microgravity on the structure and function of the testis and epididymis cells was investigated in rats subjected to 7 days of tail suspension. Results of a histological examination revealed presence of disorganized seminiferous tubules and accumulation of large multinucleated cells and spermatids in the lumen of the epididymis. In addition, decreases in the content of testis protein and in testosterone levels in the testis, the interstitial fluid, and the epididymis were observed.

Computer simulation of the carbon activity in austenite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murch, G.E.; Thorn, R.J.

1979-02-01

Carbon activity in austenite is described in terms of an Ising-like f.c.c. lattice gas model in which carbon interstitials repel only at the distance of nearest neighbors. A Monte Carlo simulation method in the petit canonical ensemble is employed to calculate directly the carbon activity as a function of composition and temperature. The computed activities are in satisfactory agreement with the experimental data, similarly for the decompostion of the activity to the partial molar enthalpy and entropy.

Fluid shifts and muscle function in humans during acute simulated weightlessness

NASA Technical Reports Server (NTRS)

Hargens, A. R.; Tipton, C. M.; Gollnick, P. D.; Mubarak, S. J.; Tucker, B. J.; Akeson, W. H.

1983-01-01

The acute effects of simulated weightlessness on transcapillary fluid balance, tissue fluid shifts, muscle function, and triceps surface reflex time were studied in eight supine human subjects who were placed in a 5 degrees head-down tilt position for 8 hr. Results show a cephalic fluid shift from the legs as indicated by facial edema, nasal congestion, increased urine flow, decreased creatinine excretion, reduced calf girth, and decreased lower leg volume. The interstitial fluid pressure in the tibialis anterior muscle and subcutaneous tissue of the lower leg was found to fall significantly, while other transcapillary pressures (capillary and interstitial fluid colloid osmotic pressures) were relatively unchanged. The total water content of the soleus muscle was unchanged during the head-down tilt. After head-down tilt, isometric strength and isokinetic strength of the plantar flexors were unchanged, while the triceps surae reflex time associated with plantar flexion movement slowed slightly. These results demonstrate a dehydration effect of head-down tilt on muscle and subcutaneous tissue of the lower leg that may affect muscle function.

Point defect evolution in Ni, NiFe and NiCr alloys from atomistic simulations and irradiation experiments

DOE PAGES

Aidhy, Dilpuneet S.; Lu, Chenyang; Jin, Ke; ...

2015-08-08

Using molecular dynamics simulations, we elucidate irradiation-induced point defect evolution in fcc pure Ni, Ni 0.5Fe 0.5, and Ni 0.8Cr 0.2 solid solution alloys. We find that irradiation-induced interstitials form dislocation loops that are of 1/3 <111>{111}-type, consistent with our experimental results. While the loops are formed in all the three materials, the kinetics of formation is considerably slower in NiFe and NiCr than in pure Ni, indicating that defect migration barriers and extended defect formation energies could be higher in the alloys than pure Ni. As a result, while larger size clusters are formed in pure Ni, smaller andmore » more clusters are observed in the alloys. The vacancy diffusion occurs at relatively higher temperatures than interstitials, and their clustering leads to formation of stacking fault tetrahedra, also consistent with our experiments. The results also show that the surviving Frenkel pairs are composition-dependent and are largely Ni dominated.« less

Detection of one-dimensional migration of single self-interstitial atoms in tungsten using high-voltage electron microscopy

PubMed Central

Amino, T.; Arakawa, K.; Mori, H.

2016-01-01

The dynamic behaviour of atomic-size disarrangements of atoms—point defects (self-interstitial atoms (SIAs) and vacancies)—often governs the macroscopic properties of crystalline materials. However, the dynamics of SIAs have not been fully uncovered because of their rapid migration. Using a combination of high-voltage transmission electron microscopy and exhaustive kinetic Monte Carlo simulations, we determine the dynamics of the rapidly migrating SIAs from the formation process of the nanoscale SIA clusters in tungsten as a typical body-centred cubic (BCC) structure metal under the constant-rate production of both types of point defects with high-energy electron irradiation, which must reflect the dynamics of individual SIAs. We reveal that the migration dimension of SIAs is not three-dimensional (3D) but one-dimensional (1D). This result overturns the long-standing and well-accepted view of SIAs in BCC metals and supports recent results obtained by ab-initio simulations. The SIA dynamics clarified here will be one of the key factors to accurately predict the lifetimes of nuclear fission and fusion materials. PMID:27185352

A molecular dynamics study of thermal transport in nanoparticle doped Argon like solid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shahadat, Muhammad Rubayat Bin, E-mail: rubayat37@gmail.com; Ahmed, Shafkat; Morshed, A. K. M. M.

2016-07-12

Interfacial phenomena such as mass and type of the interstitial atom, nano scale material defect influence heat transfer and the effect become very significant with the reduction of the material size. Non Equilibrium Molecular Dynamics (NEMD) simulation was carried out in this study to investigate the effect of the interfacial phenomena on solid. Argon like solid was considered in this study and LJ potential was used for atomic interaction. Nanoparticles of different masses and different molecular defects were inserted inside the solid. From the molecular simulation, it was observed that a large interfacial mismatch due to change in mass inmore » the homogenous solid causes distortion of the phonon frequency causing increase in thermal resistance. Position of the doped nanoparticles have more profound effect on the thermal conductivity of the solid whereas influence of the mass ratio is not very significant. Interstitial atom positioned perpendicular to the heat flow causes sharp reduction in thermal conductivity. Structural defect caused by the molecular defect (void) also observed to significantly affect the thermal conductivity of the solid.« less

Enhanced photoluminescence and heterojunction characteristics of pulsed laser deposited ZnO nanostructures

NASA Astrophysics Data System (ADS)

Mannam, Ramanjaneyulu; Kumar, E. Senthil; Priyadarshini, D. M.; Bellarmine, F.; DasGupta, Nandita; Ramachandra Rao, M. S.

2017-10-01

We report on the growth of ZnO nanostructures in different gas ambient (Ar and N2) using pulsed laser deposition technique. Despite the similar growth temperature, use of N2 ambient gas resulted in well-aligned nanorods with flat surface at the tip, whereas, nanorods grown with Ar ambient exhibited tapered tips. The Nanorods grown under N2 ambient exhibited additional Raman modes corresponding to N induced zinc interstitials. The nanorods are c-axis oriented and highly epitaxial in nature. Photoluminescence spectroscopy reveals that the UV emission can be significantly enhanced by 10 times for the nanorods grown under Ar ambient. The enhanced UV emission is attributed to the reduction in polarization electric field along the c-axis. n-ZnO nanorods/p-Si heterojunction showed rectifying I-V characteristics with a turn of voltage of 3.4 V.

Qualification of Ti6Al4V ELI Alloy Produced by Laser Powder Bed Fusion for Biomedical Applications

NASA Astrophysics Data System (ADS)

Yadroitsev, I.; Krakhmalev, P.; Yadroitsava, I.; Du Plessis, A.

2018-03-01

Rectangular Ti6Al4V extralow interstitials (ELI) samples were manufactured by laser powder bed fusion (LPBF) in vertical and horizontal orientations relative to the build platform and subjected to various heat treatments. Detailed analyses of porosity, microstructure, residual stress, tensile properties, fatigue, and fracture surfaces were performed based on x-ray micro-computed tomography, scanning electron microscopy, and x-ray diffraction methods. The types of fracture and the tensile fracture mechanisms of the LPBF Ti6Al4V ELI alloy were also studied. Detailed analysis of the microstructure and the corresponding mechanical properties were compared against standard specifications for conventional Ti6Al4V alloy for use in surgical implant applications. Conclusions regarding the mechanical properties and heat treatment of LPBF Ti6Al4V ELI for biomedical applications are made.

Femtosecond laser melting of silver nanoparticles: comparison of model simulations and experimental results

NASA Astrophysics Data System (ADS)

Cheng, Chung-Wei; Chang, Chin-Lun; Chen, Jinn-Kuen; Wang, Ben

2018-05-01

Ultrafast laser-induced melting of silver nanoparticles (NPs) using a femtosecond laser pulse is investigated both theoretically and experimentally. The sintered Ag structure fabricated from printed Ag NP ink using femtosecond laser (1064 nm, 300 fs) irradiation is experimentally studied. A two-temperature model with dynamic optical properties and particle size effects on the melting temperature of Ag NPs is considered. The rapid phase change model is incorporated to simulate the Ag NPs' ultrafast laser-induced melting process, and a multi-shot melting threshold fluence predicted from the simulated single-shot melting threshold is developed.

Laser manipulation of atomic and molecular flows

NASA Astrophysics Data System (ADS)

Lilly, Taylor C.

The continuing advance of laser technology enables a range of broadly applicable, laser-based flow manipulation techniques. The characteristics of these laser-based flow manipulations suggest that they may augment, or be superior to, such traditional electro-mechanical methods as ionic flow control, shock tubes, and small scale wind tunnels. In this study, methodology was developed for investigating laser flow manipulation techniques, and testing their feasibility for a number of aerospace, basic physics, and micro technology applications. Theories for laser-atom and laser-molecule interactions have been under development since the advent of laser technology. The theories have yet to be adequately integrated into kinetic flow solvers. Realizing this integration would greatly enhance the scaling of laser-species interactions beyond the realm of ultra-cold atomic physics. This goal was realized in the present study. A representative numerical investigation, of laser-based neutral atomic and molecular flow manipulations, was conducted using near-resonant and non-resonant laser fields. To simulate the laser interactions over a range of laser and flow conditions, the following tools were employed: a custom collisionless gas particle trajectory code and a specifically modified version of the Direct Simulation Monte Carlo statistical kinetic solver known as SMILE. In addition to the numerical investigations, a validating experiment was conducted. The experimental results showed good agreement with the numerical simulations when experimental parameters, such as finite laser line width, were taken into account. Several areas of interest were addressed: laser induced neutral flow steering, collimation, direct flow acceleration, and neutral gas heating. Near-resonant continuous wave laser, and non-resonant pulsed laser, interactions with cesium and nitrogen were simulated. These simulations showed trends and some limitations associated with these interactions, used for flow steering and collimation. The use of one of these interactions, the induced dipole force, was extended beyond a single Gaussian laser field. The interference patterns associated with counter-propagating laser fields, or "optical lattices," were shown to be capable of both direct species acceleration and gas heating. This study resulted in predictions for a continuous, resonant laser-cesium flow with accelerations of 106 m/s2. For this circumstance, a future straightforward proof of principle experiment has been identified. To demonstrate non-resonant gas heating, a series of pulsed optical lattices were simulated interacting with neutral non-polar species. An optimum time between pulses was identified as a function of the collisional relaxation time. Using the optimum time between pulses, molecular nitrogen simulations showed an increase in gas temperature from 300 K to 2470 K at 1 atm, for 50 successive optical lattice pulses. A second proof of principle experiment was identified for future investigation.

Fabrication of novel bundled fiber and performance assessment for clinical applications.

PubMed

Kim, Changhwan; Jeon, Myung Jin; Jung, Jin Hyang; Yang, Jung Dug; Park, Hoyong; Kang, Hyun Wook; Lee, Ho

2014-11-01

During laser vaporization of benign prostate hyperplasia (BPH), high precision of optical fiber handling is pivotal to minimize any post-operative complications. The aim of the study was to evaluate the feasible applications of a bundled fiber to treat BPH by directionally and selectively manipulating laser light onto the targeted tissue. A bundled optical fiber, consisting of four side-firing fibers, was fabricated to selectively emit laser beams in from one to four directions. Both transmission efficiency and light distribution were qualitatively and quantitatively characterized on the bundled fiber. In terms of interstitial application of the proposed fiber with 1064 nm on porcine liver tissue, the extent of thermal denaturation was estimated and compared at various laser parameterizations and for different directions of light. From the laser source to the fiber tip, the fabricated fiber device demonstrated a total light transmission of 52%. Due to internal light reflection, a secondary beam was emitted backward from the fiber tip and was responsible for 25% of the transmission loss. According to tissue testing, the extent of tissue denaturation generally increased with laser power, irradiation time, and number of light directions. The geometrical shape of thermal coagulation correlated well with the direction of light emission. Thermal damage to the glass tube occurred during excessive heat accumulation generated by continuous irradiation. The proposed fiber can be beneficial for laser vaporization of BPH by providing a selective light direction irradiation along with minimal thermal damage. Further studies will extend the applicability of the bundled fiber to treat tubular tissue structure. © 2014 Wiley Periodicals, Inc.

Simulations of Foils Irradiated by Finite Laser Spots

NASA Astrophysics Data System (ADS)

Phillips, Lee

2006-10-01

Recent proposed designs (Obenchain et al., Phys. Plasmas 13 056320 (2006)) for direct-drive ICF targets for energy applications involve high implosion velocities with lower laser energies combined with higher irradiances. The use of high irradiances increases the likelihood of deleterious laser plasma instabilities (LPI) that may lead, for example, to the generation of fast electrons. The proposed use of a 248 nm KrF laser is expected to minimize LPI, and this is being studied by experiments on NRL's NIKE laser. Here we report on simulations aimed at designing and interpreting these experiments. The 2d simulations employ a modification of the FAST code to ablate plasma from CH and DT foils using laser pulses with arbitrary spatial and temporal profiles. These include the customary hypergaussian NIKE profile, gaussian profiles, and combinations of these. The simulations model the structure of the ablating plasma and the absorption of the laser light, providing parameters for design of the experiment and indicating where the relevant LPI (two-plasmon, Raman) may be observed.

Molecular dynamics simulations of the diffusion and coalescence of helium in tungsten

NASA Astrophysics Data System (ADS)

Zhou, Y. L.; Wang, J.; Hou, Q.; Deng, A. H.

2014-03-01

Molecular dynamics (MD) simulations are performed on the diffusion and coalescence of helium in tungsten. A new method for determining the effective capture radii (ECRs) and the dissociation energies of helium-related defects is proposed in this work. It is observed that the ECR of an interstitial helium atom trapping helium interstitials (denoted as He-Hen, n = 1-3) decreases with increasing temperature, except for He-He2 at T < 400 K. The traditional view that the ECR is approximately equal to the lattice constant, which has been widely used in kinetic Monte Carlo (KMC) and rate theory (RT) models, is only valid in some cases. However, the ECR between an interstitial helium atom and a substitutional helium atom (denoted as He-HeV) always approximates the third nearest-neighbor tetrahedral positions of the HeV. The diffusion coefficients Dn for helium clusters are also investigated. He2 migrates more quickly than a single He atom does at T < 400 K, whereas the diffusion path of He2 changes at higher temperatures. Another counterintuitive observation is that D5 > D3 > D4 at T < 500 K, which can be attributed to the disordered structure of He5. The Arrhenius relation describes the diffusion of Hen well in the temperature range from 300 K to 550 K, whereas the diffusion is not a standard thermally activated process at higher temperatures. Taken together, these results help elucidate the initial stage of helium bubble formation in tungsten as well as the requirements of long-term evolution methods such as KMC or RT models.

Flow through internal elastic lamina affects shear stress on smooth muscle cells (3D simulations).

PubMed

Tada, Shigeru; Tarbell, John M

2002-02-01

We describe a three-dimensional numerical simulation of interstitial flow through the medial layer of an artery accounting for the complex entrance condition associated with fenestral pores in the internal elastic lamina (IEL) to investigate the fluid mechanical environment around the smooth muscle cells (SMCs) right beneath the IEL. The IEL was modeled as an impermeable barrier to water flow except for the fenestral pores, which were assumed to be uniformly distributed over the IEL. The medial layer was modeled as a heterogeneous medium composed of a periodic array of cylindrical SMCs embedded in a continuous porous medium representing the interstitial proteoglycan and collagen matrix. Depending on the distance between the IEL bottom surface and the upstream end of the proximal layer of SMCs, the local shear stress on SMCs right beneath the fenestral pore could be more than 10 times higher than that on the cells far removed from the IEL under the conditions that the fenestral pore diameter and area fraction of pores were kept constant at 1.4 microm and 0.05, respectively. Thus these proximal SMCs may experience shear stress levels that are even higher than endothelial cells exposed to normal blood flow (order of 10 dyn/cm(2)). Furthermore, entrance flow through fenestral pores alters considerably the interstitial flow field in the medial layer over a spatial length scale of the order of the fenestral pore diameter. Thus the spatial gradient of shear stress on the most superficial SMC is noticeably higher than computed for endothelial cell surfaces.

Primary radiation damage characterization of α-iron under irradiation temperature for various PKA energies

NASA Astrophysics Data System (ADS)

Sahi, Qurat-ul-ain; Kim, Yong-Soo

2018-04-01

The understanding of radiation-induced microstructural defects in body-centered cubic (BCC) iron is of major interest to those using advanced steel under extreme conditions in nuclear reactors. In this study, molecular dynamics (MD) simulations were implemented to examine the primary radiation damage in BCC iron with displacement cascades of energy 1, 5, 10, 20, and 30 keV at temperatures ranging from 100 to 1000 K. Statistical analysis of eight MD simulations of collision cascades were carried out along each [110], [112], [111] and a high index [135] direction and the temperature dependence of the surviving number of point defects and the in-cascade clustering of vacancies and interstitials were studied. The peak time and the corresponding number of defects increase with increasing irradiation temperature and primary knock-on atom (PKA) energy. However, the final number of surviving point defects decreases with increasing lattice temperature. This is associated with the increase of thermal spike at high PKA energy and its long timespan at higher temperatures. Defect production efficiency (i.e., surviving MD defects, per Norgett-Robinson-Torrens displacements) also showed a continuous decrease with the increasing irradiation temperature and PKA energy. The number of interstitial clusters increases with both irradiation temperature and PKA energy. However, the increase in the number of vacancy clusters with PKA energy is minimal-to-constant and decreases as the irradiation temperature increases. Similarly, the probability and cluster size distribution for larger interstitials increase with temperature, whereas only smaller size vacancy clusters were observed at higher temperatures.

Simulations of laser undulators

NASA Astrophysics Data System (ADS)

Milton, S. V.; Biedron, S. B.; Einstein, J. E.

2016-09-01

We perform a series of single-pass, one-D free-electron laser simulations based on an electron beam from a standard linear accelerator coupled with a so-called laser undulator, a specialized device that is more compact than a standard undulator based on magnetic materials. The longitudinal field profiles of such lasers undulators are intriguing as one must and can tailor the profile for the needs of creating the virtual undulator. We present and discuss several results of recent simulations and our future steps.

Modeling laser-plasma acceleration in the laboratory frame

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

2011-01-01

A simulation of laser-plasma acceleration in the laboratory frame. Both the laser and the wakefield buckets must be resolved over the entire domain of the plasma, requiring many cells and many time steps. While researchers often use a simulation window that moves with the pulse, this reduces only the multitude of cells, not the multitude of time steps. For an artistic impression of how to solve the simulation by using the boosted-frame method, watch the video "Modeling laser-plasma acceleration in the wakefield frame".

Simulation based analysis of laser beam brazing

NASA Astrophysics Data System (ADS)

Dobler, Michael; Wiethop, Philipp; Schmid, Daniel; Schmidt, Michael

2016-03-01

Laser beam brazing is a well-established joining technology in car body manufacturing with main applications in the joining of divided tailgates and the joining of roof and side panels. A key advantage of laser brazed joints is the seam's visual quality which satisfies highest requirements. However, the laser beam brazing process is very complex and process dynamics are only partially understood. In order to gain deeper knowledge of the laser beam brazing process, to determine optimal process parameters and to test process variants, a transient three-dimensional simulation model of laser beam brazing is developed. This model takes into account energy input, heat transfer as well as fluid and wetting dynamics that lead to the formation of the brazing seam. A validation of the simulation model is performed by metallographic analysis and thermocouple measurements for different parameter sets of the brazing process. These results show that the multi-physical simulation model not only can be used to gain insight into the laser brazing process but also offers the possibility of process optimization in industrial applications. The model's capabilities in determining optimal process parameters are exemplarily shown for the laser power. Small deviations in the energy input can affect the brazing results significantly. Therefore, the simulation model is used to analyze the effect of the lateral laser beam position on the energy input and the resulting brazing seam.

Advances in the treatment of rheumatic interstitial lung disease.

PubMed

Vassallo, Robert; Thomas, Charles F

2004-05-01

Interstitial lung disease frequently complicates the rheumatic diseases. The purpose of this review is to outline recent advances and current concepts regarding the management of these interstitial lung diseases. Several histologic lesions cause interstitial lung disease in rheumatic diseases, including nonspecific interstitial pneumonia, usual interstitial pneumonia, organizing pneumonia, lymphocytic interstitial pneumonia, desquamative interstitial pneumonia, and acute interstitial pneumonia. Although the relative frequency of occurrence of these histopathologic lesions is not definitively established, it seems that nonspecific interstitial pneumonia accounts for a large proportion of rheumatic disease-associated interstitial lung diseases. Although usual interstitial pneumonia generally responds poorly to corticosteroid therapy, other forms of interstitial pneumonia are often steroid responsive and have a more favorable long-term prognosis. Pulmonary hypertension is increasingly recognized as a complication of these interstitial lung diseases. Treatment of pulmonary hypertension in these patients provides clinical benefit and may suppress pulmonary inflammation and fibrosis. Lung transplantation is a treatment option for selected patients with severe pulmonary involvement and limited life expectancy. Interstitial lung disease is common in the rheumatic diseases, may be caused by a variety of lesions that respond differently to treatment, and may lead to the development of pulmonary hypertension. Whether the prognosis of interstitial lung disease associated with rheumatic disease is similar to that associated with the idiopathic interstitial pneumonias is not known. Treatment of these interstitial lung diseases should take into account the specific histologic lesion, the activity of the underlying rheumatic disease, and associated pulmonary hypertension, if present. The diagnosis of a rheumatic disease is no longer an absolute contraindication to lung transplantation.

Design of welding parameters for laser welding of thin-walled stainless steel tubes using numerical simulation

NASA Astrophysics Data System (ADS)

Nagy, M.; Behúlová, M.

2017-11-01

Nowadays, the laser technology is used in a wide spectrum of applications, especially in engineering, electronics, medicine, automotive, aeronautic or military industries. In the field of mechanical engineering, the laser technology reaches the biggest increase in the automotive industry, mainly due to the introduction of automation utilizing 5-axial movements. Modelling and numerical simulation of laser welding processes has been exploited with many advantages for the investigation of physical principles and complex phenomena connected with this joining technology. The paper is focused on the application of numerical simulation to the design of welding parameters for the circumferential laser welding of thin-walled exhaust pipes from theAISI 304 steel for automotive industry. Using the developed and experimentally verified simulation model for laser welding of tubes, the influence of welding parameters including the laser velocity from 30 mm.s-1 to 60 mm.s-1 and the laser power from 500 W to 1200 W on the temperature fields and dimensions of fusion zone was investigated using the program code ANSYS. Based on obtained results, the welding schedule for the laser beam welding of thin-walled tubes from the AISI 304 steel was suggested.

Bardoxolone Methyl Evaluation in Patients With Pulmonary Hypertension (PH) - LARIAT

ClinicalTrials.gov

2018-06-08

Pulmonary Arterial Hypertension; Pulmonary Hypertension; Interstitial Lung Disease; Idiopathic Interstitial Pneumonia; Idiopathic Pulmonary Fibrosis; Sarcoidosis; Respiratory Bronchiolitis Associated Interstitial Lung Disease; Desquamative Interstitial Pneumonia; Cryptogenic Organizing Pneumonia; Acute Interstitial Pneumonitis; Idiopathic Lymphoid Interstitial Pneumonia; Idiopathic Pleuroparenchymal Fibroelastosis

Three dimensional particle-in-cell simulations of electron beams created via reflection of intense laser light from a water target

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ngirmang, Gregory K., E-mail: ngirmang.1@osu.edu; Orban, Chris; Feister, Scott

We present 3D Particle-in-Cell (PIC) modeling of an ultra-intense laser experiment by the Extreme Light group at the Air Force Research Laboratory using the Large Scale Plasma (LSP) PIC code. This is the first time PIC simulations have been performed in 3D for this experiment which involves an ultra-intense, short-pulse (30 fs) laser interacting with a water jet target at normal incidence. The laser-energy-to-ejected-electron-energy conversion efficiency observed in 2D(3v) simulations were comparable to the conversion efficiencies seen in the 3D simulations, but the angular distribution of ejected electrons in the 2D(3v) simulations displayed interesting differences with the 3D simulations' angular distribution;more » the observed differences between the 2D(3v) and 3D simulations were more noticeable for the simulations with higher intensity laser pulses. An analytic plane-wave model is discussed which provides some explanation for the angular distribution and energies of ejected electrons in the 2D(3v) simulations. We also performed a 3D simulation with circularly polarized light and found a significantly higher conversion efficiency and peak electron energy, which is promising for future experiments.« less

Effect of tin etiopurpurin and light on the canine prostate

NASA Astrophysics Data System (ADS)

Selman, Steven H.; Keck, Rick W.; Doiron, Daniel R.

1995-03-01

A series of experiments was undertaken to determine the effects of the combination of light and the tissue photosensitizer, tin etiopurpurin, on the canine prostate. Mongrel dogs were injected intravenously with 1.0 mg/kg of photosensitizer twenty-four hours prior to light delivery. Laser light, 660 nm, was administered either transurethrally or interstitially and tissue effects were assessed by histopathologic examination. Both techniques of light delivery resulted in hemorrhagic necrosis of the surrounding tissue. Photodynamic therapy may offer a novel approach to the treatment of both benign and malignant diseases of the prostate.

Dynamic Angular Control Of Thermal Therapy With Stationary Multi-Sectored Tubular Ultrasound Applicators Under MR Temperature Monitoring

NASA Astrophysics Data System (ADS)

Kinsey, Adam M.; Diederich, Chris J.; Nau, William H.; Ross, Anthony B.; Butts Pauly, Kim; Rieke, Viola; Sommer, Graham

2006-05-01

Multi-sectored ultrasound heating applicators with dynamic angular and longitudinal control of heating profiles are being investigated for the thermal treatment of tumors in sites such as prostate, uterus, and brain. Multi-sectored tubular ultrasound transducers with independent sector power control were incorporated into interstitial and transurethral applicators and provided dynamic angular control of a heating pattern without requiring device manipulation during treatment. Acoustic beam measurements of each applicator type demonstrated a 35-40° acoustic dead zone between each independent sector, with negligible mechanical or electrical coupling. Despite the acoustic dead zone between sectors, simulations and experiments under MR temperature (MRT) monitoring showed that the variance from the maximum lesion radius (scalloping) with all elements activated on a transducer was minimal and did not affect conformal heating of a target area. A biothermal model with a multi-point controller was used to adjust the applied power and treatment time of individual transducer segments as the tissue temperature changed in simulations of thermal lesions with both interstitial and transurethral applicators. Transurethral ultrasound applicators for benign prostatic hyperplasia (BPH) treatment with either three or four sectors conformed a thermal dose to a simulated target area in the angular and radial dimensions. The simulated treatment was controlled to a maximum temperature of 85°C, and had a maximum duration of 5 min when power was turned off as the 52°C temperature contour reach a predetermined control point for each sector in the tissue. Experiments conducted with multi-sectored applicators under MRT monitoring showed thermal ablation and hyperthermia treatments had little or no border `scalloping', conformed to a pretreatment target area, and correlated very well with the simulated thermal lesions. The radial penetration of the heat treatments in tissue with interstitial (1.5-1.8 mm OD transducer) and transurethral (2.5-4.0 mm OD transducer) applicators was at least 1.5 cm and 2.0 cm, respectively, for a treatment duration of 10 min. Angular control of thermal ablation and hyperthermia therapy often relies upon non-adjustable angular power deposition patterns and/or mechanical manipulation of the heating device. The multi-sectored ultrasound applicators developed in this study provide dynamic control of the angular heating distribution during treatment without device manipulation and maintain previously reported heating penetration and spatial control characteristics of similar ultrasound devices.

A mathematical model of intestinal oedema formation.

PubMed

Young, Jennifer; Rivière, Béatrice; Cox, Charles S; Uray, Karen

2014-03-01

Intestinal oedema is a medical condition referring to the build-up of excess fluid in the interstitial spaces of the intestinal wall tissue. Intestinal oedema is known to produce a decrease in intestinal transit caused by a decrease in smooth muscle contractility, which can lead to numerous medical problems for the patient. Interstitial volume regulation has thus far been modelled with ordinary differential equations, or with a partial differential equation system where volume changes depend only on the current pressure and not on updated tissue stress. In this work, we present a computational, partial differential equation model of intestinal oedema formation that overcomes the limitations of past work to present a comprehensive model of the phenomenon. This model includes mass and momentum balance equations which give a time evolution of the interstitial pressure, intestinal volume changes and stress. The model also accounts for the spatially varying mechanical properties of the intestinal tissue and the inhomogeneous distribution of fluid-leaking capillaries that create oedema. The intestinal wall is modelled as a multi-layered, deforming, poroelastic medium, and the system of equations is solved using a discontinuous Galerkin method. To validate the model, simulation results are compared with results from four experimental scenarios. A sensitivity analysis is also provided. The model is able to capture the final submucosal interstitial pressure and total fluid volume change for all four experimental cases, and provide further insight into the distribution of these quantities across the intestinal wall.

A model for a continuous-wave iodine laser

NASA Technical Reports Server (NTRS)

Hwang, In H.; Tabibi, Bagher M.

1990-01-01

A model for a continuous-wave (CW) iodine laser has been developed and compared with the experimental results obtained from a solar-simulator-pumped CW iodine laser. The agreement between the calculated laser power output and the experimental results is generally good for various laser parameters even when the model includes only prominent rate coefficients. The flow velocity dependence of the output power shows that the CW iodine laser cannot be achieved with a flow velocity below 1 m/s for the present solar-simulator-pumped CW iodine laser system.

Oxidation at through-hole defects in fused slurry silicide coated columbium alloys FS-85 and Cb-752

NASA Technical Reports Server (NTRS)

Levine, S. R.

1973-01-01

Metal recession and interstitial contamination at 0.08-centimeter-diameter through-hole intentional defects in fused slurry silicide coated FS-85 and Cb-752 columbium alloys were studied to determine the tolerance of these materials to coating defects. Five external pressure reentry simulation exposures to 1320 C and 4.7 x 1,000 N/sq m (maximum pressure) resulted in a consumed metal zone having about twice the initial defect diameter for both alloys with an interstitial contamination zone extending about three to four initial defect diameters. Self-healing occurred in the 1.33 x 10 N/sq m, 1320 C exposures and to a lesser extent in internal pressure reentry cycles to 1320 C and 1.33 x 100 N/sq m (maximum pressure).

Research on simulation system with the wide range and high-precision laser energy characteristics

NASA Astrophysics Data System (ADS)

Dong, Ke-yan; Lou, Yan; He, Jing-yi; Tong, Shou-feng; Jiang, Hui-lin

2012-10-01

The Hardware-in-the-loop(HWIL) simulation test is one of the important parts for the development and performance testing of semi-active laser-guided weapons. In order to obtain accurate results, the confidence level of the target environment should be provided for a high-seeker during the HWIL simulation test of semi-active laser-guided weapons, and one of the important simulation parameters is the laser energy characteristic. In this paper, based on the semi-active laser-guided weapon guidance principles, an important parameter of simulation of confidence which affects energy characteristics in performance test of HWIL simulation was analyzed. According to the principle of receiving the same energy by using HWIL simulation and in practical application, HWIL energy characteristics simulation systems with the crystal absorption structure was designed. And on this basis, the problems of optimal design of the optical system were also analyzed. The measured results show that the dynamic attenuation range of the system energy is greater than 50dB, the dynamic attenuation stability is less than 5%, and the maximum energy changing rate driven by the servo motor is greater than 20dB/s.

Extracorporeal Membrane Oxygenation for End-Stage Interstitial Lung Disease With Secondary Pulmonary Hypertension at Rest and Exercise: Insights From Simulation Modeling.

PubMed

Chicotka, Scott; Burkhoff, Daniel; Dickstein, Marc L; Bacchetta, Matthew

Interstitial lung disease (ILD) represents a collection of lung disorders with a lethal trajectory with few therapeutic options with the exception of lung transplantation. Various extracorporeal membrane oxygenation (ECMO) configurations have been used for bridge to transplant (BTT), yet no optimal configuration has been clearly demonstrated. Using a cardiopulmonary simulation, we assessed different ECMO configurations for patients with end-stage ILD to assess the physiologic deficits and help guide the development of new long-term pulmonary support devices. A cardiopulmonary ECMO simulation was created, and changes in hemodynamics and blood gases were compared for different inflow and outflow anatomic locations and for different sweep gas and blood pump flow rates. The system simulated the physiologic response of patients with severe ILD at rest and during exercise with central ECMO, peripheral ECMO, and with no ECMO. The output parameters were total cardiac output (CO), mixed venous oxygen (O2) saturation, arterial pH, and O2 delivery (DO2)/O2 utilization (VO2) at different levels of exercise. The model described the physiologic state of progressive ILD and showed the relative effects of using various ECMO configurations to support them. It elucidated the optimal device configurations and required physiologic pump performance and provided insight into the physiologic demands of exercise in ILD patients. The simulation program was able to model the pathophysiologic state of progressive ILD with PH and demonstrate how mechanical support devices can be implemented to improve cardiopulmonary function at rest and during exercise. The information generated from simulation can be used to optimize ECMO configuration selection for BTT patients and provide design guidance for new devices to better meet the physiologic demands of exercise associated with normal activities of daily living.

Optical simulations of laser focusing for optimization of laser betatron

NASA Astrophysics Data System (ADS)

Stanke, L.; Thakur, A.; Šmíd, M.; Gu, Y. J.; Falk, K.

2017-05-01

This work presents optical simulations that are used to design a betatron driven by a short-pulse laser based on the Laser Wakefield Acceleration (LWFA) concept. These simulations explore how the optical setup and its components influence the performance of the betatron. The impact of phase irregularities induced by optical elements is investigated. In order to obtain a good estimate of the future performance of this design a combination of two distinct techniques are used - Field Tracing for optical simulations employing a combination of the Zemax and VirtualLab computational platforms for the laser beam propagation and focusing with the given optical system and particle-in-cell simulation (PIC) for simulating the short-pulse laser interaction with a gas target. The result of the optical simulations serves as an input for the PIC simulations. Application of Field Tracing in combination with the PIC for the purposes of high power laser facility introduces the new application for VirtualLab Fusion. Based on the result of these simulations an alternative design with a hole in the final folding mirror coupled with a spherical focusing mirror is considered in favour of more commonly used off-axis parabola focusing setup. Results are demonstrating, that the decrease of the irradiance due to the presence of the central hole in the folding mirror is negligible (9.69× 1019 W/cm2 for the case without the hole vs. 9.73× 1019 W/cm2 for the case with hole). However, decrease caused by the surface irregularities (surface RMS λ/4 , λ/20 and λ/40 ) is more significant and leads to the poor performance of particle production.

Hydrodynamic modeling of laser interaction with micro-structured targets

DOE PAGES

Velechovsky, Jan; Limpouch, Jiri; Liska, Richard; ...

2016-08-03

A model is developed for numerical simulations of laser absorption in plasmas made of porous materials, with particular interest in low-density foams. Laser absorption is treated on two spatial scales simultaneously. At the microscale, the expansion of a thin solid pore wall is modeled in one dimension and the information obtained is used in the macroscale fluid simulations for the description of the plasma homogenization behind the ionization front. This two-scale laser absorption model is implemented in the arbitrary Lagrangian–Eulerian hydrocode PALE. In conclusion, the numerical simulations of laser penetration into low-density foams compare favorably with published experimental data.

