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Sample records for aids-related diffuse small

  1. Gene Therapy After Frontline Chemotherapy in Treating Patients With AIDS-Related Non-Hodgkin Lymphoma

    ClinicalTrials.gov

    2016-03-14

    AIDS-related Diffuse Large Cell Lymphoma; AIDS-related Diffuse Mixed Cell Lymphoma; AIDS-related Diffuse Small Cleaved Cell Lymphoma; AIDS-related Immunoblastic Large Cell Lymphoma; AIDS-related Lymphoblastic Lymphoma; AIDS-related Small Noncleaved Cell Lymphoma; HIV Infection

  2. Treatment outcomes in AIDS-related diffuse large B-cell lymphoma in the setting roll-out of combination antiretroviral therapy in South Africa

    PubMed Central

    de Witt, Pieter; Maartens, Deborah J; Uldrick, Thomas S; Sissolak, Gerhard

    2013-01-01

    Background Long term survival for patients with AIDS-related diffuse large B-cell lymphoma (DLBCL) is feasible in settings with available combination antiretroviral therapy (cART). However, given limited oncology resources, outcomes for AIDS-associated DLBCL in South Africa are unknown. Methods We performed a retrospective analysis of survival in patients with newly diagnosed AIDS-related diffuse large B-cell lymphoma (DLBCL) treated at a tertiary teaching hospital in Cape Town, South Africa with CHOP or CHOP-like chemotherapy (January 2004 until Dec 2010). HIV and lymphoma related prognostic factors were evaluated. Results 36 patients evaluated; median age 37.3 years, 52.8% men, and 61.1% black South Africans. Median CD4 count 184 cells/μl (in 27.8% this was < 100 cells/μl), 80% high-risk according to the age-adjusted International Prognostic Index. Concurrent Mycobacterium tuberculosis in 25%. Two-year overall survival (OS) was 40.5% (median OS 10.5 months, 95%CI 6.5 – 31.8). ECOG performance status of 2 or more (25.4% versus 50.0%, p = 0.01) and poor response to cART (18.0% versus 53.9%, p = 0.03) predicted inferior 2-year OS. No difference in 2-year OS was demonstrated in patients co-infected with Mycobacterium tuberculosis (p = 0.87). Conclusions Two-year OS for patients with AIDS-related DLBCL treated with CHOP like regimens and cART is comparable to that seen in the US and Europe. Important factors effecting OS in AIDS-related DLBCL in South Africa include performance status at presentation and response to cART. Patients with co-morbid Mycobacterium tuberculosis or hepatitis B seropositivity appear to tolerate CHOP in our setting. Additional improvements in outcomes are likely possible. PMID:23797692

  3. Immunophenotypic Analysis of AIDS-Related Diffuse Large B-Cell Lymphoma and Clinical Implications in Patients From AIDS Malignancies Consortium Clinical Trials 010 and 034

    PubMed Central

    Chadburn, Amy; Chiu, April; Lee, Jeannette Y.; Chen, Xia; Hyjek, Elizabeth; Banham, Alison H.; Noy, Ariela; Kaplan, Lawrence D.; Sparano, Joseph A.; Bhatia, Kishor; Cesarman, Ethel

    2009-01-01

    Purpose Diffuse large B-cell lymphoma (DLBCL) represents a clinically heterogeneous disease. Models based on immunohistochemistry predict clinical outcome. These include subdivision into germinal center (GC) versus non-GC subtypes; proliferation index (measured by expression of Ki-67), and expression of BCL-2, FOXP1, or B-lymphocyte-induced maturation protein (Blimp-1)/PRDM1. We sought to determine whether immunohistochemical analyses of biopsies from patients with DLBCL having HIV infection are similarly relevant for prognosis. Patients and Methods We examined 81 DLBCLs from patients with AIDS in AMC010 (cyclophosphamide, doxorubicin, vincristine, and prednisone [CHOP] v CHOP-rituximab) and AMC034 (etoposide, doxorubicin, vincristine, prednisone, and dose-adjusted cyclophosphamide plus rituximab concurrent v sequential) clinical trials and compared the immunophenotype with survival data, Epstein-Barr virus (EBV) positivity, and CD4 counts. Results The GC and non-GC subtypes of DLBCL did not differ significantly with respect to overall survival or CD4 count at cancer presentation. EBV could be found in both subtypes of DLBCL, although less frequently in the GC subtype, and did not affect survival. Expression of FOXP1, Blimp-1/PRDM1, or BCL-2 was not correlated with the outcome in patients with AIDS-related DLBCL. Conclusion These data indicate that with current treatment strategies for lymphoma and control of HIV infection, commonly used immunohistochemical markers may not be clinically relevant in HIV-infected patients with DLBCL. The only predictive immunohistochemical marker was found to be Ki-67, where a higher proliferation index was associated with better survival, suggesting a better response to therapy in patients whose tumors had higher proliferation rates. PMID:19752343

  4. General Information about AIDS-Related Lymphoma

    MedlinePlus

    ... AIDS-Related Lymphoma Treatment (PDQ®)–Patient Version General Information About AIDS-Related Lymphoma Go to Health Professional ... the PDQ Adult Treatment Editorial Board . Clinical Trial Information A clinical trial is a study to answer ...

  5. Small-scale Anisotropies of Cosmic Rays from Relative Diffusion

    NASA Astrophysics Data System (ADS)

    Ahlers, Markus; Mertsch, Philipp

    2015-12-01

    The arrival directions of multi-TeV cosmic rays show significant anisotropies at small angular scales. It has been argued that this small-scale structure can naturally arise from cosmic ray scattering in local turbulent magnetic fields that distort a global dipole anisotropy set by diffusion. We study this effect in terms of the power spectrum of cosmic ray arrival directions and show that the strength of small-scale anisotropies is related to properties of relative diffusion. We provide a formalism for how these power spectra can be inferred from simulations and motivate a simple analytic extension of the ensemble-averaged diffusion equation that can account for the effect.

  6. Aids-Related Cancers in Africa

    NASA Astrophysics Data System (ADS)

    Mbulaiteye, Sam M.

    2014-07-01

    Thank you Professor Zichichi for inviting me to give a talk about AIDS-related cancers in Africa. Let me begin by congratulating the team that organized the 46th Session of the Erice International Seminar Series, whose theme is THE ROLE OF SCIENCE IN THE THIRD MILLENIUM. I also congratulate the scientists from 38 countries who are attending these seminars. They are perpetuating the principle of SCIENCE WITHOUT SECRETS in the true spirit espoused by Archimedes, Galileo, and Fermi. It is a wonderful honor for me to be here to shed some light on the health impacts of the HIV epidemic in the area of cancer...

  7. Thymostimulin treatment in AIDS-related complex.

    PubMed

    Palmisano, L; Chisesi, T; Galli, M; Gritti, F M; Ielasi, G; Lazzarin, A; Mezzaroma, I; Moroni, M; Raise, E; Vaglia, A

    1988-06-01

    Thirty-four patients with AIDS-related complex (ARC) were treated for 6 months with thymostimulin, a thymic hormone. Clinical and immunological findings after a 1-year follow-up were compared with those in 24 age- and sex-matched controls receiving no immunotherapy. Statistical evaluation after 6 and 12 months showed significant differences in the two groups. The thymostimulin-treated group had higher leukocyte and lymphocyte counts, more positivity in intradermal tests with multiple recall antigens, and less lymphadenopathy and weight loss. The number of OKT3+ and OKT4+ lymphocytes decreased significantly in the control group, but did not change in the thymostimulin-treated patients. Finally, after 18 months of follow-up, no progression to AIDS was seen among the treated subjects, whereas 3 of the controls developed the disease. We conclude that thymostimulin, alone or in combination with antiviral drugs, may be helpful in the management of ARC patients. PMID:3259480

  8. Pancreatic abnormalities and AIDS related sclerosing cholangitis.

    PubMed Central

    Teare, J P; Daly, C A; Rodgers, C; Padley, S P; Coker, R J; Main, J; Harris, J R; Scullion, D; Bray, G P; Summerfield, J A

    1997-01-01

    OBJECTIVES: Biliary tract abnormalities are well recognised in AIDS, most frequently related to opportunistic infection with Cryptosporidium, Microsporidium, and cytomegalovirus. We noted a high frequency of pancreatic abnormalities associated with biliary tract disease. To define these further we reviewed the clinical and radiological features in these patients. METHODS: Notes and radiographs were available from two centres for 83 HIV positive patients who had undergone endoscopic retrograde cholangiopancreatography for the investigation of cholestatic liver function tests or abdominal pain. RESULTS: 56 patients had AIDS related sclerosing cholangitis (ARSC); 86% of these patients had epigastric or right upper quadrant pain and 52% had hepatomegaly. Of the patients with ARSC, 10 had papillary stenosis alone, 11 had intra- and extrahepatic sclerosing cholangitis alone, and 35 had a combination of the two. Ampullary biopsies performed in 24 patients confirmed an opportunistic infection in 16. In 15 patients, intraluminal polyps were noted on the cholangiogram. Pancreatograms were available in 34 of the 45 patients with papillary stenosis, in which 29 (81%) had associated pancreatic duct dilatation, often with associated features of chronic pancreatitis. In the remaining 27 patients, final diagnoses included drug induced liver disease, acalculous cholecystitis, gall bladder empyema, chronic B virus hepatitis, and alcoholic liver disease. CONCLUSION: Pancreatic abnormalities are commonly seen with ARSC and may be responsible for some of the pain not relieved by biliary sphincterotomy. The most frequent radiographic biliary abnormality is papillary stenosis combined with ductal sclerosis. Images PMID:9389948

  9. Detection of optical properties in small region by diffuse reflectance

    NASA Astrophysics Data System (ADS)

    Wang, Lijun; Li, Shengcai; Wang, Kai; Zhu, Zongping; Wang, Wei

    2015-11-01

    The optical properties of small and highly absorbing tissues can be determined by measurement of spatially resolved diffuse reflectance at short source-detector separations. Spatial resolution and number of measuring point influence the inverting precision of optical property directly from the experimental diffuse reflectance. To increase spatial resolution and number of measuring point, a high-resolution and multiple points detection system is designed. A special optical fiber array probe is employed. Its spatial resolution is 0.125mm. The system is proved to be reliable by comparing the experimental result of diffuse reflectance from small region 0.125mm-1.25mm with that of numerical simulation. The inverting method based on Monte Carlo simulation is designed, by which optical properties can be achieved by building optical parameter date base and training artificial neural network (ANN).

  10. Quantum Phase Diffusion in a Small Underdamped Josephson Junction

    NASA Astrophysics Data System (ADS)

    Yu, H. F.; Zhu, X. B.; Peng, Z. H.; Tian, Ye; Cui, D. J.; Chen, G. H.; Zheng, D. N.; Jing, X. N.; Lu, Li; Zhao, S. P.; Han, Siyuan

    2011-08-01

    Quantum phase diffusion in a small underdamped Nb/AlOx/Nb junction (˜0.4μm2) is demonstrated in a wide temperature range of 25-140 mK where macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We propose a two-step transition model to describe the switching process in which the escape rate out of the potential well and the transition rate from phase diffusion to the running state are considered. The transition rate extracted from the experimental switching current distribution follows the predicted Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes dominant.

  11. Functional imaging of small tissue volumes with diffuse optical tomography

    NASA Astrophysics Data System (ADS)

    Klose, Alexander D.; Hielscher, Andreas H.

    2006-03-01

    Imaging of dynamic changes in blood parameters, functional brain imaging, and tumor imaging are the most advanced application areas of diffuse optical tomography (DOT). When dealing with the image reconstruction problem one is faced with the fact that near-infrared photons, unlike X-rays, are highly scattered when they traverse biological tissue. Image reconstruction schemes are required that model the light propagation inside biological tissue and predict measurements on the tissue surface. By iteratively changing the tissue-parameters until the predictions agree with the real measurements, a spatial distribution of optical properties inside the tissue is found. The optical properties can be related to the tissue oxygenation, inflammation, or to the fluorophore concentration of a biochemical marker. If the model of light propagation is inaccurate, the reconstruction process will lead to an inaccurate result as well. Here, we focus on difficulties that are encountered when DOT is employed for functional imaging of small tissue volumes, for example, in cancer studies involving small animals, or human finger joints for early diagnosis of rheumatoid arthritis. Most of the currently employed image reconstruction methods rely on the diffusion theory that is an approximation to the equation of radiative transfer. But, in the cases of small tissue volumes and tissues that contain low scattering regions diffusion theory has been shown to be of limited applicability Therefore, we employ a light propagation model that is based on the equation of radiative transfer, which promises to overcome the limitations.

  12. Endoscopic appearance of AIDS-related gastrointestinal lymphoma with c-MYC rearrangements: Case report and literature review

    PubMed Central

    Tanaka, Shohei; Nagata, Naoyoshi; Mine, Sohtaro; Igari, Toru; Kobayashi, Taiichiro; Sugihara, Jun; Honda, Haruhito; Teruya, Katsuji; Kikuchi, Yoshimi; Oka, Shinichi; Uemura, Naomi

    2013-01-01

    Acquired immune deficiency syndrome (AIDS)-related lymphoma (ARL) remains the main cause of AIDS-related deaths in the highly active anti-retroviral therapy (HAART) era. Recently, rearrangement of MYC is associated with poor prognosis in patients with diffuse large B-cell lymphoma. Here, we report a rare case of gastrointestinal (GI)-ARL with MYC rearrangements and coinfected with Epstein-Barr virus (EBV) infection presenting with various endoscopic findings. A 38-year-old homosexual man who presented with anemia and was diagnosed with an human immunodeficiency virus infection for the first time. GI endoscopy revealed multiple dish-like lesions, ulcerations, bloody spots, nodular masses with active bleeding in the stomach, erythematous flat lesions in the duodenum, and multiple nodular masses in the colon and rectum. Magnified endoscopy with narrow band imaging showed a honeycomb-like pattern without irregular microvessels in the dish-like lesions of the stomach. Biopsy specimens from the stomach, duodenum, colon, and rectum revealed diffuse large B-cell lymphoma concomitant with EBV infection that was detected by high tissue EBV-polymerase chain reaction levels and Epstein-Barr virus small RNAs in situ hybridization. Fluorescence in situ hybridization analysis revealed a fusion between the immunoglobulin heavy chain (IgH) and c-MYC genes, but not between the IgH and BCL2 loci. After 1-mo of treatment with HAART and R-CHOP, endoscopic appearance improved remarkably, and the histological features of the biopsy specimens revealed no evidence of lymphoma. However, he died from multiple organ failure on the 139th day after diagnosis. The cause of his poor outcome may be related to MYC rearrangement. The GI tract involvement in ARL is rarely reported, and its endoscopic findings are various and may be different from those in non-AIDS GI lymphoma; thus, we also conducted a literature review of GI-ARL cases. PMID:23922484

  13. Endoscopic appearance of AIDS-related gastrointestinal lymphoma with c-MYC rearrangements: case report and literature review.

    PubMed

    Tanaka, Shohei; Nagata, Naoyoshi; Mine, Sohtaro; Igari, Toru; Kobayashi, Taiichiro; Sugihara, Jun; Honda, Haruhito; Teruya, Katsuji; Kikuchi, Yoshimi; Oka, Shinichi; Uemura, Naomi

    2013-08-01

    Acquired immune deficiency syndrome (AIDS)-related lymphoma (ARL) remains the main cause of AIDS-related deaths in the highly active anti-retroviral therapy (HAART) era. Recently, rearrangement of MYC is associated with poor prognosis in patients with diffuse large B-cell lymphoma. Here, we report a rare case of gastrointestinal (GI)-ARL with MYC rearrangements and coinfected with Epstein-Barr virus (EBV) infection presenting with various endoscopic findings. A 38-year-old homosexual man who presented with anemia and was diagnosed with an human immunodeficiency virus infection for the first time. GI endoscopy revealed multiple dish-like lesions, ulcerations, bloody spots, nodular masses with active bleeding in the stomach, erythematous flat lesions in the duodenum, and multiple nodular masses in the colon and rectum. Magnified endoscopy with narrow band imaging showed a honeycomb-like pattern without irregular microvessels in the dish-like lesions of the stomach. Biopsy specimens from the stomach, duodenum, colon, and rectum revealed diffuse large B-cell lymphoma concomitant with EBV infection that was detected by high tissue EBV-polymerase chain reaction levels and Epstein-Barr virus small RNAs in situ hybridization. Fluorescence in situ hybridization analysis revealed a fusion between the immunoglobulin heavy chain (IgH) and c-MYC genes, but not between the IgH and BCL2 loci. After 1-mo of treatment with HAART and R-CHOP, endoscopic appearance improved remarkably, and the histological features of the biopsy specimens revealed no evidence of lymphoma. However, he died from multiple organ failure on the 139(th) day after diagnosis. The cause of his poor outcome may be related to MYC rearrangement. The GI tract involvement in ARL is rarely reported, and its endoscopic findings are various and may be different from those in non-AIDS GI lymphoma; thus, we also conducted a literature review of GI-ARL cases. PMID:23922484

  14. Small and Large Molecules in the Diffuse Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Oka, Takeshi; Huang, Jane

    2014-06-01

    Although molecules with a wide range of sizes exist in dense clouds (e.g. H(C≡C)_nC≡N with n = 0 - 5), molecules identified in diffuse clouds are all small ones. Since the initial discovery of CH, CN, and CH^+, all molecules detected in the optical region are diatomics except for H_3^+ in the infrared and C_3 in the visible. Radio observations have been limited up to triatomic molecules except for H_2CO and the ubiquitous C_3H_2. The column densities of all molecules are less than 1014 cm-2 with the two exceptions of CO and H_3^+ as well as CH and C_2 in a few special sightlines. Larger molecules with many carbon atoms have been searched for but have not been detected. On the other hand, the observations of a great many diffuse interstellar bands (380 toward HD 204827 and 414 toward HD 183143) with equivalent widths from 1 to 5700 m Å indicate high column densities of many heavy molecules. If an electronic transition dipole moment of 1 Debye is assumed, the observed equivalent widths translate to column densities from 5 × 1011 cm-2 to 3 × 1015 cm-2. It seems impossible that these large molecules are formed from chemical reactions in space from small molecules. It is more likely that they are fragments of aggregates, perhaps mixed aromatic/aliphatic organic nanoparticles (MAONS). MAONS and their large fragment molecules are stable against photodissociation in the diffuse ISM because the energy of absorbed photons is divided into statistical distributions of vibrational energy and emitted in the infrared rather than breaking a chemical bond. We use a simple Rice-Ramsperger-Kassel-Marcus theory to estimate the molecular size required for the stabilization. Snow, T. P. & McCall, B. J. 2006, ARA&A, 44 367 Hobbs, L. M., York, D. G., Snow, T. P., Oka, T., Thorburn, J. A., et al. 2008, ApJ, 680 1256 Hobbs, L. M., York, D. G., Thorburn, J. A., Snow, T. P., Bishof, M., et al. 2009, ApJ, 705 32 Kwok, S. & Zhang, S. 2013, ApJ, 771 5 Freed, K. F., Oka, T., & Suzuki, H

  15. A Temporal Model of Technology Diffusion into Small Firms in Wales.

    ERIC Educational Resources Information Center

    Thomas, Brychan; Packham, Gary; Miller, Chris

    2001-01-01

    Discusses technology diffusion through formal and informal networks. Develops a model that includes channels and mechanisms involved in transferring technology into innovative small businesses. The model depicts influences that increase or slow the rate of diffusion. (SK)

  16. Psychological Consequences of AIDS-Related Bereavement among Gay Men.

    ERIC Educational Resources Information Center

    Martin, John L.