Building A Simulation Model For The Prediction Of Temperature Distribution In Pulsed Laser Spot Welding Of Dissimilar Low Carbon Steel 1020 To Aluminum Alloy 6061

NASA Astrophysics Data System (ADS)

Yousef, Adel K. M.; Taha, Ziad. A.; Shehab, Abeer A.

2011-01-01

This paper describes the development of a computer model used to analyze the heat flow during pulsed Nd: YAG laser spot welding of dissimilar metal; low carbon steel (1020) to aluminum alloy (6061). The model is built using ANSYS FLUENT 3.6 software where almost all the environments simulated to be similar to the experimental environments. A simulation analysis was implemented based on conduction heat transfer out of the key hole where no melting occurs. The effect of laser power and pulse duration was studied. Three peak powers 1, 1.66 and 2.5 kW were varied during pulsed laser spot welding (keeping the energy constant), also the effect of two pulse durations 4 and 8 ms (with constant peak power), on the transient temperature distribution and weld pool dimension were predicated using the present simulation. It was found that the present simulation model can give an indication for choosing the suitable laser parameters (i.e. pulse durations, peak power and interaction time required) during pulsed laser spot welding of dissimilar metals.

A way to improve dose rate laser simulation adequacy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skorobogatov, P.K.; Nikiforov, A.Y.; Demidov, A.A.

1998-12-01

A method for improving laser simulation of dose rate radiation in silicon IC`s (Integrated Circuit) is analyzed based on the application of noncoherent laser radiation. Experimental validation was performed using test structures with up to 90% surface metallization coverage.

Phosphorescence quenching microrespirometry of skeletal muscle in situ

PubMed Central

Golub, Aleksander S.; Tevald, Michael A.

2011-01-01

We have developed an optical method for the evaluation of the oxygen consumption (V̇o2) in microscopic volumes of spinotrapezius muscle. Using phosphorescence quenching microscopy (PQM) for the measurement of interstitial Po2, together with rapid pneumatic compression of the organ, we recorded the oxygen disappearance curve (ODC) in the muscle of the anesthetized rats. A 0.6-mm diameter area in the tissue, preloaded with the phosphorescent oxygen probe, was excited once a second by a 532-nm Q-switched laser with pulse duration of 15 ns. Each of the evoked phosphorescence decays was analyzed to obtain a sequence of Po2 values that constituted the ODC. Following flow arrest and tissue compression, the interstitial Po2 decreased rapidly and the initial slope of the ODC was used to calculate the V̇o2. Special analysis of instrumental factors affecting the ODC was performed, and the resulting model was used for evaluation of V̇o2. The calculation was based on the observation of only a small amount of residual blood in the tissue after compression. The contribution of oxygen photoconsumption by PQM and oxygen inflow from external sources was evaluated in specially designed tests. The average oxygen consumption of the rat spinotrapezius muscle was V̇o2 = 123.4 ± 13.4 (SE) nl O2/cm3·s (N = 38, within 6 muscles) at a baseline interstitial Po2 of 50.8 ± 2.9 mmHg. This technique has opened the opportunity for monitoring respiration rates in microscopic volumes of functioning skeletal muscle. PMID:20971766

Ab initio molecular dynamics investigations of low-energy recoil events in Ni and NiCo

DOE PAGES

Liu, Bin; Yuan, Fenglin; Jin, Ke; ...

2015-10-06

Low-energy recoil events in pure Ni and the equiatomic NiCo alloy are studied using ab initio molecular dynamics simulations. We found that the threshold displacement energies are strongly dependent on orientation and weakly dependent on composition. The minimum threshold displacement energies are along the [1 1 0] direction in both pure Ni and the NiCo alloy. Compared to pure Ni, the threshold displacement energies increase slightly in the NiCo alloy due to stronger bonds in the alloy, irrespective of the element type of the PKA. A single Ni interstitial occupying the center of a tetrahedron formed by four Ni atomsmore » and a <1 0 0> split interstitial is produced in pure Ni by the recoils, while only the <1 0 0> split interstitial is formed in the NiCo alloy. Compared to the replacement sequences in pure Ni, anti-site defect sequences are observed in the alloy, which have high efficiency for both producing defects and transporting energy outside of the cascade core. These results provide insights into energy transfer processes occurring in equiatomic alloys under irradiation.« less

Predictive models for pressure-driven fluid infusions into brain parenchyma

NASA Astrophysics Data System (ADS)

Raghavan, Raghu; Brady, Martin

2011-10-01

Direct infusions into brain parenchyma of biological therapeutics for serious brain diseases have been, and are being, considered. However, individual brains, as well as distinct cytoarchitectural regions within brains, vary in their response to fluid flow and pressure. Further, the tissue responds dynamically to these stimuli, requiring a nonlinear treatment of equations that would describe fluid flow and drug transport in brain. We here report in detail on an individual-specific model and a comparison of its prediction with simulations for living porcine brains. Two critical features we introduced into our model—absent from previous ones, but requirements for any useful simulation—are the infusion-induced interstitial expansion and the backflow. These are significant determinants of the flow. Another feature of our treatment is the use of cross-property relations to obtain individual-specific parameters that are coefficients in the equations. The quantitative results are at least encouraging, showing a high fraction of overlap between the computed and measured volumes of distribution of a tracer molecule and are potentially clinically useful. Several improvements are called for; principally a treatment of the interstitial expansion more fundamentally based on poroelasticity and a better delineation of the diffusion tensor of a particle confined to the interstitial spaces.

LIMAO: Cross-platform software for simulating laser-induced alignment and orientation dynamics of linear-, symmetric- and asymmetric tops

NASA Astrophysics Data System (ADS)

Szidarovszky, Tamás; Jono, Maho; Yamanouchi, Kaoru

2018-07-01

A user-friendly and cross-platform software called Laser-Induced Molecular Alignment and Orientation simulator (LIMAO) has been developed. The program can be used to simulate within the rigid rotor approximation the rotational dynamics of gas phase molecules induced by linearly polarized intense laser fields at a given temperature. The software is implemented in the Java and Mathematica programming languages. The primary aim of LIMAO is to aid experimental scientists in predicting and analyzing experimental data representing laser-induced spatial alignment and orientation of molecules.

Computational simulation of laser heat processing of materials

NASA Astrophysics Data System (ADS)

Shankar, Vijaya; Gnanamuthu, Daniel

1987-04-01

A computational model simulating the laser heat treatment of AISI 4140 steel plates with a CW CO2 laser beam has been developed on the basis of the three-dimensional, time-dependent heat equation (subject to the appropriate boundary conditions). The solution method is based on Newton iteration applied to a triple-approximate factorized form of the equation. The method is implicit and time-accurate; the maintenance of time-accuracy in the numerical formulation is noted to be critical for the simulation of finite length workpieces with a finite laser beam dwell time.

GPU-based optical propagation simulator of a laser-processed crystal block for the X'tal cube PET detector.

PubMed

Ogata, Yuma; Ohnishi, Takashi; Moriya, Takahiro; Inadama, Naoko; Nishikido, Fumihiko; Yoshida, Eiji; Murayama, Hideo; Yamaya, Taiga; Haneishi, Hideaki

2014-01-01

The X'tal cube is a next-generation DOI detector for PET that we are developing to offer higher resolution and higher sensitivity than is available with present detectors. It is constructed from a cubic monolithic scintillation crystal and silicon photomultipliers which are coupled on various positions of the six surfaces of the cube. A laser-processing technique is applied to produce 3D optical boundaries composed of micro-cracks inside the monolithic scintillator crystal. The current configuration is based on an empirical trial of a laser-processed boundary. There is room to improve the spatial resolution by optimizing the setting of the laser-processed boundary. In fact, the laser-processing technique has high freedom in setting the parameters of the boundary such as size, pitch, and angle. Computer simulation can effectively optimize such parameters. In this study, to design optical characteristics properly for the laser-processed crystal, we developed a Monte Carlo simulator which can model arbitrary arrangements of laser-processed optical boundaries (LPBs). The optical characteristics of the LPBs were measured by use of a setup with a laser and a photo-diode, and then modeled in the simulator. The accuracy of the simulator was confirmed by comparison of position histograms obtained from the simulation and from experiments with a prototype detector composed of a cubic LYSO monolithic crystal with 6 × 6 × 6 segments and multi-pixel photon counters. Furthermore, the simulator was accelerated by parallel computing with general-purpose computing on a graphics processing unit. The calculation speed was about 400 times faster than that with a CPU.

Simulation of planetary entry radiative heating with a CO2 gasdynamic laser

NASA Technical Reports Server (NTRS)

Lundell, J. H.; Dickey, R. R.; Howe, J. T.

1975-01-01

Heating encountered during entry into the atmospheres of Jupiter, Saturn, and Uranus is described, followed by a discussion of the use of a CO2 gasdynamic laser to simulate the radiative component of the heating. Operation and performance of the laser is briefly described. Finally, results of laser tests of some candidate heat-shield materials are presented.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohori, N.P.; Sciurba, F.C.; Owens, G.R.

We report four cases of giant-cell interstitial pneumonia that occurred in association with exposure to hard metals. All patients presented with chronic interstitial lung disease and had open-lung biopsies that revealed marked interstitial fibrosis, cellular interstitial infiltrates, and prominent intraalveolar macrophages as well as giant cells displaying cellular cannibalism. We also review the literature to determine the sensitivity and specificity of giant-cell interstitial pneumonia for hard-metal pneumoconiosis. Although hard-metal pneumoconiosis may take the form of usual interstitial pneumonia, desquamative interstitial pneumonia, and giant-cell interstitial pneumonia, the finding of giant-cell interstitial pneumonia is almost pathognomonic of hard-metal disease and should provokemore » an investigation of occupational exposure. 25 references.« less

The Development of a 3D LADAR Simulator Based on a Fast Target Impulse Response Generation Approach

NASA Astrophysics Data System (ADS)

Al-Temeemy, Ali Adnan

2017-09-01

A new laser detection and ranging (LADAR) simulator has been developed, using MATLAB and its graphical user interface, to simulate direct detection time of flight LADAR systems, and to produce 3D simulated scanning images under a wide variety of conditions. This simulator models each stage from the laser source to data generation and can be considered as an efficient simulation tool to use when developing LADAR systems and their data processing algorithms. The novel approach proposed for this simulator is to generate the actual target impulse response. This approach is fast and able to deal with high scanning requirements without losing the fidelity that accompanies increments in speed. This leads to a more efficient LADAR simulator and opens up the possibility for simulating LADAR beam propagation more accurately by using a large number of laser footprint samples. The approach is to select only the parts of the target that lie in the laser beam angular field by mathematically deriving the required equations and calculating the target angular ranges. The performance of the new simulator has been evaluated under different scanning conditions, the results showing significant increments in processing speeds in comparison to conventional approaches, which are also used in this study as a point of comparison for the results. The results also show the simulator's ability to simulate phenomena related to the scanning process, for example, type of noise, scanning resolution and laser beam width.

Rheumatoid Arthritis-Associated Interstitial Lung Disease and Idiopathic Pulmonary Fibrosis: Shared Mechanistic and Phenotypic Traits Suggest Overlapping Disease Mechanisms.

PubMed

Paulin, Francisco; Doyle, Tracy J; Fletcher, Elaine A; Ascherman, Dana P; Rosas, Ivan O

2015-01-01

The prevalence of clinically evident interstitial lung disease in patients with rheumatoid arthritis is approximately 10%. An additional 33% of undiagnosed patients have interstitial lung abnormalities that can be detected with high-resolution computed tomography. Rheumatoid arthritis-interstitial lung disease patients have three times the risk of death compared to those with rheumatoid arthritis occurring in the absence of interstitial lung disease, and the mortality related to interstitial lung disease is rising. Rheumatoid arthritis-interstitial lung disease is most commonly classified as the usual interstitial pneumonia pattern, overlapping mechanistically and phenotypically with idiopathic pulmonary fibrosis, but can occur in a non-usual interstitial pneumonia pattern, mainly nonspecific interstitial pneumonia. Based on this, we propose two possible pathways to explain the coexistence of rheumatoid arthritis and interstitial lung disease: (i) Rheumatoid arthritis-interstitial lung disease with a non-usual interstitial pneumonia pattern may come about when an immune response against citrullinated peptides taking place in another site (e.g. the joints) subsequently affects the lungs; (ii) Rheumatoid arthritis-interstitial lung disease with a usual interstitial pneumonia pattern may represent a disease process in which idiopathic pulmonary fibrosis-like pathology triggers an immune response against citrullinated proteins that promotes articular disease indicative of rheumatoid arthritis. More studies focused on elucidating the basic mechanisms leading to different sub-phenotypes of rheumatoid arthritis-interstitial lung disease and the overlap with idiopathic pulmonary fibrosis are necessary to improve our understanding of the disease process and to define new therapeutic targets.

Numerically Simulating Collisions of Plastic and Foam Laser-Driven Foils

NASA Astrophysics Data System (ADS)

Zalesak, S. T.; Velikovich, A. L.; Schmitt, A. J.; Aglitskiy, Y.; Metzler, N.

2007-11-01

Interest in experiments on colliding planar foils has recently been stimulated by (a) the Impact Fast Ignition approach to laser fusion [1], and (b) the approach to a high-repetition rate ignition facility based on direct drive with the KrF laser [2]. Simulating the evolution of perturbations to such foils can be a numerical challenge, especially if the initial perturbation amplitudes are small. We discuss the numerical issues involved in such simulations, describe their benchmarking against recently-developed analytic results, and present simulations of such experiments on NRL's Nike laser. [1] M. Murakami et al., Nucl. Fusion 46, 99 (2006) [2] S. P. Obenschain et al., Phys. Plasmas 13, 056320 (2006).

Numerical simulation of temperature at drilling micro-hole on moving CO2 laser irradiated sticking plaster

NASA Astrophysics Data System (ADS)

Rao, Zhiming; He, Zhifang; Du, Jianqiang; Zhang, Xinyou; Ai, Guoping; Zhang, Chunqiang; Wu, Tao

2012-03-01

This paper applied numerical simulation of temperature by using finite element analysis software Ansys to study a model of drilling on sticking plaster. The continuous CO2 laser doing uniform linear motion and doing uniform circular motion irradiated sticking plaster to vaporize. The sticking plaster material was chosen as the thermal conductivity, the heat capacity and the density. For temperatures above 450 °C, sticking plaster would be vaporized. Based on the mathematical model of heat transfer, the process of drilling sticking plaster by laser beams could be simulated by Ansys. The simulation results showed the distribution of the temperature at the surface of the sticking plaster with the time of vaporizing at CO2 laser to do uniform linear motion and to do uniform circular motion. The temperature of sticking plaster CO2 laser to do uniform linear motion was higher than CO2 laser to do uniform circular motion in the same condition.

Microvascular Permeability of Skeletal Muscle After Eccentric Contraction-Induced Muscle Injury: In Vivo Imaging Using Two-Photon Laser Scanning Microscopy.

PubMed

Hotta, Kazuki; Behnke, Bradley Jon; Masamoto, Kazuto; Shimotsu, Rie; Onodera, Naoya; Yamaguchi, Akihiko; Poole, David C; Kano, Yutaka

2018-05-03

Via modulation of endothelial integrity and vascular permeability in response to damage skeletal muscle microvessels play a crucial permissive role in tissue leukocyte invasion. However, direct visual evidence of altered microvascular permeability of skeletal muscle has not been technically feasible impairing mechanistic understanding of these responses. Two-photon laser scanning microscopy (TPLSM) allows three-dimensional in vivo imaging of skeletal muscle microcirculation. We hypothesized that the regulation of microvessels permeability in vivo is temporally related to acute inflammatory and regenerative processes following muscle injury. To test our hypothesis, tibialis anterior muscle of anesthetized male Wistar rats were subjected to eccentric contractions (ECC) via electrical stimulation. The skeletal muscle microcirculation was imaged by an intravenously infused fluorescent dye (rhodamine b isothiocyanate dextran) to assess microvascular permeability via TPLSM 1, 3 and 7 days after ECC. Immunohistochemistry on muscle sections was performed to determine the proportion of VEGF-A positive fibers in the damaged muscle. Compared with control rats, the volumetrically-determined interstitial leakage of fluorescent dye (5.1 {plus minus} 1.4, 5.3 {plus minus} 1.2 vs. 0.51 {plus minus} 0.14 μm 3 x 10 6 , P < 0.05 respectively days 1 and 3 vs. control) and percentage of VEGF-A positive fibers in the damaged muscle (10 {plus minus} 0.4, 22 {plus minus} 1.1 vs. 0%; days 1 and 3 vs. control) were significantly higher on days 1 and 3 after ECC. The interstitial leakage volume returned to control by day 7. These results suggest that microvascular hyperpermeability assessed by in vivo TPLSM imaging is associated with ECC-induced muscle damage and increased VEGF expression.

Simulation study of interaction of pulse laser with tumor-embedded gastric tissue using finite element analysis

NASA Astrophysics Data System (ADS)

Liu, Lantian; Li, Zhifang; Li, Hui

2018-01-01

The study of interaction of laser with tumor-embedded gastric tissue is of great theoretical and practical significance for the laser diagnosis and treatment of gastric cancer in medicine. A finite element (FE)-based simulation model has been developed incorporating light propagation and heat transfer in soft tissues using a commercial FE simulation package, COMSOL Multiphysics. In this study, FE model is composed of three parts of 1) homogeneous background soft tissues submerged in water, 2) tumor tissue inclusion, and 3) different wavelengths of short pulsed laser source (450nm, 550nm, 632nm and 800nm). The laser point source is placed right under the tissues submerged in water. This laser source light propagation through the multi-layer tissues using the diffusion equation and bioheat transfer in tissues is simulated using bioheat equation for temperature change. The simulation results show that the penetration depth and light energy distribution mainly depend on the optical parameters of the different wavelengths of the tissue. In the process of biological heat transfer, the temperature of the tissue decreases exponentially with the depth and the deep tissues are almost unaffected. The results are helpful to optimize the laser source in a photoacoustic imaging system and provide some significance for the further study of the early diagnosis of gastric cancer.

Method to simulate and analyse induced stresses for laser crystal packaging technologies.

PubMed

Ribes-Pleguezuelo, Pol; Zhang, Site; Beckert, Erik; Eberhardt, Ramona; Wyrowski, Frank; Tünnermann, Andreas

2017-03-20

A method to simulate induced stresses for a laser crystal packaging technique and the consequent study of birefringent effects inside the laser cavities has been developed. The method has been implemented by thermo-mechanical simulations implemented with ANSYS 17.0. ANSYS results were later imported in VirtualLab Fusion software where input/output beams in terms of wavelengths and polarization were analysed. The study has been built in the context of a low-stress soldering technique implemented for glass or crystal optics packaging's called the solderjet bumping technique. The outcome of the analysis showed almost no difference between the input and output laser beams for the laser cavity constructed with an yttrium aluminum garnet active laser crystal, a second harmonic generator beta-barium borate, and the output laser mirror made of fused silica assembled by the low-stress solderjet bumping technique.

Absorptivity Measurements and Heat Source Modeling to Simulate Laser Cladding

NASA Astrophysics Data System (ADS)

Wirth, Florian; Eisenbarth, Daniel; Wegener, Konrad

The laser cladding process gains importance, as it does not only allow the application of surface coatings, but also additive manufacturing of three-dimensional parts. In both cases, process simulation can contribute to process optimization. Heat source modeling is one of the main issues for an accurate model and simulation of the laser cladding process. While the laser beam intensity distribution is readily known, the other two main effects on the process' heat input are non-trivial. Namely the measurement of the absorptivity of the applied materials as well as the powder attenuation. Therefore, calorimetry measurements were carried out. The measurement method and the measurement results for laser cladding of Stellite 6 on structural steel S 235 and for the processing of Inconel 625 are presented both using a CO2 laser as well as a high power diode laser (HPDL). Additionally, a heat source model is deduced.

Simplification of the laser absorption process in the particle simulation for the laser-induced shockwave processing

NASA Astrophysics Data System (ADS)

Shimamura, Kohei

2016-09-01

To reduce the computational cost in the particle method for the numerical simulation of the laser plasma, we examined the simplification of the laser absorption process. Because the laser frequency is sufficiently larger than the collision frequency between the electron and heavy particles, we assumed that the electron obtained the constant value from the laser irradiation. First of all, the simplification of the laser absorption process was verified by the comparison of the EEDF and the laser-absorptivity with PIC-FDTD method. Secondary, the laser plasma induced by TEA CO2 laser in Argon atmosphere was modeled using the 1D3V DSMC method with the simplification of the laser-absorption. As a result, the LSDW was observed with the typical electron and neutral density distribution.

Computer simulation of the relationship between selected properties of laser remelted tool steel surface layer

NASA Astrophysics Data System (ADS)

Bonek, Mirosław; Śliwa, Agata; Mikuła, Jarosław

2016-12-01

Investigations >The language in this paper has been slightly changed. Please check for clarity of thought, and that the meaning is still correct, and amend if necessary.include Finite Element Method simulation model of remelting of PMHSS6-5-3 high-speed steel surface layer using the high power diode laser (HPDL). The Finite Element Method computations were performed using ANSYS software. The scope of FEM simulation was determination of temperature distribution during laser alloying process at various process configurations regarding the laser beam power and method of powder deposition, as pre-coated past or surface with machined grooves. The Finite Element Method simulation was performed on five different 3-dimensional models. The model assumed nonlinear change of thermal conductivity, specific heat and density that were depended on temperature. The heating process was realized as heat flux corresponding to laser beam power of 1.4, 1.7 and 2.1 kW. Latent heat effects are considered during solidification. The molten pool is composed of the same material as the substrate and there is no chemical reaction. The absorptivity of laser energy was dependent on the simulated materials properties and their surface condition. The Finite Element Method simulation allows specifying the heat affected zone and the temperature distribution in the sample as a function of time and thus allows the estimation of the structural changes taking place during laser remelting process. The simulation was applied to determine the shape of molten pool and the penetration depth of remelted surface. Simulated penetration depth and molten pool profile have a good match with the experimental results. The depth values obtained in simulation are very close to experimental data. Regarding the shape of molten pool, the little differences have been noted. The heat flux input considered in simulation is only part of the mechanism for heating; thus, the final shape of solidified molten pool will depend on more variables.

Modeling target normal sheath acceleration using handoffs between multiple simulations

NASA Astrophysics Data System (ADS)

McMahon, Matthew; Willis, Christopher; Mitchell, Robert; King, Frank; Schumacher, Douglass; Akli, Kramer; Freeman, Richard

2013-10-01

We present a technique to model the target normal sheath acceleration (TNSA) process using full-scale LSP PIC simulations. The technique allows for a realistic laser, full size target and pre-plasma, and sufficient propagation length for the accelerated ions and electrons. A first simulation using a 2D Cartesian grid models the laser-plasma interaction (LPI) self-consistently and includes field ionization. Electrons accelerated by the laser are imported into a second simulation using a 2D cylindrical grid optimized for the initial TNSA process and incorporating an equation of state. Finally, all of the particles are imported to a third simulation optimized for the propagation of the accelerated ions and utilizing a static field solver for initialization. We also show use of 3D LPI simulations. Simulation results are compared to recent ion acceleration experiments using SCARLET laser at The Ohio State University. This work was performed with support from ASOFR under contract # FA9550-12-1-0341, DARPA, and allocations of computing time from the Ohio Supercomputing Center.

Influence of Ionization and Beam Quality on Interaction of TW-Peak CO2 Laser with Hydrogen Plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samulyak, Roman

3D numerical simulations of the interaction of a powerful CO2 laser with hydrogen jets demonstrating the role of ionization and laser beam quality are presented. Simulations are performed in support of the plasma wakefield accelerator experiments being conducted at the BNL Accelerator Test Facility (ATF). The CO2 laser at BNL ATF has several potential advantages for laser wakefield acceleration compared to widely used solid-state lasers. SPACE, a parallel relativistic Particle-in-Cell code, developed at SBU and BNL, has been used in these studies. A novelty of the code is its set of efficient atomic physics algorithms that compute ionization and recombinationmore » rates on the grid and transfer them to particles. The primary goal of the initial BNL experiments was to characterize the plasma density by measuring the sidebands in the spectrum of the probe laser. Simulations, that resolve hydrogen ionization and laser spectra, help explain several trends that were observed in the experiments.« less

The impact of minimally invasive surgeries for the treatment of symptomatic benign prostatic hyperplasia on male sexual function: a systematic review.

PubMed

Frieben, Ryan W; Lin, Hao-Cheng; Hinh, Peter P; Berardinelli, Francesco; Canfield, Steven E; Wang, Run

2010-07-01

A systematic review of randomized controlled trials and cohort studies was conducted to evaluate data for the effects of minimally invasive procedures for treatment of symptomatic benign prostatic hyperplasia (BPH) on male sexual function. The studies searched were trials that enrolled men with symptomatic BPH who were treated with laser surgeries, transurethral microwave therapy (TUMT), transurethral needle ablation of the prostate (TUNA), transurethral ethanol ablation of the prostate (TEAP) and high-intensity frequency ultrasound (HIFU), in comparison with traditional transurethral resection of the prostate (TURP) or sham operations. A total of 72 studies were identified, of which 33 met the inclusion criteria. Of the 33 studies, 21 were concerned with laser surgeries, six with TUMT, four with TUNA and two with TEAP containing information regarding male sexual function. No study is available regarding the effect of HIFU for BPH on male sexual function. Our analysis shows that minimally invasive surgeries for BPH have comparable effects to those of TURP on male erectile function. Collectively, less than 15.4% or 15.2% of patients will have either decrease or increase, respectively, of erectile function after laser procedures, TUMT and TUNA. As observed with TURP, a high incidence of ejaculatory dysfunction (EjD) is common after treatment of BPH with holmium, potassium-titanyl-phosphate and thulium laser therapies (> 33.6%). TUMT, TUNA and neodymium:yttrium aluminum garnet visual laser ablation or interstitial laser coagulation for BPH has less incidence of EjD, but these procedures are considered less effective for BPH treatment when compared with TURP.

The impact of minimally invasive surgeries for the treatment of symptomatic benign prostatic hyperplasia on male sexual function: a systematic review

PubMed Central

Frieben, Ryan W.; Lin, Hao-Cheng; Hinh, Peter P.; Berardinelli, Francesco; Canfield, Steven E.; Wang, Run

2010-01-01

A systematic review of randomized controlled trials and cohort studies was conducted to evaluate data for the effects of minimally invasive procedures for treatment of symptomatic benign prostatic hyperplasia (BPH) on male sexual function. The studies searched were trials that enrolled men with symptomatic BPH who were treated with laser surgeries, transurethral microwave therapy (TUMT), transurethral needle ablation of the prostate (TUNA), transurethral ethanol ablation of the prostate (TEAP) and high-intensity frequency ultrasound (HIFU), in comparison with traditional transurethral resection of the prostate (TURP) or sham operations. A total of 72 studies were identified, of which 33 met the inclusion criteria. Of the 33 studies, 21 were concerned with laser surgeries, six with TUMT, four with TUNA and two with TEAP containing information regarding male sexual function. No study is available regarding the effect of HIFU for BPH on male sexual function. Our analysis shows that minimally invasive surgeries for BPH have comparable effects to those of TURP on male erectile function. Collectively, less than 15.4% or 15.2% of patients will have either decrease or increase, respectively, of erectile function after laser procedures, TUMT and TUNA. As observed with TURP, a high incidence of ejaculatory dysfunction (EjD) is common after treatment of BPH with holmium, potassium-titanyl-phosphate and thulium laser therapies (> 33.6%). TUMT, TUNA and neodymium:yttrium aluminum garnet visual laser ablation or interstitial laser coagulation for BPH has less incidence of EjD, but these procedures are considered less effective for BPH treatment when compared with TURP. PMID:20473318

Molecular dynamics growth modeling of InAs1-xSbx-based type-II superlattice

NASA Astrophysics Data System (ADS)

Ciani, Anthony J.; Grein, Christoph H.; Irick, Barry; Miao, Maosheng; Kioussis, Nicholas

2017-09-01

Type-II strained-layer superlattices (T2SL) based on InAs1-xSbx are a promising photovoltaic detector material technology for thermal imaging; however, Shockley-Read-Hall recombination and generation rates are still too high for thermal imagers based on InAs1-xSbx T2SL to reach their ideal performance. Molecular dynamics simulations using the Stillinger-Weber (SW) empirical potentials are a useful tool to study the growth of tetrahedral coordinated crystals and the nonequilibrium formation of defects within them, including the long-range effects of strain. SW potentials for the possible atomic interactions among {Ga, In, As, Sb} were developed by fitting to ab initio calculations of elastically distorted zinc blende and diamond unit cells. The SW potentials were tested against experimental observations of molecular beam epitaxial (MBE) growth and then used to simulate the MBE growth of InAs/InAs0.5Sb0.5 T2SL on GaSb substrates over a range of processes parameters. The simulations showed and helped to explain Sb cross-incorporation into the InAs T2SL layers, Sb segregation within the InAsSb layers, and identified medium-range defect clusters involving interstitials and their induction of interstitial-vacancy pairs. Defect formation was also found to be affected by growth temperature and flux stoichiometry.

Characterization of the spectral phase of an intense laser at focus via ionization blueshift

DOE PAGES

Mittelberger, D. E.; Nakamura, K.; Lehe, R.; ...

2016-01-01

An in situ diagnostic for verifying the spectral phase of an intense laser pulse at focus is shown. This diagnostic relies on measuring the effect of optical compression on ionization-induced blueshifting of the laser spectrum. Experimental results from the Berkeley Lab Laser Accelerator, a laser source rigorously characterized by conventional techniques, are presented and compared with simulations to illustrate the utility of this technique. These simulations show distinguishable effects from second-, third-, and fourth-order spectral phase.

Energy partitioning and impulse dispersion in the decorated, tapered, strongly nonlinear granular alignment: A system with many potential applications

NASA Astrophysics Data System (ADS)

Doney, Robert L.; Agui, Juan H.; Sen, Surajit

2009-09-01

Rapid absorption of impulses using light-weight, small, reusable systems is a challenging problem. An axially aligned set of progressively shrinking elastic spheres, a "tapered chain," has been shown to be a versatile and scalable shock absorber in earlier simulational, theoretical, and experimental works by several authors. We have recently shown (see R. L. Doney and S. Sen, Phys. Rev. Lett. 97, 155502 (2006)) that the shock absorption ability of a tapered chain can be dramatically enhanced by placing small interstitial grains between the regular grains in the tapered chain systems. Here we focus on a detailed study of the problem introduced in the above mentioned letter, present extensive dynamical simulations using parameters for a titanium-aluminum-vanadium alloy Ti6Al4V, derive attendant hard-sphere analyses based formulae to describe energy dispersion, and finally discuss some preliminary experimental results using systems with chrome spheres and small Nitinol interstitial grains to present the underlying nonlinear dynamics of this so-called decorated tapered granular alignment. We are specifically interested in small systems, comprised of several grains. This is because in real applications, mass and volume occupied must inevitably be minimized. Our conclusion is that the decorated tapered chain offers enhanced energy dispersion by locking in much of the input energy in the grains of the tapered chain rather than in the small interstitial grains. Thus, the present study offers insights into how the shock absorption capabilities of these systems can be pushed even further by improving energy absorption capabilities of the larger grains in the tapered chains. We envision that these scalable, decorated tapered chains may be used as shock absorbing components in body armor, armored vehicles, building applications and in perhaps even in applications in rehabilitation science.

Energy Losses Estimation During Pulsed-Laser Seam Welding

NASA Astrophysics Data System (ADS)

Sebestova, Hana; Havelkova, Martina; Chmelickova, Hana

2014-06-01

The finite-element tool SYSWELD (ESI Group, Paris, France) was adapted to simulate pulsed-laser seam welding. Besides temperature field distribution, one of the possible outputs of the welding simulation is the amount of absorbed power necessary to melt the required material volume including energy losses. Comparing absorbed or melting energy with applied laser energy, welding efficiencies can be calculated. This article presents achieved results of welding efficiency estimation based on the assimilation both experimental and simulation output data of the pulsed Nd:YAG laser bead on plate welding of 0.6-mm-thick AISI 304 stainless steel sheets using different beam powers.

Studies of a novel photosensitizer Pd-bacteriopheophorbide (Tookad) for the prostate cancer PDT in canine model

NASA Astrophysics Data System (ADS)

Huang, Zheng; Chen, Qun; Brun, Pierre-Herve; Wilson, Brian C.; Scherz, Avigdor; Salomon, Yoram; Luck, David L.; Beckers, Jill; Hetzel, Fred W.

2003-12-01

Photodynamic therapy (PDT) mediated with vascular acting photosensitizer pd-bacteriopheophorbide (Tookad), is investigated as an alternative modality for the total ablation of prostate cancer. In vivo normal canine prostate is used as the animal model. Interstitial PDT was performed by irradiating the surgically exposed prostates with a diode laser (763 nm, 150 mW/cm) to activate the i.v. infused photosensitizer drug. The effects of two-session PDT were evaluated. The prostate and its adjacent tissues were harvested and subjected to histopathological examination. At one-week, post second-session PDT, the animals recovered well with little or no urethral complications. Prostatic urethra and prostate adjacent tissues (bladder and underlying colon) were well preserved. Two-session PDT or one single session PDT induced a similar extent of damage. PDT induced prostate lesions were characterized by marked hemorrhagic necrosis. Maximum lesion size of over 3 cm in dimension could be achieved with a single 1-cm interstitial treatment, suggesting the therapy is very effective in ablating prostatic tissue. Pharmacokinetic studies show that the photosensitizer is cleared rapidly from the circulation. In conclusion, the novel photosensitizer Tookad mediated PDT may provide an effective alternative to treat prostate cancer.

Geochemistry of zircons from basic rocks of the Korosten anorthosite-mangerite-charnockite-granite complex, north-western region of the Ukrainian Shield

NASA Astrophysics Data System (ADS)

Shumlyanskyy, Leonid; Belousova, Elena; Petrenko, Oksana

2017-09-01

The concentrations of 26 trace elements have been determined by laser ablation ICP-MS in zircons from four samples of basic rocks of the Korosten anorthosite-mangerite-charnockite-granite plutonic complex, the Ukrainian Shield. Zircons from the Fedorivka and Torchyn gabbroic intrusions and Volynsky anorthosite massif have distinctive abundances of many trace elements (REE, Sr, Y, Mn, Th). Zircons from the gabbroic massifs are unusually enriched in trace elements, while zircons from pegmatites in anorthosite are relatively depleted in trace elements. High concentrations of trace elements in zircons from gabbroic intrusions can be explained by their crystallization from residual interstitial melts enriched in incompatible elements. The zircons studied demonstrate a wide range of Ti concentrations, which reflects their temperature of crystallization: the zircons most enriched in Ti, from mafic pegmatites of the Horbuliv quarry (20-40 ppm), have the highest temperature of crystallization (845 ± 40 °C). Lower (720-770 °C) temperatures of zircon crystallization in gabbroic rocks are explained by its crystallization from the latest portions of the interstitial melt or by simultaneous crystallization of ilmenite. The Ce anomaly in zircons correlates with the degree of oxidation of the coexisting ilmenite.

Theoretical studies of solar lasers and converters

NASA Technical Reports Server (NTRS)

Heinbockel, John H.

1990-01-01

The research described consisted of developing and refining the continuous flow laser model program including the creation of a working model. The mathematical development of a two pass amplifier for an iodine laser is summarized. A computer program for the amplifier's simulation is included with output from the simulation model.