    1988-01-01

    Interviewed 745 homosexual men to examine relation between Acquired Immune Deficiency Syndrome (AIDS)-related bereavement and psychological distress. Loss of lover or close friend to AIDS was reported by 27 percent of sample. Found direct relation between number of bereavements and symptoms of traumatic stress response, demoralization, sleep…

  17. Shadowing and the role of small diffusivity in the chaotic advection of scalars

    NASA Technical Reports Server (NTRS)

    Klapper, I.

    1992-01-01

    Using techniques from shadowing theory, the solution of the scalar advection-diffusion equation is studied. It is shown that, under certain circumstances, the effect of small scalar diffusivity is to smooth the zero-diffusivity solution by averaging local fine-scaled structure against a Gaussian. The method of study depends on shadowing and thus fails for nonuniformly stretching systems, its failure suggesting the ways in which the effects of asymptotically small molecular diffusion can become nonlocal in chaotic fluid flows.

  18. Patterns of gallium-67 scintigraphy in patients with acquired immunodeficiency syndrome and the AIDS related complex

    SciTech Connect

    Bitran, J.; Bekerman, C.; Weinstein, R.; Bennett, C.; Ryo, U.; Pinsky, S.

    1987-07-01

    Thirty-two patients with AIDS related complex (ARC) or acquired immunodeficiency syndrome (AIDS) underwent /sup 67/Ga scans as part of their evaluation. Three patterns of /sup 67/Ga biodistribution were found: lymph node uptake alone; diffuse pulmonary uptake; normal scan. Gallium-67 scans were useful in identifying clinically occult Pneumocystis carinii pneumonia in seven of 15 patients with ARC who were asymptomatic and had normal chest radiographs. Gallium scans are a useful ancillary procedure in the evaluation of patients with ARC or AIDS.

  19. Small-scale structure in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Meyer, David M.

    1990-01-01

    The initial results of a study to probe the small-scale structure in the diffuse interstellar medium (ISM) through IUE and optical observations of interstellar absorption lines toward both components of resolvable binary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR 1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected linear separations ranging from 5700 to 700 Au. Except for Kappa CrA, the strengths of the interstellar absorption lines toward both components of these binaries agree to within 10 percent. In the case of Kappa CrA, the optically thin interstellar Mg I and Mn II lines are about 50 percent stronger toward Kappa-2 CrA than Kappa-1 CrA. Higher resolution observations of interstellar Ca II show that this difference is concentrated in the main interstellar component at V(LSR) = 9 + or - 2 km/s. Interestingly, this velocity corresponds to an intervening cloud that may be associated with the prominent Loop I shell in the local ISM. Given the separation (23 arcsec) and distance (120 pc) of Kappa CrA, the line strength variations indicate that this cloud has structure on scales of 2800 AU or less.

  20. Transforming a spatially coherent light beam into a diffused beam of small diffusion angle using suitable surface scattering

    NASA Astrophysics Data System (ADS)

    Dashtdar, M.; Tavassoly, M. T.

    2013-11-01

    Imposing a phase random distribution in an interval larger than 2π on a spatially coherent light beam transforms the beam into a diffuse one. However, if the required random phase distribution is imposed by a rough transparent plate immersed in a transparent liquid or covered by another transparent material of refractive index close to that of the plate, the diffused light is confined in a small cone around the light incident angle. This renders to fabricate diffusers with high transmission efficiency that has applications in computer displays, bar code scanners, and image forming systems including conventional optical microscopes.

  1. Properties of small molecular drug loading and diffusion in a fluorinated PEG hydrogel studied by H molecular diffusion NMR and F spin diffusion NMR.

    PubMed

    Mathias, Errol V; Aponte, Julia; Kornfield, Julia A; Ba, Yong

    2010-12-01

    R(f)-PEG (fluoroalkyl double-ended poly(ethylene glycol)) hydrogel is potentially useful as a drug delivery depot due to its advanced properties of sol-gel two-phase coexistence and low surface erosion. In this study, (1)H molecular diffusion nuclear magnetic resonance (NMR) and (19)F spin diffusion NMR were used to probe the drug loading and diffusion properties of the R(f)-PEG hydrogel for small anticancer drugs, 5-fluorouracil (FU) and its hydrophobic analog, 1,3-dimethyl-5-fluorouracil (DMFU). It was found that FU has a larger apparent diffusion coefficient than that of DMFU, and the diffusion of the latter was more hindered. The result of (19)F spin diffusion NMR for the corresponding freeze-dried samples indicates that a larger portion of DMFU resided in the R(f) core/IPDU intermediate-layer region (where IPDU refers to isophorone diurethane, as a linker to interconnect the R(f) group and the PEG chain) than that of FU while the opposite is true in the PEG-water phase. To understand the experimental data, a diffusion model was proposed to include: (1) hindered diffusion of the drug molecules in the R(f) core/IPDU-intermediate-layer region; (2) relatively free diffusion of the drug molecules in the PEG-water phase (or region); and (3) diffusive exchange of the probe molecules between the above two regions. This study also shows that molecular diffusion NMR combined with spin diffusion NMR is useful in studying the drug loading and diffusion properties in hydrogels for the purpose of drug delivery applications. PMID:21170115

  2. VERTICAL DIFFUSION IN SMALL STRATIFIED LAKES: DATA AND ERROR ANALYSIS

    EPA Science Inventory

    Water temperature profiles were measured at 2-min intervals in a stratified temperate lake with a surface area of 0.06 km2 and a aximum depth of 10 m from May 7 to August 9, 1989. he data were used to calculate the vertical eddy diffusion coefficient K2 in the hypolimnion. he dep...

  3. Quantifying sound-field diffuseness in small rooms using multifractals.

    PubMed

    Loutridis, S J

    2009-03-01

    With the aim of quantifying sound-field uniformity in spaces of relatively low volume, four different configurations in terms of acoustic treatment and sound-field diffuseness were constructed and tested. In a diffuse sound field, reflections are not strongly correlated both to the original sound and to earlier reflections. The degree of correlation is embedded in the impulse response structure, but is not trivial to identify. The room impulse responses exhibit self-similarity and therefore may be treated as multifractal signals characterized by a singularity spectrum. The singularity spectrum contains a wealth of information about the acoustic field established in the room. The width of the singularity spectrum, in particular, is directly related to the complexity of the impulse response structure. The uniformity of the sound field in the room can be evaluated by examining the variation of the singularity spectra with position. A new definition for sound field diffuseness is given that is not based on the concept of the energy density. The proposed method is simple to apply, statistically robust, and provides a measure of diffusion independent of the room reverberation. PMID:19275308

  4. HIV/AIDS-related stigma in Kumasi, Ghana

    PubMed Central

    Ulasi, Chijioke I; Preko, Peter O; Baidoo, Joseph A.; Bayard, Budry; Ehiri, John E; Jolly, Curtis M; Jolly, Pauline E

    2009-01-01

    Objective To assess HIV/AIDS-related stigma and discrimination of people living with HIV/AIDS (PLWHA) in Kumasi, Ghana. Methods A cross-sectional survey of 104 adults from the four sub-districts in Kumasi was conducted. Results Four stigma constructs, employment-based discrimination, screening and identification of HIV positive people, revelation of HIV status and social contact stigma were determined based on reliability measures from responses to the questionnaire. Regression analysis showed that participants with higher educational attainment were more likely to favor policies denying employment to PLWHA (p<0.05), but disapproved of revealing HIV sero-status (p<0.05). Muslims were more likely than Christians to agree with identifying PLWHA (p<0.05) and more likely to advocate revealing HIV sero-status (p<0.05). Males were more likely to favor revealing HIV status (p<0.05). Employed persons were more likely to have social contact with PLWHA (p<0.05). Conclusions These findings are useful in guiding the design of interventions against HIV/AIDS-related stigma in Kumasi. PMID:18632302

  5. Small area silicon diffused junction x-ray detectors

    SciTech Connect

    Walton, J.T.; Pehl, R.H.; Larsh, A.E.

    1981-10-01

    The low temperature performance of silicon diffused junction detectors in the measurement of low energy x-rays is reported. The detectors have an area of 0.04 cm/sup 2/ and a thickness of 100 ..mu..m. The spectral resolutions of these detectors were found to be in close agreement with expected values indicating that the defects introduced by the high temperature processing required in the device fabrication were not deleteriously affecting the detection of low energy x-rays. Device performance over a temperature range of 77 to 150/sup 0/K is given. These detectors were designed to detect low energy x-rays in the presence of minimum ionizing electrons. The successful application of silicon diffused junction technology to x-ray detector fabrication may facilitate the development of other novel silicon x-ray detector designs.

  6. Photodynamic therapy for treatment of AIDS-related mucocutaneous Kaposi's sarcoma (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Schweitzer, Vanessa G.

    1992-06-01

    Since 1975, Phase I/II studies have demonstrated the successfulness of hematoporphyrin derivative photodynamic therapy (PDT) in the treatment of various malignancies of the skin, eye, bladder, lung, and head and neck. Moreover, in 1981 two cases of traditional Western cutaneous Kaposi's sarcoma (TKS) have been treated with photodynamic therapy with both early and late complete response. To date, attempts to cure and palliation of the more aggressive AIDS-related oral Kaposi's sarcoma with conventional radiation, chemotherapy or immunotherapy, or surgical excision have been limited and often associated with debilitating mucositis and further immunosuppression. Certain aspects of photodynamic therapy may be efficacious for treatment of mucocutaneous Kaposi's sarcoma: (1) the selective retention of hematoporphyrin derivative by neoplastic lesions (endothelial cell tumors); (2) a tumor- specific cytotoxic agent (i.e., free oxygen radical); (3) absence of systemic toxicity from immunosuppression; (4) the potential for retreatment without increasing side effects; and (5) porphyrin-mediated photoinactivation of enveloped viruses. Herein presented are seven cases of AIDS-related KS (EKS) with diffuse, superficial, and nodular mucocutaneous lesions treated with dihematoporphyrin derivative and photodynamic therapy with subsequent dramatic early partial and complete responses.

  7. Risk Sensitive Control of Diffusions with Small Running Cost

    SciTech Connect

    Biswas, Anup

    2011-08-15

    Infinite horizon risk-sensitive control of diffusions is analyzed under a stability condition coupled with a bound on the running cost. It is shown that the corresponding Hamilton-Jacobi-Bellman equation has a solution (w( Dot-Operator ),{lambda}{sup Asterisk-Operator }) where the scalar {lambda}{sup Asterisk-Operator} is in fact the optimal cost. This also leads to an existence result for optimal controls.

  8. Diffusion of small molecules in polymer nanocomposites: relationship between local free volume dynamics and penetrant diffusivity

    NASA Astrophysics Data System (ADS)

    Pryamitsyn, Victor; Ganesan, Venkat

    2011-03-01

    Polymer membranes are widely used as barrier or gas/vapors separation materials. Recent experiments have demonstrated that the barrier properties of the polymer nanocomposites (PNC) dramatically different from pure polymer. Usually such properties are quantified by the permeability P of the material to a penetrant which consists of two contributions: the penetrant solubility S and diffusivity D : P = S D In present work we only discuss term D . We use the Bond Fluctuation Model, which allows us to model the diffusivity of the penetrant, the dynamics of the polymer and the dynamics of the polymer free volume in a single framework. We modeled PNC's at different particle load and the penetrant size and found that addition of nanoparticles increseses the penetrant diffusivity and selectivity to the penetrant size. This increase is attributed to the free volume increase and the acceleration of the free volume relaxation in PNC relatively to the pure polymer. We have compared the penetrant diffusivity in a rubbery and glassy PNC's and found than the effect of the PNC load on diffusivity and selectivity is much stronger for the glassy system which is due to rubbery system D is controlled by the rate of matrix free volume relaxation and in glassy regime it is controlled by the static free volume percolation, which is more sensitive to the PNC load.

  9. Small animal optical diffusion tomography with targeted fluorescence.

    PubMed

    Gaind, Vaibhav; Tsai, Hsiao-Rho; Webb, Kevin J; Chelvam, Venkatesh; Low, Philip S

    2013-06-01

    Despite the broad impact in medicine that optics can bring, thus far practical approaches are limited to weak scatter or near-surface monitoring. We show a method that utilizes a laser topography scan and a diffusion equation model to describe the photon transport, together with a multiresolution unstructured grid solution to the nonlinear optimization measurement functional, that overcomes these limitations. We conclude that it is possible to achieve whole body optical imaging with a resolution suitable for finding cancer nodules within an organ during surgery, with the aid of a targeted imaging agent. PMID:24323101

  10. Lateral diffusion of small compounds in human stratum corneum and model lipid bilayer systems.

    PubMed Central

    Johnson, M E; Berk, D A; Blankschtein, D; Golan, D E; Jain, R K; Langer, R S

    1996-01-01

    An image-based technique of fluorescence recovery after photobleaching (video-FRAP) was used to measure the lateral diffusion coefficients of a series of nine fluorescent probes in two model lipid bilayer systems, dimyristoylphosphatidylcholine (DMPC) and DMPC/cholesterol (40 mol%), as well as in human stratum corneum-extracted lipids. The probes were all lipophilic, varied in molecular weight from 223 to 854 Da, and were chosen to characterize the lateral diffusion of small compounds in these bilayer systems. A clear molecular weight dependence of the lateral diffusion coefficients in DMPC bilayers was observed. Values ranged from 6.72 x 10(-8) to 16.2 x 10(-8) cm2/s, with the smaller probes diffusing faster than the larger ones. Measurements in DMPC/cholesterol bilayers, which represent the most thorough characterization of small-solute diffusion in this system, exhibited a similar molecular weight dependence, although the diffusion coefficients were lower, ranging from 1.62 x 10(-8) to 5.60 x 10(-8) cm2/s. Lateral diffusion measurements in stratum corneum-extracted lipids, which represent a novel examination of diffusion in this unique lipid system, also exhibited a molecular weight dependence, with values ranging from 0.306 x 10(-8) to 2.34 x 10(-8) cm2/s. Literature data showed that these strong molecular weight dependencies extend to even smaller compounds than those examined in this study. A two-parameter empirical expression is presented that describes the lateral diffusion coefficient in terms of the solute's molecular weight and captures the size dependence over the range examined. This study illustrates the degree to which small-molecule lateral diffusion in stratum corneum-extracted lipids can be represented by diffusion in DMPC and DMPC/cholesterol bilayer systems, and may lead to a better understanding of small-solute transport across human stratum corneum. PMID:8913603

  11. A diffusive information preservation method for small Knudsen number flows

    NASA Astrophysics Data System (ADS)

    Fei, Fei; Fan, Jing

    2013-06-01

    The direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker-Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn ˜ 10-3-10-4 have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively.

  12. Magnetic field diffusion modeling of a small enclosed firing system

    SciTech Connect

    Warne, L.K.; Merewether, K.O.

    1996-01-01

    Intense magnetic fields exist in the immediate vicinity of a lightning strike (and near power lines). Conducting barriers increase the rise time (and thus decrease the rise rate) interior to the barrier, but typically do not prevent penetration of the magnetic field, since the lightning current fall time may be larger than the barrier diffusion time. Thus, substantial energy is present in the interior field, although the degradation of rise rate makes it more difficult to couple into electrical circuits. This report assesses the threat posed by the diffusive magnetic field to interior components and wire loops (where voltages are induced). Analytical and numerical bounding analyses are carried out on a pill box shaped conducting barrier to develop estimates for the worst case magnetic field threats inside the system. Worst case induced voltages and energies are estimated and compared with threshold charge voltages and energies on the output capacitor of the system. Variability of these quantities with respect to design parameters are indicated. The interior magnetic field and induced voltage estimates given in this report can be used as excitations for more detailed interior and component models.

  13. A diffusive information preservation method for small Knudsen number flows

    SciTech Connect

    Fei, Fei; Fan, Jing

    2013-06-15

    The direct simulation Monte Carlo (DSMC) method is a powerful particle-based method for modeling gas flows. It works well for relatively large Knudsen (Kn) numbers, typically larger than 0.01, but quickly becomes computationally intensive as Kn decreases due to its time step and cell size limitations. An alternative approach was proposed to relax or remove these limitations, based on replacing pairwise collisions with a stochastic model corresponding to the Fokker–Planck equation [J. Comput. Phys., 229, 1077 (2010); J. Fluid Mech., 680, 574 (2011)]. Similar to the DSMC method, the downside of that approach suffers from computationally statistical noise. To solve the problem, a diffusion-based information preservation (D-IP) method has been developed. The main idea is to track the motion of a simulated molecule from the diffusive standpoint, and obtain the flow velocity and temperature through sampling and averaging the IP quantities. To validate the idea and the corresponding model, several benchmark problems with Kn ∼ 10{sup −3}–10{sup −4} have been investigated. It is shown that the IP calculations are not only accurate, but also efficient because they make possible using a time step and cell size over an order of magnitude larger than the mean collision time and mean free path, respectively.

  14. The small ice cap instability in diffusive climate models

    NASA Technical Reports Server (NTRS)

    North, G. R.

    1984-01-01

    Simple climate models which invoke diffusive heat transport and ice cap albedo feedback have equilibrium solutions with no stable ice cap smaller than a radius of about 20 deg on a great circle. Attention is presently given to a solution of this phenomenon which is physically appealing. The ice-free solution has a thermal minimum, and if the minimum temperature is just above the critical value for ice formation, then the artificial addition of a patch of ice leads to a widespread depression of the temperature below the critical freezing temperature. A second stable solution will then exist whose spatial extent is determined by the range of the influence function of a point sink of heat, due to the albedo shift in the patch.

  15. Ergodicity testing for anomalous diffusion: Small sample statistics

    NASA Astrophysics Data System (ADS)

    Janczura, Joanna; Weron, Aleksander

    2015-04-01

    The analysis of trajectories recorded in experiments often requires calculating time averages instead of ensemble averages. According to the Boltzmann hypothesis, they are equivalent only under the assumption of ergodicity. In this paper, we implement tools that allow to study ergodic properties. This analysis is conducted in two classes of anomalous diffusion processes: fractional Brownian motion and subordinated Ornstein-Uhlenbeck process. We show that only first of them is ergodic. We demonstrate this by applying rigorous statistical methods: mean square displacement, confidence intervals, and dynamical functional test. Our methodology is universal and can be implemented for analysis of many experimental data not only if a large sample is available but also when there are only few trajectories recorded.

  16. Ergodicity testing for anomalous diffusion: small sample statistics.

    PubMed

    Janczura, Joanna; Weron, Aleksander

    2015-04-14

    The analysis of trajectories recorded in experiments often requires calculating time averages instead of ensemble averages. According to the Boltzmann hypothesis, they are equivalent only under the assumption of ergodicity. In this paper, we implement tools that allow to study ergodic properties. This analysis is conducted in two classes of anomalous diffusion processes: fractional Brownian motion and subordinated Ornstein-Uhlenbeck process. We show that only first of them is ergodic. We demonstrate this by applying rigorous statistical methods: mean square displacement, confidence intervals, and dynamical functional test. Our methodology is universal and can be implemented for analysis of many experimental data not only if a large sample is available but also when there are only few trajectories recorded. PMID:25877558

  17. Exciton diffusion in disordered small molecules for organic photovoltaics: insights from first-principles simulations.

    PubMed

    Li, Z; Zhang, X; Lu, G

    2014-05-01

    Exciton diffusion in small molecules 3,6-bis(5-(benzofuran-2-yl)thiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione [DPP(TBFu)2] is studied using first-principles simulations. We have examined dependence of exciton diffusion on structure disorder, temperature and exciton energy. We find that exciton diffusion length and diffusivity increase with structural order, temperature and the initial exciton energy. Compared to conjugated polymer poly(3-hexylthiophene) (P3HT), DPP(TBFu)2 small molecules exhibit a much higher exciton diffusivity, but a shorter lifetime. The exciton diffusion length in DPP(TBFu)2 is 50% longer than that in P3HT, yielding a higher exciton harvesting efficiency; the physical origin behind these differences is discussed. The time evolutions of exciton energy, electron-hole distance, and exciton localization are explored, and the widely speculated exciton diffusion mechanism is confirmed theoretically. The connection between exciton diffusion and carrier mobilities is also studied. Finally we point out the possibility to estimate exciton diffusivity by measuring carrier mobilities under AC electric fields. PMID:24759042

  18. Computation of Rate Constants for Diffusion of Small Ligands to and from Buried Protein Active Sites.

    PubMed

    Wang, P-H; De Sancho, D; Best, R B; Blumberger, J

    2016-01-01

    The diffusion of ligands to actives sites of proteins is essential to enzyme catalysis and many cellular signaling processes. In this contribution we review our recently developed methodology for calculation of rate constants for diffusion and binding of small molecules to buried protein active sites. The diffusive dynamics of the ligand obtained from molecular dynamics simulation is coarse grained and described by a Markov state model. Diffusion and binding rate constants are then obtained either from the reactive flux formalism or by fitting the time-dependent population of the Markov state model to a phenomenological rate law. The method is illustrated by applications to diffusion of substrate and inhibitors in [NiFe] hydrogenase, CO-dehydrogenase, and myoglobin. We also discuss a recently developed sensitivity analysis that allows one to identify hot spots in proteins, where mutations are expected to have the strongest effects on ligand diffusion rates. PMID:27497172

  19. AIDS-related apprehensions among nursing students of Delhi.

    PubMed

    Kumar, A; Lal, P; Ingle, G K; Gulati, N

    1999-12-01

    Students from a nursing school of Delhi were surveyed anonymously using a self-administered questionnaire to explore various AIDS-related apprehensions and their possible reasons. The observations revealed that, majority of the students and their families/friends feared that these students were at risk of contracting HIV infection while providing routine patient care. A large number of students also opined that they would feel uncomfortable while talking, hugging, shaking hands, and sharing a room with an HIV positive person. The main reasons for their apprehensions were unsatisfactory anti-AIDS campaigning by the government, non-availability of sufficient protective measures in the health care settings, inadequate professional education related to prevention of HIV infection, and increase in HIV transmission following false sense of security due to excessive condom promotion. Findings of the study imply imparting factual knowledge addressing the concerns and removing misconceptions which influence attitudes and willingness of the nursing students to provide care to the HIV positives/AIDS patients, facts regarding efficacy of various preventive measures, and provision of counselling services in the event of exposure. PMID:10937297

  20. The tumor virus landscape of AIDS-related lymphomas.

    PubMed

    Arvey, Aaron; Ojesina, Akinyemi I; Pedamallu, Chandra Sekhar; Ballon, Gianna; Jung, Joonil; Duke, Fujiko; Leoncini, Lorenzo; De Falco, Giulia; Bressman, Eric; Tam, Wayne; Chadburn, Amy; Meyerson, Matthew; Cesarman, Ethel

    2015-05-14

    Immunodeficiency dramatically increases susceptibility to cancer as a result of reduced immune surveillance and enhanced opportunities for virus-mediated oncogenesis. Although AIDS-related lymphomas (ARLs) are frequently associated with known oncogenic viruses, many cases contain no known transforming virus. To discover novel transforming viruses, we profiled a set of ARL samples using whole transcriptome sequencing. We determined that Epstein-Barr virus (EBV) was the only virus detected in the tumor samples of this cohort, suggesting that if unidentified pathogens exist in this disease, they are present in <10% of cases or undetectable by our methods. To evaluate the role of EBV in ARL pathogenesis, we analyzed viral gene expression and found highly heterogeneous patterns of viral transcription across samples. We also found significant heterogeneity of viral antigen expression across a large cohort, with many patient samples presenting with restricted type I viral latency, indicating that EBV latency proteins are under increased immunosurveillance in the post-combined antiretroviral therapies era. Furthermore, EBV infection of lymphoma cells in HIV-positive individuals was associated with a distinct host gene expression program. These findings provide insight into the joint host-virus regulatory network of primary ARL tumor samples and expand our understanding of virus-associated oncogenesis. Our findings may also have therapeutic implications, as treatment may be personalized to target specific viral and virus-associated host processes that are only present in a subset of patients. PMID:25827832

  1. Generalized diffusion approximation for highly absorbing media and small source-detector separations

    NASA Astrophysics Data System (ADS)

    Zhu, Dan; Wu, Guiling; Luo, Qingming; Gong, Hui

    2006-01-01

    The diffusion approximation to the transport equation is commonly used in biomedical optical diagnostic techniques, but constrains its applicability to highly scattering system. The generalized diffusion approximation was developed by Venugopalan can be used to quantify optical properties of turbid media using small source detector separations and allow the measurement of media with highly absorption. Unfortunately, the simulated result from this theory was larger than the real value because δ-Eddington phase function contained too much forward scattering. Here a new independent control parameter is introduced to δ-Eddington phase function so as to modify the generalized diffusion approximation presented. The solution is presented in the stationary case for infinite media with a collimated source of finite size exhibiting spherical symmetry. The solution is compared to results given by the conventional diffusion theory, the generalized diffusion approximation as well as to the Monte-Carlo simulation in steady state diffusion equation for slab boundary condition. The simulation results show that the modified generalized diffusion approximation with an appropriate control parameter is more closed to Monte-Carlo simulation. The modified generalized formulation of diffusion theory presented here may enable the quantitative application of present optical diagnostic techniques to turbid systems which are more highly absorbing and allow these systems to be probed using smaller source-detector separations.

  2. Intravenous Chemotherapy or Oral Chemotherapy in Treating Patients With Previously Untreated Stage III-IV HIV-Associated Non-Hodgkin Lymphoma

    ClinicalTrials.gov

    2016-06-09

    AIDS-related Diffuse Large Cell Lymphoma; AIDS-related Diffuse Mixed Cell Lymphoma; AIDS-related Diffuse Small Cleaved Cell Lymphoma; AIDS-related Immunoblastic Large Cell Lymphoma; AIDS-related Lymphoblastic Lymphoma; AIDS-related Peripheral/Systemic Lymphoma; AIDS-related Small Noncleaved Cell Lymphoma; Stage III AIDS-related Lymphoma; Stage IV AIDS-related Lymphoma

  3. Impacts of small-scale variability on the determination of bulk thermal diffusivity in snowpacks

    NASA Astrophysics Data System (ADS)

    Oldroyd, H. J.; Higgins, C. W.; Huwald, H.; Selker, J. S.; Parlange, M. B.

    2012-04-01

    Thermal diffusivity of snow is an important physical property associated with key hydrological phenomena such as snowmelt and heat and water vapor exchange with the atmosphere. These phenomena have broad implications in studies of climate and heat and water budgets on many scales. Furthermore, sub grid scale phenomena may enhance these heat and mass exchanges in the snow pack due to its porous nature. We hypothesize that the heat transfer effects of these small-scale variabilities may be seen as an increased bulk thermal diffusivity of the snow. Direct measurements of snow thermal diffusivity require coupled measurements of thermal conductivity and density, which are nonstationary due to snow metamorphism. Furthermore, thermal conductivity measurements are typically obtained with specialized heating probes or plates and snow density measurements require digging snow pits. Therefore, direct measurements are difficult to obtain with high enough temporal resolution such that direct comparisons with atmospheric conditions can be made. This study uses highly resolved temperature measurements from the Plaine Morte glacier in Switzerland as initial and boundary conditions to numerically solve the 1D heat equation and iteratively optimize for thermal diffusivity. The method uses flux boundary conditions to constrain thermal diffusivity such that spuriously high values in thermal diffusivity are eliminated. Additionally, a t-test ensuring statistical significance between solutions of varied thermal diffusivity results in further constraints on thermal diffusivity that eliminate spuriously low values. The results show that time resolved thermal diffusivity can be determined from easily implemented and inexpensive temperature measurements of seasonal snow with good agreement to widely used parameterizations based on snow density. This high time resolution further affords the ability to explore possible turbulence-induced enhancements to heat and mass transfer in the snow.

  4. Measuring HIV/AIDS-Related Stigma across South Africa: A Versatile and Multidimensional Scale

    ERIC Educational Resources Information Center

    Smith, Edward A.; Miller, Jacqueline A.; Newsome, Valerie; Sofolahan, Yewande A.; Airhihenbuwa, Collins O.

    2014-01-01

    Reducing HIV/AIDS-related stigma is critical in the fight against HIV/AIDS. Although national campaigns and prevention programs have been implemented across South Africa to address this critical concern, assessing the impact of these initiatives is difficult as it requires that measurement of HIV/AIDS-related stigma is uniform and comparable…

  5. Molecular dynamics simulations of interfacial interactions between small nanoparticles during diffusion-limited aggregation

    NASA Astrophysics Data System (ADS)

    Lu, Jing; Liu, Dongmei; Yang, Xiaonan; Zhao, Ying; Liu, Haixing; Tang, Huan; Cui, Fuyi

    2015-12-01

    Due to the limitations of experimental methods at the atomic level, research on the aggregation of small nanoparticles (D < 5 nm) in aqueous solutions is quite rare. The aggregation of small nanoparticles in aqueous solutions is very different than that of normal sized nanoparticles. The interfacial interactions play a dominant role in the aggregation of small nanoparticles. In this paper, molecular dynamics simulations, which can explore the microscopic behavior of nanoparticles during the diffusion-limited aggregation at an atomic level, were employed to reveal the aggregation mechanism of small nanoparticles in aqueous solutions. First, the aggregation processes and aggregate structure were depicted. Second, the particle-particle interaction and surface diffusion of nanoparticles during aggregation were investigated. Third, the water-mediated interactions during aggregation were ascertained. The results indicate that the aggregation of nanoparticle in aqueous solutions is affected by particle size. The strong particle-particle interaction and high surface diffusion result in the formation of particle-particle bonds of 2 nm TiO2 nanoparticles, and the water-mediated interaction plays an important role in the aggregation process of 3 and 4 nm TiO2 nanoparticles.

  6. Expression of immunohistochemical markers in patients with AIDS-related lymphoma.

    PubMed

    Barreto, Luciana; Azambuja, Denize; Morais, José Carlos de

    2012-01-01

    AIDS-related lymphomas (ARL) present high biological heterogeneity. For better characterization of this type of lymphoma, the objectives of the present study were to evaluate the expression of immunohistochemical markers of cell differentiation (CD10, Bcl-6, MUM-1) and determine cell origin profile according to Hans' classification of diffuse large B-cell lymphoma in AIDS patients. This study included 72 consecutive patients with ARL diagnosed at the University Hospital, Universidade Federal do Rio de Janeiro (UFRJ) and at the Brazilian Instituto Nacional de Câncer (INCA) from 2000 to 2006. The morphologic distribution of the lymphomas was the following: 61% were diffuse large B-cell lymphomas (DLBCLs), 15% were Burkitt's lymphomas, 13% were plasmablastic lymphomas, 10% were high-grade lymphomas and 1% was follicular lymphoma. The positivity for each immunohistochemical marker in DLBCLs, Burkitt's lymphoma and plasmablastic lymphoma was respectively: CD20, 84%, 100%, and 0; CD10, 55%, 100%, and 0; Bcl-6, 45%, 80%, and 0; MUM-1, 41%, 20%, and 88%. A higher positivity of CD20 (84% x 56%, p = 0.01) was found in DLBCL compared to non-DLBCL; in Burkitt's lymphomas a higher positivity of CD10 (100% x 49%, p = 0.04) and Bcl-6 (80% x 39%, p = 0.035) were found compared to non-Burkitt's lymphomas. Germinal center (GC) profile was detected in 60% of DLBCLs. Our study suggests particular findings in ARL, as the most frequent phenotype was GC, different from HIV-negative patients. PMID:22358360

  7. Sphingolipid–Cholesterol Rafts Diffuse as Small Entities in the Plasma Membrane of Mammalian Cells

    PubMed Central

    Pralle, A.; Keller, P.; Florin, E.-L.; Simons, K.; Hörber, J.K.H.

    2000-01-01

    To probe the dynamics and size of lipid rafts in the membrane of living cells, the local diffusion of single membrane proteins was measured. A laser trap was used to confine the motion of a bead bound to a raft protein to a small area (diam ≤ 100 nm) and to measure its local diffusion by high resolution single particle tracking. Using protein constructs with identical ectodomains and different membrane regions and vice versa, we demonstrate that this method provides the viscous damping of the membrane domain in the lipid bilayer. When glycosylphosphatidylinositol (GPI) -anchored and transmembrane proteins are raft-associated, their diffusion becomes independent of the type of membrane anchor and is significantly reduced compared with that of nonraft transmembrane proteins. Cholesterol depletion accelerates the diffusion of raft-associated proteins for transmembrane raft proteins to the level of transmembrane nonraft proteins and for GPI-anchored proteins even further. Raft-associated GPI-anchored proteins were never observed to dissociate from the raft within the measurement intervals of up to 10 min. The measurements agree with lipid rafts being cholesterol-stabilized complexes of 26 ± 13 nm in size diffusing as one entity for minutes. PMID:10704449

  8. SMALL-SCALE STRUCTURE OF THE INTERSTELLAR MEDIUM TOWARD {rho} Oph STARS: DIFFUSE BAND OBSERVATIONS

    SciTech Connect

    Cordiner, M. A.; Smith, A. M.; Sarre, P. J.; Fossey, S. J.