Rapid, controllable, one-pot and room-temperature aqueous synthesis of ZnO:Cu nanoparticles by pulsed UV laser and its application for photocatalytic degradation of methyl orange.

PubMed

Arabi, Mozhgan; Baizaee, Seyyed Mahdy; Bahador, Alireza; Otaqsara, Seyed Mohammad Taheri

2018-05-01

Zinc oxide (ZnO) and ZnO:Cu nanoparticles (NPs) were synthesized using a rapid, controllable, one-pot and room-temperature pulsed UV-laser assisted method. UV-laser irradiation was used as an effective energy source in order to gain better control over the NPs size and morphology in aqueous media. Parameters effective in laser assisted synthesis of NPs such as irradiation time and laser shot repetition rate were optimized. Photoluminescence (PL) spectra of ZnO NPs showed a broad emission with two trap state peaks located at 442 and 485 nm related to electronic transition from zinc interstitial level (I Zn ) to zinc vacancy level (V Zn ) and electronic transition from conduction band to the oxygen vacancy level (V O ), respectively. For ZnO:Cu NPs, trap state emissions disappeared completely and a copper (Cu)-related emission appeared. PL intensity of Cu-related emission increased with the increase in concentration of Cu 2+ , so that for molar ratio of Cu:Zn 2%, optimal value of PL intensity was obtained. The photocatalytic activity of Cu-doped ZnO revealed 50 and 100% increasement than that of undoped NPs under UV and visible irradiation, respectively. The enhanced photocatalytic activity could be attributed to smaller crystal size, as well as creation of impurity acceptor levels (T 2 ) inside the ZnO energy band gap. Copyright © 2017 John Wiley & Sons, Ltd.

Bias of cylinder diameter estimation from ground-based laser scanners with different beam widths: A simulation study

NASA Astrophysics Data System (ADS)

Forsman, Mona; Börlin, Niclas; Olofsson, Kenneth; Reese, Heather; Holmgren, Johan

2018-01-01

In this study we have investigated why diameters of tree stems, which are approximately cylindrical, are often overestimated by mobile laser scanning. This paper analyzes the physical processes when using ground-based laser scanning that may contribute to a bias when estimating cylinder diameters using circle-fit methods. A laser scanner simulator was implemented and used to evaluate various properties, such as distance, cylinder diameter, and beam width of a laser scanner-cylinder system to find critical conditions. The simulation results suggest that a positive bias of the diameter estimation is expected. Furthermore, the bias follows a quadratic function of one parameter - the relative footprint, i.e., the fraction of the cylinder width illuminated by the laser beam. The quadratic signature opens up a possibility to construct a compensation model for the bias.

An insight into the dopant selection for CeO2-based resistive-switching memory system: a DFT and experimental study

NASA Astrophysics Data System (ADS)

Hussain, Fayyaz; Imran, Muhammad; Rana, Anwar Manzoor; Khalil, R. M. Arif; Khera, Ejaz Ahmad; Kiran, Saira; Javid, M. Arshad; Sattar, M. Atif; Ismail, Muhammad

2018-03-01

The aim of this study is to figure out better metal dopants for CeO2 for designing highly efficient non-volatile memory (NVM) devices. The present DFT work involves four different metals doped interstitially and substitutionally in CeO2 thin films. First principle calculations involve electron density of states (DOS) and partial density of states (PDOS), and isosurface charge densities are carried out within the plane-wave density functional theory using GGA and GGA + U approach by employing the Vienna ab initio simulation package VASP. Isosurface charge density plots confirmed that interstitial doping of Zr and Ti metals truly assists in generating conduction filaments (CFs), while substitutional doping of these metals cannot do so. Substitutional doping of W may contribute in generating CFs in CeO2 directly, but its interstitial doping improves conductivity of CeO2. However, Ni-dopant is capable of directly generating CFs both as substitutional and interstitial dopants in ceria. Such a capability of Ni appears acting as top electrode in Ni/CeO2/Pt memory devices, but its RS behavior is not so good. On inserting Zr layer to make Ni/Zr:CeO2/Pt memory stacks, Ni does not contribute in RS characteristics, but Zr plays a vital role in forming CFs by creating oxygen vacancies and forming ZrO2 interfacial layer. Therefore, Zr-doped devices exhibit high-resistance ratio of 104 and good endurance as compared to undoped devices suitable for RRAM applications.

Improved pulse laser ranging algorithm based on high speed sampling

NASA Astrophysics Data System (ADS)

Gao, Xuan-yi; Qian, Rui-hai; Zhang, Yan-mei; Li, Huan; Guo, Hai-chao; He, Shi-jie; Guo, Xiao-kang

2016-10-01

Narrow pulse laser ranging achieves long-range target detection using laser pulse with low divergent beams. Pulse laser ranging is widely used in military, industrial, civil, engineering and transportation field. In this paper, an improved narrow pulse laser ranging algorithm is studied based on the high speed sampling. Firstly, theoretical simulation models have been built and analyzed including the laser emission and pulse laser ranging algorithm. An improved pulse ranging algorithm is developed. This new algorithm combines the matched filter algorithm and the constant fraction discrimination (CFD) algorithm. After the algorithm simulation, a laser ranging hardware system is set up to implement the improved algorithm. The laser ranging hardware system includes a laser diode, a laser detector and a high sample rate data logging circuit. Subsequently, using Verilog HDL language, the improved algorithm is implemented in the FPGA chip based on fusion of the matched filter algorithm and the CFD algorithm. Finally, the laser ranging experiment is carried out to test the improved algorithm ranging performance comparing to the matched filter algorithm and the CFD algorithm using the laser ranging hardware system. The test analysis result demonstrates that the laser ranging hardware system realized the high speed processing and high speed sampling data transmission. The algorithm analysis result presents that the improved algorithm achieves 0.3m distance ranging precision. The improved algorithm analysis result meets the expected effect, which is consistent with the theoretical simulation.

A simulation model for the infiltration of heterogeneous sediment into a stream bed

Treesearch

Tim Lauck; Roland Lamberson; Thomas E. Lisle

1993-01-01

Abstract - Salmonid embryos depend on the adequate flow of oxygenated water to survive and interstitial passageways to emerge from the gravel bed. Spawning gravels are initially cleaned by the spawning female, but sediment transported during subsequent high-runoff events can nfiltrate the porous substrate. In many gravel-bed channels used for spawning, most of the...

Photoexcited ZnO nanoparticles with controlled defects as a highly sensitive oxygen sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goto, Taku; Ito, Tsuyohito, E-mail: tsuyohito@ppl.eng.osaka-u.ac.jp; Shimizu, Yoshiki

Conductance of photoexcited ZnO nanoparticles with various defects has been investigated in oxygen. ZnO nanoparticles, which show strong photoluminescence peaks originating from interstitial zinc atom (Zn{sub i}) and singly charged oxygen vacancy (V{sub O}{sup +}), show oxygen-pressure-dependent conductance changes caused by photoexcitation. Herein, a model is proposed to simulate the conductance changes.

New understanding of nano-scale interstitial dislocation loops in BCC iron

NASA Astrophysics Data System (ADS)

Gao, N.; Chen, J.; Kurtz, R. J.; Wang, Z. G.; Zhang, R. F.; Gao, F.

2017-11-01

Complex states of nanoscale interstitial dislocation loop can be described by its habit plane and Burgers vector. Using atomistic simulations, we provide direct evidences on the change of the habit plane of a 1/2〈1 1 1〉 loop from {1 1 1} to {1 1 0} and {2 1 1}, in agreement with TEM observations. A new {1 0 0} habit plane of this loop is also predicted by simulations. The non-conservation of the Burgers vector is approved theoretically for: (1) dislocation reactions between loops with different Burgers vectors and (2) the transition between 〈1 0 0〉 loops and 1/2〈1 1 1〉 loops. The rotation from a 1/2〈1 1 1〉 to a 〈1 0 0〉 loop has also been explored, which occurs at 570 K for time on the order of 10 s. The dislocation-precipitate phase duality and change of habit plane are then proposed as new features for nano-scale dislocation loops.

Interstitial hyperthermia treatment of countercurrent vascular tissue: a comparison of Pennes, WJ and porous media bioheat models.

PubMed

Hassanpour, Saied; Saboonchi, Ahmad

2014-12-01

Development of appropriate heat transfer models to investigate the thermal behavior of living tissues has become increasingly important in simulations of cancer hyperthermia. In this paper, a review is initially presented of the more important general models developed for heat transfer description of perfused tissues. Comparisons are then made between Pennes' simplified Weinbaum and Jiji "WJ" and the more recent porous media "PM" bioheat models. For this purpose, a mathematical model is developed for the heat transfer in a cylindrical medium containing parallel counter-current pairs of small vessels with characteristics as much as possible similar to those of living tissues. The validity of the models is examined and confirmed using the Pennes in vivo experiments and one-dimensional analytical solutions. For consideration of interstitial hyperthermia treatment the smaller cylindrical zone with typical heat generation, is assumed in the center of the main cylinder. The numerical simulation results revealed that, despite difference in temperature distributions calculated by these three models at normal condition, the heat affected zone at hyperthermic condition predicted by all three models are similar. Copyright © 2014 Elsevier Ltd. All rights reserved.

Simulation of Laser Induced Thermal Damage in Nd:YVO4 Crystals

NASA Astrophysics Data System (ADS)

Nagi, Richie

Neodymium-doped yttrium orthovanadate (Nd:YVO4) is a commonly used gain medium in Diode Pumped Solid State (DPSS) lasers, but high heat loading of Nd:YVO4 at high pump powers (≥ 5 W) leads to thermal distortions and crystal fracture, which limits the utility of Nd:YVO 4 for high power applications. In this thesis, a Nd:YVO4 crystal suffered thermal damage during experiments for investigating the optical gain characteristics of the crystal. This thesis examines the thermal damage mechanisms in detail. Principally, laser induced melting, as well as laser induced thermal stress fracture were studied, all in the absence of stimulated emission in the crystal. The optical system for coupling the pump laser light into the crystal was first simulated in Zemax, an optical design software, and the simulations were then compared to the experimental coupling efficiency results, which were found to be in agreement. The simulations for the laser coupling system were then used in conjunction with LASCAD, a finite element analysis software, to obtain the temperatures inside the crystal, as a function of optical power coupled into the crystal. The temperature simulations were then compared to the experimental results, which were in excellent agreement, and the temperature simulations were then generalized to other crystal geometries and Nd doping levels. Zemax and LASCAD were also used to simulate the thermal stress in the crystal as a function of the coupled optical power, and the simulations were compared to experiments, both of which were found to be in agreement. The thermal stress simulations were then generalized to different crystal geometries and Nd doping levels as well.

Effects of dimensionality on kinetic simulations of laser-ion acceleration in the transparency regime

NASA Astrophysics Data System (ADS)

Stark, D. J.; Yin, L.; Albright, B. J.; Guo, F.

2017-05-01

A particle-in-cell study of laser-ion acceleration mechanisms in the transparency regime illustrates how two-dimensional (2D) S and P simulations (laser polarization in and out of the simulation plane, respectively) capture different physics characterizing these systems, visible in their entirety often in cost-prohibitive three-dimensional (3D) simulations. The electron momentum anisotropy induced in the target by a laser pulse is dramatically different in the two 2D cases, manifested in differences in target expansion timescales, electric field strengths, and density thresholds for the onset of relativistically induced transparency. In particular, 2D-P simulations exhibit dramatically greater electron heating in the simulation plane, whereas 2D-S ones show a much more isotropic energy distribution, similar to 3D. An ion trajectory analysis allows one to isolate the fields responsible for ion acceleration and to characterize the acceleration regimes in time and space. The artificial longitudinal electron heating in 2D-P exaggerates the effectiveness of target-normal sheath acceleration into its dominant acceleration mechanism throughout the laser-plasma interaction, whereas 2D-S and 3D both have sizable populations accelerated preferentially during transparency.

Effects of dimensionality on kinetic simulations of laser-ion acceleration in the transparency regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stark, David James; Yin, Lin; Albright, Brian James

2017-05-03

A particle-in-cell study of laser-ion acceleration mechanisms in the transparency regime illustrates how two-dimensional (2D) S and P simulations (laser polarization in and out of the simulation plane, respectively) capture different physics characterizing these systems, visible in their entirety in often cost-prohibitive three-dimensional (3D) simulations. The electron momentum anisotropy induced in the target by the laser pulse is dramatically different in the two 2D cases, manifested in differences in target expansion timescales, electric field strengths, and density thresholds for the onset of relativistically induced transparency. In particular, 2D-P simulations exhibit dramatically greater electron heating in the simulation plane, whereas 2D-Smore » ones show a much more isotropic energy distribution, similar to 3D. An ion trajectory analysis allows one to isolate the fields responsible for ion acceleration and to characterize the acceleration regimes in time and space. The artificial longitudinal electron heating in 2D-P exaggerates the effectiveness of target-normal sheath acceleration into its dominant acceleration mechanism throughout the laser-plasma interaction, whereas 2D-S and 3D both have sizable populations accelerated preferentially during transparency.« less

Effects of dimensionality and laser polarization on kinetic simulations of laser-ion acceleration in the transparency regime

NASA Astrophysics Data System (ADS)

Stark, David; Yin, Lin; Albright, Brian; Guo, Fan

2017-10-01

The often cost-prohibitive nature of three-dimensional (3D) kinetic simulations of laser-plasma interactions has resulted in heavy use of two-dimensional (2D) simulations to extract physics. However, depending on whether the polarization is modeled as 2D-S or 2D-P (laser polarization in and out of the simulation plane, respectively), different results arise. In laser-ion acceleration in the transparency regime, VPIC particle-in-cell simulations show that 2D-S and 2D-P capture different physics that appears in 3D simulations. The electron momentum distribution is virtually two-dimensional in 2D-P, unlike the more isotropic distributions in 2D-S and 3D, leading to greater heating in the simulation plane. As a result, target expansion time scales and density thresholds for the onset of relativistic transparency differ dramatically between 2D-S and 2D-P. The artificial electron heating in 2D-P exaggerates the effectiveness of target-normal sheath acceleration (TNSA) into its dominant acceleration mechanism, whereas 2D-S and 3D both have populations accelerated preferentially during transparency to higher energies than those of TNSA. Funded by the LANL Directed Research and Development Program.

Northwest Africa 5298: A Basaltic Shergottite

NASA Technical Reports Server (NTRS)

Hui, Hejiu; Peslier, Anne; Lapen, Thomas J.; Brandon, Alan; Shafer, John

2009-01-01

NWA 5298 is a single 445 g meteorite found near Bir Gandouz, Morocco in March 2008 [1]. This rock has a brown exterior weathered surface instead of a fusion crust and the interior is composed of green mineral grains with interstitial dark patches containing small vesicles and shock melts [1]. This meteorite is classified as a basaltic shergottite [2]. A petrologic study of this Martian meteorite is being carried out with electron microprobe analysis and soon trace element analyses by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Oxygen fugacity is calculated from Fe-Ti oxides pairs in the sample. The data from this study constrains the petrogenesis of basaltic shergottites.

Quenched-in defects in flashlamp-annealed silicon

NASA Technical Reports Server (NTRS)

Borenstein, J. T.; Jones, J. T.; Corbett, J. W.; Oehrlein, G. S.; Kleinhenz, R. L.

1986-01-01

Deep levels introduced in boron-doped silicon by heat-pulse annealing with a tungsten-halogen flashlamp are investigated using deep-level transient spectroscopy. Two majority-carrier trapping levels in the band gap, at Ev + 0.32 eV and at Ev + 0.45 eV, are observed. These results are compared to those obtained by furnace-quenching and laser-annealing studies. Both the position in the gap and the annealing kinetics of the hole trap at Ev + 0.45 eV suggest that this center is due to an interstitial iron impurity in the lattice. The deep levels are not consistently observed in all flashlamp-annealed Si crystals utilized.

The origin of chondrules - Experimental investigation of metastable liquids in the system Mg2SiO4-SiO2

NASA Technical Reports Server (NTRS)

Blander, M.; Planner, H. N.; Keil, K.; Nelson, L. S.; Richardson, N. L.

1976-01-01

Laser-melted magnesium silicate droplets were supercooled 400-750 C below their equilibrium liquidus temperatures before crystallization and their texture was compared with that of meteoritic and lunar chondrules. Crystal morphology, width and texture were studied in relation to nucleation temperature and bulk composition. It was found that the only phase to nucleate from the forsterite-enstatite normative melts was forsterite. Highly siliceous glass, about 65% SiO2 by weight, was identified interstitially to the forsterite crystals in seven of the MgSiO4 spherules and was thought to be present in all.

Annihilating vacancies via dynamic reflection and emission of interstitials in nano-crystal tungsten

NASA Astrophysics Data System (ADS)

Li, Xiangyan; Duan, Guohua; Xu, Yichun; Zhang, Yange; Liu, Wei; Liu, C. S.; Liang, Yunfeng; Chen, Jun-Ling; Luo, G.-N.

2017-11-01

Radiation damage not only seriously degrades the mechanical properties of tungsten (W) but also enhances hydrogen retention in the material. Introducing a large amount of defect sinks, e.g. grain boundaries (GBs) is an effective method for improving radiation-resistance of W. However, the mechanism by which the vacancies are dynamically annihilated at long timescale in nano-crystal W is still not clear. The dynamic picture for eliminating vacancies with single interstitials and small interstitial-clusters has been investigated by combining molecular dynamics, molecular statics and object Kinetic Monte Carlo methods. On one hand, the annihilation of bulk vacancies was enhanced due to the reflection of an interstitial-cluster of parallel ≤ft< 1 1 1 \\right> crowdions by the GB. The interstitial-cluster was observed to be reflected back into the grain interior when approaching a locally dense GB region. Near this region, the energy landscape for the interstitial was featured by a shoulder, different to the decreasing energy landscape of the interstitial near a locally loose region as indicative of the sink role of the GB. The bulk vacancy on the reflection path was annihilated. On the other hand, the dynamic interstitial emission efficiently anneals bulk vacancies. The single interstitial trapped at the GB firstly moved along the GB quickly and clustered to be the di-interstitial therein, reducing its mobility to a value comparable to that that for bulk vacancy diffusion. Then, the bulk vacancy was recombined via the coupled motion of the di-interstitial along the GB, the diffusion of the vacancy towards the GB and the accompanying interstitial emission. These results suggest that GBs play an efficient role in improving radiation-tolerance of nano-crystal W via reflecting highly-mobile interstitials and interstitial-clusters into the bulk and annihilating bulk vacancies, and via complex coupling of in-boundary interstitial diffusion, clustering of the interstitial and vacancy diffusion in the bulk.

Simulation and experimental research on spherical dome by 3D laser forming of square feet

NASA Astrophysics Data System (ADS)

Yang, Lijun; Wang, Yang

2007-01-01

Laser forming is a technique of using the energy from a laser beam to modify and adjust the curvature of sheet metals or hard materials. 2-dimensional laser forming can reasonably accurately control bend angles with various materials. To advance this process further for realistic forming applications in a manufacturing industry, it is necessary to consider larger scale controlled 3-dimensional laser forming. However, this is a different situation for 3-dimensional laser forming. The work presented in this paper uses the spider scanning path to form the thin square sheet to spherical dome by laser forming. The explicit dynamic analysis on 3-dimentional laser forming is shown in the article. On the base of temperature gradient mechanism of 2-dimensional laser forming, depending on the geometry and the thermo-physical properties of stainless steel lCrl8Ni9Ti, develop the mechanism of laser forming of thin square sheet to the spherical dome. This paper discusses the interaction between moving laser beam and sheet, the temperature field on the sheet, and the step transition of stress and deformation in laser forming. In order to give the verification on the results of simulation, the correlative experiment has progressed with Lumonics JK7O2H Nd:YAG laser. The results of experiments are in accord with the simulation.

Hardware Verification of Laser Noise Cancellation and Gravitational Wave Extraction using Time-Delay Interferometry

NASA Astrophysics Data System (ADS)

Mitryk, Shawn; Mueller, Guido

The Laser Interferometer Space Antenna (LISA) is a space-based modified Michelson interfer-ometer designed to measure gravitational radiation in the frequency range from 30 uHz to 1 Hz. The interferometer measurement system (IMS) utilizes one-way laser phase measurements to cancel the laser phase noise, reconstruct the proof-mass motion, and extract the gravitational wave (GW) induced laser phase modulations in post-processing using a technique called time-delay interferometry (TDI). Unfortunately, there exist few hard-ware verification experiments of the IMS. The University of Florida LISA Interferometry Simulator (UFLIS) is designed to perform hardware-in-the-loop simulations of the LISA interferometry system, modeling the characteris-tics of the LISA mission as accurately as possible. This depends, first, on replicating the laser pre-stabilization by locking the laser phase to an ultra-stable Zerodur cavity length reference using the PDH locking method. Phase measurements of LISA-like photodetector beat-notes are taken using the UF-phasemeter (PM) which can measure the laser BN frequency to within an accuracy of 0.22 uHz. The inter-space craft (SC) laser links including the time-delay due to the 5 Gm light travel time along the LISA arms, the laser Doppler shifts due to differential SC motion, and the GW induced laser phase modulations are simulated electronically using the electronic phase delay (EPD) unit. The EPD unit replicates the laser field propagation between SC by measuring a photodetector beat-note frequency with the UF-phasemeter and storing the information in memory. After the requested delay time, the frequency information is added to a Doppler offset and a GW-like frequency modulation. The signal is then regenerated with the inter-SC laser phase affects applied. Utilizing these components, I will present the first complete TDI simulations performed using the UFLIS. The LISA model is presented along-side the simulation, comparing the generation and measurement of LISA-like signals. Phasemeter measurements are used in post-processing and combined in the linear combinations defined by TDI, thus, canceling the laser phase and phase-lock loop noise to extract the applied GW modulation buried under the noise. Nine order of magnitude common mode laser noise cancellation is achieved at a frequency of 1 mHz and the GW signal is clearly visible after the laser and PLL noise cancellation.

Numerical simulation of the laser welding process for the prediction of temperature distribution on welded aluminium aircraft components

NASA Astrophysics Data System (ADS)

Tsirkas, S. A.

2018-03-01

The present investigation is focused to the modelling of the temperature field in aluminium aircraft components welded by a CO2 laser. A three-dimensional finite element model has been developed to simulate the laser welding process and predict the temperature distribution in T-joint laser welded plates with fillet material. The simulation of the laser beam welding process was performed using a nonlinear heat transfer analysis, based on a keyhole formation model analysis. The model employs the technique of element ;birth and death; in order to simulate the weld fillet. Various phenomena associated with welding like temperature dependent material properties and heat losses through convection and radiation were accounted for in the model. The materials considered were 6056-T78 and 6013-T4 aluminium alloys, commonly used for aircraft components. The temperature distribution during laser welding process has been calculated numerically and validated by experimental measurements on different locations of the welded structure. The numerical results are in good agreement with the experimental measurements.

Simulation of the impact of refractive surgery ablative laser pulses with a flying-spot laser beam on intrasurgery corneal temperature.

PubMed

Shraiki, Mario; Arba-Mosquera, Samuel

2011-06-01

To evaluate ablation algorithms and temperature changes in laser refractive surgery. The model (virtual laser system [VLS]) simulates different physical effects of an entire surgical process, simulating the shot-by-shot ablation process based on a modeled beam profile. The model is comprehensive and directly considers applied correction; corneal geometry, including astigmatism; laser beam characteristics; and ablative spot properties. Pulse lists collected from actual treatments were used to simulate the temperature increase during the ablation process. Ablation efficiency reduction in the periphery resulted in a lower peripheral temperature increase. Steep corneas had lesser temperature increases than flat ones. The maximum rise in temperature depends on the spatial density of the ablation pulses. For the same number of ablative pulses, myopic corrections showed the highest temperature increase, followed by myopic astigmatism, mixed astigmatism, phototherapeutic keratectomy (PTK), hyperopic astigmatism, and hyperopic treatments. The proposed model can be used, at relatively low cost, for calibration, verification, and validation of the laser systems used for ablation processes and would directly improve the quality of the results.

Experimental and simulated ultrasonic characterization of complex damage in fused silica.

PubMed

Martin, L Peter; Chambers, David H; Thomas, Graham H

2002-02-01

The growth of a laser-induced, surface damage site in a fused silica window was monitored by the ultrasonic pulse-echo technique. The laser damage was grown using 12-ns pulses of 1.053-microm wavelength light at a fluence of approximately 27 J/cm2. The ultrasonic data were acquired after each pulse of the laser beam for 19 pulses. In addition, optical images of the surface and subsurface damage shape were recorded after each pulse of the laser. The ultrasonic signal amplitude exhibited variations with the damage size, which were attributed to the subsurface morphology of the damage site. A mechanism for the observed ultrasonic data based on the interaction of the ultrasound with cracks radiating from the damage site was tested using two-dimensional numerical simulations. The simulated results exhibit qualitatively similar characteristics to the experimental data and demonstrate the usefulness of numerical simulation as an aid for ultrasonic signal interpretation. The observed sensitivity to subsurface morphology makes the ultrasonic methodology a promising tool for monitoring laser damage in large aperture laser optics used in fusion energy research.

Earth-to-Orbit Laser Launch Simulation for a Lightcraft Technology Demonstrator

NASA Astrophysics Data System (ADS)

Richard, J. C.; Morales, C.; Smith, W. L.; Myrabo, L. N.

2006-05-01

Optimized laser launch trajectories have been developed for a 1.4 m diameter, 120 kg (empty mass) Lightcraft Technology Demonstrator (LTD). The lightcraft's combined-cycle airbreathing/rocket engine is designed for single-stage-to-orbit flights with a mass ratio of 2 propelled by a 100 MW class ground-based laser built on a 3 km mountain peak. Once in orbit, the vehicle becomes an autonomous micro-satellite. Two types of trajectories were simulated with the SORT (Simulation and Optimization of Rocket Trajectories) software package: a) direct GBL boost to orbit, and b) GBL boost aided by laser relay satellite. Several new subroutines were constructed for SORT to input engine performance (as a function of Mach number and altitude), vehicle aerodynamics, guidance algorithms, and mass history. A new guidance/steering option required the lightcraft to always point at the GBL or laser relay satellite. SORT iterates on trajectory parameters to optimize vehicle performance, achieve a desired criteria, or constrain the solution to avoid some specific limit. The predicted laser-boost performance for the LTD is undoubtedly revolutionary, and SORT simulations have helped to define this new frontier.

Analysis of laser energy characteristics of laser guided weapons based on the hardware-in-the-loop simulation system

NASA Astrophysics Data System (ADS)

Zhu, Yawen; Cui, Xiaohong; Wang, Qianqian; Tong, Qiujie; Cui, Xutai; Li, Chenyu; Zhang, Le; Peng, Zhong

2016-11-01

The hardware-in-the-loop simulation system, which provides a precise, controllable and repeatable test conditions, is an important part of the development of the semi-active laser (SAL) guided weapons. In this paper, laser energy chain characteristics were studied, which provides a theoretical foundation for the SAL guidance technology and the hardware-in-the-loop simulation system. Firstly, a simplified equation was proposed to adjust the radar equation according to the principles of the hardware-in-the-loop simulation system. Secondly, a theoretical model and calculation method were given about the energy chain characteristics based on the hardware-in-the-loop simulation system. We then studied the reflection characteristics of target and the distance between the missile and target with major factors such as the weather factors. Finally, the accuracy of modeling was verified by experiment as the values measured experimentally generally follow the theoretical results from the model. And experimental results revealed that ratio of attenuation of the laser energy exhibited a non-linear change vs. pulse number, which were in accord with the actual condition.

Simulation of medical Q-switch flash-pumped Er:YAG laser

NASA Astrophysics Data System (ADS)

-Yan-lin, Wang; Huang-Chuyun; Yao-Yucheng; Xiaolin, Zou

2011-01-01

Er: YAG laser, the wavelength is 2940nm, can be absorbed strongly by water. The absorption coefficient is as high as 13000 cm-1. As the water strong absorption, Erbium laser can bring shallow penetration depth and smaller surrounding tissue injury in most soft tissue and hard tissue. At the same time, the interaction between 2940nm radiation and biological tissue saturated with water is equivalent to instantaneous heating within limited volume, thus resulting in the phenomenon of micro-explosion to removal organization. Different parameters can be set up to cut enamel, dentin, caries and soft tissue. For the development and optimization of laser system, it is a practical choice to use laser modeling to predict the influence of various parameters for laser performance. Aim at the status of low Erbium laser output power, flash-pumped Er: YAG laser performance was simulated to obtain optical output in theory. the rate equation model was obtained and used to predict the change of population densities in various manifolds and use the technology of Q-switch the simulate laser output for different design parameters and results showed that Er: YAG laser output energy can achieve the maximum average output power of 9.8W under the given parameters. The model can be used to find the potential laser systems that meet application requirements.

Variations in laser energy outputs over a series of simulated treatments.

PubMed

Lister, T S; Brewin, M P

2014-10-01

Test patches are routinely employed to determine the likely efficacy and the risk of adverse effects from cutaneous laser treatments. However, the degree to which these represent a full treatment has not been investigated in detail. This study aimed to determine the variability in pulse-to-pulse output energy from a representative selection of cutaneous laser systems in order to assess the value of laser test patches. The output energies of each pulse from seven cutaneous laser systems were measured using a pyroelectric measurement head over a 2-h period, employing a regime of 10-min simulated treatments followed by a 5-min rest period (between patients). Each laser system appeared to demonstrate a different pattern of variation in output energy per pulse over the period measured. The output energies from a range of cutaneous laser systems have been shown to vary considerably between a representative test patch and a full treatment, and over the course of an entire simulated clinic list. © 2014 British Association of Dermatologists.

Thermal effect of laser ablation on the surface of carbon fiber reinforced plastic during laser processing

NASA Astrophysics Data System (ADS)

Ohkubo, Tomomasa; Sato, Yuji; Matsunaga, Ei-ichi; Tsukamoto, Masahiro

2018-02-01

Although laser processing is widely used for many applications, the cutting quality of carbon fiber reinforced plastic (CFRP) decreases around the heat-affected zone (HAZ) during laser processing. Carbon fibers are exposed around the HAZ, and tensile strength decreases with increasing length of the HAZ. Some theoretical studies of thermal conductions that do not consider fluid dynamics have been performed; however, theoretical considerations that include the dynamics of laser ablation are scarce. Using removed mass and depth observed from experiments, the dynamics of laser ablation of CFRP with high-temperature and high-pressure of compressive gas is simulated herein. In this calculation, the mushroom-like shape of laser ablation is qualitatively simulated compared with experiments using a high-speed camera. Considering the removal temperature of the resin and the temperature distribution at each point on the surface, the simulation results suggest that a wide area of the resin is removed when the processing depth is shallow, and a rounded kerf is generated as the processing depth increases.

Potential of solar-simulator-pumped alexandrite lasers

NASA Technical Reports Server (NTRS)

Deyoung, Russell J.

1990-01-01

An attempt was made to pump an alexandrite laser rod using a Tamarak solar simulator and also a tungsten-halogen lamp. A very low optical laser cavity was used to achieve the threshold minimum pumping-power requirement. Lasing was not achieved. The laser threshold optical-power requirement was calculated to be approximately 626 W/sq cm for a gain length of 7.6 cm, whereas the Tamarak simulator produces 1150 W/sq cm over a gain length of 3.3 cm, which is less than the 1442 W/sq cm required to reach laser threshold. The rod was optically pulsed with 200 msec pulses, which allowed the alexandrite rod to operate at near room temperature. The optical intensity-gain-length product to achieve laser threshold should be approximately 35,244 solar constants-cm. In the present setup, this product was 28,111 solar constants-cm.

Data collection and simulation of high range resolution laser radar for surface mine detection

NASA Astrophysics Data System (ADS)

Steinvall, Ove; Chevalier, Tomas; Larsson, Håkan

2006-05-01

Rapid and efficient detection of surface mines, IED's (Improvised Explosive Devices) and UXO (Unexploded Ordnance) is of high priority in military conflicts. High range resolution laser radars combined with passive hyper/multispectral sensors offer an interesting concept to help solving this problem. This paper reports on laser radar data collection of various surface mines in different types of terrain. In order to evaluate the capability of 3D imaging for detecting and classifying the objects of interest a scanning laser radar was used to scan mines and surrounding terrain with high angular and range resolution. These data were then fed into a laser radar model capable of generating range waveforms for a variety of system parameters and combinations of different targets and backgrounds. We can thus simulate a potential system by down sampling to relevant pixel sizes and laser/receiver characteristics. Data, simulations and examples will be presented.

FDTD method for laser absorption in metals for large scale problems.

PubMed

Deng, Chun; Ki, Hyungson

2013-10-21

The FDTD method has been successfully used for many electromagnetic problems, but its application to laser material processing has been limited because even a several-millimeter domain requires a prohibitively large number of grids. In this article, we present a novel FDTD method for simulating large-scale laser beam absorption problems, especially for metals, by enlarging laser wavelength while maintaining the material's reflection characteristics. For validation purposes, the proposed method has been tested with in-house FDTD codes to simulate p-, s-, and circularly polarized 1.06 μm irradiation on Fe and Sn targets, and the simulation results are in good agreement with theoretical predictions.

Interstitial cystitis - resources

MedlinePlus

Resources - interstitial cystitis ... The following organizations are good resources for information on interstitial cystitis : Interstitial Cystitis Association -- www.ichelp.org National Institute of Diabetes and Digestive and Kidney Diseases -- www. ...

Experimental and clinical standards, and evolution of lasers in neurosurgery.

PubMed

Devaux, B C; Roux, F X

1996-01-01

From initial experiments of ruby, argon and CO2 lasers on the nervous system so far, dramatic progress was made in delivery systems technology as well as in knowledge of laser-tissue interaction effects and hazards through various animal experiments and clinical experience. Most surgical effects of laser light on neural tissue and the central nervous system (CNS) are thermal lesions. Haemostasis, cutting and vaporization depend on laser emission parameters--wavelength, fluence and mode--and on the exposed tissues optical and thermal properties--water and haemoglobin content, thermal conductivity and specific heat. CO2 and Nd-YAG lasers have today a large place in the neurosurgical armamentarium, while new laser sources such as high power diode lasers will have one in the near future. Current applications of these lasers derive from their respective characteristics, and include CNS tumour and vascular malformation surgery, and stereotactic neurosurgery. Intracranial, spinal cord and intra-orbital meningiomas are the best lesions for laser use for haemostasis, dissection and tissue vaporization. Resection of acoustic neuromas, pituitary tumours, spinal cord neuromas, intracerebral gliomas and metastases may also benefit from lasers as accurate, haemostatic, non-contact instruments which reduce surgical trauma to the brain and eloquent structures such as brain stem and cranial nerves. Coagulative lasers (1.06 microns and 1.32 microns Nd-YAG, argon, or diode laser) will find an application for arteriovenous malformations and cavernomas. Any fiberoptic-guided laser will find a use during stereotactic neurosurgical procedures, including image-guided resection of tumours and vascular malformations and endoscopic tumour resection and cysts or entry into a ventricle. Besides these routine applications of lasers, laser interstitial thermotherapy (LITT) and photodynamic therapy (PDT) of brain tumours are still in the experimental stage. The choice of a laser in a neurosurgical operating room implies an evaluation of the laser use (applications, frequency), of the available budget and costs--including purchase, maintenance and staff training--, and material that will be necessary: unit, peripherals, safety devices and measures, training programme. Future applications of lasers in neurosurgery will come from technological advances and refined experimental applications. The availability of new wavelength, tunable, small sized and "smart" laser units, will enlarge the thermal and non-thermal interactions between laser energy and neural tissue leading to new surgical applications. Tissue photo-ablation, photohynamic therapy using second generation of photosensitizers, updated thermotherapy protocols, are current trends for further use of lasers in neurosurgery.