    2013-02-10

    We present an investigation of small-scale structure in the distribution of large molecules/dust in the interstellar medium through observations of diffuse interstellar bands (DIBs). High signal-to-noise optical spectra were recorded toward the stars {rho} Oph A, B, C, and DE using the University College London Echelle Spectrograph on the Anglo-Australian Telescope. The strengths of some of the DIBs are found to differ by about 5%-9% between the close binary stars {rho} Oph A and B, which are separated by a projected distance on the sky of only c. 344 AU. This is the first star system in which such small-scale DIB strength variations have been reported. The observed variations are attributed to differences between a combination of carrier abundance and the physical conditions present along each sightline. The sightline toward {rho} Oph C contains relatively dense, molecule-rich material and has the strongest {lambda}{lambda}5850 and 4726 DIBs. The gas toward DE is more diffuse and is found to exhibit weak ''C{sub 2}'' (blue) DIBs and strong yellow/red DIBs. The differences in diffuse band strengths between lines of sight are, in some cases, significantly greater in magnitude than the corresponding variations among atomic and diatomic species, indicating that the DIBs can be sensitive tracers of interstellar cloud conditions.

  9. Diffusion of Small He Clusters in Bulk and Grain Boundaries in α-Fe

    SciTech Connect

    Deng, Huiqiu; Hu, W. Y.; Gao, Fei; Heinisch, Howard L.; Hu, Shenyang Y.; Li, Yulan; Kurtz, Richard J.

    2013-11-02

    The diffusion properties of He interstitials and He clusters in the bulk and grain boundaries (GBs) of α-Fe have been studied using molecular dynamics with a newly developed Fe-He potential. The low migration energy barrier for a single He interstitial in the bulk is consistent with that obtained using ab initio methods. Small He clusters can migrate at low temperatures, but at higher temperatures they will kick out a self-interstitial atom (SIA) and become trapped by the vacancy, forming an He-vacancy complex. It is of great interest to note that small Henvacancy clusters (n<5) in the bulk are able to absorb an SIA, and the clusters become mobile again. Trapping and de-trapping of He clusters by emitting and absorbing an SIA represent an important dynamic process that provides a mechanism for the diffusion of He clusters and the nucleation of He bubbles in bulk Fe, particularly under irradiation in which numerous SIAs and vacancies are constantly being produced. A single He interstitial can migrate one-dimensionally or two-dimensionally within GBs, depending on the GB structure. Small interstitial Hen clusters 2 (n ~ 1 - 10) can easily kick out an SIA, and become trapped by the vacancy, while the SIA quickly diffuses away from the clusters, disappearing into the GB, such that de-trapping of the He clusters by absorbing an SIA is less likely to occur. This suggests that small He clusters may be treated as relatively immobile defects in GBs. The different behavior of He clusters in the bulk compared to their behavior in GBs may explain the different He bubble sizes experimentally observed in the bulk and in GBs in reduced activation ferritic/martensitic steels that have been simultaneously neutron irradiated and He implanted.

  10. Small Crowders Slow Down Kinesin-1 Stepping by Hindering Motor Domain Diffusion

    NASA Astrophysics Data System (ADS)

    Sozański, Krzysztof; Ruhnow, Felix; Wiśniewska, Agnieszka; Tabaka, Marcin; Diez, Stefan; Hołyst, Robert

    2015-11-01

    The dimeric motor protein kinesin-1 moves processively along microtubules against forces of up to 7 pN. However, the mechanism of force generation is still debated. Here, we point to the crucial importance of diffusion of the tethered motor domain for the stepping of kinesin-1: small crowders stop the motor at a viscosity of 5 m P a .s —corresponding to a hydrodynamic load in the sub-fN (˜1 0-4 pN ) range—whereas large crowders have no impact even at viscosities above 100 m P a .s . This indicates that the scale-dependent, effective viscosity experienced by the tethered motor domain is a key factor determining kinesin's functionality. Our results emphasize the role of diffusion in the kinesin-1 stepping mechanism and the general importance of the viscosity scaling paradigm in nanomechanics.

  11. The small-voxel tracking algorithm for simulating chemical reactions among diffusing molecules

    SciTech Connect

    Gillespie, Daniel T. Gillespie, Carol A.; Seitaridou, Effrosyni

    2014-12-21

    Simulating the evolution of a chemically reacting system using the bimolecular propensity function, as is done by the stochastic simulation algorithm and its reaction-diffusion extension, entails making statistically inspired guesses as to where the reactant molecules are at any given time. Those guesses will be physically justified if the system is dilute and well-mixed in the reactant molecules. Otherwise, an accurate simulation will require the extra effort and expense of keeping track of the positions of the reactant molecules as the system evolves. One molecule-tracking algorithm that pays careful attention to the physics of molecular diffusion is the enhanced Green's function reaction dynamics (eGFRD) of Takahashi, Tănase-Nicola, and ten Wolde [Proc. Natl. Acad. Sci. U.S.A. 107, 2473 (2010)]. We introduce here a molecule-tracking algorithm that has the same theoretical underpinnings and strategic aims as eGFRD, but a different implementation procedure. Called the small-voxel tracking algorithm (SVTA), it combines the well known voxel-hopping method for simulating molecular diffusion with a novel procedure for rectifying the unphysical predictions of the diffusion equation on the small spatiotemporal scale of molecular collisions. Indications are that the SVTA might be more computationally efficient than eGFRD for the problematic class of non-dilute systems. A widely applicable, user-friendly software implementation of the SVTA has yet to be developed, but we exhibit some simple examples which show that the algorithm is computationally feasible and gives plausible results.

  12. The small-voxel tracking algorithm for simulating chemical reactions among diffusing molecules

    NASA Astrophysics Data System (ADS)

    Gillespie, Daniel T.; Seitaridou, Effrosyni; Gillespie, Carol A.

    2014-12-01

    Simulating the evolution of a chemically reacting system using the bimolecular propensity function, as is done by the stochastic simulation algorithm and its reaction-diffusion extension, entails making statistically inspired guesses as to where the reactant molecules are at any given time. Those guesses will be physically justified if the system is dilute and well-mixed in the reactant molecules. Otherwise, an accurate simulation will require the extra effort and expense of keeping track of the positions of the reactant molecules as the system evolves. One molecule-tracking algorithm that pays careful attention to the physics of molecular diffusion is the enhanced Green's function reaction dynamics (eGFRD) of Takahashi, Tănase-Nicola, and ten Wolde [Proc. Natl. Acad. Sci. U.S.A. 107, 2473 (2010)]. We introduce here a molecule-tracking algorithm that has the same theoretical underpinnings and strategic aims as eGFRD, but a different implementation procedure. Called the small-voxel tracking algorithm (SVTA), it combines the well known voxel-hopping method for simulating molecular diffusion with a novel procedure for rectifying the unphysical predictions of the diffusion equation on the small spatiotemporal scale of molecular collisions. Indications are that the SVTA might be more computationally efficient than eGFRD for the problematic class of non-dilute systems. A widely applicable, user-friendly software implementation of the SVTA has yet to be developed, but we exhibit some simple examples which show that the algorithm is computationally feasible and gives plausible results.

  13. Small-scale properties of a stochastic cubic-autocatalytic reaction-diffusion model

    NASA Astrophysics Data System (ADS)

    Gagnon, Jean-Sébastien; Hochberg, David; Pérez-Mercader, Juan

    2015-10-01

    We investigate the small-scale properties of a stochastic cubic-autocatalytic reaction-diffusion (CARD) model using renormalization techniques. We renormalize noise-induced ultraviolet divergences and obtain β functions for the decay rate and coupling at one loop. Assuming colored (power-law) noise, our results show that the behavior of both decay rate and coupling with scale depends crucially on the noise exponent. Interpreting the CARD model as a proxy for a (very simple) living system, our results suggest that power-law correlations in environmental fluctuations can both decrease or increase the growth of structures at smaller scales.

  14. Diffuse fluorescence tomography based on the radiative transfer equation for small animal imaging

    NASA Astrophysics Data System (ADS)

    Wang, Yihan; Zhang, Limin; Zhao, Huijuan; Gao, Feng; Li, Jiao

    2014-02-01

    Diffuse florescence tomography (DFT) as a high-sensitivity optical molecular imaging tool, can be applied to in vivo visualize interior cellular and molecular events for small-animal disease model through quantitatively recovering biodistributions of specific molecular probes. In DFT, the radiative transfer equation (RTE) and its approximation, such as the diffuse equation (DE), have been used as the forward models. The RTE-based DFT methodology is more suitable for biological tissue having void-like regions and the near-source area as in the situations of small animal imaging. We present a RTE-based scheme for the steady state DFT, which combines the discrete solid angle method and the finite difference method to obtain numerical solutions of the 2D steady RTE, with the natural boundary condition and collimating light source model. The approach is validated using the forward data from the Monte Carlo simulation for its better performances in the spatial resolution and reconstruction fidelity compared to the DE-based scheme.

  15. Dynamic studies of small animals with a four-color diffuse optical tomography imager

    NASA Astrophysics Data System (ADS)

    Schmitz, Christoph H.; Graber, Harry L.; Pei, Yaling; Farber, Mark; Stewart, Mark; Levina, Rita D.; Levin, Mikhail B.; Xu, Yong; Barbour, Randall L.

    2005-09-01

    We present newly developed instrumentation for full-tomographic four-wavelength, continuous wave, diffuse optical tomography (DOT) imaging on small animals. A small-animal imaging stage was constructed, from materials compatible with in-magnet studies, which offers stereotaxic fixation of the animal and precise, stable probe positioning. Instrument performance, based on calibration and phantom studies, demonstrates excellent long-term signal stability. DOT measurements of the functional rat brain response to electric paw stimulation are presented, and these demonstrate high data quality and excellent sensitivity to hemodynamic changes. A general linear model analysis on individual trials is used to localize and quantify the occurrence of functional behavior associated with the different hemoglobin state responses. Statistical evaluation of outcomes of individual trials is employed to identify significant regional response variations for different stimulation sites. Image results reveal a diffuse cortical response and a strong reaction of the thalamus, both indicative of activation of pain pathways by the stimulation. In addition, a weaker lateralized functional component is observed in the brain response, suggesting presence of motor activation. An important outcome of the experiment is that it shows that reactions to individual provocations can be monitored, without having to resort to signal averaging. Thus the described technology may be useful for studies of long-term trends in hemodynamic response, as would occur, for example, in behavioral studies involving freely moving animals.

  16. Self-learning kinetic Monte Carlo simulations of self-diffusion of small Ag islands on the Ag(111) surface.

    PubMed

    Shah, Syed Islamuddin; Nandipati, Giridhar; Karim, Altaf; Rahman, Talat S

    2016-01-20

    We studied self-diffusion of small two-dimensional Ag islands, containing up to ten atoms, on the Ag(111) surface using self-learning kinetic Monte Carlo (SLKMC) simulations. Activation barriers are calculated using the semi-empirical embedded atom method (EAM) potential. We find that two- to seven-atom islands primarily diffuse via concerted translation processes with small contributions from multi-atom and single-atom processes, while eight- to ten-atom islands diffuse via single-atom processes, especially edge diffusion, corner rounding and kink detachment, along with a minimal contribution from concerted processes. For each island size, we give a detailed description of the important processes, and their activation barriers, responsible for its diffusion. PMID:26657883

  17. Self-learning kinetic Monte Carlo simulations of self-diffusion of small Ag islands on the Ag(111) surface

    NASA Astrophysics Data System (ADS)

    Islamuddin Shah, Syed; Nandipati, Giridhar; Karim, Altaf; Rahman, Talat S.

    2016-01-01

    We studied self-diffusion of small two-dimensional Ag islands, containing up to ten atoms, on the Ag(111) surface using self-learning kinetic Monte Carlo (SLKMC) simulations. Activation barriers are calculated using the semi-empirical embedded atom method (EAM) potential. We find that two- to seven-atom islands primarily diffuse via concerted translation processes with small contributions from multi-atom and single-atom processes, while eight- to ten-atom islands diffuse via single-atom processes, especially edge diffusion, corner rounding and kink detachment, along with a minimal contribution from concerted processes. For each island size, we give a detailed description of the important processes, and their activation barriers, responsible for its diffusion.

  18. A Model for Occupational Safety and Health Intervention Diffusion to Small Businesses

    PubMed Central

    Sinclair, Raymond C.; Cunningham, Thomas R.; Schulte, Paul A.

    2015-01-01

    Background Smaller businesses differ from their larger counterparts in having higher rates of occupational injuries and illnesses and fewer resources for preventing those losses. Intervention models developed outside the United States have addressed the resource deficiency issue by incorporating intermediary organizations such as trade associations. Methods This paper extends previous models by using exchange theory and by borrowing from the diffusion of innovations model. It emphasizes that occupational safety and health (OSH) organizations must understand as much about intermediary organizations as they do about small businesses. OSH organizations (“initiators”) must understand how to position interventions and information to intermediaries as added value to their relationships with small businesses. Examples from experiences in two midwestern states are used to illustrate relationships and types of analyses implied by the extended model. Results The study found that intermediary organizations were highly attuned to providing smaller businesses with what they want, including OSH services. The study also found that there are opinion leader organizations and individual champions within intermediaries who are key to decisions and actions about OSH programming. Conclusions The model places more responsibility on both initiators and intermediaries to develop and market interventions that will be valued in the competitive small business environment where the resources required to adopt each new business activity could always be used in other ways. The model is a candidate for empirical validation, and it offers some encouragement that the issue of sustainable OSH assistance to small businesses might be addressed. PMID:24115112

  19. Radiation pressure of standing waves on liquid columns and small diffusion flames

    NASA Astrophysics Data System (ADS)

    Thiessen, David B.; Marr-Lyon, Mark J.; Wei, Wei; Marston, Philip L.

    2002-11-01

    The radiation pressure of standing ultrasonic waves in air is demonstrated in this investigation to influence the dynamics of liquid columns and small flames. With the appropriate choice of the acoustic amplitude and wavelength, the natural tendency of long columns to break because of surface tension was suppressed in reduced gravity [M. J. Marr-Lyon, D. B. Thiessen, and P. L. Marston, Phys. Rev. Lett. 86, 2293-2296 (2001); 87(20), 9001(E) (2001)]. Evaluation of the radiation force shows that narrow liquid columns are attracted to velocity antinodes. The response of a small vertical diffusion flame to ultrasonic radiation pressure in a horizontal standing wave was observed in normal gravity. In agreement with our predictions of the distribution of ultrasonic radiation stress on the flame, the flame is attracted to a pressure antinode and becomes slightly elliptical with the major axis in the plane of the antinode. The radiation pressure distribution and the direction of the radiation force follow from the dominance of the dipole scattering for small flames. Understanding radiation stress on flames is relevant to the control of hot fluid objects. [Work supported by NASA.

  20. Small effect of water on upper-mantle rheology based on silicon self-diffusion coefficients.

    PubMed

    Fei, Hongzhan; Wiedenbeck, Michael; Yamazaki, Daisuke; Katsura, Tomoo

    2013-06-13

    Water has been thought to affect the dynamical processes in the Earth's interior to a great extent. In particular, experimental deformation results suggest that even only a few tens of parts per million of water by weight enhances the creep rates in olivine by orders of magnitude. However, those deformation studies have limitations, such as considering only a limited range of water concentrations and very high stresses, which might affect the results. Rock deformation can also be understood as an effect of silicon self-diffusion, because the creep rates of minerals at temperatures as high as those in the Earth's interior are limited by self-diffusion of the slowest species. Here we experimentally determine the silicon self-diffusion coefficient DSi in forsterite at 8 GPa and 1,600 K to 1,800 K as a function of water content CH2O from less than 1 to about 800 parts per million of water by weight, yielding the relationship, DSi ≈ (CH2O)(1/3). This exponent is strikingly lower than that obtained by deformation experiments (1.2; ref. 7). The high nominal creep rates in the deformation studies under wet conditions may be caused by excess grain boundary water. We conclude that the effect of water on upper-mantle rheology is very small. Hence, the smooth motion of the Earth's tectonic plates cannot be caused by mineral hydration in the asthenosphere. Also, water cannot cause the viscosity minimum zone in the upper mantle. And finally, the dominant mechanism responsible for hotspot immobility cannot be water content differences between their source and surrounding regions. PMID:23765497

  1. Drag force, diffusion coefficient, and electric mobility of small particles. II. Application.

    PubMed

    Li, Zhigang; Wang, Hai

    2003-12-01

    We propose a generalized treatment of the drag force of a spherical particle due to its motion in a laminar fluid media. The theory is equally applicable to analysis of particle diffusion and electric mobility. The focus of the current analysis is on the motion of spherical particles in low-density gases with Knudsen number Kn>1. The treatment is based on the gas-kinetic theory analysis of drag force in the specular and diffuse scattering limits obtained in a preceding paper [Z. Li and H. Wang, Phys. Rev. E., 68, 061206 (2003)]. Our analysis considers the influence of van der Waals interactions on the momentum transfer upon collision of a gas molecule with the particle and expresses this influence in terms of an effective, reduced collision integral. This influence is shown to be significant for nanosized particles. In the present paper, the reduced collision integral values are obtained for specular and diffuse scattering, using a Lennard-Jones-type potential energy function suitable for the interactions of a gas molecule with a particle. An empirical formula for the momentum accommodation function, used to determine the effective, reduced collision integral, is obtained from available experimental data. The resulting treatment is shown to be accurate for interpreting the mobility experiments for particles as small as approximately 1 nm in radius. The treatment is subsequently extended to the entire range of the Knudsen number, following a semiempirical, gas-kinetic theory analysis. We demonstrate that the proposed formula predicts very well Millikan's oil-droplet experiments [R. A. Millikan, Philos. Mag. 34, 1 (1917); Phys. Rev. 22, 1 (1923)]. The rigorous theoretical foundation of the proposed formula in the Kn>1 limit makes the current theory far more general than the semiempirical Stokes-Cunningham formula in terms of the particle size and condition of the fluid and, therefore, more attractive than the Stokes-Cunningham formula. PMID:14754192

  2. Drag force, diffusion coefficient, and electric mobility of small particles. II. Application

    NASA Astrophysics Data System (ADS)

    Li, Zhigang; Wang, Hai

    2003-12-01

    We propose a generalized treatment of the drag force of a spherical particle due to its motion in a laminar fluid media. The theory is equally applicable to analysis of particle diffusion and electric mobility. The focus of the current analysis is on the motion of spherical particles in low-density gases with Knudsen number Kn≫1. The treatment is based on the gas-kinetic theory analysis of drag force in the specular and diffuse scattering limits obtained in a preceding paper [Z. Li and H. Wang, Phys. Rev. E., 68, 061206 (2003)]. Our analysis considers the influence of van der Waals interactions on the momentum transfer upon collision of a gas molecule with the particle and expresses this influence in terms of an effective, reduced collision integral. This influence is shown to be significant for nanosized particles. In the present paper, the reduced collision integral values are obtained for specular and diffuse scattering, using a Lennard-Jones-type potential energy function suitable for the interactions of a gas molecule with a particle. An empirical formula for the momentum accommodation function, used to determine the effective, reduced collision integral, is obtained from available experimental data. The resulting treatment is shown to be accurate for interpreting the mobility experiments for particles as small as ˜1 nm in radius. The treatment is subsequently extended to the entire range of the Knudsen number, following a semiempirical, gas-kinetic theory analysis. We demonstrate that the proposed formula predicts very well Millikan’s oil-droplet experiments [R. A. Millikan, Philos. Mag. 34, 1 (1917); Phys. Rev. 22, 1 (1923)]. The rigorous theoretical foundation of the proposed formula in the Kn≫1 limit makes the current theory far more general than the semiempirical Stokes-Cunningham formula in terms of the particle size and condition of the fluid and, therefore, more attractive than the Stokes-Cunningham formula.