Numerical simulation of temperature field in K9 glass irradiated by ultraviolet pulse laser

NASA Astrophysics Data System (ADS)

Wang, Xi; Fang, Xiaodong

2015-10-01

The optical component of photoelectric system was easy to be damaged by irradiation of high power pulse laser, so the effect of high power pulse laser irradiation on K9 glass was researched. A thermodynamic model of K9 glass irradiated by ultraviolet pulse laser was established using the finite element software ANSYS. The article analyzed some key problems in simulation process of ultraviolet pulse laser damage of K9 glass based on ANSYS from the finite element models foundation, meshing, loading of pulse laser, setting initial conditions and boundary conditions and setting the thermal physical parameters of material. The finite element method (FEM) model was established and a numerical analysis was performed to calculate temperature field in K9 glass irradiated by ultraviolet pulse laser. The simulation results showed that the temperature of irradiation area exceeded the melting point of K9 glass, while the incident laser energy was low. The thermal damage dominated in the damage mechanism of K9 glass, the melting phenomenon should be much more distinct.

Simulations of ultrafast x-ray laser experiments

NASA Astrophysics Data System (ADS)

Fortmann-Grote, C.; Andreev, A. A.; Appel, K.; Branco, J.; Briggs, R.; Bussmann, M.; Buzmakov, A.; Garten, M.; Grund, A.; Huebl, A.; Jurek, Z.; Loh, N. D.; Nakatsutsumi, M.; Samoylova, L.; Santra, R.; Schneidmiller, E. A.; Sharma, A.; Steiniger, K.; Yakubov, S.; Yoon, C. H.; Yurkov, M. V.; Zastrau, U.; Ziaja-Motyka, B.; Mancuso, A. P.

2017-06-01

Simulations of experiments at modern light sources, such as optical laser laboratories, synchrotrons, and free electron lasers, become increasingly important for the successful preparation, execution, and analysis of these experiments investigating ever more complex physical systems, e.g. biomolecules, complex materials, and ultra-short lived states of matter at extreme conditions. We have implemented a platform for complete start-to-end simulations of various types of photon science experiments, tracking the radiation from the source through the beam transport optics to the sample or target under investigation, its interaction with and scattering from the sample, and registration in a photon detector. This tool allows researchers and facility operators to simulate their experiments and instruments under real life conditions, identify promising and unattainable regions of the parameter space and ultimately make better use of valuable beamtime. In this paper, we present an overview about status and future development of the simulation platform and discuss three applications: 1.) Single-particle imaging of biomolecules using x-ray free electron lasers and optimization of x-ray pulse properties, 2.) x-ray scattering diagnostics of hot dense plasmas in high power laser-matter interaction and identification of plasma instabilities, and 3.) x-ray absorption spectroscopy in warm dense matter created by high energy laser-matter interaction and pulse shape optimization for low-isentrope dynamic compression.

A gas-dynamical approach to radiation pressure acceleration

NASA Astrophysics Data System (ADS)

Schmidt, Peter; Boine-Frankenheim, Oliver

2016-06-01

The study of high intensity ion beams driven by high power pulsed lasers is an active field of research. Of particular interest is the radiation pressure acceleration, for which simulations predict narrow band ion energies up to GeV. We derive a laser-piston model by applying techniques for non-relativistic gas-dynamics. The model reveals a laser intensity limit, below which sufficient laser-piston acceleration is impossible. The relation between target thickness and piston velocity as a function of the laser pulse length yields an approximation for the permissible target thickness. We performed one-dimensional Particle-In-Cell simulations to confirm the predictions of the analytical model. These simulations also reveal the importance of electromagnetic energy transport. We find that this energy transport limits the achievable compression and rarefies the plasma.

Continuum-atomistic simulation of picosecond laser heating of copper with electron heat capacity from ab initio calculation

NASA Astrophysics Data System (ADS)

Ji, Pengfei; Zhang, Yuwen

2016-03-01

On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron subsystem to the lattice subsystem is modeled by including the electron-phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM integrated simulation and pure MD-TTM coupled simulation. The successful construction of the QM-MD-TTM integrated simulation provides a general way that is accessible to other metals in laser heating.

Observation of laser beam profile progression inside an extended laser cavity

NASA Astrophysics Data System (ADS)

Wu, Frank F.; Farrell, Thomas C.

2013-03-01

This report presents the result of the laser beam profile progression in target-in-the-loop (TIL) system. This simulation experiment is to verify whether it is possible to form a tight hot spot similar to a single transversal mode in an extended laser cavity. Therefore, it is very important to observe the progression of the laser profile at a laser cavity mirror when a seeded high energy laser pulse is injected into the TIL system. The extended laser cavity is formed with a high reflectivity mirror on one end and an optical phase conjugated mirror as the second mirror, with potential disturbance media inside. The laser oscillation occurs only when it is triggered with a single frequency high energy laser pulse to overcome the threshold condition. With a laser cavity length of around 11 meters and a seeded laser pulse of 10 ns, we have been able to acquire and distinguish the laser beam profiles of each round-trip. Inserting a scattering media and other distortion elements can simulate atmospheric effects.

Macroscopic and bulk-controlled elastic modes in an interaction of interstitial alcali metal cations within a face-centered cubic crystalline fullerine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tatarenko, V.A.; Tsysman, C.L.; Oltarzhevskaya, Y.T.

1994-12-31

The calculations in a majority of previous works for the fulleride (AqC{sub 60}) crystals were performed within the framework of the rigid-lattice model, neglecting the distoration relaxation of the host fullerene (C{sub 60}) crystal caused by the interstitial alkali-metal (A) cations. However, an each cation is a source of a static distoration field, and the resulting field is a superposition of such fields generated by all cations. This is a reason why the host-crystal distortions depend on the A-cations configurations, i.e. on a type of a spatial bulk distribution of interstitial cations. This paper seeks to find a functional relationmore » between the amplitudes of the doping-induced structure-distortion waves and of statistic concentration ones. A semiphenomenological model is constructed here within the scope of statistical-thermodynamic treatment and using the lattice-statistics simulation method. In this model the effects due to the presence of q solute A cations over available interstices (per unit cell) on the statistic inherent reorientation and/or displacements of the solvent molecules from the average-lattice sites as well as on the lattice parameter a of the elastically-anysotropic cubic C{sub 60} crystal are taken into account.« less

Application of Markov chain Monte Carlo analysis to biomathematical modeling of respirable dust in US and UK coal miners

PubMed Central

Sweeney, Lisa M.; Parker, Ann; Haber, Lynne T.; Tran, C. Lang; Kuempel, Eileen D.

2015-01-01

A biomathematical model was previously developed to describe the long-term clearance and retention of particles in the lungs of coal miners. The model structure was evaluated and parameters were estimated in two data sets, one from the United States and one from the United Kingdom. The three-compartment model structure consists of deposition of inhaled particles in the alveolar region, competing processes of either clearance from the alveolar region or translocation to the lung interstitial region, and very slow, irreversible sequestration of interstitialized material in the lung-associated lymph nodes. Point estimates of model parameter values were estimated separately for the two data sets. In the current effort, Bayesian population analysis using Markov chain Monte Carlo simulation was used to recalibrate the model while improving assessments of parameter variability and uncertainty. When model parameters were calibrated simultaneously to the two data sets, agreement between the derived parameters for the two groups was very good, and the central tendency values were similar to those derived from the deterministic approach. These findings are relevant to the proposed update of the ICRP human respiratory tract model with revisions to the alveolar-interstitial region based on this long-term particle clearance and retention model. PMID:23454101

Radiation tolerance of nanocrystalline ceramics: insights from Yttria Stabilized Zirconia.

PubMed

Dey, Sanchita; Drazin, John W; Wang, Yongqiang; Valdez, James A; Holesinger, Terry G; Uberuaga, Blas P; Castro, Ricardo H R

2015-01-13

Materials for applications in hostile environments, such as nuclear reactors or radioactive waste immobilization, require extremely high resistance to radiation damage, such as resistance to amorphization or volume swelling. Nanocrystalline materials have been reported to present exceptionally high radiation-tolerance to amorphization. In principle, grain boundaries that are prevalent in nanomaterials could act as sinks for point-defects, enhancing defect recombination. In this paper we present evidence for this mechanism in nanograined Yttria Stabilized Zirconia (YSZ), associated with the observation that the concentration of defects after irradiation using heavy ions (Kr(+), 400 keV) is inversely proportional to the grain size. HAADF images suggest the short migration distances in nanograined YSZ allow radiation induced interstitials to reach the grain boundaries on the irradiation time scale, leaving behind only vacancy clusters distributed within the grain. Because of the relatively low temperature of the irradiations and the fact that interstitials diffuse thermally more slowly than vacancies, this result indicates that the interstitials must reach the boundaries directly in the collision cascade, consistent with previous simulation results. Concomitant radiation-induced grain growth was observed which, as a consequence of the non-uniform implantation, caused cracking of the nano-samples induced by local stresses at the irradiated/non-irradiated interfaces.

Radiation Tolerance of Nanocrystalline Ceramics: Insights from Yttria Stabilized Zirconia

PubMed Central

Dey, Sanchita; Drazin, John W.; Wang, Yongqiang; Valdez, James A.; Holesinger, Terry G.; Uberuaga, Blas P.; Castro, Ricardo H. R.

2015-01-01

Materials for applications in hostile environments, such as nuclear reactors or radioactive waste immobilization, require extremely high resistance to radiation damage, such as resistance to amorphization or volume swelling. Nanocrystalline materials have been reported to present exceptionally high radiation-tolerance to amorphization. In principle, grain boundaries that are prevalent in nanomaterials could act as sinks for point-defects, enhancing defect recombination. In this paper we present evidence for this mechanism in nanograined Yttria Stabilized Zirconia (YSZ), associated with the observation that the concentration of defects after irradiation using heavy ions (Kr+, 400 keV) is inversely proportional to the grain size. HAADF images suggest the short migration distances in nanograined YSZ allow radiation induced interstitials to reach the grain boundaries on the irradiation time scale, leaving behind only vacancy clusters distributed within the grain. Because of the relatively low temperature of the irradiations and the fact that interstitials diffuse thermally more slowly than vacancies, this result indicates that the interstitials must reach the boundaries directly in the collision cascade, consistent with previous simulation results. Concomitant radiation-induced grain growth was observed which, as a consequence of the non-uniform implantation, caused cracking of the nano-samples induced by local stresses at the irradiated/non-irradiated interfaces. PMID:25582769

Radiation tolerance of nanocrystalline ceramics: Insights from yttria stabilized zirconia

DOE PAGES

Dey, Sanchita; Drazin, John W.; Wang, Yongqiang; ...

2015-01-13

Materials for applications in hostile environments, such as nuclear reactors or radioactive waste immobilization, require extremely high resistance to radiation damage, such as resistance to amorphization or volume swelling. Nanocrystalline materials have been reported to present exceptionally high radiation-tolerance to amorphization. In principle, grain boundaries that are prevalent in nanomaterials could act as sinks for point-defects, enhancing defect recombination. In this paper we present evidence for this mechanism in nanograined Yttria Stabilized Zirconia (YSZ), associated with the observation that the concentration of defects after irradiation using heavy ions (Kr⁺, 400 keV) is inversely proportional to the grain size. HAADF imagesmore » suggest the short migration distances in nanograined YSZ allow radiation induced interstitials to reach the grain boundaries on the irradiation time scale, leaving behind only vacancy clusters distributed within the grain. Because of the relatively low temperature of the irradiations and the fact that interstitials diffuse thermally more slowly than vacancies, this result indicates that the interstitials must reach the boundaries directly in the collision cascade, consistent with previous simulation results. Concomitant radiation-induced grain growth was observed which, as a consequence of the non-uniform implantation, caused cracking of the nano-samples induced by local stresses at the irradiated/non-irradiated interfaces.« less

Macroscopic and bulk-controlled elastic modes in an interaction of interstitial alcali metal cations within a face-centered cubic crystalline fullerine

NASA Technical Reports Server (NTRS)

Tatarenko, Valentine A.; Tsysman, Constantin L.; Oltarzhevskaya, Yelena T.

1995-01-01

The calculations in a majority of previous works for the fulleride (AqC-60) crystals were performed within the framework of the rigid-lattice model, neglecting the distortion relaxation of the host fullerene (C-60) crystal caused by the interstitial alkali-metal (A) cations. However, an each cation is a source of a static distortion field, and the resulting field is a superposition of such fields generated by all cations. This is a reason why the host-crystal distortions depend on the A-cations configurations, i.e. on a type of a spatial bulk distribution of interstitial cations. The given paper seeks to find a functional relation between the amplitudes of the doping-induced structure-distortion waves and of static concentration ones. A semiphenomenological model is constructed here within the scope of statistical-thermodynamic treatment and using the lattice-statistics simulation method(*). In this model the effects due to the presence of q solute A cations over available interstices (per unit cell) on the static inherent reorientation and/or displacements of the solvent molecules from the 'average-lattice' sites' as well as on the lattice parameter a of a elastically-anysotropic 'cubic' C-60 crystal are taken into account.

Porcine cadaver iris model for iris heating during corneal surgery with a femtosecond laser

NASA Astrophysics Data System (ADS)

Sun, Hui; Fan, Zhongwei; Wang, Jiang; Yan, Ying; Juhasz, Tibor; Kurtz, Ron

2015-03-01

Multiple femtosecond lasers have now been cleared for use for ophthalmic surgery, including for creation of corneal flaps in LASIK surgery. Preliminary study indicated that during typical surgical use, laser energy may pass beyond the cornea with potential effects on the iris. As a model for laser exposure of the iris during femtosecond corneal surgery, we simulated the temperature rise in porcine cadaver iris during direct illumination by the femtosecond laser. Additionally, ex-vivo iris heating due to femtosecond laser irradiation was measured with an infrared thermal camera (Fluke corp. Everett, WA) as a validation of the simulation.

The effect of interstitial pressure on therapeutic agent transport: coupling with the tumor blood and lymphatic vascular systems.

PubMed

Wu, Min; Frieboes, Hermann B; Chaplain, Mark A J; McDougall, Steven R; Cristini, Vittorio; Lowengrub, John S

2014-08-21

Vascularized tumor growth is characterized by both abnormal interstitial fluid flow and the associated interstitial fluid pressure (IFP). Here, we study the effect that these conditions have on the transport of therapeutic agents during chemotherapy. We apply our recently developed vascular tumor growth model which couples a continuous growth component with a discrete angiogenesis model to show that hypertensive IFP is a physical barrier that may hinder vascular extravasation of agents through transvascular fluid flux convection, which drives the agents away from the tumor. This result is consistent with previous work using simpler models without blood flow or lymphatic drainage. We consider the vascular/interstitial/lymphatic fluid dynamics to show that tumors with larger lymphatic resistance increase the agent concentration more rapidly while also experiencing faster washout. In contrast, tumors with smaller lymphatic resistance accumulate less agents but are able to retain them for a longer time. The agent availability (area-under-the curve, or AUC) increases for less permeable agents as lymphatic resistance increases, and correspondingly decreases for more permeable agents. We also investigate the effect of vascular pathologies on agent transport. We show that elevated vascular hydraulic conductivity contributes to the highest AUC when the agent is less permeable, but to lower AUC when the agent is more permeable. We find that elevated interstitial hydraulic conductivity contributes to low AUC in general regardless of the transvascular agent transport capability. We also couple the agent transport with the tumor dynamics to simulate chemotherapy with the same vascularized tumor under different vascular pathologies. We show that tumors with an elevated interstitial hydraulic conductivity alone require the strongest dosage to shrink. We further show that tumors with elevated vascular hydraulic conductivity are more hypoxic during therapy and that the response slows down as the tumor shrinks due to the heterogeneity and low concentration of agents in the tumor interior compared with the cases where other pathological effects may combine to flatten the IFP and thus reduce the heterogeneity. We conclude that dual normalizations of the micronevironment - both the vasculature and the interstitium - are needed to maximize the effects of chemotherapy, while normalization of only one of these may be insufficient to overcome the physical resistance and may thus lead to sub-optimal outcomes. Copyright © 2014 Elsevier Ltd. All rights reserved.

The effect of interstitial pressure on therapeutic agent transport: coupling with the tumor blood and lymphatic vascular systems

PubMed Central

Wu, Min; Frieboes, Hermann B.; Chaplain, Mark A.J.; McDougall, Steven R.; Cristini, Vittorio; Lowengrub, John

2014-01-01

Vascularized tumor growth is characterized by both abnormal interstitial fluid flow and the associated interstitial fluid pressure (IFP). Here, we study the effect that these conditions have on the transport of therapeutic agents during chemotherapy. We apply our recently developed vascular tumor growth model which couples a continuous growth component with a discrete angiogenesis model to show that hypertensive IFP is a physical barrier that may hinder vascular extravasation of agents through transvascular fluid flux convection, which drives the agents away from the tumor. This result is consistent with previous work using simpler models without blood flow or lymphatic drainage. We consider the vascular/interstitial/lymphatic fluid dynamics to show that tumors with larger lymphatic resistance increase the agent concentration more rapidly while also experiencing faster washout. In contrast, tumors with smaller lymphatic resistance accumulate less agents but are able to retain them for a longer time. The agent availability (area-under-the curve, or AUC) increases for less permeable agents as lymphatic resistance increases, and correspondingly decreases for more permeable agents. We also investigate the effect of vascular pathologies on agent transport. We show that elevated vascular hydraulic conductivity contributes to the highest AUC when the agent is less permeable, but leads to lower AUC when the agent is more permeable. We find that elevated interstitial hydraulic conductivity contributes to low AUC in general regardless of the transvascular agent transport capability. We also couple the agent transport with the tumor dynamics to simulate chemotherapy with the same vascularized tumor under different vascular pathologies. We show that tumors with an elevated interstitial hydraulic conductivity alone require the strongest dosage to shrink. We further show that tumors with elevated vascular hydraulic conductivity are more hypoxic during therapy and that the response slows down as the tumor shrinks due to the heterogeneity and low concentration of agents in the tumor interior compared with the cases where other pathological effects may combine to flatten the IFP and thus reduce the heterogeneity. We conclude that dual normalizations of the micronevironment - both the vasculature and the interstitium - are needed to maximize the effects of chemotherapy, while normalization of only one of these may be insufficient to overcome the physical resistance and thus leads to sub-optimal outcomes. PMID:24751927

Numerical simulation of hydrogen fluorine overtone chemical lasers

NASA Astrophysics Data System (ADS)

Chen, Jinbao; Jiang, Zhongfu; Hua, Weihong; Liu, Zejin; Shu, Baihong

1998-08-01

A two-dimensional program was applied to simulate the chemical dynamic process, gas dynamic process and lasing process of a combustion-driven CW HF overtone chemical lasers. Some important parameters in the cavity were obtained. The calculated results included HF molecule concentration on each vibration energy level while lasing, averaged pressure and temperature, zero power gain coefficient of each spectral line, laser spectrum, the averaged laser intensity, output power, chemical efficiency and the length of lasing zone.

Finite element simulation of the mechanism of laser ultrasound induced pain weapon

NASA Astrophysics Data System (ADS)

Zhou, Bo; Zhan, Ren Jun; Shan, Ning

2018-03-01

The Laser-Ultrasonic technique uses laser energy to generate ultrasound waves in various solids. In normal conditions, this technique is used to inspect large structures without destruction, but in military use, we hope get this destruction. Nociceptors in Human skin can feel cold, heat, mechanical and other stimuli, when the stimulus exceeds a certain threshold will produce pain. Based on this principle, a laser induced pain weapon may be made. The generated ultrasound wave form is affected by features of laser pulse. The results obtained from the finite element model of laser generated ultrasound are presented in terms of temperature and displacement. At first step, the transient temperature field can be precisely calculated by using the finite element method. Then, laser generated surface acoustic wave forms are calculated by coupling the temperature distribution. Displacement is used to represent the mechanical action of skin caused by laser ultrasound. Results from numerical simulation are compared with other references; the accuracy of the method is proved accordingly. The results of simulation in the given conditions demonstrate that the stresses generated by pulse laser in human skin model were about -8 and +4 MPa. According to the results of simulation, the max and min stress are both emerged in the range of 0 600 um, that is exactly the location of myelinated Aδ and unmyelinated C nociceptor. The value of stress is can be adjusted by chose suitable parameters of laser. The study provides a possibility for developing a new non-lethal weapon to control riots or crowd.

Quasi-monoenergetic protons accelerated by laser radiation pressure and shocks in thin gaseous targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

He Minqing; Shao Xi; Liu Chuansheng

Recent experiments and simulations have demonstrated effective CO{sub 2} laser acceleration of quasi-monoenergetic protons from thick gaseous hydrogen target (of thickness tens of laser wavelengths) via hole boring and shock accelerations. We present here an alternative novel acceleration scheme by combining laser radiation pressure acceleration with shock acceleration of protons in a thin gaseous target of thickness several laser wavelengths. The laser pushes the thin gaseous plasma forward while compressing it with protons trapped in it. We demonstrated the combined acceleration with two-dimensional particle-in-cell simulation and obtained quasi-monoenergetic protons {approx}44 MeV in a gas target of thickness twice of themore » laser wavelength irradiated by circularly polarized CO{sub 2} laser with normalized laser amplitude a{sub 0}=10.« less

Modeling of endoluminal and interstitial ultrasound hyperthermia and thermal ablation: applications to device design, feedback control, and treatment planning

PubMed Central

Prakash, Punit; Salgaonkar, Vasant A.; Diederich, Chris J.

2014-01-01

Endoluminal and catheter-based ultrasound applicators are currently under development and are in clinical use for minimally invasive hyperthermia and thermal ablation of various tissue targets. Computational models play a critical role in in device design and optimization, assessment of therapeutic feasibility and safety, devising treatment monitoring and feedback control strategies, and performing patient-specific treatment planning with this technology. The critical aspects of theoretical modeling, applied specifically to endoluminal and interstitial ultrasound thermotherapy, are reviewed. Principles and practical techniques for modeling acoustic energy deposition, bioheat transfer, thermal tissue damage, and dynamic changes in the physical and physiological state of tissue are reviewed. The integration of these models and applications of simulation techniques in identification of device design parameters, development of real time feedback-control platforms, assessing the quality and safety of treatment delivery strategies, and optimization of inverse treatment plans are presented. PMID:23738697

Atomistic Simulation of Interstitial Dislocation Loop Evolution under Applied Stresses in BCC Iron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, Xue Hao; Wang, Dong; Setyawan, Wahyu

Evolution of an interstitial 1/2⟨111⟩ dislocation loop under tensile, shear, and torsion stresses is studied with molecular statics method. Under a tensile stress, the dependence of ultimate tensile strength on size of loop is calculated. The formation of small shear loops around the initial prismatic loop is confirmed as an intermediate state to form the final dislocation network. Under a shear stress, the rotation of a loop is observed not only by a change of the habit plane but also through a transformation between a shear and a prismatic loop. Under torsion, a perfect BCC crystal may undergo a BCCmore » to FCC or BCC to HCP transformation. The present work indicates that a 1/2⟨111⟩ loop can delay these transformations, resulting in the formation of micro-crack on the surface.« less

Defect processes in Be12X (X = Ti, Mo, V, W)

NASA Astrophysics Data System (ADS)

Jackson, M. L.; Burr, P. A.; Grimes, R. W.

2017-08-01

The stability of intrinsic point defects in Be12X intermetallics (where X  =  Ti, V, Mo or W) are predicted using density functional theory simulations and discussed with respect to fusion energy applications. Schottky disorder is found to be the lowest energy complete disorder process, closely matched by Be Frenkel disorder in the cases of Be12V and Be12Ti. Antitisite and X Frenkel disorder are of significantly higher energy. Small clusters of point defects including Be divacancies, Be di-interstitials and accommodation of the X species on two Be sites were considered. Some di-interstitial, divacancy and X2Be combinations exhibit negative binding enthalpy (i.e. clustering is favourable), although this is orientationally dependent. None of the Be12X intermetallics are predicted to exhibit significant non-stoichiometry, ruling out non-stoichiometry as a mechanism for accommodating Be depletion due to neutron transmutation.

Simulation of xenon, uranium vacancy and interstitial diffusion and grain boundary segregation in UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersson, Anders D.; Tonks, Michael R.; Casillas, Luis

2014-10-31

In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. Based on the mechanisms established from density functional theory (DFT) and empirical potential calculations 1, continuum models for diffusion of xenon (Xe), uranium (U) vacancies and U interstitials in UO 2 have been derived for both intrinsic conditions and under irradiation. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model for the interaction between Xe atoms and three different grain boundaries in UO 2 ( Σ5 tilt, Σ5more » twist and a high angle random boundary),as derived from atomistic calculations. All models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as redistribution for a few simple microstructures.« less

A Rate-Theory-Phase-Field Model of Irradiation-Induced Recrystallization in UMo Nuclear Fuels

NASA Astrophysics Data System (ADS)

Hu, Shenyang; Joshi, Vineet; Lavender, Curt A.

2017-12-01

In this work, we developed a recrystallization model to study the effect of microstructures and radiation conditions on recrystallization kinetics in UMo fuels. The model integrates the rate theory of intragranular gas bubble and interstitial loop evolutions and a phase-field model of recrystallization zone evolution. A first passage method is employed to describe one-dimensional diffusion of interstitials with a diffusivity value several orders of magnitude larger than that of fission gas xenons. With the model, the effect of grain sizes on recrystallization kinetics is simulated. The results show that (1) recrystallization in large grains starts earlier than that in small grains, (2) the recrystallization kinetics (recrystallization volume fraction) decrease as the grain size increases, (3) the predicted recrystallization kinetics are consistent with the experimental results, and (4) the recrystallization kinetics can be described by the modified Avrami equation, but the parameters of the Avrami equation strongly depend on the grain size.

Analysis of Dissolved Organic Nutrients in the Interstitial Water of Natural Biofilms.

PubMed

Tsuchiya, Yuki; Eda, Shima; Kiriyama, Chiho; Asada, Tomoya; Morisaki, Hisao

2016-07-01

In biofilms, the matrix of extracellular polymeric substances (EPSs) retains water in the interstitial region of the EPS. This interstitial water is the ambient environment for microorganisms in the biofilms. The nutrient condition in the interstitial water may affect microbial activity in the biofilms. In the present study, we measured the concentrations of dissolved organic nutrients, i.e., saccharides and proteins, contained in the interstitial water of biofilms formed on the stones. We also analyzed the molecular weight distribution, chemical species, and availability to bacteria of some saccharides in the interstitial water. Colorimetric assays showed that the concentrations of saccharides and proteins in the biofilm interstitial water were significantly higher (ca. 750 times) than those in the surrounding lake waters (p < 0.05). Chromatographic analyses demonstrated that the saccharides in the interstitial waters were mainly of low molecular-weight saccharides such as glucose and maltose, while proteins in the interstitial water were high molecular-weight proteins (over 7000 Da). Bacterial growth and production of EPS occurred simultaneously with the decrease in the low molecular-weight saccharide concentrations when a small portion of biofilm suspension was inoculated to the collected interstitial water, suggesting that the dissolved saccharides in the interstitial water support bacterial growth and formation of biofilms.

Laser acceleration of electrons to giga-electron-volt energies using highly charged ions.

PubMed

Hu, S X; Starace, Anthony F

2006-06-01

The recent proposal to use highly charged ions as sources of electrons for laser acceleration [S. X. Hu and A. F. Starace, Phys. Rev. Lett. 88, 245003 (2002)] is investigated here in detail by means of three-dimensional, relativistic Monte Carlo simulations for a variety of system parameters, such as laser pulse duration, ionic charge state, and laser focusing spot size. Realistic laser focusing effects--e.g., the existence of longitudinal laser field components-are taken into account. Results of spatial averaging over the laser focus are also presented. These numerical simulations show that the proposed scheme for laser acceleration of electrons from highly charged ions is feasible with current or near-future experimental conditions and that electrons with GeV energies can be obtained in such experiments.

a Study of Dynamic Powder Consolidation Based on a Particle-Level Mathematical Model.

NASA Astrophysics Data System (ADS)

Williamson, Richard L.

A mathematical model is developed to investigate the effects of large amplitude shock waves on powder materials during dynamic consolidation. The model is constructed at the particle level, focusing on a region containing a few powder particles and the surrounding interstices. The general equations of continuum mechanics are solved over this region, using initial and boundary conditions appropriate for the consolidation process. Closure of the equation system is obtained using an analytical equation of state; relations are included to account for solid to liquid phase changes. An elastic, perfectly-plastic constitutive law, specifically modified to describe material behavior at high-strain-rates, is applied to the solid materials. To reduce complexity, the model is restricted to two dimensions, therefore individual particles are approximated as infinitely long cylinders rather than spheres. The equation system is solved using standard finite-difference numerical techniques. It is demonstrated that for typical consolidation conditions, energy diffusion mechanisms are insignificant during the rapid densification phase of consolidation. Using type 304 stainless steel powder material, the particle-level model is used to investigate the mechanisms responsible for particle surface heating and metallurgical bonding during consolidation. It is demonstrated that energy deposition near particle surfaces results both from rapid particle deformation during interstitial filling and large localized impacts occurring at the final instant of interstitial closure; particle interior regions remain at sufficiently low temperatures to avoid microstructural modification. Nonuniform metallurgical bonding is predicted around the particle periphery, ranging from complete fusion to mechanical abutment. Simulation results are used to investigate the detailed wave propagation phenomena at the particle level, providing an improved understanding of this complex behavior. A variety of parametric studies are conducted including investigations of the effects of stress wave amplitude and rise time, the role of interstitial gases during consolidation, and various geometric aspects including the importance of initial void fraction. The model is applied to a metal matrix composite system to investigate the consolidation of mixtures of differing materials; results of a two-dimensional experiment are included. Available experimental data are compared with simulation results. In general, very good agreement between simulation results and data is obtained.

Simulation of Temperature Field Distribution for Cutting the Temperated Glass by Ultraviolet Laser

NASA Astrophysics Data System (ADS)

Yang, B. J.; He, Y. C.; Dai, F.; Lin, X. C.

2017-03-01

The finite element software ANSYS was adopted to simulate the temperature field distribution for laser cutting tempered glass, and the influence of different process parameters, including laser power, glass thickness and cutting speed, on temperature field distribution was studied in detail. The results show that the laser power has a greater influence on temperature field distribution than other paremeters, and when the laser power gets to 60W, the highest temperature reaches 749°C, which is higher than the glass softening temperature. It reflects the material near the laser spot is melted and the molten slag is removed by the high-energy water beam quickly. Finally, through the water guided laser cutting tempered glass experiment the FEM theoretical analysis was verified.

Simulation of free-electron lasers seeded with broadband radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bajlekov, Svetoslav; Fawley, William; Schroeder, Carl

2011-03-10

The longitudinal coherence of free-electron laser (FEL) radiation can be enhanced by seeding the FEL with high harmonics of an optical laser pulse. The radiation produced by high-harmonic generation (HHG), however, has a fast-varying temporal profile that can violate the slowly varying envelope approximation and limited frequency window that is employed in conventional free-electron laser simulation codes. Here we investigate the implications of violating this approximation on the accuracy of simulations. On the basis of both analytical considerations and 1D numerical studies, it is concluded that, for most realistic scenarios, conventional FEL codes are capable of accurately simulating the FELmore » process even when the seed radiation violates the slowly varying envelope approximation. We additionally discuss the significance of filtering the harmonic content of broadband HHG seeds.« less

Ab initio and Molecular Dynamic models of displacement damage in crystalline and turbostratic graphite

NASA Astrophysics Data System (ADS)

McKenna, Alice

One of the functions of graphite is as a moderator in several nuclear reactor designs, including the Advanced Gas-cooled Reactor (AGR). In the reactor graphite is used to thermalise the neutrons produced in the fission reaction thus allowing a self-sustained reaction to occur. The graphite blocks, acting as the moderator, are constantly irradiated and consequently suffer damage. This thesis examines the types of damage caused using molecular dynamic (MD) simulations and ab intio calculations. Neutron damage starts with a primary knock-on atom (PKA), which is travelling so fast that it creates damage through electronic and thermal excitation (this is addressed with thermal spike simulations). When the PKA has lost energy the subsequent cascade is based on ballistic atomic displacement. These two types of simulations were performed on single crystal graphite and other carbon structures such as diamond and amorphous carbon as a comparison. The thermal spike in single crystal graphite produced results which varied from no defects to a small number of permanent defects in the structure. It is only at the high energy range that more damage is seen but these energies are less likely to occur in the nuclear reactor. The thermal spike does not create damage but it is possible that it can heal damaged sections of the graphite, which can be demonstrated with the motion of the defects when a thermal spike is applied. The cascade simulations create more damage than the thermal spike even though less energy is applied to the system. A new damage function is found with a threshold region that varies with the square root of energy in excess of the energy threshold. This is further broken down in to contributions from primary and subsequent knock-on atoms. The threshold displacement energy (TDE) is found to be Ed=25eV at 300K. In both these types of simulation graphite acts very differently to the other carbon structures. There are two types of polycrystalline graphite structures which simulations have been performed on. The difference between the two is at the grain boundaries with one having dangling bonds and the other one being bonded. The cascade showed the grain boundaries acting as a trap for the knock-on atoms which produces more damage compared with the single crystal. Finally the effects of turbostratic disorder on damage is considered. Density functional theory (DFT) was used to look at interstitials in (002) twist boundaries and how they act compared to AB stacked graphite. The results of these calculations show that the spiro interstitial is more stable in these grain boundaries, so at temperatures where the interstitial can migrate along the c direction they will segregate to (002) twist boundaries.

Application of a dislocation based model for Interstitial Free (IF) steels to typical stamping simulations

NASA Astrophysics Data System (ADS)

Carvalho Resende, T.; Balan, T.; Abed-Meraim, F.; Bouvier, S.; Sablin, S.-S.

2010-06-01

With a view to environmental, economic and safety concerns, car manufacturers need to design lighter and safer vehicles in ever shorter development times. In recent years, High Strength Steels (HSS) like Interstitial Free (IF) steels which have higher ratios of yield strength to elastic modulus, are increasingly used for sheet metal parts in automotive industry to meet the demands. Moreover, the application of sheet metal forming simulations has proven to be beneficial to reduce tool costs in the design stage and to optimize current processes. The Finite Element Method (FEM) is quite successful to simulate metal forming processes but accuracy largely depends on the quality of the material properties provided as input to the material model. Common phenomenological models roughly consist in the fitting of functions on experimental results and do not provide any predictive character for different metals from the same grade. Therefore, the use of accurate plasticity models based on physics would increase predictive capability, reduce parameter identification cost and allow for robust and time-effective finite element simulations. For this purpose, a 3D physically based model at large strain with dislocation density evolution approach was presented in IDDRG2009 by the authors [1]. This model allows the description of work-hardening's behavior for different loading paths (i.e. uni-axial tensile, simple shear and Bauschinger tests) taking into account several data from microstructure (i.e. grain size, texture, etc…). The originality of this model consists in the introduction of microstructure data in a classical phenomenological model in order to achieve work-hardening's predictive character for different metals from the same grade. Indeed, thanks to a microstructure parameter set for an Interstitial Free steel, it is possible to describe work-hardening behavior for different loading paths of other IF steels by only changing the mean grain size and the chemical composition. During sheet metal forming processes local material points may experience multi-axial and multi-path loadings. Before simulating actual industrial parts, automotive manufacturers use validation tools—e.g. the Cross-Die stamping test. Such typical stamping tests enable the evaluation of a complex distribution of strains. The work described is an implementation [2] of a 3D dislocation based model in ABAQUS/Explicit and its validation on a Finite Element (FE) Cross-Die model. In order to assess the performance and relevance of the 3D dislocation based model in the simulation of industrial forming applications, the results of thinning profiles predicted along several directions and the strain distribution were obtained and compared with experimental results for IF steels with grain sizes varying in the 8-22 μm value range.