  3. Diffusion and transformation kinetics of small helium clusters in bulk tungsten

    NASA Astrophysics Data System (ADS)

    Perez, Danny; Vogel, Thomas; Uberuaga, Blas P.

    2014-07-01

    The production of energy through nuclear fusion poses serious challenges related to the stability and performance of materials in extreme conditions. In particular, the constant bombardment of the walls of the reactor with high doses of He ions is known to lead to deleterious changes in their microstructures. These changes follow from the aggregation of He into bubbles that can grow and blister, potentially leading to the contamination of the plasma, or to the degradation of their mechanical properties. We computationally study the behavior of small clusters of He atoms in W in conditions relevant to fusion energy production. Using a wide range of techniques, we investigate the thermodynamics of the clusters and their kinetics in terms of diffusivity, growth, and breakup, as well as mutation into nanobubbles. Our study provides the essential ingredients to model the early stages of He exposure leading up to the nucleation of He bubbles.

  4. Fractional diffusion on circulant networks: emergence of a dynamical small world

    NASA Astrophysics Data System (ADS)

    Riascos, A. P.; Mateos, José L.

    2015-07-01

    In this paper, we study fractional random walks on networks defined from the equivalent of the fractional diffusion equation in graphs. We explore this process analytically in circulant networks; in particular, interacting cycles and limit cases such as a ring and a complete graph. From the spectra and the eigenvectors of the Laplacian matrix, we deduce explicit results for different quantities that characterize this dynamical process. We obtain analytical expressions for the fractional transition matrix, the fractional degrees and the average probability of return of the random walker. Also, we discuss the Kemeny constant, which gives the average number of steps necessary to reach any site of the network. Throughout this work, we analyze the mechanisms behind fractional transport on circulant networks and how this long-range process dynamically induces the small-world property in different structures.

  5. PHASE II AIDS MALIGNANCY CONSORTIUM TRIAL OF TOPICAL HALOFUGINONE IN AIDS-RELATED KAPOSI’S SARCOMA

    PubMed Central

    Koon, Henry B.; Fingleton, Barbara; Lee, Jeannette Y.; Geyer, Julia T.; Cesarman, Ethel; Parise, Robert A.; Egorin, Merrill J.; Dezube, Bruce J.; Aboulafia, David; Krown, Susan E.

    2010-01-01

    Using a novel blinded intra-patient vehicle control design, we conducted a phase II study of topically-administered halofuginone, an angiogenesis inhibitor that inhibits collagen type-I and matrix metalloproteinases (MMPs), in patients with AIDS-related Kaposi’s sarcoma (KS). Serial KS biopsies assessed treatment effects on angiogenic factors and KSHV-LANA. We observed marked heterogeneity of KSHV-LANA expression. Although the small number of subjects whose response could be evaluated precluded definitive assessment of halofuginone’s efficacy, we observed a significant decrease in type-I collagen only in halofuginone-treated lesions, but no effect on MMP-2. The trial design is applicable to future studies of topical agents. PMID:21068672

  6. Note: Molecular diffusivity in a small pore zeolite measured by a variable pressure (piezometric) uptake method

    NASA Astrophysics Data System (ADS)

    Wang, Fei; Kobayashi, Yasukazu; Muhammad, Usman; Wang, Dezheng; Wang, Yao

    2016-03-01

    The use of numerical analysis to solve the diffusion equation in the uptake method allowed the measurement of molecular diffusivity in a zeolite with a variable pressure around it. The diffusivity was obtained from the data in the measurement of the adsorption isotherm, which means that the diffusivity measurement now needs neither a special instrument nor procedure. The diffusivities of all the gases are readily available from the measurement of their adsorption isotherms and these data include how the diffusivity changes versus adsorbed concentration. The modeling introduced can also be used for a zeolite with a surface barrier.

  7. Measurement of Small Molecular Dopant F4TCNQ and C60F36 Diffusion in Organic Bilayer Architectures.

    PubMed

    Li, Jun; Rochester, Chris W; Jacobs, Ian E; Friedrich, Stephan; Stroeve, Pieter; Riede, Moritz; Moulé, Adam J

    2015-12-30

    The diffusion of molecules through and between organic layers is a serious stability concern in organic electronic devices. In this work, the temperature-dependent diffusion of molecular dopants through small molecule hole transport layers is observed. Specifically we investigate bilayer stacks of small molecules used for hole transport (MeO-TPD) and p-type dopants (F4TCNQ and C60F36) used in hole injection layers for organic light emitting diodes and hole collection electrodes for organic photovoltaics. With the use of absorbance spectroscopy, photoluminescence spectroscopy, neutron reflectometry, and near-edge X-ray absorption fine structure spectroscopy, we are able to obtain a comprehensive picture of the diffusion of fluorinated small molecules through MeO-TPD layers. F4TCNQ spontaneously diffuses into the MeO-TPD material even at room temperature, while C60F36, a much bulkier molecule, is shown to have a substantially higher morphological stability. This study highlights that the differences in size/geometry and thermal properties of small molecular dopants can have a significant impact on their diffusion in organic device architectures. PMID:26673846

  8. Brief Report: Role of Thymic Reconstitution in the Outcome of AIDS-Related PML.

    PubMed

    Chalkias, Spyridon G; Gheuens, Sarah; Bord, Evelyn; Batson, Stephanie; Koralnik, Igor J

    2015-12-01

    Implications of thymopoiesis in AIDS-related opportunistic infections remain unexplored. We used progressive multifocal leukoencephalopathy (PML), caused by JC virus (JCV), as an opportunistic infection model, and we simultaneously investigated thymic output and T-cell responses against JCV in 22 patients with PML treated with combined antiretroviral therapy. Thymic output was significantly associated with JCV-specific CD4⁺ and CD8⁺ T-cell responses and improved survival. Our data suggest that patients with AIDS-related PML and impaired thymopoiesis are less likely to develop a robust JCV-specific cellular immune response and consequently are at an increased risk for a poor clinical outcome. PMID:26181821

  9. Approaches for quantifying and managing diffuse phosphorus exports at the farm/small catchment scale.

    PubMed

    McDowell, Richard W; Nash, David; George, Anja; Wang, Q J; Duncan, Ruth

    2009-01-01

    Quantifying and managing diffuse P losses from small catchments or at the farm scale requires detailed knowledge of farming practices and their interaction with catchment processes. However, detailed knowledge may not be available and hence modeling is required. This paper demonstrates two approaches to developing tools that assist P losses from New Zealand or Australian dairy farms. The first is largely empirical and separates sources of P within a paddock into soil, fertilizer, dung, and treading impacts (including damage to grazed pasture). This information is combined with expert knowledge of hydrological processes and potential point sources (e.g., stream crossings) to create a deterministic model that can be used to evaluate the most cost and labor efficient method of mitigating P losses. For instance, in one example, 45% of annual P lost was attributed to the application of superphosphate just before a runoff event for which a mitigation strategy could be to use a less water soluble P fertilizer. The second approach uses a combination of interviews, expert knowledge and relationships to develop a Bayesian Network that describes P exports. The knowledge integration process helped stakeholders develop a comprehensive understanding of the problem. The Network, presented in the form of a "cause and effect", diagram provided a simple, visual representation of current knowledge that could be easily applied to individual circumstances and isolate factors having the greatest influence on P loss. Both approaches demonstrate that modeling P losses and mitigation strategies does not have to cover every process or permutation and that a degree of uncertainty can be handled to create a working model of P losses at a farm or small catchment scale. PMID:19704140

  10. Predicting AIDS-related events using CD4 percentage or CD4 absolute counts

    PubMed Central

    Pirzada, Yasmin; Khuder, Sadik; Donabedian, Haig

    2006-01-01

    Background The extent of immunosuppression and the probability of developing an AIDS-related complication in HIV-infected people is usually measured by the absolute number of CD4 positive T-cells. The percentage of CD4 positive cells is a more easily measured and less variable number. We analyzed sequential CD4 and CD8 numbers, percentages and ratios in 218 of our HIV infected patients to determine the most reliable predictor of an AIDS-related event. Results The CD4 percentage was an unsurpassed predictor of the occurrence of AIDS-related events when all subsets of patients are considered. The CD4 absolute count was the next most reliable, followed by the ratio of CD4/CD8 percentages. The value of CD4 percentage over the CD4 absolute count was seen even after the introduction of highly effective HIV therapy. Conclusion The CD4 percentage is unsurpassed as a parameter for predicting the onset of HIV-related diseases. The extra time and expense of measuring the CD4 absolute count may be unnecessary. PMID:16916461

  11. AIDS-Related Factors Predictive of Suicidal Ideation of Low and High Intent among Gay and Bisexual Men.

    ERIC Educational Resources Information Center

    Schneider, Stephen G.; And Others

    1991-01-01

    Studied Acquired Immune Deficiency Syndrome (AIDS)-related stressors and suicidal ideation/intent among 778 gay and bisexual men (none with AIDS). Compared to those who reported no suicidal ideation over past six months, those who reported ideation (n=212) were more likely to report recent bereavement of partner, AIDS-Related Disorder (ARC)…

  12. Advective-diffusive motion on large scales from small-scale dynamics with an internal symmetry

    NASA Astrophysics Data System (ADS)

    Marino, Raffaele; Aurell, Erik

    2016-06-01

    We consider coupled diffusions in n -dimensional space and on a compact manifold and the resulting effective advective-diffusive motion on large scales in space. The effective drift (advection) and effective diffusion are determined as a solvability conditions in a multiscale analysis. As an example, we consider coupled diffusions in three-dimensional space and on the group manifold SO(3) of proper rotations, generalizing results obtained by H. Brenner [J. Colloid Interface Sci. 80, 548 (1981), 10.1016/0021-9797(81)90214-9]. We show in detail how the analysis can be conveniently carried out using local charts and invariance arguments. As a further example, we consider coupled diffusions in two-dimensional complex space and on the group manifold SU(2). We show that although the local operators may be the same as for SO(3), due to the global nature of the solvability conditions the resulting diffusion will differ and generally be more isotropic.

  13. Successful treatment with autologous peripheral blood stem cell transplantation for acquired immunodeficiency syndrome (AIDS)-related malignant lymphoma.

    PubMed

    NAGAI, Yuya; MORI, Minako; INOUE, Daichi; KIMURA, Takaharu; SHIMOJI, Sonoko; TOGAMI, Katsuhiro; TABATA, Sumie; MATSUSHITA, Akiko; NAGAI, Kenichi; Imai, Yukihiro; Takafuta, Toshiro; Takahashi, Takayuki

    2009-11-01

    A 62-year-old man was diagnosed with human immunodeficiency virus (HIV) infection while suffering from recurrent herpes zoster infection. Laboratory examination revealed CD4(+) lymphocyte count 16 cells/mul and HIV loading 150,000 copies/ml at presentation. In addition, he had multiple lymph node swelling. Histologic diagnosis of a biopsied lymph node was diffuse, large, B cell-type malignant lymphoma. The karyotype of the lymphoma cells was t(8;14)(q24;q32), which was confirmed by G-banding and fluorescent in situ hybridization. Positron emission tomography (PET)-combined CT scanning revealed systemic extranodal tumors involving the gastrointestinal tract, pancreas, and bone marrow. The clinical stage of the lymphoma was IVB and the international prognosis index was categorized as high. Complete remission (CR) of the lymphoma was obtained after 2 courses of CHOP (cyclophosphamide, adriamycin, vincristine, prednisolone) chemotherapy and 4 subsequent courses of rituximab-combined CHOP (R-CHOP). Highly active antiretroviral therapy (HAART) was started at the initiation of CHOP. Because of the poor prognosis of AIDS-related lymphoma, he received autologous peripheral blood stem cell transplantation with the MEAM protocol (ranimustine, etoposide, cytarabine, melphalan) as a conditioning procedure without a severe infectious episode. He remains in CR 24 months after the transplantation. PMID:20009441

  14. Network topology and Turing instabilities in small arrays of diffusively coupled reactors

    NASA Astrophysics Data System (ADS)

    Horsthemke, Werner; Lam, Kwan; Moore, Peter K.

    2004-08-01

    We study the effect of the network structure on the diffusion-induced instability to nonuniform steady states in arrays of diffusively coupled reactors. The kinetics is given by the Lengyel-Epstein model, and we derive the conditions for Turing instabilities in all arrays of two, three, and four reactors.

  15. Diffuse Idiopathic Skeletal Hyperostosis (DISH) and non small cell lung cancer: case presentation and review of the literature.

    PubMed

    Tomos, Ioannis; Vlami, Aikaterini; Karakatsani, Anna; Korbila, Ioanna; Manali, Effrosyni D; Papiris, Spyros A

    2016-01-01

    Diffuse idiopathic skeletal hyperostosis (DISH), also known as Forestier's disease, is a systemic non inflammatory disease of unknown cause. It is characterized by the presence of osteophytes due to calcification and ossification of spinal ligaments and entheses. Moreover, diffuse idiopathic skeletal hyperostosis has been associated with a variety of metabolic disorders. However, to the best of our knowledge no association with non small cell lung cancer (NSCLC) has been reported so far. In the present study we report a case of a patient with NSCLC and DISH. PMID:27238170

  16. Productive human immunodeficiency virus infection levels correlate with AIDS-related manifestations in the patient

    SciTech Connect

    Mathez, D.; Paul, D.; de Belilovsky, C.; Sultan, Y.; Deleuze, J.; Gorin, I.; Saurin, W.; Decker, R.; Leibowitch, J. )

    1990-10-01

    Mononuclear cells were obtained from 71 human immunodeficiency virus type 1 (HIV-1) seropositive subjects presenting and first visit either as asymptomatic or with minor symptoms and with CD4 lymphocytes greater than 550 per mm3 (group A, 35 patients) or as patients with AIDS, AIDS-related illnesses, or CD4 lymphocytes less than 400 per mm3 (group B, 36 patients). After 1-5 years of follow-up, 13 patients of group A had essentially retained their initial status (asymptomatics); the 22 others had suffered clinical or immunological deterioration (progressors). Frozen cells were thawed and submitted to lethal gamma-irradiation in vitro (4500 rads; 1 rad = 0.01 Gy) before they were cultured with normal phytohemagglutinin-stimulated lymphocytes to determine radiation-resistant HIV expression ex vivo (R-HEV). HIV antigenemia correlated with R-HEV values in 142 samples (r = 0.92, P less than 0.001) but was a less sensitive predictor of disease than R-HEV. R-HEV was detected in all specimens from patients with major AIDS-related illnesses or HIV-associated CD4 lymphopenia. In 77% of the progressors from group A, R-HEV detection preceded the onset of AIDS-associated disease or CD4 lymphopenia by 1 year (average). Conversely, R-HEV was low or was not detected in 36 sequential specimens from the 13 patients who remained asymptomatic over the following 2-5 years. Thus, persistently low HIV expression in vivo predicted a nondiseased state, whereas higher HIV expression levels seemed necessary for disease to occur. These data indicate that R-HEV is related to productive HIV infection in vivo, the latter acting as a determinant of AIDS-related illnesses. In view of this, measurement of HIV expression levels in the patient should be useful in antiviral efficacy trials.

  17. Drag force, diffusion coefficient, and electric mobility of small particles. I. Theory applicable to the free-molecule regime.

    PubMed

    Li, Zhigang; Wang, Hai

    2003-12-01

    The transport of small particles in the free-molecule regime is investigated on the basis of gas kinetic theory. Drag force formulations were derived in two limiting collision models-namely, specular and diffuse scattering-by considering the potential force of interactions between the particle and fluid molecules. A parametrized drag coefficient equation is proposed and accounts for the transition from specular to diffuse scattering as particle size exceeds a critical value. The resulting formulations are shown to be consistent with the Chapman-Enskog theory of molecular diffusion. In the limit of rigid-body interactions, these formulations can be simplified also to Epstein's solutions [P. S. Epstein, Phys. Rev. 23, 710 (1924)]. PMID:14754191

  18. AIDS-related knowledge, attitudes, and behaviors among juvenile delinquents in Israel.

    PubMed

    Slonim-Nevo, V

    Fifty-six Israeli adolescents under the care of probation officers were interviewed about their AIDS-related knowledge, attitudes, and behaviors. The results suggest that these adolescents put themselves at risk of HIV infection. A substantial proportion of the sample demonstrated a lack of knowledge on issues relevant for AIDS prevention. The majority held negative attitudes toward condoms but were also sexually active, and some had experienced unprotected sexual intercourse, anal sex, and drug use. Most of the respondents, moreover, showed a lack of competence in handling situations that pressure them to act unsafely. Implications for practice are discussed. PMID:1343361

  19. Diffusion of small two-dimensional Cu islands on Cu(111) studied with a kinetic Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Karim, Altaf; Al-Rawi, Ahlam N.; Kara, Abdelkader; Rahman, Talat S.; Trushin, Oleg; Ala-Nissila, Tapio

    2006-04-01

    Diffusion of small two-dimensional Cu islands (containing up to 10 atoms) on Cu(111) has been studied using the newly developed self-learning Kinetic Monte Carlo (SLKMC) method which is based on a database of diffusion processes and their energetics accumulated automatically during the implementation of the SLKMC code. Results obtained from simulations in which atoms hop from one fcc hollow site to another are compared with those obtained from a parallel set of simulations in which the database is supplemented by processes revealed in complementary molecular dynamics simulations at 500K . They include processes involving the hcp (stacking-fault) sites, which facilitate concerted motion of the islands (simultaneous motion of all atoms in the island). A significant difference in the scaling of the effective diffusion barriers with island size is observed in the two cases. In particular, the presence of concerted island motion leads to an almost linear increase in the effective diffusion barrier with size, while its absence accounts for strong size-dependent oscillations and anomalous behavior for trimers and heptamers. We also identify and discuss in detail the key microscopic processes responsible for the diffusion and examine the frequencies of their occurrence, as a function of island size and substrate temperature.

  20. Combined system of fluorescence diffuse optical tomography and microcomputed tomography for small animal imaging

    NASA Astrophysics Data System (ADS)

    Yang, Xiaoquan; Gong, Hui; Quan, Guotao; Deng, Yong; Luo, Qingming

    2010-05-01

    We developed a dual-modality system that combines fluorescence diffuse optical tomography (fDOT) and flat panel detector-based microcomputed tomography (micro-CT) to simultaneously reveal molecular and structural information in small animals. In fDOT, a 748 nm diode laser was used as an excitation source, while a cooled charge coupled device camera was adopted to collect transmission fluorescence. In micro-CT, a flat panel detector based on amorphous silicon, with active area of 13×13 cm2, and a microfocus x-ray tube were used. The fDOT system was mounted orthogonally to the micro-CT and the projection images were acquired without rotation of the sample, which is different from the method used for micro-CT alone. Both the finite element method and the algebraic reconstruction technique were used to reconstruct images from the fDOT. Phantom data showed that the resolution of the fDOT system was about 3 mm at an imaging depth of 7 mm. Quantitative error was no more than 5% and imaging sensitivity for 1,1'-dioctadecyl-3,3,3',3'-etramethylindotricarbocyanine iodide bis-oleate (DiR-BOA) was estimated to be higher than 100 nM at a depth of 7 mm. Calculations of the phantom's center of mass showed that the location accuracy of fDOT was about 0.7 mm. We applied a Feldkamp algorithm to reconstruct the micro-CT image. By measuring the presampled modulation transfer function with a 30 μm tungsten thread, we estimated that the micro-CT has a resolution of 5 mm-1 when the field of view was 6.5 cm. Our results indicate the uniformity of the transaxial micro-CT image and the contrast-to-noise ratio was measured as 1.95 for a radiation dose of 1 cGy. A non-image-based method was employed for merging images from the two imaging modalities. A nude mouse with DiR-BOA, imaged ex vivo, was used to validate the feasibility of the dual-modality system.

  1. Economic empowerment and AIDS-related stigma in rural Kenya: a double-edged sword?

    PubMed

    Gnauck, Katherine; Ruiz, Jamie; Kellett, Nicole; Sussman, Andrew; Sullivan, Mary Ann; Montoya, Maria; Levin, Nick; Tomedi, Angelo; Mwanthi, Mutuku A

    2013-01-01

    Economic empowerment, HIV risk and AIDS-related stigma appear intricately intertwined for women in Kenya. Their interaction must be understood in order to implement effective economic interventions that also decrease HIV risk and stigma. We conducted a qualitative study amongst women in a rural Kamba-speaking community of southeastern Kenya to pursue whether engagement in an economic empowerment initiative (a basket weaving cooperative) influences women's perspectives and experiences with HIV risk and AIDS-related stigma. We conducted seven women's focus groups: participants in the local basket-weaving cooperative comprised four focus groups and non-participants comprised the remaining three groups. The HIV status of the women was not known. Three dominant themes emerged from the focus groups: empowerment, pervasive vulnerability and unanticipated social paradoxes. Contradictions found in these themes suggest that economic empowerment can become a double-edged sword. Economic empowerment enhanced perceived individual, domestic and social community status. However, this enhancement was not protective of domestic violence and perceived HIV risk. Social perceptions may have paradoxically contributed barriers to HIV testing and treatment putting women at greater HIV risk. In conclusion, economic empowerment initiatives for women in developing countries in the context of the HIV epidemic should be coupled with peer mediated support and HIV-risk education. PMID:23668536

  2. HIV and AIDS-related stigma and discrimination: a conceptual framework and implications for action.

    PubMed

    Parker, Richard; Aggleton, Peter

    2003-07-01

    Internationally, there has been a recent resurgence of interest in HIV and AIDS-related stigma and discrimination, triggered at least in part by growing recognition that negative social responses to the epidemic remain pervasive even in seriously affected communities. Yet, rarely are existing notions of stigma and discrimination interrogated for their conceptual adequacy and their usefulness in leading to the design of effective programmes and interventions. Taking as its starting point, the classic formulation of stigma as a 'significantly discrediting' attribute, but moving beyond this to conceptualize stigma and stigmatization as intimately linked to the reproduction of social difference, this paper offers a new framework by which to understand HIV and AIDS-related stigma and its effects. It so doing, it highlights the manner in which stigma feeds upon, strengthens and reproduces existing inequalities of class, race, gender and sexuality. It highlights the limitations of individualistic modes of stigma alleviation and calls instead for new programmatic approaches in which the resistance of stigmatized individuals and communities is utilized as a resource for social change. PMID:12753813

  3. AIDS related knowledge and behaviours among college students, Gondar, Ethiopia: a comparative study.

    PubMed

    Teka, T

    1997-07-01

    AIDS-related knowledge and behaviours among students at the Gondar College of Medical Sciences, Gondar, Ethiopia were evaluated based on identical surveys conducted in 1990 and 1992. One hundred three second year students provided information in 1992. Analysis indicated that 49% were engaged in sexual intercourse and only a third of these group used condom despite their improved knowledge and belief on condom compared to their previous position in 1990 (p < 0.004). On the other hand, their sexual behaviours regarding sexual contact with high risk individuals decreased compared to 1990 (p < 0.0005). Their general level of AIDS-related preventive knowledge increased over time (p < 0.002), although there was no significant difference in knowledge observed among different sexes and departments. Among the sexually active, a large proportion of students (22%) still had sexual contact with high risk individuals and only 33% of them were using safer methods. Continuing efforts, including peer education, specific health education interventions are still crucially needed to bring a positive change in sexual behaviour. PMID:9558757

  4. Thermal Diffusion Dynamic Behavior of Two-Dimensional Ag-SMALL Clusters on Ag(1 1 1) Surface

    NASA Astrophysics Data System (ADS)

    Zakirur-Rehman; Hayat, Sardar Sikandar

    2015-07-01

    In this paper, the thermal diffusion behavior of small two-dimensional Ag-islands on Ag(1 1 1) surface has been explored using molecular dynamics (MD) simulations. The approach is based on semi-empirical potentials. The key microscopic processes responsible for the diffusion of Ag1-5 adislands on Ag(1 1 1) surface are identified. The hopping and zigzag concerted motion along with rotation are observed for Ag one-atom to three-atom islands while single-atom and multi-atom processes are revealed for Ag four-atom and five-atom islands, during the diffusion on Ag(1 1 1) surface. The same increasing/decreasing trend in the diffusion coefficient and effective energy barrier is observed in both the self learning kinetic Monte Carlo (SLKMC) and MD calculations, for the temperature range of 300-700 K. An increase in the value of effective energy barrier is noticed with corresponding increase in the number of atoms in Ag-adislands. A reasonable linear fit is observed for the diffusion coefficient for studied temperatures (300, 500 and 700 K). For the observed diffusion mechanisms, our findings are in good agreement with ab initio density-functional theory (DFT) calculations for Al/Al(1 1 1) while the energy barrier values are in same range as the experimental values for Cu/Ag(1 1 1) and the theoretical values using ab initio DFT supplemented with embedded-atom method for Ag/Ag(1 1 1).

  5. SINGLE-BREATH DIFFUSING CAPACITY AND LUNG VOLUMES IN SMALL LABORATORY MAMMALS

    EPA Science Inventory

    The authors measured the single-breath diffusing capacity for carbon monoxide (DLco), total lung capacity(TLC), functional residue capacity(FRC), and residual volume(RV) in anesthetized male hamsters, rats, guinea pigs, and rabbits whose weights varied from 40 to 3,500g. TLC (def...

  6. Responding to AIDS-related bereavement in the South African context.

    PubMed

    Demmer, Craig

    2007-10-01

    AIDS continues to be a death sentence for many individuals living in South Africa where it remains the leading cause of death. Little is currently known about what it is like to experience the loss of a loved one to AIDS from the South African perspective and how to assist individuals who are living in a context vastly different from similarly bereaved individuals in the West. The purpose of this article is to discuss contextual issues that may affect individuals in South Africa who are grieving AIDS-related deaths and to offer preliminary suggestions on how to help these individuals. The author draws on his experience in the province of KwaZulu-Natal working with people affected by the HIV/AIDS epidemic, as well as discussions with practitioners involved in HIV/AIDS care in this region. PMID:17886413

  7. Gender and AIDS-related psychosocial processes: a study of perceived susceptibility, social distance, and homophobia.

    PubMed

    Schieman, S

    1998-06-01

    Over the past decade, researchers have accumulated evidence that suggests six main factors are associated with AIDS-related risk reduction behavior: (a) perceived susceptibility (Dolcini et al., 1995; van der Plight & Richard, 1994); (b) attitudes toward condoms (Catania et al., 1994; Maticka-Tynadale, 1991); (c) personally knowing someone with HIV/AIDS (Joseph et al., 1987); (d) perceived peer norms about risk-reduction (Maticka-Tyndale, 1991); (e) previous sexual activity (Joseph et al., 1987); and (f) self-efficacy (Aspinwall, Kemeny, Taylor, & Schneider, 1991; van der Plight & Richard, 1994). Furthermore, there is some suggestion that the epidemiology and sociocultural constructions of the disease has led to considerable gender, racial, and class differences in awareness of AIDS, perception of HIV threat, and HIV-relevant behavior (Cohan & Atwood, 1994; Dolcini et al., 1995; Gillies, 1994). PMID:9642424

  8. Understanding and Addressing AIDS-Related Stigma: From Anthropological Theory to Clinical Practice in Haiti

    PubMed Central

    Castro, Arachu; Farmer, Paul

    2005-01-01

    For the past several years, diverse and often confused concepts of stigma have been invoked in discussions on AIDS. Many have argued compellingly that AIDS-related stigma acts as a barrier to voluntary counseling and testing. Less compelling are observations regarding the source of stigma or its role in decreasing interest in HIV care. We reviewed these claims as well as literature from anthropology, sociology, and public health. Preliminary data from research in rural Haiti suggest that the introduction of quality HIV care can lead to a rapid reduction in stigma, with resulting increased uptake of testing. Rather than stigma, logistic and economic barriers determine who will access such services. Implications for scale-up of integrated AIDS prevention and care are explored. PMID:15623859

  9. Understanding Internalized HIV/AIDS-Related Stigmas in the Dominican Republic: A Short Report

    PubMed Central

    Hampanda, Karen

    2016-01-01

    HIV/AIDS-related stigmas can become internalized, resulting in declines in physical and mental health. Pathways to internalized HIV-related stigma (IS), characterized by persistently negative, self-abasing thoughts, are not well established among women living with HIV/AIDS (WLWHA) in the Dominican Republic (DR). Identifying factors involved in self-directed shaming and blaming is important, given the high HIV prevalence in the DR’s most vulnerable populations. The present study sheds light on factors involved in negative and self-abasing thoughts in WLWHA in the DR by examining the relationship between depression, perceived HIV-related stigma from the community (PSC), perceived HIV-related stigma from family (PSF) and IS. The Internalized AIDS-Related Stigma Scale (IA-RSS), the Center for Epidemiologic Studies Short Depression Scale (CES-D 10), and an instrument designed to measure perceived HIV-related stigma from the community and family was administered to 233 WLWHA in Puerto Plata, DR. Data were analyzed using descriptive statistics and ordered multiple logistic regression. Results showed that depression (OR=1.60; p<0.05), PSC (OR=3.68; p<0.001), and PSF (OR=1.60; p<0.01) were positively associated with IS. These findings indicate that IS-reducing interventions should address HIV-related depression. Additionally, HIV-related treatment and care services should work with WLWHA to adopt healthier attitudes about how community members view people living with HIV/AIDS in the Dominican Republic. PMID:26466239

  10. Understanding internalized HIV/AIDS-related stigmas in the Dominican Republic: a short report.

    PubMed

    Rael, Christine Tagliaferri; Hampanda, Karen

    2016-03-01

    HIV/AIDS-related stigmas can become internalized, resulting in declines in physical and mental health. Pathways to internalized HIV-related stigma (IS), characterized by persistently negative, self-abasing thoughts, are not well established among women living with HIV/AIDS (WLWHA) in the Dominican Republic (DR). Identifying factors involved in self-directed shaming and blaming is important, given the high HIV prevalence in the DR's most vulnerable populations. The present study sheds light on factors involved in negative and self-abasing thoughts in WLWHA in the DR by examining the relationship between depression, perceived HIV-related stigma from the community (PSC), perceived HIV-related stigma from family (PSF), and IS. The Internalized AIDS-Related Stigma Scale (IA-RSS), the Center for Epidemiologic Studies Short Depression Scale (CES-D 10), and an instrument designed to measure perceived HIV-related stigma from the community and family was administered to 233 WLWHA in Puerto Plata, DR. Data were analyzed using descriptive statistics and ordered multiple logistic regression. Results showed that depression (OR = 1.60; p < .05), PSC (OR = 3.68; p < .001), and PSF (OR = 1.60; p < .01) were positively associated with IS. These findings indicate that IS-reducing interventions should address HIV-related depression. Additionally, HIV-related treatment and care services should work with WLWHA to adopt healthier attitudes about how community members view people living with HIV/AIDS in the DR. PMID:26466239

  11. Circulating Mediators of Inflammation and Immune Activation in AIDS-Related Non-Hodgkin Lymphoma

    PubMed Central

    Nolen, Brian M.; Breen, Elizabeth Crabb; Bream, Jay H.; Jenkins, Frank J.; Kingsley, Lawrence A.; Rinaldo, Charles R.; Lokshin, Anna E.

    2014-01-01

    Background Non-Hodgkin lymphoma (NHL) is the most common AIDS-related malignancy in developed countries. An elevated risk of developing NHL persists among HIV-infected individuals in comparison to the general population despite the advent of effective antiretroviral therapy. The mechanisms underlying the development of AIDS-related NHL (A-NHL) are not fully understood, but likely involve persistent B-cell activation and inflammation. Methods This was a nested case-control study within the ongoing prospective Multicenter AIDS Cohort Study (MACS). Cases included 47 HIV-positive male subjects diagnosed with high-grade B-cell NHL. Controls were matched to each case from among participating HIV-positive males who did not develop any malignancy. Matching criteria included time HIV+ or since AIDS diagnosis, age, race and CD4+ cell count. Sera were tested for 161 serum biomarkers using multiplexed bead-based immunoassays. Results A subset of 17 biomarkers, including cytokines, chemokines, acute phase proteins, tissue remodeling agents and bone metabolic mediators was identified to be significantly altered in A-NHL cases in comparison to controls. Many of the biomarkers included in this subset were positively correlated with HIV viral load. A pathway analysis of our results revealed an extensive network of interactions between current and previously identified biomarkers. Conclusions These findings support the current hypothesis that A-NHL develops in the context of persistent immune stimulation and inflammation. Further analysis of the biomarkers identified in this report should enhance our ability to diagnose, monitor and treat this disease. PMID:24922518

  12. The political context of AIDS-related stigma and knowledge in a South African township community.

    PubMed

    Forsyth, Brian; Vandormael, Alain; Kershaw, Trace; Grobbelaar, Janis

    2008-07-01

    The purpose of this study was to examine the presentation of AIDS-related stigma and knowledge within the political context of the South African government's response to the AIDS epidemic. It was during the 2000 - 2004 period that key government officials publicly challenged the orthodox views of HIV/AIDS, with the South African president, Thabo Mbeki, actively positing the primary role of poverty and other socio-economic stressors in the progression of the AIDS epidemic. This discursive position had real-time effects for AIDS policy-making and ultimately delayed the implementation of a national antiretroviral (ARV) rollout programme. Consequently this position was criticised by commentators in the media and elsewhere for contributing to an already widespread climate of AIDS stigmatization and misinformation. To shed more light on these claims we conducted a survey in 2005 in Atteridgeville, a South African township, and compared results with those of a similar survey conducted shortly after ARV medications became available in 2004. Results indicated a reduction in AIDS stigma levels across the 1-year period, and that those participants who endorsed contentious political views (such as those expressed by key government officials) were more likely to have a higher level of AIDS-related stigma than those who disagreed. Nevertheless, this study cautions against drawing a causal relationship between the South African government's position and IDS-stigmatizing attitudes, and suggests that further political and social factors be accounted for in an attempt to gain a fuller understanding of this seemingly complex relationship. PMID:18709210

  13. Binding energies and spatial structures of small carrier complexes in monolayer transition-metal dichalcogenides via diffusion Monte Carlo

    DOE PAGESBeta

    Mayers, Matthew Z.; Berkelbach, Timothy C.; Hybertsen, Mark S.; Reichman, David R.