Analysis of calibration-free wavelength-scanned wavelength modulation spectroscopy for practical gas sensing using tunable diode lasers

NASA Astrophysics Data System (ADS)

Sun, K.; Chao, X.; Sur, R.; Goldenstein, C. S.; Jeffries, J. B.; Hanson, R. K.

2013-12-01

A novel strategy has been developed for analysis of wavelength-scanned, wavelength modulation spectroscopy (WMS) with tunable diode lasers (TDLs). The method simulates WMS signals to compare with measurements to determine gas properties (e.g., temperature, pressure and concentration of the absorbing species). Injection-current-tuned TDLs have simultaneous wavelength and intensity variation, which severely complicates the Fourier expansion of the simulated WMS signal into harmonics of the modulation frequency (fm). The new method differs from previous WMS analysis strategies in two significant ways: (1) the measured laser intensity is used to simulate the transmitted laser intensity and (2) digital lock-in and low-pass filter software is used to expand both simulated and measured transmitted laser intensities into harmonics of the modulation frequency, WMS-nfm (n = 1, 2, 3,…), avoiding the need for an analytic model of intensity modulation or Fourier expansion of the simulated WMS harmonics. This analysis scheme is valid at any optical depth, modulation index, and at all values of scanned-laser wavelength. The method is demonstrated and validated with WMS of H2O dilute in air (1 atm, 296 K, near 1392 nm). WMS-nfm harmonics for n = 1 to 6 are extracted and the simulation and measurements are found in good agreement for the entire WMS lineshape. The use of 1f-normalization strategies to realize calibration-free wavelength-scanned WMS is also discussed.

Novel approach for beacon formation through simulated turbulence: initial lab-test results

NASA Astrophysics Data System (ADS)

Khizhnyak, A.; Markov, V.; Tomov, I.; Wu, F.

2010-02-01

In this paper we report the results of the analysis and experimental modeling of the target-in-the-loop (TIL) approach that is used to form a localized beacon for a laser beam propagating through turbulent atmosphere. The analogy between the TIL system and the laser cavity has been used here to simulate the process shaping the laser beacon on a remote image-resolved target with rough surface. The TIL breadboard was integrated and used for laboratory modeling of the proposed approach. This breadboard allowed to simulate the TIL arrangement with a rough-surface target and laser beam propagation through the turbulent atmospheric layer. Here we present the initial results of the performed studies.

PIC Simulation of Laser Plasma Interactions with Temporal Bandwidths

NASA Astrophysics Data System (ADS)

Tsung, Frank; Weaver, J.; Lehmberg, R.

2015-11-01

We are performing particle-in-cell simulations using the code OSIRIS to study the effects of laser plasma interactions in the presence of temperal bandwidths under conditions relevant to current and future shock ignition experiments on the NIKE laser. Our simulations show that, for sufficiently large bandwidth, the saturation level, and the distribution of hot electrons, can be effected by the addition of temporal bandwidths (which can be accomplished in experiments using smoothing techniques such as SSD or ISI). We will show that temporal bandwidth along play an important role in the control of LPI's in these lasers and discuss future directions. This work is conducted under the auspices of NRL.

Laser welding in space

NASA Technical Reports Server (NTRS)

Kaukler, W. F.; Workman, G. L.

1991-01-01

Autogenous welds in 304 stainless steel were performed by Nd-YAG laser heating in a simulated space environment. Simulation consists of welding on the NASA KC-135 aircraft to produce the microgravity and by containing the specimen in a vacuum chamber. Experimental results show that the microgravity welds are stronger, harder in the fusion zone, have deeper penetration and have a rougher surface rippling of the weld pool than one-g welds. To perform laser welding in space, a solar-pumped laser concept that significantly increases the laser conversion efficiency and makes welding viable despite the limited power availability of spacecraft is proposed.

A solar simulator-pumped atomic iodine laser

NASA Technical Reports Server (NTRS)

Lee, J. H.; Weaver, W. R.

1981-01-01

An atomic iodine laser, a candidate for the direct solar-pumped gas laser, was excited with a 4-kW beam from a xenon arc solar simulator. Continuous lasing at 1.315 micron for over 10 ms was obtained for static filling of n-C3F7I vapor. By momentarily flowing the lasant, a 30-Hz pulsed output was obtained for about 200 ms. The peak laser power observed was 4 W for which the system efficiency reached 0.1%. These results indicate that direct solar pumping of a gas laser for power conversion in space is indeed feasible.

Monte-Carlo Simulation and Measurements of Electrons, Positrons, And Gamma-Rays Generated by Laser-Solid Interactions

NASA Astrophysics Data System (ADS)

Henderson, Alexander Hastings

Lasers have grown more powerful in recent years, opening up new frontiers in physics. From early intensities of less than 1010 W/cm 2, lasers can now achieve intensities over 1021 W/cm 2. Ultraintense laser can become powerful new tools to produce relativistic electrons, positron-electron pairs, and gamma-rays. The pair production efficiency is equal to or greater than that of linear accelerators, the most common method of antimatter generation in the past. The gamma-rays and electrons produced can be highly collimated, making these interactions of interest for beam generation. Monte-Carlo particle transport simulation has long been used in physics for simulating various particle and radiation processes, and is well-suited to simulating both electromagnetic cascades resulting from laser-solid interactions and the response of electron/positron spectrometers and gamma-ray detectors. We have used GEANT4 Monte-Carlo particle transport simulation to design and calibrate charged-particle spectrometers using permanent magnets as well as a Forward Compton Electron Spectrometer to measure gamma-rays of higher energies than have previously been achieved. We have had some success simulating and measuring high positron and gamma-rays yields from laser-solid interactions using gold target at the Texas Petawatt Laser (TPW). While similar spectrometers have been developed in the past, we are to our knowledge the first to successfully use permanent magnet spectrometers to detect positrons originating from laser-solid interactions in this energy range. We believe we are also the first to successfully detect multi-MeV gamma rays using a permanent magnet Forward Compton Electron Spectrometer. Monte-Carlo particle transport simulation has been used by other groups to model positron production from laser-solid ineraction, but at the time that we began we were, as far as we know, the first to have a significant amount of empirical data to work with. We were thus at liberty to estimate the initial conditions, compare simulation results to data, and adjust as needed to obtain a better estimate of the actual initial conditions. We have also developed a new method for measuring the yield and angular distribution of gamma-rays using a two-dimensional dosimeter array. In this work, we examine the experimental and simulation results as well as the physical processes behind them. In addition, the gamma-rays produced by our experiments could be useful for photo-nuclear reactors and homeland security purposes. In our experiments, we measured narrow energy-band positrons and electrons which have potential medical uses.

Simulation and Technology of Hybrid Welding of Thick Steel Parts with High Power Fiber Laser

NASA Astrophysics Data System (ADS)

Turichin, Gleb; Valdaytseva, Ekaterina; Tzibulsky, Igor; Lopota, Alexander; Velichko, Olga

The article devoted to steady state and dynamic simulation of melt pool behavior during hybrid laser-arc welding of pipes and shipbuilding sections. The quasi-stationary process-model was used to determine an appropriate welding mode. The dynamical model of laser welding was used for investigation of keyhole depth and width oscillations. The experiments of pipe steel and stainless steel hybrid laser-MAG welding have been made with 15-kW fiber laser in wide range of welding mode parameters. Comparison of experimentally measured and simulated behavior of penetration depth as well as their oscillation spectra approved the self-oscillation nature of melt pool behavior. The welding mode influence of melt pool stability has also been observed. The technological peculiarities, which allow provide high quality weld seam, has been discussed also.

Numerical simulation of a soft-x-ray Li laser pumped with synchrotron radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rozsnyai, B.; Watanabe, H.; Csonka, P.L.

1985-07-01

Results of a computer simulation are reported for a lithium soft-x-ray laser pumped by synchro- tron radiation. Coherent stimulated emission of the photons of interest occurs in Li II 1s2p..-->..Li II 1s/sup 2/ transitions. Calculated results include the dominant ion and photon densities and the laser gain.

Atomistic simulation of laser-pulse surface modification: Predictions of models with various length and time scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Starikov, Sergey V., E-mail: starikov@ihed.ras.ru; Pisarev, Vasily V.; Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow 125412

2015-04-07

In this work, the femtosecond laser pulse modification of surface is studied for aluminium (Al) and gold (Au) by use of two-temperature atomistic simulation. The results are obtained for various atomistic models with different scales: from pseudo-one-dimensional to full-scale three-dimensional simulation. The surface modification after laser irradiation can be caused by ablation and melting. For low energy laser pulses, the nanoscale ripples may be induced on a surface by melting without laser ablation. In this case, nanoscale changes of the surface are due to a splash of molten metal under temperature gradient. Laser ablation occurs at a higher pulse energymore » when a crater is formed on the surface. There are essential differences between Al ablation and Au ablation. In the first step of shock-wave induced ablation, swelling and void formation occur for both metals. However, the simulation of ablation in gold shows an additional athermal type of ablation that is associated with electron pressure relaxation. This type of ablation takes place at the surface layer, at a depth of several nanometers, and does not induce swelling.« less

Multi-dimensional simulation package for ultrashort pulse laser-matter interactions

NASA Astrophysics Data System (ADS)

Suslova, Anastassiya; Hassanein, Ahmed

2017-10-01

Advanced simulation models recently became a popular tool of investigation of ultrashort pulse lasers (USPLs) to enhance understanding of the physics and allow minimizing the experimental costs for optimization of laser and target parameters for various applications. Our research interest is focused on developing multi-dimensional simulation package FEMTO-2D to investigate the USPL-matter interactions and laser induced effects. The package is based on solution of two heat conduction equations for electron and lattice sub-systems - enhanced two temperature model (TTM). We have implemented theoretical approach based on the collision theory to define the thermal dependence of target material optical properties and thermodynamic parameters. Our approach allowed elimination of fitted parameters commonly used in TTM based simulations. FEMTO-2D is used to simulated the light absorption and interactions for several metallic targets as a function of wavelength and pulse duration for wide range of laser intensity. The package has capability to consider different angles of incidence and polarization. It has also been used to investigate the damage threshold of the gold coated optical components with the focus on the role of the film thickness and substrate heat sink effect. This work was supported by the NSF, PIRE project.

Two-dimensional simulation of high-power laser-surface interaction

NASA Astrophysics Data System (ADS)

Goldman, S. Robert; Wilke, Mark D.; Green, Ray E.; Busch, George E.; Johnson, Randall P.

1998-09-01

For laser intensities in the range of 108 - 109 W/cm2, and pulse lengths of order 10 microseconds or longer, we have modified the inertial confinement fusion code Lasnex to simulate gaseous and some dense material aspects of the laser-matter interaction. The unique aspect of our treatment consists of an ablation model which defines a dense material-vapor interface and then calculates the mass flow across this interface. The model treats the dense material as a rigid two-dimensional mass and heat reservoir suppressing all hydrodynamic motion in the dense material. The computer simulations and additional post-processors provide predictions for measurements including impulse given to the target, pressures at the target interface, electron temperatures and densities in the vapor-plasma plume region, and emission of radiation from the target. We will present an analysis of some relatively well diagnosed experiments which have been useful in developing our modeling. The simulations match experimentally obtained target impulses, pressures at the target surface inside the laser spot, and radiation emission from the target to within about 20%. Hence our simulational technique appears to form a useful basis for further investigation of laser-surface interaction in this intensity, pulse-width range.

Interstitial distribution of charged macromolecules in the dog lung: a kinetic model.

PubMed

Parker, J C; Miniati, M; Pitt, R; Taylor, A E

1987-01-01

A mathematic model was constructed to investigate conflicting physiologic data concerning the charge effect of continuous capillaries to macromolecules in the lung. We simulated the equilibration kinetics of lactate dehydrogenase (MR 4.2 nM) isozymes LDH 1 (pI = 5.0) and LDH 5 (pI = 7.9) between plasma and lymph using previously measured permeability coefficients, lung tissue distribution volumes (VA) and plasma concentrations (CP) in lung tissue. Our hypothesis is that the fixed anionic charges in interstitium, basement membrane, and cell surfaces determine equilibration rather than charged membrane effects at the capillary barrier, so the same capillary permeability coefficients were used for both isozymes. Capillary filtration rates and protein fluxes were calculated using conventional flux equations. Initial conditions at baseline and increased left atrial pressures (PLA) were those measured in animal studies. Simulated equilibration of isozymes over 30 h in the model at baseline capillary pressures accurately predicted the observed differences in lymph/plasma concentration ratios (CL/CP) between isotopes at 4 h and equilibration of these ratios at 24 h. Quantitative prediction of isozyme CL/CP ratios was also obtained at increased PLA. However, an additional cation selective compartment representing the surface glycocalyx was required to accurately simulate the initial higher transcapillary clearances of cationic LDH 5. Thus experimental data supporting the negative barrier, positive barrier, and no charge barrier hypotheses were accurately reproduced by the model using only the observed differences in interstitial partitioning of isozymes without differences in capillary selectivity.

Statistical study of defects caused by primary knock-on atoms in fcc Cu and bcc W using molecular dynamics

NASA Astrophysics Data System (ADS)

Warrier, M.; Bhardwaj, U.; Hemani, H.; Schneider, R.; Mutzke, A.; Valsakumar, M. C.

2015-12-01

We report on molecular Dynamics (MD) simulations carried out in fcc Cu and bcc W using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code to study (i) the statistical variations in the number of interstitials and vacancies produced by energetic primary knock-on atoms (PKA) (0.1-5 keV) directed in random directions and (ii) the in-cascade cluster size distributions. It is seen that around 60-80 random directions have to be explored for the average number of displaced atoms to become steady in the case of fcc Cu, whereas for bcc W around 50-60 random directions need to be explored. The number of Frenkel pairs produced in the MD simulations are compared with that from the Binary Collision Approximation Monte Carlo (BCA-MC) code SDTRIM-SP and the results from the NRT model. It is seen that a proper choice of the damage energy, i.e. the energy required to create a stable interstitial, is essential for the BCA-MC results to match the MD results. On the computational front it is seen that in-situ processing saves the need to input/output (I/O) atomic position data of several tera-bytes when exploring a large number of random directions and there is no difference in run-time because the extra run-time in processing data is offset by the time saved in I/O.

Simulated full-waveform lidar compared to Riegl VZ-400 terrestrial laser scans

NASA Astrophysics Data System (ADS)

Kim, Angela M.; Olsen, Richard C.; Béland, Martin

2016-05-01

A 3-D Monte Carlo ray-tracing simulation of LiDAR propagation models the reflection, transmission and ab- sorption interactions of laser energy with materials in a simulated scene. In this presentation, a model scene consisting of a single Victorian Boxwood (Pittosporum undulatum) tree is generated by the high-fidelity tree voxel model VoxLAD using high-spatial resolution point cloud data from a Riegl VZ-400 terrestrial laser scanner. The VoxLAD model uses terrestrial LiDAR scanner data to determine Leaf Area Density (LAD) measurements for small volume voxels (20 cm sides) of a single tree canopy. VoxLAD is also used in a non-traditional fashion in this case to generate a voxel model of wood density. Information from the VoxLAD model is used within the LiDAR simulation to determine the probability of LiDAR energy interacting with materials at a given voxel location. The LiDAR simulation is defined to replicate the scanning arrangement of the Riegl VZ-400; the resulting simulated full-waveform LiDAR signals compare favorably to those obtained with the Riegl VZ-400 terrestrial laser scanner.

Laser cooling of molecular anions.

PubMed

Yzombard, Pauline; Hamamda, Mehdi; Gerber, Sebastian; Doser, Michael; Comparat, Daniel

2015-05-29

We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_{2}^{-}, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped C_{2}^{-}, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.

A numerical simulation of machining glass by dual CO 2-laser beams

NASA Astrophysics Data System (ADS)

Jiao, Junke; Wang, Xinbing

2008-03-01

In the flat panel display (FPD) industry, lasers may be used to cut glass plates. In order to reduce the possibility of fracture in the process of cutting glass by lasers, the thermal stress has to be less than the critical rupture strength. In this paper, a dual-laser-beam method is proposed, where an off-focus CO 2-laser beam was used to preheat the glass sample to reduce the thermal gradients and a focused CO 2-laser beam was used to machine the glass. The distribution of the thermal stress and the temperature was simulated by using finite element analysis software, Ansys. The thermal stress was studied both when the glass sample was machined by a single CO 2-laser beam and by dual CO 2-laser beams. It was concluded that the thermal stress can be reduced by means of the dual-laser-beam method.

Physiological water model development

NASA Technical Reports Server (NTRS)

Doty, Susan

1993-01-01

The water of the human body can be categorized as existing in two main compartments: intracellular water and extracellular water. The intracellular water consists of all the water within the cells and constitutes over half of the total body water. Since red blood cells are surrounded by plasma, and all other cells are surrounded by interstitial fluid, the intracellular compartment has been subdivided to represent these two cell types. The extracellular water, which includes all of the fluid outside of the cells, can be further subdivided into compartments which represent the interstitial fluid, circulating blood plasma, lymph, and transcellular water. The interstitial fluid surrounds cells outside of the vascular system whereas plasma is contained within the blood vessels. Avascular tissues such as dense connective tissue and cartilage contain interstitial water which slowly equilibrates with tracers used to determine extracellular fluid volume. For this reason, additional compartments are sometimes used to represent these avascular tissues. The average size of each compartment, in terms of percent body weight, has been determined for adult males and females. These compartments and the forces which cause flow between them are presented. The kidneys, a main compartment, receive about 25 percent of the cardiac output and filters out a fluid similar to plasma. The composition of this filtered fluid changes as it flows through the kidney tubules since compounds are continually being secreted and reabsorbed. Through this mechanism, the kidneys eliminate wastes while conserving body water, electrolytes, and metabolites. Since sodium accounts for over 90 percent of the cations in the extracellular fluid, and the number of cations is balanced by the number of anions, considering the renal handling sodium and water only should sufficiently describe the relationship between the plasma compartment and kidneys. A kidney function model is presented which has been adapted from a previous model of normal renal function in man. To test the validity of the proposed kidney model, results predicted by the model will be compared to actual data involving injected or ingested fluids and subsequent urine flow rates. Comparison of the model simulation to actual data following the ingestion of 1 liter of water is shown. The model simulation is also shown with actual data following the intravenous infusion of hypertonic saline.

Quasi-monoenergetic ion generation by hole-boring radiation pressure acceleration in inhomogeneous plasmas using tailored laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weng, S. M., E-mail: weng-sm@ile.osaka-u.ac.jp; Murakami, M.; Azechi, H.

It is proposed that laser hole-boring at a steady speed in inhomogeneous overdense plasma can be realized by the use of temporally tailored intense laser pulses, producing high-fluence quasi-monoenergetic ion beams. A general temporal profile of such laser pulses is formulated for arbitrary plasma density distribution. As an example, for a precompressed deuterium-tritium fusion target with an exponentially increasing density profile, its matched laser profile for steady hole-boring is given theoretically and verified numerically by particle-in-cell simulations. Furthermore, we propose to achieve fast ignition by the in-situ hole-boring accelerated ions using a tailored laser pulse. Simulations show that the effectivemore » energy fluence, conversion efficiency, energy spread, and collimation of the resulting ion beam can be significantly improved as compared to those found with un-tailored laser profiles. For the fusion fuel with an areal density of 1.5 g cm{sup –2}, simulation indicates that it is promising to realize fast ion ignition by using a tailored driver pulse with energy about 65 kJ.« less

FLASH hydrodynamic simulations of experiments to explore the generation of cosmological magnetic fields

NASA Astrophysics Data System (ADS)

Scopatz, A.; Fatenejad, M.; Flocke, N.; Gregori, G.; Koenig, M.; Lamb, D. Q.; Lee, D.; Meinecke, J.; Ravasio, A.; Tzeferacos, P.; Weide, K.; Yurchak, R.

2013-03-01

We report the results of FLASH hydrodynamic simulations of the experiments conducted by the University of Oxford High Energy Density Laboratory Astrophysics group and its collaborators at the Laboratoire pour l'Utilisation de Lasers Intenses (LULI). In these experiments, a long-pulse laser illuminates a target in a chamber filled with Argon gas, producing shock waves that generate magnetic fields via the Biermann battery mechanism. The simulations show that the result of the laser illuminating the target is a series of complex hydrodynamic phenomena.

Diagnostics of Particles emitted from a Laser generated Plasma: Experimental Data and Simulations

NASA Astrophysics Data System (ADS)

Costa, Giuseppe; Torrisi, Lorenzo

2018-01-01

The charge particle emission form laser-generated plasma was studied experimentally and theoretically using the COMSOL simulation code. The particle acceleration was investigated using two lasers at two different regimes. A Nd:YAG laser, with 3 ns pulse duration and 1010 W/cm2 intensity, when focused on solid target produces a non-equilibrium plasma with average temperature of about 30-50 eV. An Iodine laser with 300 ps pulse duration and 1016 W/cm2 intensity produces plasmas with average temperatures of the order of tens keV. In both cases charge separation occurs and ions and electrons are accelerated at energies of the order of 200 eV and 1 MeV per charge state in the two cases, respectively. The simulation program permits to plot the charge particle trajectories from plasma source in vacuum indicating how they can be deflected by magnetic and electrical fields. The simulation code can be employed to realize suitable permanent magnets and solenoids to deflect ions toward a secondary target or detectors, to focalize ions and electrons, to realize electron traps able to provide significant ion acceleration and to realize efficient spectrometers. In particular it was applied to the study two Thomson parabola spectrometers able to detect ions at low and at high laser intensities. The comparisons between measurements and simulation is presented and discussed.

Laser acceleration of electrons to giga-electron-volt energies using highly charged ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, S. X.; Starace, Anthony F.

2006-06-15

The recent proposal to use highly charged ions as sources of electrons for laser acceleration [S. X. Hu and A. F. Starace, Phys. Rev. Lett. 88, 245003 (2002)] is investigated here in detail by means of three-dimensional, relativistic Monte Carlo simulations for a variety of system parameters, such as laser pulse duration, ionic charge state, and laser focusing spot size. Realistic laser focusing effects--e.g., the existence of longitudinal laser field components--are taken into account. Results of spatial averaging over the laser focus are also presented. These numerical simulations show that the proposed scheme for laser acceleration of electrons from highlymore » charged ions is feasible with current or near-future experimental conditions and that electrons with GeV energies can be obtained in such experiments.« less

High coupling efficiency of foam spherical hohlraum driven by 2ω laser light

NASA Astrophysics Data System (ADS)

Chen, Yao-Hua; Lan, Ke; Zheng, Wanguo; Campbell, E. M.

2018-02-01

The majority of solid state laser facilities built for laser fusion research irradiate targets with third harmonic light (0.35 μm) up-converted from the fundamental Nd wavelength at 1.05 μm. The motivation for this choice of wavelength is improved laser-plasma coupling. Significant disadvantages to this choice of wavelength are the reduced damage threshold of optical components and the efficiency of energy conversion to third harmonic light. Both these issues are significantly improved if second harmonic (0.53 μm) radiation is used, but theory and experiments have shown lower optical to x-ray energy conversion efficiency and increased levels of laser-plasma instabilities, resulting in reduced laser-target coupling. In this letter, we propose to use a 0.53 μm laser for the laser ignition facilities and use a low density foam wall to increase the coupling efficiency from the laser to the capsule and present two-dimensional radiation-hydrodynamic simulations of 0.53 μm laser light irradiating an octahedral-spherical hohlraum with a low density foam wall. The simulations show that the reduced optical depth of the foam wall leads to an increased laser-light conversion into thermal x-rays and about 10% higher radiation flux on the capsule than that achieved with 0.35 μm light irradiating a solid density wall commonly used in laser indirect drive fusion research. The details of the simulations and their implications and suggestions for wavelength scaling coupled with innovative hohlraum designs will be discussed.

First-principles simulation for strong and ultra-short laser pulse propagation in dielectrics

NASA Astrophysics Data System (ADS)

Yabana, K.

2016-05-01

We develop a computational approach for interaction between strong laser pulse and dielectrics based on time-dependent density functional theory (TDDFT). In this approach, a key ingredient is a solver to simulate electron dynamics in a unit cell of solids under a time-varying electric field that is a time-dependent extension of the static band calculation. This calculation can be regarded as a constitutive relation, providing macroscopic electric current for a given electric field applied to the medium. Combining the solver with Maxwell equations for electromagnetic fields of the laser pulse, we describe propagation of laser pulses in dielectrics without any empirical parameters. An important output from the coupled Maxwell+TDDFT simulation is the energy transfer from the laser pulse to electrons in the medium. We have found an abrupt increase of the energy transfer at certain laser intensity close to damage threshold. We also estimate damage threshold by comparing the transferred energy with melting and cohesive energies. It shows reasonable agreement with measurements.

Patterns of interstitial lung disease during everolimus treatment in patients with metastatic renal cell carcinoma.

PubMed

Mizuno, Ryuichi; Asano, Koichiro; Mikami, Shuji; Nagata, Hirohiko; Kaneko, Gou; Oya, Mototsugu

2012-05-01

To elucidate the patterns of interstitial lung disease during everolimus treatment in patients with metastatic renal cell carcinoma, we reviewed seven cases of everolimus-induced interstitial lung disease. Seven patients with metastatic renal cell carcinoma, which continued to progress despite treatment with sunitinib or sorafenib, developed interstitial lung disease after treatment with everolimus. Chest X-ray demonstrated diffuse infiltrates in lung fields, and chest computed tomography showed bilateral reticular and ground-glass opacities. Serum levels of lactate dehydrogenase (7/7), C-reactive protein (6/7), pulmonary surfactant associated protein D (1/7) and Krebs von den Lungen 6 (5/7) were elevated. The bronchoalveolar lavage fluid obtained from four patients with Grade 3 interstitial lung disease showed lymphocytosis. The transbronchial lung biopsy specimens showed interstitial lymphocytic infiltration and septal thickening of alveolar walls. In two cases with mild interstitial lung disease, the everolimus therapy was successfully continued. In four cases with Grade 3 interstitial lung disease, the drug was discontinued and steroid therapy was initiated. Pulmonary symptoms and radiological abnormalities resolved within 2 months. Serum Krebs von den Lungen 6 was elevated compared with baseline in all cases with interstitial lung disease. Some patients who developed mild interstitial lung disease during everolimus treatment could continue to receive the treatment. Even when severe interstitial lung disease developed, withdrawal of the drug and short-term use of high-dose steroids resulted in rapid recovery. Prompt recognition of interstitial lung disease exacerbation as well as exclusion of progressive disease or infection is of primary importance.

Changes in the interstitial fluid and the muscle water in rabbits in hemorrhagic shock.

PubMed Central

Wolcott, M W; Malinin, T I; Wu, N M

1976-01-01

Dynamics and changes in the biochemical composition in the interstitial fluid and the muscle water were studied in hemorrhagic shock. The interstitial fluid was collected from implanted perforated capsules. Muscle biopsies were examined with regard to their water content by the steady state magnetic nuclear resonance spectroscopy. The consistent and what appears to be the most significant changes were the fall in the interstitial fluid pressures, the quantitative reduction of muscle water, a sharp fall in the blood and interstitial blood pH, the moderate hyperkalemia and lack of change in blood an interstitial fluid sodium, and the rise in blood glucose levels not accompanied by a rise in the interstitial fluid glucose levels. PMID:11754

Nuclear-Pumped Lasers. [efficient conversion of energy liberated in nuclear reactions to coherent radiation

NASA Technical Reports Server (NTRS)

1979-01-01

The state of the art in nuclear pumped lasers is reviewed. Nuclear pumped laser modeling, nuclear volume and foil excitation of laser plasmas, proton beam simulations, nuclear flashlamp excitation, and reactor laser systems studies are covered.

TEA CO 2 Laser Simulator: A software tool to predict the output pulse characteristics of TEA CO 2 laser

NASA Astrophysics Data System (ADS)

Abdul Ghani, B.

2005-09-01

"TEA CO 2 Laser Simulator" has been designed to simulate the dynamic emission processes of the TEA CO 2 laser based on the six-temperature model. The program predicts the behavior of the laser output pulse (power, energy, pulse duration, delay time, FWHM, etc.) depending on the physical and geometrical input parameters (pressure ratio of gas mixture, reflecting area of the output mirror, media length, losses, filling and decay factors, etc.). Program summaryTitle of program: TEA_CO2 Catalogue identifier: ADVW Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADVW Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: P.IV DELL PC Setup: Atomic Energy Commission of Syria, Scientific Services Department, Mathematics and Informatics Division Operating system: MS-Windows 9x, 2000, XP Programming language: Delphi 6.0 No. of lines in distributed program, including test data, etc.: 47 315 No. of bytes in distributed program, including test data, etc.:7 681 109 Distribution format:tar.gz Classification: 15 Laser Physics Nature of the physical problem: "TEA CO 2 Laser Simulator" is a program that predicts the behavior of the laser output pulse by studying the effect of the physical and geometrical input parameters on the characteristics of the output laser pulse. The laser active medium consists of a CO 2-N 2-He gas mixture. Method of solution: Six-temperature model, for the dynamics emission of TEA CO 2 laser, has been adapted in order to predict the parameters of laser output pulses. A simulation of the laser electrical pumping was carried out using two approaches; empirical function equation (8) and differential equation (9). Typical running time: The program's running time mainly depends on both integration interval and step; for a 4 μs period of time and 0.001 μs integration step (defaults values used in the program), the running time will be about 4 seconds. Restrictions on the complexity: Using a very small integration step might leads to stop the program run due to the huge number of calculating points and to a small paging file size of the MS-Windows virtual memory. In such case, it is recommended to enlarge the paging file size to the appropriate size, or to use a bigger value of integration step.

Active illuminated space object imaging and tracking simulation

NASA Astrophysics Data System (ADS)

Yue, Yufang; Xie, Xiaogang; Luo, Wen; Zhang, Feizhou; An, Jianzhu

2016-10-01

Optical earth imaging simulation of a space target in orbit and it's extraction in laser illumination condition were discussed. Based on the orbit and corresponding attitude of a satellite, its 3D imaging rendering was built. General simulation platform was researched, which was adaptive to variable 3D satellite models and relative position relationships between satellite and earth detector system. Unified parallel projection technology was proposed in this paper. Furthermore, we denoted that random optical distribution in laser-illuminated condition was a challenge for object discrimination. Great randomicity of laser active illuminating speckles was the primary factor. The conjunction effects of multi-frame accumulation process and some tracking methods such as Meanshift tracking, contour poid, and filter deconvolution were simulated. Comparison of results illustrates that the union of multi-frame accumulation and contour poid was recommendable for laser active illuminated images, which had capacities of high tracking precise and stability for multiple object attitudes.

Responses of human sensory characteristics to 532 nm pulse laser stimuli.

PubMed

Kim, Ji-Sun; Oh, Han-Byeol; Kim, A-Hee; Kim, Jun-Sik; Lee, Eun-Suk; Goh, Bong-Jun; Kim, Jae-Young; Jang, Kyungmin; Park, Jong-Rak; Chung, Soon-Cheol; Jun, Jae-Hoon

2016-04-29

Lasers are advantageous in some applications to stimulate a small target area and is used in various fields such as optogenetic, photoimmunological and neurophysiological studies. This study aims to implement a non-contact sense of touch without damaging biological tissues using laser. Various laser parameters were utilized in safety range to induce a sense of touch and investigate the human responses. With heat distribution simulation, the amount of changes in the temperature and the tendency in laser parameters of sensory stimulation were analyzed. The results showed the identified tactile responses in safety range with various laser parameters and temperature distribution for the laser stimulus was obtained through the simulation. This study can be applied to the areas of sensory receptor stimulation, neurophysiology and clinical medicine.

[Airway-centered interstitial fibrosis related to exposure to fumes from cleaning products].

PubMed

Serrano, Mario; Molina-Molina, María; Ramírez, José; Sánchez, Marcelo; Xaubet, Antoni

2006-10-01

Airway-centered interstitial fibrosis is a little known clinical entity that has only recently been described in the literature. Its pathology is characterized by bronchial fibrosis and localized interstitial pulmonary fibrosis around the airways. The disease has been associated with inhalation of a variety of substances, environmental or occupational, organic or inorganic. Clinical signs, radiographic manifestations, and lung function in patients with airway-centered interstitial fibrosis are similar to those of patients with idiopathic interstitial pneumonia. We describe a case of airway-centered interstitial fibrosis related to exposure to fumes from cleaning products.

Numerical Simulations of Thick Aluminum Wire Behavior Under Megampere Current Drive

DTIC Science & Technology

2009-06-01

time dependences of the wire radii agree rather well with the experimental results obtained using laser diagnostics and light imaging. The...simulated time dependences of the wire radii agree rather well with the experimental results obtained using laser diagnostics and light imaging. The...experiments involved a wide range of diagnostics , including current probes, streaked imaging of optical emission, 4-frame laser shadowgraphy, fast

Laser propagation and soliton generation in strongly magnetized plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, W.; Li, J. Q.; Kishimoto, Y.

The propagation characteristics of various laser modes with different polarization, as well as the soliton generation in strongly magnetized plasmas are studied numerically through one-dimensional (1D) particle-in-cell (PIC) simulations and analytically by solving the laser wave equation. PIC simulations show that the laser heating efficiency substantially depends on the magnetic field strength, the propagation modes of the laser pulse and their intensities. Generally, large amplitude laser can efficiently heat the plasma with strong magnetic field. Theoretical analyses on the linear propagation of the laser pulse in both under-dense and over-dense magnetized plasmas are well confirmed by the numerical observations. Mostmore » interestingly, it is found that a standing or moving soliton with frequency lower than the laser frequency is generated in certain magnetic field strength and laser intensity range, which can greatly enhance the laser heating efficiency. The range of magnetic field strength for the right-hand circularly polarized (RCP) soliton formation with high and low frequencies is identified by solving the soliton equations including the contribution of ion's motion and the finite temperature effects under the quasi-neutral approximation. In the limit of immobile ions, the RCP soliton tends to be peaked and stronger as the magnetic field increases, while the enhanced soliton becomes broader as the temperature increases. These findings in 1D model are well validated by 2D simulations.« less

Aerosol Processing in Mixed-Phase Clouds in ECHAM5-HAM: Comparison of Single-Column Model Simulations to Observations

NASA Astrophysics Data System (ADS)

Hoose, C.; Lohmann, U.; Stier, P.; Verheggen, B.; Weingartner, E.; Herich, H.