    2015-10-09

    Ground-state diffusion Monte Carlo is used to investigate the binding energies and intercarrier radial probability distributions of excitons, trions, and biexcitons in a variety of two-dimensional transition-metal dichalcogenide materials. We compare these results to approximate variational calculations, as well as to analogous Monte Carlo calculations performed with simplified carrier interaction potentials. Our results highlight the successes and failures of approximate approaches as well as the physical features that determine the stability of small carrier complexes in monolayer transition-metal dichalcogenide materials. In conclusion, we discuss points of agreement and disagreement with recent experiments.

  14. Application of Diffusion Tensor Imaging Parameters to Detect Change in Longitudinal Studies in Cerebral Small Vessel Disease.

    PubMed

    Zeestraten, Eva Anna; Benjamin, Philip; Lambert, Christian; Lawrence, Andrew John; Williams, Owen Alan; Morris, Robin Guy; Barrick, Thomas Richard; Markus, Hugh Stephen

    2016-01-01

    Cerebral small vessel disease (SVD) is the major cause of vascular cognitive impairment, resulting in significant disability and reduced quality of life. Cognitive tests have been shown to be insensitive to change in longitudinal studies and, therefore, sensitive surrogate markers are needed to monitor disease progression and assess treatment effects in clinical trials. Diffusion tensor imaging (DTI) is thought to offer great potential in this regard. Sensitivity of the various parameters that can be derived from DTI is however unknown. We aimed to evaluate the differential sensitivity of DTI markers to detect SVD progression, and to estimate sample sizes required to assess therapeutic interventions aimed at halting decline based on DTI data. We investigated 99 patients with symptomatic SVD, defined as clinical lacunar syndrome with MRI confirmation of a corresponding infarct as well as confluent white matter hyperintensities over a 3 year follow-up period. We evaluated change in DTI histogram parameters using linear mixed effect models and calculated sample size estimates. Over a three-year follow-up period we observed a decline in fractional anisotropy and increase in diffusivity in white matter tissue and most parameters changed significantly. Mean diffusivity peak height was the most sensitive marker for SVD progression as it had the smallest sample size estimate. This suggests disease progression can be monitored sensitively using DTI histogram analysis and confirms DTI's potential as surrogate marker for SVD. PMID:26808982

  15. Permeability and hydraulic diffusivity of Waste Isolation Pilot Plant repository salt inferred from small-scale brine inflow experiments

    SciTech Connect

    McTigue, D.F.

    1993-06-01

    Brine seepage to 17 boreholes in salt at the Waste Isolation Pilot Plant (WIPP) facility horizon has been monitored for several years. A simple model for one-dimensional, radial, darcy flow due to relaxation of ambient pore-water pressure is applied to analyze the field data. Fits of the model response to the data yield estimates of two parameters that characterize the magnitude of the flow and the time scale over which it evolves. With further assumptions, these parameters are related to the permeability and the hydraulic diffusivity of the salt. For those data that are consistent with the model prediction, estimated permeabilities are typically 10{sup {minus}22} to 10{sup {minus}21} m{sup 2}. The relatively small range of inferred permeabilities reflects the observation that the measured seepage fluxes are fairly consistent from hole to hole, of the order of 10{sup {minus}10} m/s. Estimated diffusivities are typically 10{sup {minus}10} to 10{sup {minus}8} m{sup 2}/s. The greater scatter in inferred hydraulic diffusivities is due to the difficulty of matching the idealized model history to the observed evolution of the flows. The data obtained from several of the monitored holes are not consistent with the simple model adopted here; material properties could not be inferred in these cases.

  16. Application of Diffusion Tensor Imaging Parameters to Detect Change in Longitudinal Studies in Cerebral Small Vessel Disease

    PubMed Central

    Zeestraten, Eva Anna; Benjamin, Philip; Lambert, Christian; Lawrence, Andrew John; Williams, Owen Alan; Morris, Robin Guy; Barrick, Thomas Richard; Markus, Hugh Stephen

    2016-01-01

    Cerebral small vessel disease (SVD) is the major cause of vascular cognitive impairment, resulting in significant disability and reduced quality of life. Cognitive tests have been shown to be insensitive to change in longitudinal studies and, therefore, sensitive surrogate markers are needed to monitor disease progression and assess treatment effects in clinical trials. Diffusion tensor imaging (DTI) is thought to offer great potential in this regard. Sensitivity of the various parameters that can be derived from DTI is however unknown. We aimed to evaluate the differential sensitivity of DTI markers to detect SVD progression, and to estimate sample sizes required to assess therapeutic interventions aimed at halting decline based on DTI data. We investigated 99 patients with symptomatic SVD, defined as clinical lacunar syndrome with MRI confirmation of a corresponding infarct as well as confluent white matter hyperintensities over a 3 year follow-up period. We evaluated change in DTI histogram parameters using linear mixed effect models and calculated sample size estimates. Over a three-year follow-up period we observed a decline in fractional anisotropy and increase in diffusivity in white matter tissue and most parameters changed significantly. Mean diffusivity peak height was the most sensitive marker for SVD progression as it had the smallest sample size estimate. This suggests disease progression can be monitored sensitively using DTI histogram analysis and confirms DTI’s potential as surrogate marker for SVD. PMID:26808982

  17. Outer-membrane translocation of bulky small molecules by passive diffusion

    PubMed Central

    van den Berg, Bert; Prathyusha Bhamidimarri, Satya; Dahyabhai Prajapati, Jigneshkumar; Kleinekathöfer, Ulrich; Winterhalter, Mathias

    2015-01-01

    The outer membrane (OM) of gram-negative bacteria forms a protective layer around the cell that serves as a permeability barrier to prevent unrestricted access of noxious substances. The permeability barrier of the OM results partly from the limited pore diameters of OM diffusion channels. As a consequence, there is an “OM size-exclusion limit,” and the uptake of bulky molecules with molecular masses of more than ∼600 Da is thought to be mediated by TonB-dependent, active transporters. Intriguingly, the OM protein CymA from Klebsiella oxytoca does not depend on TonB but nevertheless mediates efficient OM passage of cyclodextrins with diameters of up to ∼15 Å. Here we show, by using X-ray crystallography, molecular dynamics simulations, and single-channel electrophysiology, that CymA forms a monomeric 14-stranded β-barrel with a large pore that is occluded on the periplasmic side by the N-terminal 15 residues of the protein. Representing a previously unidentified paradigm in OM transport, CymA mediates the passive diffusion of bulky molecules via an elegant transport mechanism in which a mobile element formed by the N terminus acts as a ligand-expelled gate to preserve the permeability barrier of the OM. PMID:26015567

  18. New solar telescope in Big Bear: evidence for super-diffusivity and small-scale solar dynamos?

    NASA Astrophysics Data System (ADS)

    Goode, Philip R.; Abramenko, Valentyna; Yurchyshyn, Vasyl

    2012-07-01

    The 1.6 m clear aperture New Solar Telescope (NST) in Big Bear Solar Observatory (BBSO) is now providing the highest resolution solar data ever. These data have revealed surprises about the Sun on small-scales including the observation that bright points (BPs), which can be used as proxies for the intense, compact magnetic elements that are apparent in photospheric intergranular lanes. The BPs are ever more numerous on ever smaller spatial scales as though there were no limit to how small the BPs can be. Here we discuss high resolution NST data on BPs that provide support for the ideas that a turbulent regime of super-diffusivity dominates in the quiet Sun, and there are local dynamos operating near the solar surface.

  19. Recent advances in the treatment of AIDS-related Kaposi's sarcoma.

    PubMed

    Cattelan, Anna M; Trevenzoli, Marco; Aversa, Savina M L

    2002-01-01

    Kaposi's sarcoma (KS) is the most common malignancy associated with HIV infection and is considered an AIDS defining condition by the US Centers of Disease Control Guidelines. Several advances in the treatment of AIDS-related KS have been achieved over the past few years, even though a gold standard therapy for KS has not yet been defined and treatment must be tailored to individual needs. Since the availability of highly active antiretroviral therapy (HAART), a dramatic clinical response has been documented in patients with KS, making HAART an essential approach in the management of KS in most, if not all, patients with AIDS-related KS. However, in case of aggressive, visceral, and/or life-threatening KS, more complex therapeutic schedules have to be taken into account, including chemotherapy, radiotherapy, and/or immunotherapy. In general, systemic treatment for KS is limited to widespread, symptomatic disease, whereas local interventions are indicated for minimal, cosmetically troublesome lesions. Among new cytotoxic agents, liposomal anthracyclines and paclitaxel are highly effective molecules for KS and have been approved by the US Food and Drug Administration (FDA) as first-line and second-line monotherapy, respectively, for advanced KS. Furthermore, a greater understanding of the pathogenesis of KS has lead to the development of an array of new experimental agents. Many antiangiogenic agents such as AGM 1470 (TNP 470), thalidomide, and glufanide disodium (IM 862) have produced encouraging responses in patients with KS and large clinical trials are in progress. Retinoic acids may also block neoangiogenesis as well as proliferation of KS cells in vitro, and they have been used either systemically or topically with a high response rate. Thus, a topical compound 0.1% alitretinoin gel was approved in 1999 by the FDA for the treatment of skin lesions associated with KS. Human chorionic gonadotropin, a hormonal agent, has shown a strong inhibitory activity in KS

  20. Diffusion-weighted images (DWI) without ADC values in assessment of small focal nodules in cirrhotic liver

    PubMed Central

    Chen, Mai-Lin; Zhang, Xiao-Yan; Qi, Li-Ping; Shi, Qing-Lei; Chen, Bin

    2014-01-01

    Objective To assess if diffusion-weighted magnetic resonance (MR) imaging without apparent diffusion coefficient (ADC) values provides added diagnostic value in combination with conventional MR imaging in the detection and characterization of small nodules in cirrhotic liver. Methods Two observers retrospectively and independently analyzed 86 nodules (≤3 cm) certified pathologically in 33 patients with liver cirrhosis, including 48 hepatocellular carcinoma (HCC) nodules, 13 high-grade dysplastic nodules (HDN), 10 low-grade dysplastic nodules (LDNs) and 15 other benign nodules. All these focal nodules were evaluated with conventional MR images (T1-weighted, T2-weighted and dynamic gadolinium-enhanced images) and breath-hold diffusion-weighted images (DWI) (b=500 s/mm2). The nodules were classified by using a scale of 1-3 (1, not seen; 3, well seen) on DWI for qualitative assessment. These small nodules were characterized by two radiologists. ADC values weren’t measured. The diagnostic performance of the combined DWI-conventional images and the conventional images alone was evaluated using receiver operating characteristic (ROC) curves. The area under the curves (Az), sensitivity and specificity values for characterizing different small nodules were also calculated. Results Among 48 HCC nodules, 33 (68.8%) were graded as 3 (well seen), 6 (12.5%) were graded as 2 (partially obscured), and 9 weren’t seen on DWI. Among 13 HDNs, there were 3 (23.1%) and 4 (30.8%) graded as 3 and 2 respectively. Five (50%) of 10 benign nodules were partially obscured and slightly hyperintense. For 86 nodules, the average diagnostic accuracy of combined DWI-conventional images was 82.56%, which was increased significantly compared with conventional MR images with 76.17%. For HCC and HDN, the diagnostic accuracy of combined DWI-conventional images increased from 78.69% to 86.07%. Conclusions Diffusion-weighted MR imaging does provide added diagnostic value in the detection and

  1. Immunoproliferative Small Intestinal Disease Associated with Overwhelming Polymicrobial Gastrointestinal Infection with Transformation to Diffuse Large B-cell Lymphoma.

    PubMed

    Ewers, Evan C; Sheffler, Robert L; Wang, James; Ngauy, Viseth

    2016-05-01

    Immunoproliferative small intestinal disease (IPSID) is an extra-nodal B-cell lymphoma most commonly described in the Mediterranean, Africa, and Asia. It is associated with poverty and poor sanitation, and is rarely encountered in developed countries. A 26-year-old previously healthy, Marshallese male was transferred to our facility with a 6-month history of watery diarrhea, weakness, and cachexia refractory to multiple short courses of oral antibiotics. Stool cultures grew Campylobacter jejuni and Vibrio fluvialis. Endoscopic evaluation showed histologic evidence of Helicobacter pylori gastritis and gross evidence of whipworm infection found in the colon. Mesenteric lymph node biopsy cultures grew Escherichia coli. Histopathology and immunohistochemical stains of the small intestine were consistent with IPSID. He subsequently transformed to diffuse large B-cell lymphoma (DLBCL) with tonsillar involvement despite treatment with rituximab and an extended course of antibiotics. Systemic chemotherapy with six cycles of rituximab, cyclophosphamide, vincristine, doxorubicin, prednisone, and lenalidomide, resulted in remission of his diffuse B cell lymphoma. This case is illustrative of IPSID developing in a previously healthy individual due to overwhelming polymicrobial gastrointestinal infection by C. jejuni and other enteric pathogens with subsequent transformation to an aggressive DLBCL. IPSID should be considered in residents of developing countries presenting with refractory chronic diarrhea, weight loss, and mesenteric lymphadenopathy. PMID:26903604

  2. AIDS as social construction: text mining of AIDS-related information in the Italian press.

    PubMed

    Caputo, Andrea; Giacchetta, Agnese; Langher, Viviana

    2016-09-01

    Given the relevance of AIDS as a public health problem in the Italian context and of the role of mass media in the social construction of the phenomenon, the aim of the present study is twofold: (1) to explore the main AIDS-related themes in the Italian popular press; (2) to analyse the temporal trends of AIDS representations over the last decades. For the research, we decided to consult Italian newspaper articles produced between 1985 and 1990 and between 2005 and 2010 using the archives of the main two national newspapers (La Repubblica and Corriere della Sera), resulting in an overall sample of 446 newspaper articles. A computer-aided content analysis allowed the detection of five different thematic domains (clusters), respectively focused on: Medical care (7.47%), Family support (37.03%), Science and religion debate (27%), Social exclusion (17.6%) and Healthcare policies (10.9%). These thematic domains are conceived along two main latent dimensions (factors) which explain 72.47% of the data variance which respectively deal with: (1) Attitudes towards people with AIDS (care versus avoidance) and (2) Social mandate on AIDS (powerlessness versus control). The study results also reveal the potential evolution of representations of people with AIDS over time: from stigmatised subjects who represent a risk for the entire society within a climate of social control to people progressively symbolised as frail subjects that need to be taken care of. PMID:26923156

  3. Three-dimensional optical metrology and models for non-contact diffuse optical tomography of small animals

    NASA Astrophysics Data System (ADS)

    Comtois, Maxime; Bérubé-Lauzière, Yves

    2007-07-01

    We introduce a novel approach for calibrating an axis of rotation in a 3D optical metrology system. The system uses a stereo camera pair, along with rotation and translation stages for obtaining a 3D model of the surface of small animals. The metrology system will be part of a fully non-contact diffuse optical tomography (DOT) scanner for small animal imaging. The rotation axis calibration technique is based on measuring, with the stereo pair, the 3D position of a small ball as it is moved by the rotation stage (turntable). Our system has the advantage of using the tomograph's laser beam to measure the outer shape of the subject, thereby reducing overall system complexity, and allowing simultaneous surface and DOT measurements. Additionnaly, the exact position where laser light penetrates the animal is measured, while traditionally, this information is indirectly inferred with less accuracy. This information plays an important role in a tomographic reconstruction algorithm. Our new approach for the calibration of the rotation axis is compared to another technique we previously developed, where a checkerboard pattern is tracked instead of a ball. We present measurements of a reference shape and a small animal taken by our system.