2007-12-01

The global aerosol-climate model ECHAM5-HAM (Stier et al., 2005) has been extended by an explicit treatment of cloud-borne particles. Two additional modes for in-droplet and in-crystal particles are introduced, which are coupled to the number of cloud droplet and ice crystal concentrations simulated by the ECHAM5 double-moment cloud microphysics scheme (Lohmann et al., 2007). Transfer, production and removal of cloud-borne aerosol number and mass by cloud droplet activation, collision scavenging, aqueous-phase sulfate production, freezing, melting, evaporation, sublimation and precipitation formation are taken into account. The model performance is demonstrated and validated with observations of the evolution of total and interstitial aerosol concentrations and size distributions during three different mixed-phase cloud events at the alpine high-altitude research station Jungfraujoch (Switzerland) (Verheggen et al, 2007). Although the single-column simulations can not be compared one-to-one with the observations, the governing processes in the evolution of the cloud and aerosol parameters are captured qualitatively well. High scavenged fractions are found during the presence of liquid water, while the release of particles during the Bergeron-Findeisen process results in low scavenged fractions after cloud glaciation. The observed coexistence of liquid and ice, which might be related to cloud heterogeneity at subgrid scales, can only be simulated in the model when forcing non-equilibrium conditions. References: U. Lohmann et al., Cloud microphysics and aerosol indirect effects in the global climate model ECHAM5-HAM, Atmos. Chem. Phys. 7, 3425-3446 (2007) P. Stier et al., The aerosol-climate model ECHAM5-HAM, Atmos. Chem. Phys. 5, 1125-1156 (2005) B. Verheggen et al., Aerosol partitioning between the interstitial and the condensed phase in mixed-phase clouds, Accepted for publication in J. Geophys. Res. (2007)

Estimated home ranges can misrepresent habitat relationships on patchy landscapes

USGS Publications Warehouse

Mitchell, M.S.; Powell, R.A.

2008-01-01

Home ranges of animals are generally structured by the selective use of resource-bearing patches that comprise habitat. Based on this concept, home ranges of animals estimated from location data are commonly used to infer habitat relationships. Because home ranges estimated from animal locations are largely continuous in space, the resource-bearing patches selected by an animal from a fragmented distribution of patches would be difficult to discern; unselected patches included in the home range estimate would bias an understanding of important habitat relationships. To evaluate potential for this bias, we generated simulated home ranges based on optimal selection of resource-bearing patches across a series of simulated resource distributions that varied in the spatial continuity of resources. For simulated home ranges where selected patches were spatially disjunct, we included interstitial, unselected cells most likely to be traveled by an animal moving among selected patches. We compared characteristics of the simulated home ranges with and without interstitial patches to evaluate how insights derived from field estimates can differ from actual characteristics of home ranges, depending on patchiness of landscapes. Our results showed that contiguous home range estimates could lead to misleading insights on the quality, size, resource content, and efficiency of home ranges, proportional to the spatial discontinuity of resource-bearing patches. We conclude the potential bias of including unselected, largely irrelevant patches in the field estimates of home ranges of animals can be high, particularly for home range estimators that assume uniform use of space within home range boundaries. Thus, inferences about the habitat relationships that ultimately define an animal's home range can be misleading where animals occupy landscapes with patchily distributed resources.

Atomistic characterisation of Li+ mobility and conductivity in Li(7-x)PS(6-x)Ix argyrodites from molecular dynamics simulations, solid-state NMR, and impedance spectroscopy.

PubMed

Pecher, Oliver; Kong, Shiao-Tong; Goebel, Thorsten; Nickel, Vera; Weichert, Katja; Reiner, Christof; Deiseroth, Hans-Jörg; Maier, Joachim; Haarmann, Frank; Zahn, Dirk

2010-07-26

The atomistic mechanisms of Li(+) ion mobility/conductivity in Li(7-x)PS(6-x)I(x) argyrodites are explored from both experimental and theoretical viewpoints. Ionic conductivity in the title compound is associated with a solid-solid phase transition, which was characterised by low-temperature differential scanning calorimetry, (7)Li and (127)I NMR investigations, impedance measurements and molecular dynamics simulations. The NMR signals of both isotopes are dominated by anisotropic interactions at low temperatures. A significant narrowing of the NMR signal indicates a motional averaging of the anisotropic interactions above 177+/-2 K. The activation energy to ionic conductivity was assessed from both impedance spectroscopy and molecular dynamics simulations. The latter revealed that a series of interstitial sites become accessible to the Li(+) ions, whilst the remaining ions stay at their respective sites in the argyrodite lattice. The interstitial positions each correspond to the centres of tetrahedra of S/I atoms, and differ only in terms of their common corners, edges, or faces with adjacent PS(4) tetrahedra. From connectivity analyses and free-energy rankings, a specific tetrahedron is identified as the key restriction to ionic conductivity, and is clearly differentiated from local mobility, which follows a different mechanism with much lower activation energy. Interpolation of the lattice parameters as derived from X-ray diffraction experiments indicates a homogeneity range for Li(7-x)PS(6-x)I(x) with 0.97 < or = x < or = 1.00. Within this range, molecular dynamics simulations predict Li(+) conductivity at ambient conditions to vary considerably.

Single-particle aerosol mass spectrometry for the detection and identification of chemical warfare agent simulants.

PubMed

Martin, Audrey N; Farquar, George R; Frank, Matthias; Gard, Eric E; Fergenson, David P

2007-08-15

Single-particle aerosol mass spectrometry (SPAMS) was used for the real-time detection of liquid nerve agent simulants. A total of 1000 dual-polarity time-of-flight mass spectra were obtained for micrometer-sized single particles each of dimethyl methyl phosphonate, diethyl ethyl phosphonate, diethyl phosphoramidate, and diethyl phthalate using laser fluences between 0.58 and 7.83 nJ/microm2, and mass spectral variation with laser fluence was studied. The mass spectra obtained allowed identification of single particles of the chemical warfare agent (CWA) simulants at each laser fluence used although lower laser fluences allowed more facile identification. SPAMS is presented as a promising real-time detection system for the presence of CWAs.

Sidelooking laser altimeter for a flight simulator

NASA Technical Reports Server (NTRS)

Webster, L. D. (Inventor)

1983-01-01

An improved laser altimeter for a flight simulator which allows measurement of the height of the simulator probe above the terrain directly below the probe tip is described. A laser beam is directed from the probe at an angle theta to the horizontal to produce a beam spot on the terrain. The angle theta that the laser beam makes with the horizontal is varied so as to bring the beam spot into coincidence with a plumb line coaxial with the longitudinal axis of the probe. A television altimeter camera observes the beam spot and has a raster line aligned with the plumb line. Spot detector circuit coupled to the output of the TV camera monitors the position of the beam spot relative to the plumb line.

Simulation studies of vapor bubble generation by short-pulse lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amendt, P.; London, R.A.; Strauss, M.

1997-10-26

Formation of vapor bubbles is characteristic of many applications of short-pulse lasers in medicine. An understanding of the dynamics of vapor bubble generation is useful for developing and optimizing laser-based medical therapies. To this end, experiments in vapor bubble generation with laser light deposited in an aqueous dye solution near a fiber-optic tip have been performed. Numerical hydrodynamic simulations have been developed to understand and extrapolate results from these experiments. Comparison of two-dimensional simulations with the experiment shows excellent agreement in tracking the bubble evolution. Another regime of vapor bubble generation is short-pulse laser interactions with melanosomes. Strong shock generationmore » and vapor bubble generation are common physical features of this interaction. A novel effect of discrete absorption by melanin granules within a melanosome is studied as a possible role in previously reported high Mach number shocks.« less

Solar-simulator-pumped atomic iodine laser kinetics

NASA Technical Reports Server (NTRS)

Wilson, H. W.; Raju, S.; Shiu, Y. J.

1983-01-01

The literature contains broad ranges of disagreement in kinetic data for the atomic iodine laser. A kinetic model of a solar-simulator-pumped iodine laser is used to select those kinetic data consistent with recent laser experiments at the Langley Research Center. Analysis of the solar-simulator-pumped laser experiments resulted in the following estimates of rate coefficients: for alkyl radical (n-C3F7) and atomic iodine (I) recombination, 4.3 x 10 to the 11th power (1.9) + or - cu cm/s; for n-C3F7I stabilized atomic iodine recombination (I + I) 3.7 x 10 to the -32nd power (2.3) + or -1 cm to the 6th power/s; and for molecular iodine (I2) quenching, 3.1 x 10 to the -11th power (1.6) + or - 1 cu cm/s. These rates are consistent with the recent measurements.

Molecular dynamics modeling of atomic displacement cascades in 3C-SiC: Comparison of interatomic potentials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samolyuk, German D.; Osetskiy, Yury N.; Stoller, Roger E.

We used molecular dynamics modeling of atomic displacement cascades to characterize the nature of primary radiation damage in 3C-SiC. We demonstrated that the most commonly used interatomic potentials are inconsistent with ab initio calculations of defect energetics. Both the Tersoff potential used in this work and a modified embedded-atom method potential reveal a barrier to recombination of the carbon interstitial and carbon vacancy which is much higher than the density functional theory (DFT) results. The barrier obtained with a newer potential by Gao and Weber is closer to the DFT result. This difference results in significant differences in the cascademore » production of point defects. We have completed both 10 keV and 50 keV cascade simulations in 3C-SiC at a range of temperatures. In contrast to the Tersoff potential, the Gao-Weber potential produces almost twice as many C vacancies and interstitials at the time of maximum disorder (~0.2 ps) but only about 25% more stable defects at the end of the simulation. Only about 20% of the carbon defects produced with the Tersoff potential recombine during the in-cascade annealing phase, while about 60% recombine with the Gao-Weber potential.« less

Molecular dynamics modeling of atomic displacement cascades in 3C-SiC: Comparison of interatomic potentials

DOE PAGES

Samolyuk, German D.; Osetskiy, Yury N.; Stoller, Roger E.

2015-06-03

We used molecular dynamics modeling of atomic displacement cascades to characterize the nature of primary radiation damage in 3C-SiC. We demonstrated that the most commonly used interatomic potentials are inconsistent with ab initio calculations of defect energetics. Both the Tersoff potential used in this work and a modified embedded-atom method potential reveal a barrier to recombination of the carbon interstitial and carbon vacancy which is much higher than the density functional theory (DFT) results. The barrier obtained with a newer potential by Gao and Weber is closer to the DFT result. This difference results in significant differences in the cascademore » production of point defects. We have completed both 10 keV and 50 keV cascade simulations in 3C-SiC at a range of temperatures. In contrast to the Tersoff potential, the Gao-Weber potential produces almost twice as many C vacancies and interstitials at the time of maximum disorder (~0.2 ps) but only about 25% more stable defects at the end of the simulation. Only about 20% of the carbon defects produced with the Tersoff potential recombine during the in-cascade annealing phase, while about 60% recombine with the Gao-Weber potential.« less

Challenges With the Diagnosis and Treatment of Cerebral Radiation Necrosis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chao, Samuel T., E-mail: chaos@ccf.org; Rose Ella Burkhardt Brain Tumor and Neuro-oncology Center, Cleveland Clinic, Cleveland, Ohio; Ahluwalia, Manmeet S.

The incidence of radiation necrosis has increased secondary to greater use of combined modality therapy for brain tumors and stereotactic radiosurgery. Given that its characteristics on standard imaging are no different that tumor recurrence, it is difficult to diagnose without use of more sophisticated imaging and nuclear medicine scans, although the accuracy of such scans is controversial. Historically, treatment had been limited to steroids, hyperbaric oxygen, anticoagulants, and surgical resection. A recent prospective randomized study has confirmed the efficacy of bevacizumab in treating radiation necrosis. Novel therapies include using focused interstitial laser thermal therapy. This article will review the diagnosismore » and treatment of radiation necrosis.« less

Validation of 3-D Ice Accretion Measurement Methodology for Experimental Aerodynamic Simulation

NASA Technical Reports Server (NTRS)

Broeren, Andy P.; Addy, Harold E., Jr.; Lee, Sam; Monastero, Marianne C.

2015-01-01

Determining the adverse aerodynamic effects due to ice accretion often relies on dry-air wind-tunnel testing of artificial, or simulated, ice shapes. Recent developments in ice-accretion documentation methods have yielded a laser-scanning capability that can measure highly three-dimensional (3-D) features of ice accreted in icing wind tunnels. The objective of this paper was to evaluate the aerodynamic accuracy of ice-accretion simulations generated from laser-scan data. Ice-accretion tests were conducted in the NASA Icing Research Tunnel using an 18-in. chord, two-dimensional (2-D) straight wing with NACA 23012 airfoil section. For six ice-accretion cases, a 3-D laser scan was performed to document the ice geometry prior to the molding process. Aerodynamic performance testing was conducted at the University of Illinois low-speed wind tunnel at a Reynolds number of 1.8 × 10(exp 6) and a Mach number of 0.18 with an 18-in. chord NACA 23012 airfoil model that was designed to accommodate the artificial ice shapes. The ice-accretion molds were used to fabricate one set of artificial ice shapes from polyurethane castings. The laser-scan data were used to fabricate another set of artificial ice shapes using rapid prototype manufacturing such as stereolithography. The iced-airfoil results with both sets of artificial ice shapes were compared to evaluate the aerodynamic simulation accuracy of the laser-scan data. For five of the six ice-accretion cases, there was excellent agreement in the iced-airfoil aerodynamic performance between the casting and laser-scan based simulations. For example, typical differences in iced-airfoil maximum lift coefficient were less than 3 percent with corresponding differences in stall angle of approximately 1 deg or less. The aerodynamic simulation accuracy reported in this paper has demonstrated the combined accuracy of the laser-scan and rapid-prototype manufacturing approach to simulating ice accretion for a NACA 23012 airfoil. For several of the ice-accretion cases tested, the aerodynamics is known to depend upon the small, three-dimensional features of the ice. These data show that the laser-scan and rapid-prototype manufacturing approach is capable of replicating these ice features within the reported accuracies of the laser-scan measurement and rapid-prototyping method; thus providing a new capability for high-fidelity ice-accretion documentation and artificial ice-shape fabrication for icing research.

Validation of 3-D Ice Accretion Measurement Methodology for Experimental Aerodynamic Simulation

NASA Technical Reports Server (NTRS)

Broeren, Andy P.; Addy, Harold E., Jr.; Lee, Sam; Monastero, Marianne C.

2014-01-01

Determining the adverse aerodynamic effects due to ice accretion often relies on dry-air wind-tunnel testing of artificial, or simulated, ice shapes. Recent developments in ice accretion documentation methods have yielded a laser-scanning capability that can measure highly three-dimensional features of ice accreted in icing wind tunnels. The objective of this paper was to evaluate the aerodynamic accuracy of ice-accretion simulations generated from laser-scan data. Ice-accretion tests were conducted in the NASA Icing Research Tunnel using an 18-inch chord, 2-D straight wing with NACA 23012 airfoil section. For six ice accretion cases, a 3-D laser scan was performed to document the ice geometry prior to the molding process. Aerodynamic performance testing was conducted at the University of Illinois low-speed wind tunnel at a Reynolds number of 1.8 x 10(exp 6) and a Mach number of 0.18 with an 18-inch chord NACA 23012 airfoil model that was designed to accommodate the artificial ice shapes. The ice-accretion molds were used to fabricate one set of artificial ice shapes from polyurethane castings. The laser-scan data were used to fabricate another set of artificial ice shapes using rapid prototype manufacturing such as stereolithography. The iced-airfoil results with both sets of artificial ice shapes were compared to evaluate the aerodynamic simulation accuracy of the laser-scan data. For four of the six ice-accretion cases, there was excellent agreement in the iced-airfoil aerodynamic performance between the casting and laser-scan based simulations. For example, typical differences in iced-airfoil maximum lift coefficient were less than 3% with corresponding differences in stall angle of approximately one degree or less. The aerodynamic simulation accuracy reported in this paper has demonstrated the combined accuracy of the laser-scan and rapid-prototype manufacturing approach to simulating ice accretion for a NACA 23012 airfoil. For several of the ice-accretion cases tested, the aerodynamics is known to depend upon the small, three dimensional features of the ice. These data show that the laser-scan and rapid-prototype manufacturing approach is capable of replicating these ice features within the reported accuracies of the laser-scan measurement and rapid-prototyping method; thus providing a new capability for high-fidelity ice-accretion documentation and artificial ice-shape fabrication for icing research.

Simulation, Theory, and Observations of the Spectrum of the Rayleigh-Taylor Instability due to Laser Imprint of Planar Targets

NASA Astrophysics Data System (ADS)

Keskinen, M. J.; Karasik, Max; Bates, J. W.; Schmitt, A. J.

2006-10-01

A limitation on the efficiency of high gain direct drive inertial confinement fusion is the extent of pellet disruption caused by the Rayleigh-Taylor (RT) instability. The RT instability can be seeded by pellet surface irregularities and/or laser imprint nonuniformities. It is important to characterize the evolution of the RT instability, e.g., the k-spectrum of areal mass. In this paper we study the time-dependent evolution of the spectrum of the Rayleigh-Taylor instability due to laser imprint in planar targets. This is achieved using the NRL FAST hydrodynamic simulation code together with analytical models. It is found that the optically smoothed laser imprint-driven RT spectrum develops into an inverse power law in k-space after several linear growth times. FAST simulation code results are compared with recent NRL Nike KrF laser experimental data. An analytical model, which is a function of Froude and Atwood numbers, is derived for the RT spectrum and favorably compared with both FAST simulation and Nike observations.

Interstitial space and collagen alterations of the developing rat diaphragm

NASA Technical Reports Server (NTRS)

Gosselin, L. E.; Martinez, D. A.; Vailas, A. C.; Sieck, G. C.

1993-01-01

The effect of growth on the relative interstitial space [%total cross-sectional area (CSA)] and collagen content of the rat diaphragm muscle was examined at postnatal ages of 0, 7, 14, and 21 days as well as in adult males. The proportion of interstitial space relative to total muscle CSA was determined by computerized image analysis of lectin-stained cross sections of diaphragm muscle. To assess collagen content and extent of collagen maturation (i.e., cross-linking), high-pressure liquid chromatography analysis was used to measure hydroxyproline concentration and the nonreducible collagen cross-link hydroxylysylpyridinoline (HP), respectively. At birth, interstitial space accounted for approximately 47% of total diaphragm muscle CSA. During postnatal growth, the relative contribution of interstitial space decreased such that by adulthood the interstitial space accounted for approximately 18% of total muscle CSA. The change in relative interstitial space occurred without a concomitant change in hydroxyproline concentration. However, the concentration of HP markedly increased with age such that the adult diaphragm contained approximately 17 times more HP than at birth. These results indicate that during development the relative CSA occupied by interstitial space decreases as muscle fiber size increases. However, the reduction in relative interstitial space is not associated with a change in collagen concentration. Thus collagen density in the interstitial space may increase with age. It is possible that the observed changes in relative interstitial space and collagen influence the passive length-force properties of the diaphragm.

Preclinical studies of vascular acting photosensitizer bacteriopheophorbide for the treatment of prostate cancer

NASA Astrophysics Data System (ADS)

Hetzel, Fred W.; Chen, Qun; Luck, David; Beckers, Jill; Huang, Zheng

2004-06-01

Photodynamic therapy (PDT) mediated with vascular acting photosensitizer pd-bacteriopheophorbide (Tookad), is investigated as an alternative modality for the total ablation of prostate cancer. In vivo normal canine prostate is used as the animal model. Interstitial PDT was performed by irradiating the surgically exposed prostates with a diode laser (763 nm, 150 mW/cm) to activate the IV infused photosensitizer drug. The prostate and its adjacent tissues were harvested and subjected to histopathological examination. At one-week post PDT, the animals recovered well with little or no urethral complications. Prostatic urethra and prostate adjacent tissues (bladder and underlying colon) were well preserved. PDT induced prostate lesions were characterized by marked hemorrhagic necrosis. Prostate lesions could be detected by MRI scan as early as 48 h post PDT. Maximum lesion size of 1.5 cm3 and 2.9 cm3 could be achieved at 50 J/cm and 100 J/cm, respectively, with interstitial treatment using a single 1-cm diffuser fiber, suggesting the Tookad-PDT is very effective in ablating prostatic tissue. Pharmacokinetic studies show that the photosensitizer is cleared rapidly from the circulation. In conclusion, the novel photosensitizer Tookad mediated PDT may provide an effective alternative to treat localized prostate cancer.

The electronic and optical properties of amorphous silica with hydrogen defects by ab initio calculations

NASA Astrophysics Data System (ADS)

Ren, Dahua; Xiang, Baoyan; Hu, Cheng; Qian, Kai; Cheng, Xinlu

2018-04-01

Hydrogen can be trapped in the bulk materials in four forms: interstitial molecular H2, interstitial atom H, O‑H+(2Si=O–H)+, Si‑H‑( {{4O}}\\bar \\equiv {{Si&x2212H}})‑ to affect the electronic and optical properties of amorphous silica. Therefore, the electronic and optical properties of defect-free and hydrogen defects in amorphous silica were performed within the scheme of density functional theory. Initially, the negative charged states hydrogen defects introduced new defect level between the valence band top and conduction band bottom. However, the neutral and positive charged state hydrogen defects made both the valence band and conduction band transfer to the lower energy. Subsequently, the optical properties such as absorption spectra, conductivity and loss functions were analyzed. It is indicated that the negative hydrogen defects caused the absorption peak ranging from 0 to 2.0 eV while the positive states produced absorption peaks at lower energy and two strong absorption peaks arose at 6.9 and 9.0 eV. However, the neutral hydrogen defects just improved the intensity of absorption spectrum. This may give insights into understanding the mechanism of laser-induced damage for optical materials. Project supported by the Science and Technology of Hubei Provincial Department of Education (No. B2017098).

Atomic-scale distortions and temperature-dependent large pseudogap in thin films of the parent iron-chalcogenide superconductor Fe1+y Te

NASA Astrophysics Data System (ADS)

Gerbi, Andrea; Buzio, Renato; Kawale, Shrikant; Bellingeri, Emilio; Martinelli, Alberto; Bernini, Cristina; Tresca, Cesare; Capone, Massimo; Profeta, Gianni; Ferdeghini, Carlo

2017-12-01

We investigate with scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT) calculations the surface structures and the electronic properties of Fe1+y Te thin films grown by pulsed laser deposition. Contrary to the regular arrangement of antiferromagnetic nanostripes previously reported on cleaved single-crystal samples, the surface of Fe1+y Te thin films displays a peculiar distribution of spatially inhomogeneous nanostripes. Both STM and DFT calculations show the bias-dependent nature of such features and support the interpretation of spin-polarized tunneling between the FeTe surface and an unintentionally magnetized tip. In addition, the spatial inhomogeneity is interpreted as a purely electronic effect related to changes in hybridization and Fe-Fe bond length driven by local variations in the concentration of excess interstitial Fe cations. Unexpectedly, the surface density of states measured by STS strongly evolves with temperature in close proximity to the antiferromagnetic-paramagnetic first-order transition, and reveals a large pseudogap of 180-250 meV at about 50-65 K. We believe that in this temperature range a phase transition takes place, and the system orders and locks into particular combinations of orbitals and spins because of the interplay between excess interstitial magnetic Fe and strongly correlated d-electrons.

Observation of laser formation inside a laser cavity containing a phase conjugate mirror

NASA Astrophysics Data System (ADS)

Wu, Frank F.

2012-03-01

Adaptive optics (AO) systems are used to compensate atmospheric perturbations on a propagating laser beam. However, AO needs a beacon to obtain the phase information. This paper presents a possible formation of beacon in target-in-theloop (TIL) geometry which is analog to a laser cavity. The TIL laser cavity is formed with a high reflectivity mirror on one end and an optical phase conjugate mirror as the second mirror. The TIL laser is initialized by a single frequency 10 ns Q-switched laser pulse. This is very similar to how an injection seeding or regenerative amplifier scheme starts a laser oscillation. With a cavity length of around 11 meters and an initial laser pulse of 10 ns, we have been able to isolate laser field images related to each round-trip pulse. Furthermore, by replacing the first mirror with a rough-surface target to simulate an uncooperative target and adding phase distortion elements to simulate atmospheric effects, we can observe the image status under such conditions.

A simulation environment for assisting system design of coherent laser doppler wind sensor for active wind turbine pitch control

NASA Astrophysics Data System (ADS)

Shinohara, Leilei; Pham Tran, Tuan Anh; Beuth, Thorsten; Umesh Babu, Harsha; Heussner, Nico; Bogatscher, Siegwart; Danilova, Svetlana; Stork, Wilhelm

2013-05-01

In order to assist a system design of laser coherent Doppler wind sensor for active pitch control of wind turbine systems (WTS), we developed a numerical simulation environment for modeling and simulation of the sensor system. In this paper we present this simulation concept. In previous works, we have shown the general idea and the possibility of using a low cost coherent laser Doppler wind sensing system for an active pitch control of WTS in order to achieve a reduced mechanical stress, increase the WTS lifetime and therefore reduce the electricity price from wind energy. Such a system is based on a 1.55μm Continuous-Wave (CW) laser plus an erbium-doped fiber amplifier (EDFA) with an output power of 1W. Within this system, an optical coherent detection method is chosen for the Doppler frequency measurement in megahertz range. A comparatively low cost short coherent length laser with a fiber delay line is used for achieving a multiple range measurement. In this paper, we show the current results on the improvement of our simulation by applying a Monte Carlo random generation method for positioning the random particles in atmosphere and extend the simulation to the entire beam penetrated space by introducing a cylindrical co-ordinate concept and meshing the entire volume into small elements in order to achieve a faster calculation and gain more realistic simulation result. In addition, by applying different atmospheric parameters, such as particle sizes and distributions, we can simulate different weather and wind situations.

Modeling laser speckle imaging of perfusion in the skin (Conference Presentation)

NASA Astrophysics Data System (ADS)

Regan, Caitlin; Hayakawa, Carole K.; Choi, Bernard

2016-02-01

Laser speckle imaging (LSI) enables visualization of relative blood flow and perfusion in the skin. It is frequently applied to monitor treatment of vascular malformations such as port wine stain birthmarks, and measure changes in perfusion due to peripheral vascular disease. We developed a computational Monte Carlo simulation of laser speckle contrast imaging to quantify how tissue optical properties, blood vessel depths and speeds, and tissue perfusion affect speckle contrast values originating from coherent excitation. The simulated tissue geometry consisted of multiple layers to simulate the skin, or incorporated an inclusion such as a vessel or tumor at different depths. Our simulation used a 30x30mm uniform flat light source to optically excite the region of interest in our sample to better mimic wide-field imaging. We used our model to simulate how dynamically scattered photons from a buried blood vessel affect speckle contrast at different lateral distances (0-1mm) away from the vessel, and how these speckle contrast changes vary with depth (0-1mm) and flow speed (0-10mm/s). We applied the model to simulate perfusion in the skin, and observed how different optical properties, such as epidermal melanin concentration (1%-50%) affected speckle contrast. We simulated perfusion during a systolic forearm occlusion and found that contrast decreased by 35% (exposure time = 10ms). Monte Carlo simulations of laser speckle contrast give us a tool to quantify what regions of the skin are probed with laser speckle imaging, and measure how the tissue optical properties and blood flow affect the resulting images.

Advanced laser modeling with BLAZE multiphysics

NASA Astrophysics Data System (ADS)

Palla, Andrew D.; Carroll, David L.; Gray, Michael I.; Suzuki, Lui

2017-01-01

The BLAZE Multiphysics™ software simulation suite was specifically developed to model highly complex multiphysical systems in a computationally efficient and highly scalable manner. These capabilities are of particular use when applied to the complexities associated with high energy laser systems that combine subsonic/transonic/supersonic fluid dynamics, chemically reacting flows, laser electronics, heat transfer, optical physics, and in some cases plasma discharges. In this paper we present detailed cw and pulsed gas laser calculations using the BLAZE model with comparisons to data. Simulations of DPAL, XPAL, ElectricOIL (EOIL), and the optically pumped rare gas laser were found to be in good agreement with experimental data.

Optical eye simulator for laser dazzle events.

PubMed

Coelho, João M P; Freitas, José; Williamson, Craig A

2016-03-20

An optical simulator of the human eye and its application to laser dazzle events are presented. The simulator combines optical design software (ZEMAX) with a scientific programming language (MATLAB) and allows the user to implement and analyze a dazzle scenario using practical, real-world parameters. Contrary to conventional analytical glare analysis, this work uses ray tracing and the scattering model and parameters for each optical element of the eye. The theoretical background of each such element is presented in relation to the model. The overall simulator's calibration, validation, and performance analysis are achieved by comparison with a simpler model based uponCIE disability glare data. Results demonstrate that this kind of advanced optical eye simulation can be used to represent laser dazzle and has the potential to extend the range of applicability of analytical models.

3D Monte Carlo simulation of light propagation for laser acupuncture and optimization of illumination parameters

NASA Astrophysics Data System (ADS)

Zhong, Fulin; Li, Ting; Pan, Boan; Wang, Pengbo

2017-02-01

Laser acupuncture is an effective photochemical and nonthermal stimulation of traditional acupuncture points with lowintensity laser irradiation, which is advantageous in painless, sterile, and safe compared to traditional acupuncture. Laser diode (LD) provides single wavelength and relatively-higher power light for phototherapy. The quantitative effect of illumination parameters of LD in use of laser acupuncture is crucial for practical operation of laser acupuncture. However, this issue is not fully demonstrated, especially since experimental methodologies with animals or human are pretty hard to address to this issue. For example, in order to protect viability of cells and tissue, and get better therapeutic effect, it's necessary to control the output power varied at 5mW 10mW range, while the optimized power is still not clear. This study aimed to quantitatively optimize the laser output power, wavelength, and irradiation direction with highly realistic modeling of light transport in acupunctured tissue. A Monte Carlo Simulation software for 3D vowelized media and the highest-precision human anatomical model Visible Chinese Human (VCH) were employed. Our 3D simulation results showed that longer wavelength/higher illumination power, larger absorption in laser acupuncture; the vertical direction emission of the acupuncture laser results in higher amount of light absorption in both the acupunctured voxel of tissue and muscle layer. Our 3D light distribution of laser acupuncture within VCH tissue model is potential to be used in optimization and real time guidance in clinical manipulation of laser acupuncture.

Two-photon laser-generated microtracks in 3D collagen lattices: principles of MMP-dependent and -independent collective cancer cell invasion

NASA Astrophysics Data System (ADS)

Ilina, Olga; Bakker, Gert-Jan; Vasaturo, Angela; Hoffman, Robert M.; Friedl, Peter

2011-02-01

Cancer invasion into an extracellular matrix (ECM) results from a biophysical reciprocal interplay between the expanding cancer lesion and tissue barriers imposed by the adjacent microenvironment. In vivo, connective tissue provides both densely packed ECM barriers adjacent to channel/track-like spaces and loosely organized zones, both of which may impact cancer invasion mode and efficiency; however little is known about how three-dimensional (3D) spaces and aligned tracks present in interstitial tissue guide cell invasion. We here describe a two-photon laser ablation procedure to generate 3D microtracks in dense 3D collagen matrices that support and guide collective cancer cell invasion. Whereas collective invasion of mammary tumor (MMT) breast cancer cells into randomly organized collagen networks required matrix metalloproteinase (MMP) activity for cell-derived collagen breakdown, re-alignment and track generation, preformed tracks supported MMP-independent collective invasion down to a track caliber of 3 µm. Besides contact guidance along the track of least resistance and initial cell deformation (squeezing), MMP-independent collective cell strands led to secondary track expansion by a pushing mechanism. Thus, two-photon laser ablation is useful to generate barrier-free microtracks in a 3D ECM which guide collective invasion independently of pericellular proteolysis.

Photodynamic effect produced by HeNe radiation in Harderian glands of Wistar rats: an experimental model for PDT studies

NASA Astrophysics Data System (ADS)

dos Reis, Edmyr R.; Nicola, Ester M. D.; Metze, Konradin; Nicola, Jorge H.

2000-06-01

In rats, the Harderian Gland secret Protoporphirin IX which is retained at acinar lumina. Since this photosensitizer is important for PDT of malignant tumors, we propose to study this gland as a model to help understanding PDT with endogenous photosensitizers. Twenty Wistar SPF adult rats were submitted to surgical exposure of both Harderian glands, revealing red fluorescence upon UV, characterizing the protoporphirin IX presence. After that, one gland of each pair (one kept as control) was irradiated with an 8 mW HeNe (6328 angstrom) for 45 minutes, delivering about 2.7 joules/mm2. After 24 hours a group of 10 animals were scarified and the glands removed for histological analysis. The remaining animals were subjected to the same procedure but the glands were removed immediately after laser treatment. Histological and fluorescence analysis immediately after laser irradiation showed cell fragmentation with loss of acinar architecture with diffusion of protoporphirin in the cytoplasm of damaged cells, as well as interstitial edema. After 24 hours these alterations were more pronounced with accentuated loss of intraluminal protoporphirin and beginning of leukocytic demarcation of necrotic areas. The innate Harderian glands of rats, exposed to HeNe laser, showed a similar behavior as tumor tissue under PDT.

Transient Plasma Photonic Crystals for High-Power Lasers.

PubMed

Lehmann, G; Spatschek, K H

2016-06-03

A new type of transient photonic crystals for high-power lasers is presented. The crystal is produced by counterpropagating laser beams in plasma. Trapped electrons and electrically forced ions generate a strong density grating. The lifetime of the transient photonic crystal is determined by the ballistic motion of ions. The robustness of the photonic crystal allows one to manipulate high-intensity laser pulses. The scheme of the crystal is analyzed here by 1D Vlasov simulations. Reflection or transmission of high-power laser pulses are predicted by particle-in-cell simulations. It is shown that a transient plasma photonic crystal may act as a tunable mirror for intense laser pulses. Generalizations to 2D and 3D configurations are possible.

Direct solar-pumped iodine laser amplifier

NASA Technical Reports Server (NTRS)

Han, Kwang S.; Kim, K. H.; Stock, L. V.

1987-01-01

The improvement on the collection system of the Tarmarack Solar Simulator beam was attemped. The basic study of evaluating the solid state laser materials for the solar pumping and also the work to construct a kinetic model algorithm for the flashlamp pumped iodine lasers were carried out. It was observed that the collector cone worked better than the lens assembly in order to collect the solar simulator beam and to focus it down to a strong power density. The study on the various laser materials and their lasing characteristics shows that the neodymium and chromium co-doped gadolinium scandium gallium garnet (Nr:Cr:GSGG) may be a strong candidate for the high power solar pumped solid state laser crystal. On the other hand the improved kinetic modeling for the flashlamp pumped iodine laser provides a good agreement between the theoretical model and the experimental data on the laser power output, and predicts the output parameters of a solar pumped iodine laser.

Design of hybrid laser structures with QD-RSOA and silicon photonic mirrors

NASA Astrophysics Data System (ADS)

Gioannini, Mariangela; Benedetti, Alessio; Bardella, Paolo; Bovington, Jock; Traverso, Matt; Siriani, Dominic; Gothoskar, Prakash

2018-02-01

We compare the design of three different single mode laser structures consisting in a Reflective Semiconductor Optical Amplifier coupled to a silicon photonic external cavity mirror. The three designs differ for the mirror structure and are compared in terms of SOA power consumption and side mode suppression ratio (SMSR). Assuming then a Quantum Dot active material, we simulate the best laser design using a numerical model that includes the peculiar physical characteristics of the QD gain medium. The simulated QD laser CW characteristics are shown and discussed.

Laser Doppler velocimeter system simulation for sensing aircraft wake vortices

NASA Technical Reports Server (NTRS)

Thomson, J. A. L.; Meng, J. C. S.

1974-01-01

A hydrodynamic model of aircraft vortex wakes in an irregular wind shear field near the ground is developed and used as a basis for modeling the characteristics of a laser Doppler detection and vortex location system. The trailing vortex sheet and the wind shear are represented by discrete free vortices distributed over a two-dimensional grid. The time dependent hydrodynamic equations are solved by direct numerical integration in the Boussinesq approximation. The ground boundary is simulated by images, and fast Fourier Transform techniques are used to evaluate the vorticity stream function. The atmospheric turbulence was simulated by constructing specific realizations at time equal to zero, assuming that Kolmogoroff's law applies, and that the dissipation rate is constant throughout the flow field. The response of a simulated laser Doppler velocimeter is analyzed by simulating the signal return from the flow field as sensed by a simulation of the optical/electronic system.

An empirical potential for simulating vacancy clusters in tungsten.

PubMed

Mason, D R; Nguyen-Manh, D; Becquart, C S

2017-12-20

We present an empirical interatomic potential for tungsten, particularly well suited for simulations of vacancy-type defects. We compare energies and structures of vacancy clusters generated with the empirical potential with an extensive new database of values computed using density functional theory, and show that the new potential predicts low-energy defect structures and formation energies with high accuracy. A significant difference to other popular embedded-atom empirical potentials for tungsten is the correct prediction of surface energies. Interstitial properties and short-range pairwise behaviour remain similar to the Ackford-Thetford potential on which it is based, making this potential well-suited to simulations of microstructural evolution following irradiation damage cascades. Using atomistic kinetic Monte Carlo simulations, we predict vacancy cluster dissociation in the range 1100-1300 K, the temperature range generally associated with stage IV recovery.

Calculation of the small scale self-focusing ripple gain spectrum for the CYCLOPS laser system: a status report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fleck, J.A. Jr.; Morris, J.R.; Thompson, P.F.

1976-10-01

The FLAC code (Fourier Laser Amplifier Code) was used to simulate the CYCLOPS laser system up to the third B-module and to calculate the maximum ripple gain spectrum. The model of this portion of CYCLOPS consists of 33 segments that correspond to 20 optical elements (simulation of the cell requires 2 segments and 12 external air spaces). (MHR)

Molecular dynamics simulation of shock wave and spallation phenomena in metal foils irradiated by femtosecond laser pulse

NASA Astrophysics Data System (ADS)

Zhakhovsky, Vasily; Demaske, Brian; Inogamov, Nail; Oleynik, Ivan

2010-03-01

Femtosecond laser irradiation of metals is an effective technique to create a high-pressure frontal layer of 100-200 nm thickness. The associated ablation and spallation phenomena can be studied in the laser pump-probe experiments. We present results of a large-scale MD simulation of ablation and spallation dynamics developing in 1,2,3μm thick Al and Au foils irradiated by a femtosecond laser pulse. Atomic-scale mechanisms of laser energy deposition, transition from pressure wave to shock, reflection of the shock from the rear-side of the foil, and the nucleation of cracks in the reflected tensile wave, having a very high strain rate, were all studied. To achieve a realistic description of the complex phenomena induced by strong compression and rarefaction waves, we developed new embedded atom potentials for Al and Au based on cold pressure curves. MD simulations revealed the complex interplay between spallation and ablation processes: dynamics of spallation depends on the pressure profile formed in the ablated zone at the early stage of laser energy absorption. It is shown that the essential information such as material properties at high strain rate and spall strength can be extracted from the simulated rear-side surface velocity as a function of time.

Analysis of Thermally Denatured Depth in Laser Vaporization for Benign Prostatic Hyperplasia using a Simulation of Light Propagation and Heat Transfer (secondary publication)

PubMed Central

Takada, Junya; Honda, Norihiro; Hazama, Hisanao; Ioritani, Naomasa

2016-01-01

Background and Aims: Laser vaporization of the prostate is expected as a less invasive treatment for benign prostatic hyperplasia (BPH), via the photothermal effect. In order to develop safer and more effective laser vaporization of the prostate, it is essential to set optimal irradiation parameters based on quantitative evaluation of temperature distribution and thermally denatured depth in prostate tissue. Method: A simulation model was therefore devised with light propagation and heat transfer calculation, and the vaporized and thermally denatured depths were estimated by the simulation model. Results: The results of the simulation were compared with those of an ex vivo experiment and clinical trial. Based on the accumulated data, the vaporized depth strongly depended on the distance between the optical fiber and the prostate tissue, and it was suggested that contact laser irradiation could vaporize the prostate tissue most effectively. Additionally, it was suggested by analyzing thermally denatured depth comprehensively that laser irradiation at the distance of 3 mm between the optical fiber and the prostate tissue was useful for hemostasis. Conclusions: This study enabled quantitative and reproducible analysis of laser vaporization for BPH and will play a role in clarification of the safety and efficacy of this treatment. PMID:28765672

Simulation study of terahertz radiation generation by circularly polarized laser pulses propagating in axially magnetized plasma

NASA Astrophysics Data System (ADS)

Saroch, Akanksha; Jha, Pallavi

2017-12-01

This paper deals with a two-dimensional simulation study of terahertz radiation emission in the wake of circularly polarized laser pulses propagating in uniformly magnetized plasma, using the XOOPIC code. The external magnetic field is applied along the direction of propagation of the laser pulse. It is seen that linearly polarized terahertz radiation is emitted off-axis, along the propagation direction, in plasma. This emitted radiation is also seen to be transmitted in vacuum. Simulation studies reveal that no such radiation is generated on-axis for the given configuration.

Thermomechanically coupled conduction mode laser welding simulations using smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

Hu, Haoyue; Eberhard, Peter

2017-10-01

Process simulations of conduction mode laser welding are performed using the meshless Lagrangian smoothed particle hydrodynamics (SPH) method. The solid phase is modeled based on the governing equations in thermoelasticity. For the liquid phase, surface tension effects are taken into account to simulate the melt flow in the weld pool, including the Marangoni force caused by a temperature-dependent surface tension gradient. A non-isothermal solid-liquid phase transition with the release or absorption of additional energy known as the latent heat of fusion is considered. The major heat transfer through conduction is modeled, whereas heat convection and radiation are neglected. The energy input from the laser beam is modeled as a Gaussian heat source acting on the initial material surface. The developed model is implemented in Pasimodo. Numerical results obtained with the model are presented for laser spot welding and seam welding of aluminum and iron. The change of process parameters like welding speed and laser power, and their effects on weld dimensions are investigated. Furthermore, simulations may be useful to obtain the threshold for deep penetration welding and to assess the overall welding quality. A scalability and performance analysis of the implemented SPH algorithm in Pasimodo is run in a shared memory environment. The analysis reveals the potential of large welding simulations on multi-core machines.

Coupling of laser energy into plasma channels

NASA Astrophysics Data System (ADS)

Dimitrov, D. A.; Giacone, R. E.; Bruhwiler, D. L.; Busby, R.; Cary, J. R.; Geddes, C. G. R.; Esarey, E.; Leemans, W. P.

2007-04-01

Diffractive spreading of a laser pulse imposes severe limitations on the acceleration length and maximum electron energy in the laser wake field accelerator (LWFA). Optical guiding of a laser pulse via plasma channels can extend the laser-plasma interaction distance over many Rayleigh lengths. Energy efficient coupling of laser pulses into and through plasma channels is very important for optimal LWFA performance. Results from simulation parameter studies on channel guiding using the particle-in-cell (PIC) code VORPAL [C. Nieter and J. R. Cary, J. Comput. Phys. 196, 448 (2004)] are presented and discussed. The effects that density ramp length and the position of the laser pulse focus have on coupling into channels are considered. Moreover, the effect of laser energy leakage out of the channel domain and the effects of tunneling ionization of a neutral gas on the guided laser pulse are also investigated. Power spectral diagnostics were developed and used to separate pump depletion from energy leakage. The results of these simulations show that increasing the density ramp length decreases the efficiency of coupling a laser pulse to a channel and increases the energy loss when the pulse is vacuum focused at the channel entrance. Then, large spot size oscillations result in increased energy leakage. To further analyze the coupling, a differential equation is derived for the laser spot size evolution in the plasma density ramp and channel profiles are simulated. From the numerical solution of this equation, the optimal spot size and location for coupling into a plasma channel with a density ramp are determined. This result is confirmed by the PIC simulations. They show that specifying a vacuum focus location of the pulse in front of the top of the density ramp leads to an actual focus at the top of the ramp due to plasma focusing, resulting in reduced spot size oscillations. In this case, the leakage is significantly reduced and is negligibly affected by ramp length, allowing for efficient use of channels with long ramps.

Interstitial nephritis.

PubMed

Papper, S

1980-01-01

There are many causes of interstitial nephritis other than pyelonephritis. The term interstitial nephritis does not connote a single etiologic or pathogenetic mechanism; it rather arbitrarily places together a wider variety of renal diseases that have a predilection for early and major involvement of the renal interstitium. The prototype of acute interstitial nephritis is acute pyelonephritis. In addition, there is a drug-related acute interstitial disease that is probably of immunological nature and usually reverses with discontinuance of the offending drug. Chronic interstitial nephritis includes many diverse illnesses. Nonobstructive pyelonephritis occurs but its prevalence is debated. Analgesic abuse nephropathy is not rare and is potentially reversible. Papillary necrosis has many causes and a wide spectrum of clinical presentations. Heavy metals, such as lead, cause interstitial nephritis. Balkan nephropathy occurs in an endemic area and although not bacterial in origin is of unknown cause.

Laser Engineered Net Shape (LENS) Technology for the Repair of Ni-Base Superalloy Turbine Components

NASA Astrophysics Data System (ADS)

Liu, Dejian; Lippold, John C.; Li, Jia; Rohklin, Stan R.; Vollbrecht, Justin; Grylls, Richard

2014-09-01

The capability of the laser engineered net shape (LENS) process was evaluated for the repair of casting defects and improperly machined holes in gas turbine engine components. Various repair geometries, including indentations, grooves, and through-holes, were used to simulate the actual repair of casting defects and holes in two materials: Alloy 718 and Waspaloy. The influence of LENS parameters, including laser energy density, laser scanning speed, and deposition pattern, on the repair of these defects and holes was studied. Laser surface remelting of the substrate prior to repair was used to remove machining defects and prevent heat-affected zone (HAZ) liquation cracking. Ultrasonic nondestructive evaluation techniques were used as a possible approach for detecting lack-of-fusion in repairs. Overall, Alloy 718 exhibited excellent repair weldability, with essentially no defects except for some minor porosity in repairs representative of deep through-holes and simulated large area casting defects. In contrast, cracking was initially observed during simulated repair of Waspaloy. Both solidification cracking and HAZ liquation cracking were observed in the repairs, especially under conditions of high heat input (high laser power and/or low scanning speed). For Waspaloy, the degree of cracking was significantly reduced and, in most cases, completely eliminated by the combination of low laser energy density and relatively high laser scanning speeds. It was found that through-hole repairs of Waspaloy made using a fine powder size exhibited excellent repair weldability and were crack-free relative to repairs using coarser powder. Simulated deep (7.4 mm) blind-hole repairs, representative of an actual Waspaloy combustor case, were successfully produced by the combination use of fine powder and relatively high laser scanning speeds.

Recombination radius of a Frenkel pair and capture radius of a self-interstitial atom by vacancy clusters in bcc Fe

NASA Astrophysics Data System (ADS)

Nakashima, Kenichi; Stoller, Roger E.; Xu, Haixuan

2015-08-01

The recombination radius of a Frenkel pair is a fundamental parameter for the object kinetic Monte Carlo (OKMC) and mean field rate theory (RT) methods that are used to investigate irradiation damage accumulation in irradiated materials. The recombination radius in bcc Fe has been studied both experimentally and numerically, however there is no general consensus about its value. The detailed atomistic processes of recombination also remain uncertain. Values from 1.0a0 to 3.3a0 have been employed as a recombination radius in previous studies using OKMC and RT. The recombination process of a Frenkel pair is investigated at the atomic level using the self-evolved atomistic kinetic Monte Carlo (SEAKMC) method in this paper. SEAKMC calculations reveal that a self-interstitial atom recombines with a vacancy in a spontaneous reaction from several nearby sites following characteristic pathways. The recombination radius of a Frenkel pair is estimated to be 2.26a0 by taking the average of the recombination distances from 80 simulation cases. In addition, we apply these procedures to the capture radius of a self-interstitial atom by a vacancy cluster. The capture radius is found to gradually increase with the size of the vacancy cluster. The fitting curve for the capture radius is obtained as a function of the number of vacancies in the cluster.

Anharmonic resonance absorption of short laser pulses in clusters: A molecular dynamics simulation study

NASA Astrophysics Data System (ADS)

Mahalik, S. S.; Kundu, M.

2016-12-01

Linear resonance (LR) absorption of an intense 800 nm laser light in a nano-cluster requires a long laser pulse >100 fs when Mie-plasma frequency ( ω M ) of electrons in the expanding cluster matches the laser frequency (ω). For a short duration of the pulse, the condition for LR is not satisfied. In this case, it was shown by a model and particle-in-cell (PIC) simulations [Phys. Rev. Lett. 96, 123401 (2006)] that electrons absorb laser energy by anharmonic resonance (AHR) when the position-dependent frequency Ω [ r ( t ) ] of an electron in the self-consistent anharmonic potential of the cluster satisfies Ω [ r ( t ) ] = ω . However, AHR remains to be a debate and still obscure in multi-particle plasma simulations. Here, we identify AHR mechanism in a laser driven cluster using molecular dynamics (MD) simulations. By analyzing the trajectory of each MD electron and extracting its Ω [ r ( t ) ] in the self-generated anharmonic plasma potential, it is found that electron is outer ionized only when AHR is met. An anharmonic oscillator model, introduced here, brings out most of the features of MD electrons while passing the AHR. Thus, we not only bridge the gap between PIC simulations, analytical models, and MD calculations for the first time but also unequivocally prove that AHR process is a universal dominant collisionless mechanism of absorption in the short pulse regime or in the early time of longer pulses in clusters.

Balance point characterization of interstitial fluid volume regulation.

PubMed

Dongaonkar, R M; Laine, G A; Stewart, R H; Quick, C M

2009-07-01

The individual processes involved in interstitial fluid volume and protein regulation (microvascular filtration, lymphatic return, and interstitial storage) are relatively simple, yet their interaction is exceedingly complex. There is a notable lack of a first-order, algebraic formula that relates interstitial fluid pressure and protein to critical parameters commonly used to characterize the movement of interstitial fluid and protein. Therefore, the purpose of the present study is to develop a simple, transparent, and general algebraic approach that predicts interstitial fluid pressure (P(i)) and protein concentrations (C(i)) that takes into consideration all three processes. Eight standard equations characterizing fluid and protein flux were solved simultaneously to yield algebraic equations for P(i) and C(i) as functions of parameters characterizing microvascular, interstitial, and lymphatic function. Equilibrium values of P(i) and C(i) arise as balance points from the graphical intersection of transmicrovascular and lymph flows (analogous to Guyton's classical cardiac output-venous return curves). This approach goes beyond describing interstitial fluid balance in terms of conservation of mass by introducing the concept of inflow and outflow resistances. Algebraic solutions demonstrate that P(i) and C(i) result from a ratio of the microvascular filtration coefficient (1/inflow resistance) and effective lymphatic resistance (outflow resistance), and P(i) is unaffected by interstitial compliance. These simple algebraic solutions predict P(i) and C(i) that are consistent with reported measurements. The present work therefore presents a simple, transparent, and general balance point characterization of interstitial fluid balance resulting from the interaction of microvascular, interstitial, and lymphatic function.

The efficiency of photovoltaic cells exposed to pulsed laser light

NASA Technical Reports Server (NTRS)

Lowe, R. A.; Landis, G. A.; Jenkins, P.

1993-01-01

Future space missions may use laser power beaming systems with a free electron laser (FEL) to transmit light to a photovoltaic array receiver. To investigate the efficiency of solar cells with pulsed laser light, several types of GaAs, Si, CuInSe2, and GaSb cells were tested with the simulated pulse format of the induction and radio frequency (RF) FEL. The induction pulse format was simulated with an 800-watt average power copper vapor laser and the RF format with a frequency-doubled mode-locked Nd:YAG laser. Averaged current vs bias voltage measurements for each cell were taken at various optical power levels and the efficiency measured at the maximum power point. Experimental results show that the conversion efficiency for the cells tested is highly dependent on cell minority carrier lifetime, the width and frequency of the pulses, load impedance, and the average incident power. Three main effects were found to decrease the efficiency of solar cells exposed to simulated FEL illumination: cell series resistance, LC 'ringing', and output inductance. Improvements in efficiency were achieved by modifying the frequency response of the cell to match the spectral energy content of the laser pulse with external passive components.

Evaluation of effectiveness of Er,Cr:YSGG laser for root canal disinfection: theoretical simulation of temperature elevations in root dentin.

PubMed

Zhu, L; Tolba, M; Arola, D; Salloum, M; Meza, F

2009-07-01

Erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) lasers are currently being investigated for disinfecting the root canal system. Prior to using laser therapy, it is important to understand the temperature distribution and to assess thermal damage to the surrounding tissue. In this study, a theoretical simulation using the Pennes bioheat equation is conducted to evaluate how heat spreads from the canal surface using an Er,Cr:YSGG laser. Results of the investigation show that some of the proposed treatment protocols for killing bacteria in the deep dentin are ineffective, even for long heating durations. Based on the simulation, an alternative treatment protocol is identified that has improved effectiveness and is less likely to introduce collateral damage to the surrounding tissue. The alternative protocol uses 350 mW laser power with repeating laser tip movement to achieve bacterial disinfection in the deep dentin (800 microm lateral from the canal surface), while avoiding thermal damage to the surrounding tissue (T<47 degrees C). The alternative treatment protocol has the potential to not only achieve bacterial disinfection of deep dentin but also shorten the treatment time, thereby minimizing potential patient discomfort during laser procedures.

Effect of equation of state on laser imprinting by comparing diamond and polystyrene foils

NASA Astrophysics Data System (ADS)

Kato, H.; Shigemori, K.; Nagatomo, H.; Nakai, M.; Sakaiya, T.; Ueda, T.; Terasaki, H.; Hironaka, Y.; Shimizu, K.; Azechi, H.

2018-03-01

We present herein a comprehensive study of how the equation of state affects laser imprinting by nonuniform laser irradiation of an inertial fusion target. It has been suggested that a stiffer and denser material would reduce laser imprinting based on the equation of motion with pressure perturbation. We examine the detailed temporal evolution of the imprint amplitude by using the two-dimensional radiation hydrodynamic simulation PINOCO-2D for diamond, which is a candidate stiff-ablator material for inertial fusion targets. The simulated laser imprinting amplitude is compared with experimental measurements of areal-density perturbations obtained by using face-on x-ray backlighting for diamond and polystyrene (PS) (the latter as a reference). The experimental results are well reproduced by the results of the PINOCO-2D simulation, which indicates that the imprinting amplitude due to nonuniform irradiation (average intensity, 4.0 × 1012 to 5.0 × 1013) differs by a factor of two to three between diamond and PS. The difference in laser imprinting is mainly related to the material density and compressibility. These parameters are key factors that determine the laser imprinting amplitude.

The effect of pre-plasma formation under nonlocal transport conditions for ultra-relativistic laser-plasma interaction

NASA Astrophysics Data System (ADS)

Holec, M.; Nikl, J.; Vranic, M.; Weber, S.

2018-04-01

Interaction of high-power lasers with solid targets is in general strongly affected by the limited contrast available. The laser pre-pulse ionizes the target and produces a pre-plasma which can strongly modify the interaction of the main part of the laser pulse with the target. This is of particular importance for future experiments which will use laser intensities above 1021 W cm-2 and which are subject to the limited contrast. As a consequence the main part of the laser pulse will be modified while traversing the pre-plasma, interacting with it partially. A further complication arises from the fact that the interaction of a high-power pre-pulse with solid targets very often takes place under nonlocal transport conditions, i.e. the characteristic mean-free-path of the particles and photons is larger than the characteristic scale-lengths of density and temperature. The classical diffusion treatment of radiation and heat transport in the hydrodynamic model is then insufficient for the description of the pre-pulse physics. These phenomena also strongly modify the formation of the pre-plasma which in turn affects the propagation of the main laser pulse. In this paper nonlocal radiation-hydrodynamic simulations are carried out and serve as input for subsequent kinetic simulations of ultra-high intensity laser pulses interacting with the plasma in the ultra-relativistic regime. It is shown that the results of the kinetic simulations differ considerably whether a diffusive or nonlocal transport is used for the radiation-hydrodynamic simulations.

Mathematical simulation of the thermal diffusion in dentine irradiated with Nd:YAG laser using finite difference method

NASA Astrophysics Data System (ADS)

Moriyama, Eduardo H.; Zangaro, Renato A.; Lobo, Paulo D. d. C.; Villaverde, Antonio G. J. B.; Watanabe-Sei, Ii; Pacheco, Marcos T. T.; Otsuka, Daniel K.

2002-06-01

Thermal damage in dental pulp during Nd:YAG laser irradiation have been studied by several researchers; but due to dentin inhomogeneous structure, laser interaction with dentin in the hypersensitivity treatment are not fully understood. In this work, heat distribution profile on human dentine samples irradiated with Nd:YAG laser was simulated at surface and subjacent layers. Calculations were carried out using the Crank-Nicolson's finite difference method. Sixteen dentin samples with 1,5 mm of thickness were evenly distributed into four groups and irradiated with Nd:YAG laser pulses, according to the following scheme: (I) 1 pulse of 900 mJ, (II) 2 pulses of 450 mJ, (III) 3 pulses of 300 mJ, (IV) 6 pulses of 150 mJ; corresponding to a total laser energy of 900 mJ. The pulse interval was 300ms, the pulse duration of 900 ms and irradiated surface area of 0,005 mm2. Laser induced morphological changes in dentin were observed for all the irradiated samples. The heat distribution throughout the dentin layer, from the external dentin surface to the pulpal chamber wall, was calculated for each case, in order to obtain further information about the pulsed Nd:YAG laser-oral hard tissue interaction. The simulation showed significant differences in the final temperature at the pulpal chamber, depending on the exposition time and the energy contained in the laser pulse.

Favorable target positions for intense laser acceleration of electrons in hydrogen-like, highly-charged ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pi, Liang-Wen; Starace, Anthony F.; Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030

2015-09-15

Classical relativistic Monte Carlo simulations of petawatt laser acceleration of electrons bound initially in hydrogen-like, highly-charged ions show that both the angles and energies of the laser-accelerated electrons depend on the initial ion positions with respect to the laser focus. Electrons bound in ions located after the laser focus generally acquire higher (≈GeV) energies and are ejected at smaller angles with respect to the laser beam. Our simulations assume a tightly-focused linearly-polarized laser pulse with intensity approaching 10{sup 22 }W/cm{sup 2}. Up to fifth order corrections to the paraxial approximation of the laser field in the focal region are taken intomore » account. In addition to the laser intensity, the Rayleigh length in the focal region is shown to play a significant role in maximizing the final energy of the accelerated electrons. Results are presented for both Ne{sup 9+} and Ar{sup 17+} target ions.« less

Comparison of retina damage thresholds simulating the femtosecond-laser in situ keratomileusis (fs-LASIK) process with two laser systems in the CW- and fs-regime

NASA Astrophysics Data System (ADS)

Sander, M.; Minet, O.; Zabarylo, U.; Müller, M.; Tetz, M. R.

2012-04-01

The femtosecond-laser in situ keratomileusis procedure affords the opportunity to correct ametropia by cutting transparent corneal tissue with ultra-short laser pulses. Thereby the tissue cut is generated by a laser-induced optical breakdown in the cornea with ultra-short laser pulses in the near-infrared range. Compared to standard procedures such as photorefractive keratectomy and laser in-situ keratomileusis with the excimer laser, where the risk potential for the eye is low due to the complete absorption of ultraviolet irradiation from corneal tissue, only a certain amount of the pulse energy is deposited in the cornea during the fs-LASIK process. The remaining energy propagates through the eye and interacts with the retina and the strong absorbing tissue layers behind. The objective of the presented study was to determine and compare the retina damage thresholds during the fs-LASIK process simulated with two various laser systems in the CW- and fs-regime.

Modeling experimental plasma diagnostics in the FLASH code: Thomson scattering

NASA Astrophysics Data System (ADS)

Weide, Klaus; Flocke, Norbert; Feister, Scott; Tzeferacos, Petros; Lamb, Donald

2017-10-01

Spectral analysis of the Thomson scattering of laser light sent into a plasma provides an experimental method to quantify plasma properties in laser-driven plasma experiments. We have implemented such a synthetic Thomson scattering diagnostic unit in the FLASH code, to emulate the probe-laser propagation, scattering and spectral detection. User-defined laser rays propagate into the FLASH simulation region and experience scattering (change in direction and frequency) based on plasma parameters. After scattering, the rays propagate out of the interaction region and are spectrally characterized. The diagnostic unit can be used either during a physics simulation or in post-processing of simulation results. FLASH is publicly available at flash.uchicago.edu. U.S. DOE NNSA, U.S. DOE NNSA ASC, U.S. DOE Office of Science and NSF.

Classical-trajectory simulation of accelerating neutral atoms with polarized intense laser pulses

NASA Astrophysics Data System (ADS)

Xia, Q. Z.; Fu, L. B.; Liu, J.

2013-03-01

In the present paper, we perform the classical trajectory Monte Carlo simulation of the complex dynamics of accelerating neutral atoms with linearly or circularly polarized intense laser pulses. Our simulations involve the ion motion as well as the tunneling ionization and the scattering dynamics of valence electron in the combined Coulomb and electromagnetic fields, for both helium (He) and magnesium (Mg). We show that for He atoms, only linearly polarized lasers can effectively accelerate the atoms, while for Mg atoms, we find that both linearly and circularly polarized lasers can successively accelerate the atoms. The underlying mechanism is discussed and the subcycle dynamics of accelerating trajectories is investigated. We have compared our theoretical results with a recent experiment [Eichmann Nature (London)NATUAS0028-083610.1038/nature08481 461, 1261 (2009)].

Comparisons of angularly and spectrally resolved Bremsstrahlung measurements to two-dimensional multi-stage simulations of short-pulse laser-plasma interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, C. D.; Kemp, A. J.; Pérez, F.

2013-05-15

A 2-D multi-stage simulation model incorporating realistic laser conditions and a fully resolved electron distribution handoff has been developed and compared to angularly and spectrally resolved Bremsstrahlung measurements from high-Z planar targets. For near-normal incidence and 0.5-1 × 10{sup 20} W/cm{sup 2} intensity, particle-in-cell (PIC) simulations predict the existence of a high energy electron component consistently directed away from the laser axis, in contrast with previous expectations for oblique irradiation. Measurements of the angular distribution are consistent with a high energy component when directed along the PIC predicted direction, as opposed to between the target normal and laser axis asmore » previously measured.« less

Directional interstitial brachytherapy from simulation to application

NASA Astrophysics Data System (ADS)

Lin, Liyong

Organs at risk (OAR) are sometimes adjacent to or embedded in or overlap with the clinical target volume (CTV) to be treated. The purpose of this PhD study is to develop directionally low energy gamma-emitting interstitial brachytherapy sources. These sources can be applied between OAR to selectively reduce hot spots in the OARs and normal tissues. The reduction of dose over undesired regions can expand patient eligibility or reduce toxicities for the treatment by conventional interstitial brachytherapy. This study covers the development of a directional source from design optimization to construction of the first prototype source. The Monte Carlo code MCNP was used to simulate the radiation transport for the designs of directional sources. We have made a special construction kit to assemble radioactive and gold-shield components precisely into D-shaped titanium containers of the first directional source. Directional sources have a similar dose distribution as conventional sources on the treated side but greatly reduced dose on the shielded side, with a sharp dose gradient between them. A three-dimensional dose deposition kernel for the 125I directional source has been calculated. Treatment plans can use both directional and conventional 125I sources at the same source strength for low-dose-rate (LDR) implants to optimize the dose distributions. For prostate tumors, directional 125I LDR brachytherapy can potentially reduce genitourinary and gastrointestinal toxicities and improve potency preservation for low risk patients. The combination of better dose distribution of directional implants and better therapeutic ratio between tumor response and late reactions enables a novel temporary LDR treatment, as opposed to permanent or high-dose-rate (HDR) brachytherapy for the intermediate risk T2b and high risk T2c tumors. Supplemental external-beam treatments can be shortened with a better brachytherapy boost for T3 tumors. In conclusion, we have successfully finished the design optimization and construction of the first prototype directional source. Potential clinical applications and potential benefits of directional sources have been shown for prostate and breast tumors.

Mathematical modeling of atherosclerotic plaque destabilization: Role of neovascularization and intraplaque hemorrhage.

PubMed

Guo, Muyi; Cai, Yan; Yao, Xinke; Li, Zhiyong

2018-08-07

Observational studies have identified angiogenesis from the adventitial vasa vasorum and intraplaque hemorrhage (IPH) as critical factors in atherosclerotic plaque progression and destabilization. Here we propose a mathematical model incorporating intraplaque neovascularization and hemodynamic calculation with plaque destabilization for the quantitative evaluation of the role of neoangiogenesis and IPH in the vulnerable atherosclerotic plaque formation. An angiogenic microvasculature is generated by two-dimensional nine-point discretization of endothelial cell proliferation and migration from the vasa vasorum. Three key cells (endothelial cells, smooth muscle cells and macrophages) and three key chemicals (vascular endothelial growth factors, extracellular matrix and matrix metalloproteinase) are involved in the plaque progression model, and described by the reaction-diffusion partial differential equations. The hemodynamic calculation of the microcirculation on the generated microvessel network is carried out by coupling the intravascular, interstitial and transvascular flow. The plasma concentration in the interstitial domain is defined as the description of IPH area according to the diffusion and convection with the interstitial fluid flow, as well as the extravascular movement across the leaky vessel wall. The simulation results demonstrate a series of pathophysiological phenomena during the vulnerable progression of an atherosclerotic plaque, including the expanding necrotic core, the exacerbated inflammation, the high microvessel density (MVD) region at the shoulder areas, the transvascular flow through the capillary wall and the IPH. The important role of IPH in the plaque destabilization is evidenced by simulations with varied model parameters. It is found that the IPH can significantly speed up the plaque vulnerability by increasing necrotic core and thinning fibrous cap. In addition, the decreased MVD and vessel permeability may slow down the process of plaque destabilization by reducing the IPH dramatically. We envision that the present model and its future advances can serve as a valuable theoretical platform for studying the dynamic changes in the microenvironment during the plaque destabilization. Copyright © 2018 Elsevier Ltd. All rights reserved.

Comparison of Alexandrite and Diode Lasers for Hair Removal in Dark and Medium Skin: Which is Better?

PubMed Central

Mustafa, Farhad Hamad; Jaafar, Mohamad Suhimi; Ismail, Asaad Hamid; Mutter, Kussay Nugamesh

2014-01-01

Introduction: To improve laser hair removal (LHR) for dark skin, the fluence rate reaching the hair follicle in LHR is important. This paper presents the results of a comparative study examining the function of wavelength on dark skin types using 755 nm alexandrite and 810 nm diode lasers. Methods: The structure of the skin was created using a realistic skin model by the Advanced Systems Analysis Program. Result: In this study, the alexandrite laser (755 nm) and diode laser (810 nm) beam–skin tissue interactions were simulated. The simulation results for both lasers differed. The transmission ratio of the diode laser to the dark skin dermis was approximately 4% more than that of the alexandrite laser for the same skin type. For the diode laser at skin depth z = 0.67 mm, the average transmission ratios of both samples were 36% and 27.5%, but those for the alexandrite laser at the same skin depth were 32% and 25%. Conclusion: Both lasers were suitable in LHR for dark skin types, but the diode laser was better than the alexandrite laser because the former could penetrate deeper into the dermis layer. PMID:25653820

Comparison of Alexandrite and Diode Lasers for Hair Removal in Dark and Medium Skin: Which is Better?

PubMed

Mustafa, Farhad Hamad; Jaafar, Mohamad Suhimi; Ismail, Asaad Hamid; Mutter, Kussay Nugamesh

2014-01-01

To improve laser hair removal (LHR) for dark skin, the fluence rate reaching the hair follicle in LHR is important. This paper presents the results of a comparative study examining the function of wavelength on dark skin types using 755 nm alexandrite and 810 nm diode lasers. The structure of the skin was created using a realistic skin model by the Advanced Systems Analysis Program. In this study, the alexandrite laser (755 nm) and diode laser (810 nm) beam-skin tissue interactions were simulated. The simulation results for both lasers differed. The transmission ratio of the diode laser to the dark skin dermis was approximately 4% more than that of the alexandrite laser for the same skin type. For the diode laser at skin depth z = 0.67 mm, the average transmission ratios of both samples were 36% and 27.5%, but those for the alexandrite laser at the same skin depth were 32% and 25%. Both lasers were suitable in LHR for dark skin types, but the diode laser was better than the alexandrite laser because the former could penetrate deeper into the dermis layer.

Recycling of laser and plasma radiation energy for enhancement of extreme ultraviolet sources for nanolithography

NASA Astrophysics Data System (ADS)

Sizyuk, V.; Sizyuk, T.; Hassanein, A.; Johnson, K.

2018-01-01

We have developed comprehensive integrated models for detailed simulation of laser-produced plasma (LPP) and laser/target interaction, with potential recycling of the escaping laser and out-of-band plasma radiation. Recycling, i.e., returning the escaping laser and plasma radiation to the extreme ultraviolet (EUV) generation region using retroreflective mirrors, has the potential of increasing the EUV conversion efficiency (CE) by up to 60% according to our simulations. This would result in significantly reduced power consumption and/or increased EUV output. Based on our recently developed models, our High Energy Interaction with General Heterogeneous Target Systems (HEIGHTS) computer simulation package was upgraded for LPP devices to include various radiation recycling regimes and to estimate the potential CE enhancement. The upgraded HEIGHTS was used to study recycling of both laser and plasma-generated radiation and to predict possible gains in conversion efficiency compared to no-recycling LPP devices when using droplets of tin target. We considered three versions of the LPP system including a single CO2 laser, a single Nd:YAG laser, and a dual-pulse device combining both laser systems. The gains in generating EUV energy were predicted and compared for these systems. Overall, laser and radiation energy recycling showed the potential for significant enhancement in source efficiency of up to 60% for the dual-pulse system. Significantly higher CE gains might be possible with optimization of the pre-pulse and main pulse parameters and source size.

A case of acute kidney injury caused by granulomatous interstitial nephritis associated with sarcoidosis.

PubMed

Horino, Taro; Matsumoto, Tatsuki; Inoue, Kosuke; Ichii, Osamu; Terada, Yoshio

2018-05-01

Sarcoidosis affects multiple organs including lung, heart and kidney. Sarcoidosis causes hypercalcemia, hypergammaglobulinemia, and rarely, granulomatous interstitial nephritis, resulting in renal stromal damage. Granulomatous interstitial nephritis is characterized as interstitial nephritis with noncaseating epithelioid granulomas. Diagnosing granulomatous interstitial nephritis before patient's death is challenging; hence, only few cases proven by renal biopsy have been reported till date. We present a case of acute kidney injury caused by granulomatous interstitial nephritis as a renal manifestation of sarcoidosis proven by renal biopsy, which can be confirmed by 18 F-fluorodeoxyglucose positron emission tomography/computed tomography. Glucocorticoid therapy was helpful for improving and maintaining her renal function over a 6-year period.

Thermal analysis and experimental study of end-pumped Nd: YLF laser at 1053 nm

NASA Astrophysics Data System (ADS)

El-Agmy, R. M.; Al-Hosiny, N.

2017-12-01

We have numerically analyzed the thermal effects in Nd: YLF laser rod. The calculations of temperature and stress distributions in the Nd: YLF laser rod was performed with finite element (FE) simulations. The calculations showed that the laser rod could be pumped up to a power of 40 W without fracture caused by thermal stress. The calculated thermal lens power of thermally induced lens in Nd: YLF ( σ-polarization) laser rod was analyzed and validated experimentally with two independent techniques. A Shack-Hartmann wavefront sensor and a Mach-Zehnder interferometer were used for direct measurements of focal thermal lens at different pump powers. The obtained measurements were coinciding with the FE simulations.

Numerical simulations of novel high-power high-brightness diode laser structures

NASA Astrophysics Data System (ADS)

Boucke, Konstantin; Rogg, Joseph; Kelemen, Marc T.; Poprawe, Reinhart; Weimann, Guenter

2001-07-01

One of the key topics in today's semiconductor laser development activities is to increase the brightness of high-power diode lasers. Although structures showing an increased brightness have been developed specific draw-backs of these structures lead to a still strong demand for investigation of alternative concepts. Especially for the investigation of basically novel structures easy-to-use and fast simulation tools are essential to avoid unnecessary, cost and time consuming experiments. A diode laser simulation tool based on finite difference representations of the Helmholtz equation in 'wide-angle' approximation and the carrier diffusion equation has been developed. An optimized numerical algorithm leads to short execution times of a few seconds per resonator round-trip on a standard PC. After each round-trip characteristics like optical output power, beam profile and beam parameters are calculated. A graphical user interface allows online monitoring of the simulation results. The simulation tool is used to investigate a novel high-power, high-brightness diode laser structure, the so-called 'Z-Structure'. In this structure an increased brightness is achieved by reducing the divergency angle of the beam by angular filtering: The round trip path of the beam is two times folded using internal total reflection at surfaces defined by a small index step in the semiconductor material, forming a stretched 'Z'. The sharp decrease of the reflectivity for angles of incidence above the angle of total reflection leads to a narrowing of the angular spectrum of the beam. The simulations of the 'Z-Structure' indicate an increase of the beam quality by a factor of five to ten compared to standard broad-area lasers.

Laser dynamics in transversely inhomogeneous plasma and its relevance to wakefield acceleration

NASA Astrophysics Data System (ADS)

Pathak, V. B.; Vieira, J.; Silva, L. O.; Nam, Chang Hee

2018-05-01

We present full set of coupled equations describing the weakly relativistic dynamics of a laser in a plasma with transverse inhomogeneity. We apply variational principle approach to obtain these coupled equations governing laser spot-size, transverse wavenumber, curvature, transverse centroid, etc. We observe that such plasma inhomogeneity can lead to stronger self-focusing. We further discuss the guiding conditions of laser in parabolic plasma channels. With the help of multi-dimensional particle in cell simulations the study is extended to the blowout regime of laser wakefield acceleration to show laser as well as self-injected electron bunch steering in plasma to generate unconventional particle trajectories. Our simulation results demonstrate that such transverse inhomogeneities due to asymmetric self focusing lead to asymmetric bubble excitation, thus inducing off-axis self-injection.

Narrow bandwidth Laser-Plasma Accelerator driven Thomson photon source development

NASA Astrophysics Data System (ADS)

Geddes, C. G. R.; Tsai, H.-E.; Otero, G.; Liu, X.; van Tilborg, J.; Toth, Cs.; Vay, J.-L.; Lehe, R.; Schroeder, C. B.; Esarey, E.; Friedman, A.; Grote, D. P.; Leemans, W. P.

2017-10-01

Compact, high-quality photon sources at MeV energies can be provided by Thomson scattering of a laser from the electron beam of a Laser-Plasma Accelerator (LPA). Recent experiments and simulations demonstrate controllable LPAs in the energy range appropriate to MeV sources. Simulations indicate that high flux with narrow energy spread can be achieved via control of the scattering laser pulse shape and laser guiding, and that undesired background bremsstrahlung can be mitigated by plasma based deceleration of the electron beam after photon production. Construction of experiments and laser capabilities to combine these elements will be presented, along with initial operations, towards a compact photon source system. Work supported by US DOE NNSA DNN R&D and by Sc. HEP under contract DE-AC02-05CH11231.

Evolution of anisotropy in bcc Fe distorted by interstitial boron

NASA Astrophysics Data System (ADS)

Gölden, Dominik; Zhang, Hongbin; Radulov, Iliya; Dirba, Imants; Komissinskiy, Philipp; Hildebrandt, Erwin; Alff, Lambert

2018-01-01

The evolution of magnetic anisotropy in bcc Fe as a function of interstitial boron atoms was investigated in thin films grown by molecular beam epitaxy. The thermodynamic nonequilibrium conditions during film growth allowed one to stabilize an interstitial boron content of about 14 at .% accompanied by lattice tetragonalization. The c /a ratio scaled linearly with the boron content up to a maximum value of 1.05 at 300 °C substrate growth temperature, with a room-temperature magnetization of. In contrast to nitrogen interstitials, the magnetic easy axis remained in-plane with an anisotropy of approximately -5.1 ×106erg /cm3 . Density functional theory calculations using the measured lattice parameters confirm this value and show that boron local ordering indeed favors in-plane magnetization. Given the increased temperature stability of boron interstitials as compared to nitrogen interstitials, this study will help to find possible ways to manipulate boron interstitials into a more favorable local order.

Receiver design, performance analysis, and evaluation for space-borne laser altimeters and space-to-space laser ranging systems

NASA Technical Reports Server (NTRS)

Davidson, Frederic M.; Sun, Xiaoli; Field, Christopher T.

1994-01-01

This interim report consists of two reports: 'Space Radiation Effects on Si APDs for GLAS' and 'Computer Simulation of Avalanche Photodiode and Preamplifier Output for Laser Altimeters.' The former contains a detailed description of our proton radiation test of Si APD's performed at the Brookhaven National Laboratory. The latter documents the computer program subroutines which were written for the upgrade of NASA's GLAS simulator.

Chylothorax in dermatomyositis complicated with interstitial pneumonia.

PubMed

Isoda, Kentaro; Kiboshi, Takao; Shoda, Takeshi

2017-04-01

Chylothorax is a disease in which chyle leaks and accumulates in the thoracic cavity. Interstitial pneumonia and pneumomediastinum are common thoracic manifestations of dermatomyositis, but chylothorax complicated with dermatomyositis is not reported. We report a case of dermatomyositis with interstitial pneumonia complicated by chylothorax. A 77-year-old woman was diagnosed as dermatomyositis with Gottron's papules, skin ulcers, anti-MDA5 antibody and rapid progressive interstitial pneumonia. Treatment with betamethasone, tacrolimus and intravenous high-dose cyclophosphamide was initiated, and her skin symptoms and interstitial pneumonia improved once. However, right-sided chylothorax began to accumulate and gradually increase, and at the same time, her interstitial pneumonia began to exacerbate, and skin ulcers began to reappear on her fingers and auricles. Although her chylothorax improved by fasting and parenteral nutrition, she died due to further exacerbations of dermatomyositis and interstitial pneumonia in spite of steroid pulse therapy, increase in the betamethasone dosage, additional intravenous high-dose cyclophosphamide and plasma pheresis. An autopsy showed no lesions such as malignant tumors in the thoracic cavity. This is the first report of chylothorax complicated by dermatomyositis with interstitial pneumonia.

Smoking-related interstitial lung diseases.

PubMed

Caminati, A; Graziano, P; Sverzellati, N; Harari, S

2010-12-01

In pulmonary pathology, a wide spectrum of morphological changes is related to the consequences of smoking, and recognizing them on surgical specimens and on small transbronchial biopsies represents a challenge for the pathologist. Respiratory bronchiolitis, also referred to as smoker's bronchiolitis, is a common histologic feature found in the lung tissue of cigarette smokers. When identified as the sole histopathologic finding in the clinical setting of symptomatic interstitial lung disease, a diagnosis of respiratory bronchiolitis-interstitial lung disease is made. Since smoking is recognized to cause a variety of histologic patterns encompassing respiratory bronchiolitis, respiratory bronchiolitis-interstitial lung disease, desquamative interstitial pneumonia and pulmonary Langerhans cell hystiocytosis, smoking-related interstitial lung disease may be a useful concept to keep in mind for the pathologists. The relationship of smoking with each of these entities has been largely established on the basis of epidemiologic evidence. Although they have been retained as distinct and separate conditions in various classifications of interstitial lung diseases, these entities share a number of clinical, radiologic, and pathologic features suggesting that they represent a spectrum of patterns of interstitial lung disease occurring in predisposed individuals who smoke. Evaluation of histologic features, particularly in surgical lung biopsy samples, is important in making the distinction between these disorders. However, even after tissue biopsy, it may sometimes be difficult to clearly separate these entities. Recently, respiratory bronchiolitis-interstitial lung disease with fibrosis has been described and postulated that this is a smoking-related condition distinct from fibrotic non-specific interstitial pneumonia.

A Learning Based Fiducial-driven Registration Scheme for Evaluating Laser Ablation Changes in Neurological Disorders.

PubMed

Wan, Tao; Bloch, B Nicolas; Danish, Shabbar; Madabhushi, Anant

2014-11-20

In this work, we present a novel learning based fiducial driven registration (LeFiR) scheme which utilizes a point matching technique to identify the optimal configuration of landmarks to better recover deformation between a target and a moving image. Moreover, we employ the LeFiR scheme to model the localized nature of deformation introduced by a new treatment modality - laser induced interstitial thermal therapy (LITT) for treating neurological disorders. Magnetic resonance (MR) guided LITT has recently emerged as a minimally invasive alternative to craniotomy for local treatment of brain diseases (such as glioblastoma multiforme (GBM), epilepsy). However, LITT is currently only practised as an investigational procedure world-wide due to lack of data on longer term patient outcome following LITT. There is thus a need to quantitatively evaluate treatment related changes between post- and pre-LITT in terms of MR imaging markers. In order to validate LeFiR, we tested the scheme on a synthetic brain dataset (SBD) and in two real clinical scenarios for treating GBM and epilepsy with LITT. Four experiments under different deformation profiles simulating localized ablation effects of LITT on MRI were conducted on 286 pairs of SBD images. The training landmark configurations were obtained through 2000 iterations of registration where the points with consistently best registration performance were selected. The estimated landmarks greatly improved the quality metrics compared to a uniform grid (UniG) placement scheme, a speeded-up robust features (SURF) based method, and a scale-invariant feature transform (SIFT) based method as well as a generic free-form deformation (FFD) approach. The LeFiR method achieved average 90% improvement in recovering the local deformation compared to 82% for the uniform grid placement, 62% for the SURF based approach, and 16% for the generic FFD approach. On the real GBM and epilepsy data, the quantitative results showed that LeFiR outperformed UniG by 28% improvement in average.

Proteomics detection of S100A6 in tumor tissue interstitial fluid and evaluation of its potential as a biomarker of cholangiocarcinoma.

PubMed

Onsurathum, Sudarat; Haonon, Ornuma; Pinlaor, Porntip; Pairojkul, Chawalit; Khuntikeo, Narong; Thanan, Raynoo; Roytrakul, Sittiruk; Pinlaor, Somchai

2018-04-01

Tumor interstitial fluid contains tumor-specific proteins that may be useful biomarkers for cancers. In this study, we identified proteins present in cholangiocarcinoma interstitial fluid. Proteins derived from three samples of tumor interstitial fluid and paired samples of adjacent normal interstitial fluid from cholangiocarcinoma patients were subjected to two-dimensional liquid chromatography with tandem mass spectrometry. Candidate proteins were selected based on a greater than twofold change in expression levels between tumor interstitial fluid and normal interstitial fluid. Upregulation of six proteins in tumor interstitial fluid, including S100 calcium binding protein A6 (S100A6), S100 calcium binding protein A9, aldo-keto reductase family 1 member C4, neuropilin-1, 14-3-3 zeta/delta, and triosephosphate isomerase was assessed by western blot and immunohistochemistry. Their potential as markers was evaluated in human cholangiocarcinoma tissue arrays, and in serum using enzyme-linked immunosorbent assay. Expression of S100A6 was higher in tumor interstitial fluid than in normal interstitial fluid and showed the highest positive rate (98.96%) in cholangiocarcinoma tissues. Serum levels of S100A6 did not differ between cholangitis and cholangiocarcinoma patients, but were significantly higher than in healthy individuals ( p < 0.0001). In cholangiocarcinoma cases, S100A6 level was associated with vascular invasion ( p = 0.007) and could distinguish cholangiocarcinoma patients from healthy individuals as effectively as the carbohydrate antigen 19-9. In addition, potential for drug treatment targeting S100A6 and other candidate proteins was also demonstrated using STITCH analysis. In conclusion, proteomics analysis of tumor interstitial fluid could be a new approach for biomarker discovery, and S100A6 is a potential risk marker for screening of cholangiocarcinoma.

Shock ignition targets: gain and robustness vs ignition threshold factor

NASA Astrophysics Data System (ADS)

Atzeni, Stefano; Antonelli, Luca; Schiavi, Angelo; Picone, Silvia; Volponi, Gian Marco; Marocchino, Alberto

2017-10-01

Shock ignition is a laser direct-drive inertial confinement fusion scheme, in which the stages of compression and hot spot formation are partly separated. The hot spot is created at the end of the implosion by a converging shock driven by a final ``spike'' of the laser pulse. Several shock-ignition target concepts have been proposed and relevant gain curves computed (see, e.g.). Here, we consider both pure-DT targets and more facility-relevant targets with plastic ablator. The investigation is conducted with 1D and 2D hydrodynamic simulations. We determine ignition threshold factors ITF's (and their dependence on laser pulse parameters) by means of 1D simulations. 2D simulations indicate that robustness to long-scale perturbations increases with ITF. Gain curves (gain vs laser energy), for different ITF's, are generated using 1D simulations. Work partially supported by Sapienza Project C26A15YTMA, Sapienza 2016 (n. 257584), Eurofusion Project AWP17-ENR-IFE-CEA-01.

Measuring implosion velocities in experiments and simulations of laser-driven cylindrical implosions on the OMEGA laser

NASA Astrophysics Data System (ADS)

Hansen, E. C.; Barnak, D. H.; Betti, R.; Campbell, E. M.; Chang, P.-Y.; Davies, J. R.; Glebov, V. Yu; Knauer, J. P.; Peebles, J.; Regan, S. P.; Sefkow, A. B.

2018-05-01

Laser-driven magnetized liner inertial fusion (MagLIF) on OMEGA involves cylindrical implosions, a preheat beam, and an applied magnetic field. Initial experiments excluded the preheat beam and magnetic field to better characterize the implosion. X-ray self-emission as measured by framing cameras was used to determine the shell trajectory. The 1D code LILAC was used to model the central region of the implosion, and results were compared to 2D simulations from the HYDRA code. Post-processing of simulation output with SPECT3D and Yorick produced synthetic x-ray images that were used to compare the simulation results with the x-ray framing camera data. Quantitative analysis shows that higher measured neutron yields correlate with higher implosion velocities. The future goal is to further analyze the x-ray images to characterize the uniformity of the implosions and apply these analysis techniques to integrated laser-driven MagLIF shots to better understand the effects of preheat and the magnetic field.

Design and Analysis of Enhanced Modulation Response in Integrated Coupled Cavities DBR Lasers Using Photon-Photon Resonance

DOE PAGES

Bardella, Paolo; Chow, Weng; Montrosset, Ivo

2016-01-08

In the last decades, various solutions have been proposed to increase the modulation bandwidth and consequently the transmission bit rate of integrated semiconductor lasers. In this manuscript we discuss a design procedure for a recently proposed laser structure realized with the integration of two DBR lasers. Design guidelines will be proposed and dynamic small and large signal simulations, calculated using a Finite Difference Traveling Wave numerical simulator, will be performed to confirm the design results and the effectiveness of the analyzed integrated configuration to achieve a direct modulation bandwidth up to 80 GHz

Graphene production by laser shot on graphene oxide: An ab initio prediction

NASA Astrophysics Data System (ADS)

Zhang, Hong; Miyamoto, Yoshiyuki

2012-01-01

By performing the first-principles simulation of electron-ion dynamics based on the time-dependent density-functional theory, we propose a way to produce graphene from graphene oxides by means of the laser-induced reduction without using chemical species. Epoxy and hydroxyl groups on graphene sheets can be completely removed upon irradiation with femtosecond laser without damaging the graphene sheet. By comparing the simulated results with different pulse shapes and intensities, optimum conditions of the femtosecond laser for reduction of graphene oxide were determined. The current works will be useful for further experimental researches.

Photonic generation of ultra-wideband signals by direct current modulation on SOA section of an SOA-integrated SGDBR laser.

PubMed

Lv, Hui; Yu, Yonglin; Shu, Tan; Huang, Dexiu; Jiang, Shan; Barry, Liam P

2010-03-29

Photonic ultra-wideband (UWB) pulses are generated by direct current modulation of a semiconductor optical amplifier (SOA) section of an SOA-integrated sampled grating distributed Bragg reflector (SGDBR) laser. Modulation responses of the SOA section of the laser are first simulated with a microwave equivalent circuit model. Simulated results show a resonance behavior indicating the possibility to generate UWB signals with complex shapes in the time domain. The UWB pulse generation is then experimentally demonstrated for different selected wavelength channels with an SOA-integrated SGDBR laser.

Analysis of detection performance of multi band laser beam analyzer

NASA Astrophysics Data System (ADS)

Du, Baolin; Chen, Xiaomei; Hu, Leili

2017-10-01

Compared with microwave radar, Laser radar has high resolution, strong anti-interference ability and good hiding ability, so it becomes the focus of laser technology engineering application. A large scale Laser radar cross section (LRCS) measurement system is designed and experimentally tested. First, the boundary conditions are measured and the long range laser echo power is estimated according to the actual requirements. The estimation results show that the echo power is greater than the detector's response power. Secondly, a large scale LRCS measurement system is designed according to the demonstration and estimation. The system mainly consists of laser shaping, beam emitting device, laser echo receiving device and integrated control device. Finally, according to the designed lidar cross section measurement system, the scattering cross section of target is simulated and tested. The simulation results are basically the same as the test results, and the correctness of the system is proved.

Dependence of optimal initial density on laser parameters for multi-keV x-ray radiators generated by nanosecond laser-produced underdense plasma

NASA Astrophysics Data System (ADS)

Tu, Shao-yong; Yuan, Yong-teng; Hu, Guang-yue; Miao, Wen-yong; Zhao, Bin; Zheng, Jian; Jiang, Shao-en; Ding, Yong-kun

2016-01-01

Efficient multi-keV x-ray sources can be produced using nanosecond laser pulse-heated middle-Z underdense plasmas generated using gas or foam. Previous experimental results show that an optimal initial target density exists for efficient multi-keV x-ray emission at which the laser ionization wave is supersonic. Here we explore the influence of the laser intensity and the pulse duration on this optimal initial target density via a one-dimensional radiation hydrodynamic simulation. The simulation shows that the optimal initial density is sensitive to both the laser intensity and the pulse duration. However, the speed of the supersonic ionization wave at the end of the laser irradiation is always maintained at 1.5 to 1.7 times that of the ion acoustic wave under the optimal initial density conditions.

Simulation of the main physical processes in remote laser penetration with large laser spot size

DOE PAGES

Khairallah, S. A.; Anderson, A.; Rubenchik, A. M.; ...

2015-04-10

A 3D model is developed to simulate remote laser penetration of a 1mm Aluminum metal sheet with large laser spot size (~3x3cm²), using the ALE3D multi-physics code. The model deals with the laser-induced melting of the plate and the mechanical interaction between the solid and the melted part through plate elastic-plastic response. The effect of plate oscillations and other forces on plate rupture, the droplet formation mechanism and the influence of gravity and high laser power in further breaking the single melt droplet into many more fragments are analyzed. In the limit of low laser power, the numerical results matchmore » the available experiments. The numerical approach couples mechanical and thermal diffusion to hydrodynamics melt flow and accounts for temperature dependent material properties, surface tension, gravity and vapor recoil pressure.« less

Numerical simulation of heat transfer and fluid flow in laser drilling of metals

NASA Astrophysics Data System (ADS)

Zhang, Tingzhong; Ni, Chenyin; Zhou, Jie; Zhang, Hongchao; Shen, Zhonghua; Ni, Xiaowu; Lu, Jian

2015-05-01

Laser processing as laser drilling, laser welding and laser cutting, etc. is rather important in modern manufacture, and the interaction of laser and matter is a complex phenomenon which should be detailed studied in order to increase the manufacture efficiency and quality. In this paper, a two-dimensional transient numerical model was developed to study the temperature field and molten pool size during pulsed laser keyhole drilling. The volume-of-fluid method was employed to track free surfaces, and melting and evaporation enthalpy, recoil pressure, surface tension, and energy loss due to evaporating materials were considered in this model. Besides, the enthalpy-porosity technique was also applied to account for the latent heat during melting and solidification. Temperature fields and melt pool size were numerically simulated via finite element method. Moreover, the effectiveness of the developed computational procedure had been confirmed by experiments.

Compositional and Microstructural Evolution of Olivine Under Multiple-Cycle Pulsed Laser Irradiation as Revealed by FIB/Field-Emission TEM

NASA Technical Reports Server (NTRS)

Christoffersen, R.; Loeffler, M. J.; Dukes, C. A.; Keller, L. P.; Baragiola, R. A.

2016-01-01

The use of pulsed laser irradiation to simulate the short duration, high-energy conditions characteristic of micrometeorite impacts is now an established approach in experimental space weathering studies. The laser generates both melt and vapor deposits that contain nanophase metallic Fe (npFe(sup 0)) grains with size distributions and optical properties similar to those in natural impact-generated melt and vapor deposits. There remains uncertainty, however, about how well lasers simulate the mechanical work and internal (thermal) energy partitioning that occurs in actual impacts. We are currently engaged in making a direct comparison between the products of laser irradiation and experimental/natural hypervelocity impacts. An initial step reported here is to use analytical SEM and TEM is to attain a better understanding of how the microstructure and composition of laser deposits evolve over multiple cycles of pulsed laser irradiation.

Numerical analysis of experiments on the generation of shock waves in aluminium under indirect (X-ray) action on the Iskra-5 facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bondarenko, S V; Dolgoleva, G V; Novikova, E A

The dynamics of laser and X-ray radiation fields in experiments with cylindrical converter boxes (illuminators), which had earlier been carried out on the Iskra-5 laser facility (the second harmonic of iodine laser radiation, {lambda} = 0.66 {mu}m) was investigated in a sector approximation using the SND-LIRA numerical technique. In these experiments, the X-ray radiation temperature in the box was determined by measuring the velocity of the shock wave generated in the sample under investigation, which was located at the end of the cylindrical illuminator. Through simulations were made using the SND-LIRA code, which took into account the absorption of lasermore » driver radiation at the box walls, the production of quasithermal radiation, as well as the formation and propagation of the shock wave in the sample under investigation. An analysis of the experiments permits determining the electron thermal flux limiter f: for f = 0.03 it is possible to match the experimental scaling data for X-ray in-box radiation temperature to the data of our simulations. The shock velocities obtained from the simulations are also consistent with experimental data. In particular, in the experiment with six laser beams (and a laser energy E{sub L} = 1380 J introduced into the box) the velocity of the shock front (determined from the position of a laser mark) after passage through a 50-{mu}m thick base aluminium layer was equal to 35{+-}1.6 km s{sup -1}, and in simulations to 36 km s{sup -1}. In the experiment with four laser beams (for E{sub L} = 850 J) the shock velocity (measured from the difference of transit times through the base aluminium layer and an additional thin aluminium platelet) was equal to 30{+-}3.6 km s{sup -1}, and in simulations to 30 km s{sup -1}. (interaction of laser radiation with matter)« less

Effect of pulse profile and chirp on a laser wakefield generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Xiaomei; Shen Baifei; Ji Liangliang

2012-05-15

A laser wakefield driven by an asymmetric laser pulse with/without chirp is investigated analytically and through two-dimensional particle-in-cell simulations. For a laser pulse with an appropriate pulse length compared with the plasma wavelength, the wakefield amplitude can be enhanced by using an asymmetric un-chirped laser pulse with a fast rise time; however, the growth is small. On the other hand, the wakefield can be greatly enhanced for both positively chirped laser pulse having a fast rise time and negatively chirped laser pulse having a slow rise time. Simulations show that at the early laser-plasma interaction stage, due to the influencemore » of the fast rise time the wakefield driven by the positively chirped laser pulse is more intense than that driven by the negatively chirped laser pulse, which is in good agreement with analytical results. At a later time, since the laser pulse with positive chirp exhibits opposite evolution to the one with negative chirp when propagating in plasma, the wakefield in the latter case grows more intensely. These effects should be useful in laser wakefield acceleration experiments operating at low plasma densities.« less

Laser simulation applying Fox-Li iteration: investigation of reason for non-convergence

NASA Astrophysics Data System (ADS)

Paxton, Alan H.; Yang, Chi

2017-02-01

Fox-Li iteration is often used to numerically simulate lasers. If a solution is found, the complex field amplitude is a good indication of the laser mode. The case of a semiconductor laser, for which the medium possesses a self-focusing nonlinearity, was investigated. For a case of interest, the iterations did not yield a converged solution. Another approach was needed to explore the properties of the laser mode. The laser was treated (unphysically) as a regenerative amplifier. As the input to the amplifier, we required a smooth complex field distribution that matched the laser resonator. To obtain such a field, we found what would be the solution for the laser field if the strength of the self focusing nonlinearity were α = 0. This was used as the input to the laser, treated as an amplifier. Because the beam deteriorated as it propagated multiple passes in the resonator and through the gain medium (for α = 2.7), we concluded that a mode with good beam quality could not exist in the laser.

Development of a two photon/laser induced fluorescence technique for the detection of atmospheric OH radicals

NASA Technical Reports Server (NTRS)

Bradshaw, John

1990-01-01

The development of a new mid-IR laser source was the primary goal. Backward propagating stimulated D2 Raman frequency down conversion of a commercially available 1.06 micron Nd:YAG laser was shown to generate an efficient source of 1.56 micron radiation with near diffraction limited beam quality. The efficient generation of a 2.9 micron laser source was also achieved using backward propagating CH4 Raman frequency down conversion of the 1.56 micron pump. Slightly higher efficiencies were obtained for frequency down conversion of the 1.06 micron Nd:YAG using the H2 Raman shift yielding a near diffraction limited source in the 200 mJ range at 1.9 micron. Similar conversion efficiencies are anticipated as a result of extending the wavelength coverage of recently available Ti:sapphire pulse laser to not only cover the 740 to 860 nm fundamental wavelength range but also the .95 to 1.15 and 1.06 to 1.33 micron range using D2 and H2, respectively. The anticipated sensitivity of a TP-LIF OH sensor using this mid-IR source would give signal limited detection of 1.4 x 10(exp 5) OH/cu cm under boundary layer conditions and 5.5 x 10(exp 4) OH/cu cm under free troposphere sampling conditions for a five minute signal integration period. This level of performance coupled with the techniques non-perturbing nature and freedom from both interferences and background would allow reliable tropospheric OH measurement to be obtained under virtually any ambient condition of current interest, including interstitial and sampling.

Improved operative efficiency using a real-time MRI-guided stereotactic platform for laser amygdalohippocampotomy.

PubMed

Ho, Allen L; Sussman, Eric S; Pendharkar, Arjun V; Le, Scheherazade; Mantovani, Alessandra; Keebaugh, Alaine C; Drover, David R; Grant, Gerald A; Wintermark, Max; Halpern, Casey H

2018-04-01

OBJECTIVE MR-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive method for thermal destruction of benign or malignant tissue that has been used for selective amygdalohippocampal ablation for the treatment of temporal lobe epilepsy. The authors report their initial experience adopting a real-time MRI-guided stereotactic platform that allows for completion of the entire procedure in the MRI suite. METHODS Between October 2014 and May 2016, 17 patients with mesial temporal sclerosis were selected by a multidisciplinary epilepsy board to undergo a selective amygdalohippocampal ablation for temporal lobe epilepsy using MRgLITT. The first 9 patients underwent standard laser ablation in 2 phases (operating room [OR] and MRI suite), whereas the next 8 patients underwent laser ablation entirely in the MRI suite with the ClearPoint platform. A checklist specific to the real-time MRI-guided laser amydalohippocampal ablation was developed and used for each case. For both cohorts, clinical and operative information, including average case times and accuracy data, was collected and analyzed. RESULTS There was a learning curve associated with using this real-time MRI-guided system. However, operative times decreased in a linear fashion, as did total anesthesia time. In fact, the total mean patient procedure time was less in the MRI cohort (362.8 ± 86.6 minutes) than in the OR cohort (456.9 ± 80.7 minutes). The mean anesthesia time was significantly shorter in the MRI cohort (327.2 ± 79.9 minutes) than in the OR cohort (435.8 ± 78.4 minutes, p = 0.02). CONCLUSIONS The real-time MRI platform for MRgLITT can be adopted in an expedient manner. Completion of MRgLITT entirely in the MRI suite may lead to significant advantages in procedural times.

Temperature-controlled two-wavelength laser soldering of tissues.

PubMed

Gabay, Ilan; Abergel, Avraham; Vasilyev, Tamar; Rabi, Yaron; Fliss, Dan M; Katzir, Abraham

2011-11-01

Laser tissue soldering is a method for bonding of incisions in tissues. A biological solder is spread over the cut, laser radiation heats the solder and the underlying cut edges and the incision is bonded. This method offers many advantages over conventional techniques (e.g., sutures). Past researches have shown that laser soldering, using a single laser, does not provide sufficient strength for bonding of cuts in thick (>1 mm) tissues. This study introduces a novel method for laser soldering of thick tissues, under temperature control, using two lasers, emitting two different wavelengths. An experimental system was built, using two lasers: (i) a CO(2) laser, whose radiation heated the upper surface of the tissue and (ii) a GaAs laser that heated an albumin layer under the tissue. An infrared fiber-optic radiometer monitored the temperature of the tissue. All three devices were connected to a computer that controlled the process. A computer simulation was written to optimize the system parameters. The system was tested on tissue phantoms, to validate the simulation and ensure that both the upper and lower sides of the cut were heated, and that the temperature could be controlled on both sides. The system was then used ex vivo to bond longitudinal cuts of lengths ∼12 mm in the esophagi of large farm pigs. The theoretical simulations showed a good stabilization of the temperatures at the upper and lower tissue surfaces at the target values. Experiments on tissue phantom showed a good agreement with these simulations. Incisions in esophagi, removed from large farm pigs, were then successfully bonded. The mean burst pressure was ∼3.6 m of water. This study demonstrated the capability of soldering cuts in thick tissues, paving the way for new types of surgical applications. Copyright © 2010 Wiley Periodicals, Inc.

Intracranial evaluation and laser ablation for epilepsy with periventricular nodular heterotopia.

PubMed

Thompson, Stephen A; Kalamangalam, Giridhar P; Tandon, Nitin

2016-10-01

Surgical treatment of focal epilepsy in the presence of periventricular nodular heterotopia (PVNH) poses a challenge, as the relative roles of the nodular tissue and the overlying cortex in the generation of seizures can be complex and variable. Here, we review the literature on chronic invasive EEG recordings in humans with this substrate and present two illustrative cases from our practice. We found that while inter-ictal spiking from nodules is common, clinical seizures rarely arise solely from nodular tissue. More typically, ictal onset is simultaneous with overlying neocortex or mesial temporal structures. Surgical outcome is more favorable in cases with unilateral (as opposed to bilateral) PVNH, and when a substantial or complete ablation of PVNH is performed. In rare cases, nodular ablation alone may be sufficient, as may be completed by MRI-guided laser interstitial thermal therapy. The mechanism(s) by which PNVH interacts with overlying cortex are not fully understood, but we suggest that PVNH either orchestrates or amplifies local network epileptogenicity. At present, invasive recordings with penetrating depth electrodes are required prior to surgical therapy, as illustrated in our cases. Published by Elsevier Ltd.

A Noninvasive In Vivo Glucose Sensor Based on Mid-Infrared Quantum Cascade Laser Spectroscopy

NASA Astrophysics Data System (ADS)

Werth, Alexandra; Liakat, Sabbir; Xu, Laura; Gmachl, Claire

Diabetes affects over 387 million people worldwide; a number which grows every year. The most common method of measuring blood glucose concentration involves a finger prick which for some can be a harrowing process. Therefore, a portable, accurate, noninvasive glucose sensor can significantly improve the quality of life for many of these diabetics who draw blood multiple times a day to monitor their glucose levels. We have implemented a noninvasive, mobile glucose sensor using a mid-infrared (MIR) quantum cascade laser (QCL), integrating sphere, and thermal electrically (TE) cooled detector. The QCL is scanned from 8 - 10 microns wavelength over which are distinct absorption features of glucose molecules with little competition of absorption from other molecules found in the blood and interstitial fluid. The obtained absorption spectra are analyzed using a neural network algorithm which relates the small changes in absorption to the changing glucose concentration. The integrating sphere has increased the signal-to-noise ratio from a previous design, allowing us to use the TE-cooled detector which increases mobility without loss of accuracy.

Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties

NASA Astrophysics Data System (ADS)

Wycisk, Eric; Solbach, Andreas; Siddique, Shafaqat; Herzog, Dirk; Walther, Frank; Emmelmann, Claus

Laser Additive Manufacturing (LAM) enables economical production of complex lightweight structures as well as patient individual implants. Due to these possibilities the additive manufacturing technology gains increasing importance in the aircraft and the medical industry. Yet these industries obtain high quality standards and demand predictability of material properties for static and dynamic load cases. However, especially fatigue and crack propagation properties are not sufficiently determined. Therefore this paper presents an analysis and simulation of crack propagation behavior considering Laser Additive Manufacturing specific defects, such as porosity and surface roughness. For the mechanical characterization of laser additive manufactured titanium alloy Ti-6Al-4V, crack propagation rates are experimentally determined and used for an analytical modeling and simulation of fatigue. Using experimental results from HCF tests and simulated data, the fatigue and crack resistance performance is analyzed considering material specific defects and surface roughness. The accumulated results enable the reliable prediction of the defects influence on fatigue life of laser additive manufactured titanium components.

Laser-Plasma Interactions on NIKE and the Fusion Test Facility

NASA Astrophysics Data System (ADS)

Phillips, Lee; Weaver, James

2008-11-01

Recent proposed designs for a Fusion Test Facility (FTF) (Obenchain et al., Phys. Plasmas 13 056320 (2006)) for direct-drive ICF targets for energy applications involve high implosion velocities combined with higher laser irradiances. The use of high irradiances increases the likelihood of deleterious laser plasma instabilities (LPI) but the proposed use of a 248 nm KrF laser to drive these targets is expected to minimize the LPI risk. We examine, using simulation results from NRL's FAST hydrocode, the proposed operational regimes of the FTF in relation to the thresholds for the SRS, SBS, and 2-plasmon instabilities. Simulations are also used to help design and interpret ongoing experiments being conducted at NRL's NIKE facility for the purpose of generating and studying LPI. Target geometries and laser pulseshapes were devised in order to create plasma conditions with long scalelengths and low electron temperatures that allow the growth of parametric instabilities. These simulations include the effects of finite beam angles through the use of raytracing.

Grain boundary resistance to amorphization of nanocrystalline silicon carbide

PubMed Central

Chen, Dong; Gao, Fei; Liu, Bo

2015-01-01

Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized. PMID:26558694