  4. Multi-modal molecular diffuse optical tomography system for small animal imaging

    PubMed Central

    Guggenheim, James A.; Basevi, Hector R. A.; Frampton, Jon; Styles, Iain B.; Dehghani, Hamid

    2013-01-01

    A multi-modal optical imaging system for quantitative 3D bioluminescence and functional diffuse imaging is presented, which has no moving parts and uses mirrors to provide multi-view tomographic data for image reconstruction. It is demonstrated that through the use of trans-illuminated spectral near infrared measurements and spectrally constrained tomographic reconstruction, recovered concentrations of absorbing agents can be used as prior knowledge for bioluminescence imaging within the visible spectrum. Additionally, the first use of a recently developed multi-view optical surface capture technique is shown and its application to model-based image reconstruction and free-space light modelling is demonstrated. The benefits of model-based tomographic image recovery as compared to 2D planar imaging are highlighted in a number of scenarios where the internal luminescence source is not visible or is confounding in 2D images. The results presented show that the luminescence tomographic imaging method produces 3D reconstructions of individual light sources within a mouse-sized solid phantom that are accurately localised to within 1.5mm for a range of target locations and depths indicating sensitivity and accurate imaging throughout the phantom volume. Additionally the total reconstructed luminescence source intensity is consistent to within 15% which is a dramatic improvement upon standard bioluminescence imaging. Finally, results from a heterogeneous phantom with an absorbing anomaly are presented demonstrating the use and benefits of a multi-view, spectrally constrained coupled imaging system that provides accurate 3D luminescence images. PMID:24954977

  5. Reducing AIDS-related stigma in developing countries: the importance of theory- and evidence-based interventions.

    PubMed

    Bos, Arjan E R; Schaalma, Herman P; Pryor, John B

    2008-08-01

    In many developing countries persons living with HIV and AIDS experience strong stigma and discrimination, and AIDS-related stigma has an enormous negative impact on their social relationships, access to resources, and psychological well being. Moreover, AIDS-related stigma hampers HIV-related health promotion, including voluntary HIV counselling and testing. In this article, we will argue that programs to reduce AIDS-related stigma are most likely to be effective if these programs are based upon thorough needs assessments, theory- and evidence-based intervention strategies and collaborative planning. A protocol for health promotion programs design is outlined. Furthermore, psychosocial correlates of AIDS-related stigma in developing countries, social-psychological theories that might be useful in designing intervention strategies to reduce stigmatisation and successful elements of previous interventions aimed at stigma reduction are discussed. It is concluded that psychological theory does provide guidelines for the development of stigma-reducing intervention programs, but that such programs can only be effective when based upon context-specific needs assessment and collaborative planning. PMID:18825583

  6. Multi-modal molecular diffuse optical tomography system for small animal imaging

    NASA Astrophysics Data System (ADS)

    Guggenheim, James A.; Basevi, Hector R. A.; Frampton, Jon; Styles, Iain B.; Dehghani, Hamid

    2013-10-01

    A multi-modal optical imaging system for quantitative 3D bioluminescence and functional diffuse imaging is presented, which has no moving parts and uses mirrors to provide multi-view tomographic data for image reconstruction. It is demonstrated that through the use of trans-illuminated spectral near-infrared measurements and spectrally constrained tomographic reconstruction, recovered concentrations of absorbing agents can be used as prior knowledge for bioluminescence imaging within the visible spectrum. Additionally, the first use of a recently developed multi-view optical surface capture technique is shown and its application to model-based image reconstruction and free-space light modelling is demonstrated. The benefits of model-based tomographic image recovery as compared to two-dimensional (2D) planar imaging are highlighted in a number of scenarios where the internal luminescence source is not visible or is confounding in 2D images. The results presented show that the luminescence tomographic imaging method produces 3D reconstructions of individual light sources within a mouse-sized solid phantom that are accurately localized to within 1.5 mm for a range of target locations and depths, indicating sensitivity and accurate imaging throughout the phantom volume. Additionally the total reconstructed luminescence source intensity is consistent to within 15%, which is a dramatic improvement upon standard bioluminescence imaging. Finally, results from a heterogeneous phantom with an absorbing anomaly are presented, demonstrating the use and benefits of a multi-view, spectrally constrained coupled imaging system that provides accurate 3D luminescence images.

  7. HIV/AIDS-Related Knowledge and Behaviors Among Most-at-Risk Populations in Vietnam

    PubMed Central

    Vian, Taryn; Semrau, Katherine; Hamer, Davidson H; Loan, Le Thi Thanh; Sabin, Lora L

    2012-01-01

    The U.S. President’s Emergency Plan for AIDS Relief (PEPFAR) has supported the Vietnamese Ministry of Health (MOH) in implementing behavior change strategies to slow the HIV epidemic. These programs target commercial sex workers (CSW), injection drug users (IDU), and men who have sex with men (MSM). Using data from a program evaluation to assess effectiveness of the PEPFAR intervention, we conducted a sub-analysis of HIV/AIDS knowledge, sexual behaviors, and injection drug risk behaviors among 2,199 Vietnamese respondents, including those reporting recent contact with an outreach worker and those who did not report contact. We found overall high levels of HIV/AIDS knowledge, low rates of needle sharing, and moderate to high rates of inconsistent condom use. Average knowledge scores of IDU were significantly higher than non-IDU for antiretroviral treatment knowledge, while MSM had significantly less knowledge of treatment compared to non-MSM. HIV/AIDS-related knowledge was not significantly associated with needle-sharing practices. Knowledge was modestly but significantly associated with more consistent use of condoms with primary and commercial sex partners, even after controlling for contact with an outreach worker. Contact with an outreach worker was also an independent predictor of more consistent condom use. Outreach programs appear to play a meaningful role in changing sexual behavior, though the effect of outreach on IDU risk behaviors was less clear. More research is needed to understand the relationship between outreach programs and skill development, motivation, and use of referral services by most-at-risk populations in Vietnam. PMID:23173025

  8. HIV/AIDS Related Stigma and Discrimination against PLWHA in Nigerian Population

    PubMed Central

    Bulgiba, Awang; Oche, Oche Mansur; Adekunjo, Felix Oluyemi

    2015-01-01

    Background HIV/AIDS remain a major public health concern in Nigeria. People living with HIV/AIDS (PLWHA) face not only personal medical problems but also social problems associated with the disease such as stigma and discriminatory attitudes. This study provides an insight into HIV/AIDS related stigma and discrimination against PLWHA in Nigeria. Methods The data for this study was extracted from the 2013 Nigeria Demographic and Health Survey conducted by the National Population Commission. All men and women aged 15–49 years, permanent residents and visitors of the households were eligible for the interview. Several questionnaires were used in the survey, some covering questions on HIV/AIDS. Results A total of 56 307 men and women aged 15–49 years participated in this national survey. About half of the population in Nigeria have HIV stigma. Younger persons, men, those without formal education and those within poor wealth index are more likely to have stigma towards PLWHA. In addition, married people are more likely to have stigma on PLWHA and are more likely to blame PLWHA for bringing the disease to the community. Also about half of the population discriminates against PLWHA. However, those with higher levels of education and those from higher wealth index seem to be more compassionate towards PLWHA. About 70% in the population are willing to care for relative with AIDS, even more so among those with higher level of education. Conclusion There is a high level of HIV stigma and discrimination against PLWHA in the Nigerian population. Education seems to play a major role in the society with respect to HIV stigma and discrimination against PLWHA. Educating the population with factual information on HIV/AIDS is needed to reduce stigma and discrimination towards PLWHA in the community. PMID:26658767

  9. Diffuse barrier discharges in nitrogen with small admixtures of oxygen: discharge mechanism and transition to the filamentary regime

    NASA Astrophysics Data System (ADS)

    Brandenburg, R.; Maiorov, V. A.; Golubovskii, Yu B.; Wagner, H.-E.; Behnke, J.; Behnke, J. F.

    2005-07-01

    Diffuse barrier discharges (BDs) are characterized by the periodicity of their discharge current and by the uniform coverage of the entire electrode surface by the plasma. Up to now the discharge development, their appearance and dynamics cannot be adequately explained by elementary processes. Different processes are discussed in the literature controversially, in particular the importance of volume and surface processes on the pre-ionization (Penning-ionization, secondary (γ-) processes, role of surface charges). Diffuse BDs in nitrogen with small admixtures of oxygen are investigated by plasma diagnostics (current/voltage-oscillography, optical emission spectroscopy) and numerical modelling. Special attention is paid to the transition to the usual filamentary mode, characterized by the presence of micro-discharges and caused by the admixture of oxygen in the range of 0-1200 ppm (parts-per-million). This transition starts at low values of O2 (about 450 ppm) and is introduced by an oscillative multi-peak mode. At higher admixtures (about 1000 ppm) the micro-discharges are generated. According to the results of numerical modelling, secondary electron emission by N2(A 3Σu) metastable states plays a major role in discharge maintenance. Due to the much more effective quenching of these states by O2 and NO than by N2 the subsequent delivery of electrons will be decreased when the oxygen amount is increased.

  10. Dissecting diffusive and advective motion in colloidal sedimentation by multi-speckle Ultra-Small-Angle XPCS

    NASA Astrophysics Data System (ADS)

    Möller, Johannes; Narayanan, Theyencheri

    In colloidal suspensions internal or external fields can induce directed motions of particles in addition to Brownian diffusion. Here, gradients in temperature or chemical potential, shear flow as well as gravity can act as an external field. Examples for internal motions can be found in synthetic self-propelling particles and microorganisms, generally coined as active matter. We present multi-speckle X-ray photon correlation spectroscopy measurements in the Ultra-Small-Angle scattering range which probes an expanded length scale comparable to DLS and optical microscopy. To demonstrate the advanced capabilities, we show measurements probing the motions within a settling suspension of sub-micron sized silica particles. A global fitting procedure has been applied to separate the diffusive and advective contributions to the particle dynamics. With this, macroscopic parameters such as the sedimentation velocity can be probed on a microscopic level in highly opaque and concentrated systems, which are in general difficult to access for optical investigations. This procedure may prove its value for investigating various kinds of non-equilibrium systems.

  11. Gas exchange dependency on diffusion coefficient: direct /sup 222/Rn and /sup 3/He comparisons in a small lake

    SciTech Connect

    Torgersen, T.; Mathieu, G.; Hesslein, R.H.; Broecker, W.S.

    1982-01-20

    A direct field comparison was conducted to determine the dependency of gas exchange coefficient (k/sub x/) on the diffusion coefficient (D/sub x/). The study also sought to confirm the enhanced vertical exchange properties of limnocorrals and similar enclosures. Gas exchange coefficients for /sup 222/Rn and /sup 3/He were determined in a small northern Ontario lake, using a /sup 226/Ra and /sup 3/H spike to gain the necessary precision. The results indicate that the gas exchange coefficient is functionally dependent on the diffusion coefficient raised to the 1.22/sub -35//sup + > 12/ power (k/sub x/ = f(D/sub x//sup 1.22)), clearly supporting the stagnant film model of gas exchange. Limnocorrals were found to have gas exchange rates up to 1.7 times higher than the whole lake in spite of the observation of more calm surface conditions in the corral than in the open lake. 33 references, 6 figures, 8 tables.

  12. Knowledge, attitude, and practice of HIV/AIDS-related stigma and discrimination reduction among nursing students in southwest Nigeria

    PubMed Central

    Farotimi, Adekunbi A; Nwozichi, Chinomso Ugochukwu; Ojediran, Tolulope D

    2015-01-01

    Background: One of the reported obstacles to the achievement of universal access to Human Immunodeficiency Virus (HIV) prevention, treatment, care, and support programs includes stigma and discrimination from health workers, particularly nurses. Since nursing students would become future practising nurses and are most likely exposed to caring for people living with HIV/AIDS (PL WHA) during their training, it is of great importance to assess the knowledge, attitude, and practice of student nurses toward the reduction of HIV/AIDS-related stigma and discrimination. Materials and Methods: A descriptive survey research design was used. A total of 150 nursing students were selected using the simple random sampling technique of fish bowl method with replacement. Data were obtained using a self-administered (33-item) validated questionnaire to assess the knowledge, attitude, and practice of student nurses with regard to HIV/AIDS-related stigma and discrimination reduction strategies. Reliability of the tool was tested using Cronbach alpha (R) yielding a reliability value of 0.72. Data collected were analyzed with descriptive statistics of frequencies and percentages. Results: Majority (76.0%) of the respondents were females and 82.7% were married. Respondents were found to have high knowledge (94.0%) of strategies for reducing HIV/AIDS-related stigma and discrimination. Also, 64% had moderate discriminatory attitude, 74% engaged in low discriminatory practice, while 26% engaged in high discriminatory practice. Conclusions: Student nurses had adequate knowledge about strategies for reducing HIV/AIDS-related stigma and discrimination; negative discriminatory attitude toward PLWHA and some form of discriminatory practices exist in participants’ training schools. It is, therefore, recommended that an educational package on reduction of HIV/AIDS-related stigma and discrimination be developed and implemented for the participants. PMID:26793257

  13. Detection of polyomavirus simian virus 40 tumor antigen DNA in AIDS-related systemic non-Hodgkin lymphoma

    NASA Technical Reports Server (NTRS)

    Vilchez, Regis A.; Lednicky, John A.; Halvorson, Steven J.; White, Zoe S.; Kozinetz, Claudia A.; Butel, Janet S.

    2002-01-01

    Systemic non-Hodgkin lymphoma (S-NHL) is a common malignancy during HIV infection, and it is hypothesized that infectious agents may be involved in the etiology. Epstein-Barr virus DNA is found in <40% of patients with AIDS-related S-NHL, suggesting that other oncogenic viruses, such as polyomaviruses, may play a role in pathogenesis. We analyzed AIDS-related S-NHL samples, NHL samples from HIV-negative patients, peripheral blood leukocytes from HIV-infected and -uninfected patients without NHL, and lymph nodes without tumors from HIV-infected patients. Specimens were examined by polymerase chain reaction analysis with use of primers specific for an N-terminal region of the oncoprotein large tumor antigen ( T-ag ) gene conserved among all three polyomaviruses (simian virus 40 [SV40], JC virus, and BK virus). Polyomavirus T-ag DNA sequences, proven to be SV40-specific, were detected more frequently in AIDS-related S-NHL samples (6 of 26) than in peripheral blood leukocytes from HIV-infected patients (6 of 26 vs. 0 of 69; p =.0001), NHL samples from HIV-negative patients (6 of 26 vs. 0 of 10; p =.09), or lymph nodes (6 of 26 vs. 0 of 7; p =.16). Sequences of C-terminal T-ag DNA from SV40 were amplified from two AIDS-related S-NHL samples. Epstein-Barr virus DNA sequences were detected in 38% (10 of 26) AIDS-related S-NHL samples, 50% (5 of 10) HIV-negative S-NHL samples, and 57% (4 of 7) lymph nodes. None of the S-NHL samples were positive for both Epstein-Barr virus DNA and SV40 DNA. Further studies of the possible role of SV40 in the pathogenesis of S-NHL are warranted.

  14. Diffuse nodular lymphoid hyperplasia of the small bowel associated with common variable immunodeficiency and giardiasis: a rare case report.

    PubMed

    Olmez, Sehmus; Aslan, Mehmet; Yavuz, Alpaslan; Bulut, Gulay; Dulger, Ahmet Cumhur

    2014-05-01

    Diffuse nodular lymphoid hyperplasia (DNLH) of the intestine is an extremely rare lymphoproliferative disorder of uncertain etiology. Typically, numerous polypoid nodules composed of hyperplastic benign lymphoid tissue are present in the small and/or large intestinal mucosa. DNLH has been observed in association with common variable immunodeficiency (CVID). A 38-years-old man was admitted to our clinic due to dyspeptic complaints. An upper gastrointestinal system endoscopic examination revealed DNLH in the duodenum. A biopsy specimen showed the presence of nodular lymphoid hyperplasia and a Giardia lamblia infection in the duodenum. CVID was suspected, and the diagnosis was established by demonstrating a significant reduction in the serum gamma-globulin levels. DNLH is a rare benign condition with regards to diagnosis and treatment of unknown etiology. In patients with DNLH, screening for the immune deficiencies is being important in addition to histopathological examinations. PMID:24647448

  15. Combining Diffusive Shock Acceleration with Acceleration by Contracting and Reconnecting Small-scale Flux Ropes at Heliospheric Shocks

    NASA Astrophysics Data System (ADS)

    le Roux, J. A.; Zank, G. P.; Webb, G. M.; Khabarova, O. V.

    2016-08-01

    Computational and observational evidence is accruing that heliospheric shocks, as emitters of vorticity, can produce downstream magnetic flux ropes and filaments. This led Zank et al. to investigate a new paradigm whereby energetic particle acceleration near shocks is a combination of diffusive shock acceleration (DSA) with downstream acceleration by many small-scale contracting and reconnecting (merging) flux ropes. Using a model where flux-rope acceleration involves a first-order Fermi mechanism due to the mean compression of numerous contracting flux ropes, Zank et al. provide theoretical support for observations that power-law spectra of energetic particles downstream of heliospheric shocks can be harder than predicted by DSA theory and that energetic particle intensities should peak behind shocks instead of at shocks as predicted by DSA theory. In this paper, a more extended formalism of kinetic transport theory developed by le Roux et al. is used to further explore this paradigm. We describe how second-order Fermi acceleration, related to the variance in the electromagnetic fields produced by downstream small-scale flux-rope dynamics, modifies the standard DSA model. The results show that (i) this approach can qualitatively reproduce observations of particle intensities peaking behind the shock, thus providing further support for the new paradigm, and (ii) stochastic acceleration by compressible flux ropes tends to be more efficient than incompressible flux ropes behind shocks in modifying the DSA spectrum of energetic particles.

  16. Simulation of Ultra-Small MOSFETs Using a 2-D Quantum-Corrected Drift-Diffusion Model

    NASA Technical Reports Server (NTRS)

    Biegal, Bryan A.; Rafferty, Connor S.; Yu, Zhiping; Ancona, Mario G.; Dutton, Robert W.; Saini, Subhash (Technical Monitor)

    1998-01-01

    The continued down-scaling of electronic devices, in particular the commercially dominant MOSFET, will force a fundamental change in the process of new electronics technology development in the next five to ten years. The cost of developing new technology generations is soaring along with the price of new fabrication facilities, even as competitive pressure intensifies to bring this new technology to market faster than ever before. To reduce cost and time to market, device simulation must become a more fundamental, indeed dominant, part of the technology development cycle. In order to produce these benefits, simulation accuracy must improve markedly. At the same time, device physics will become more complex, with the rapid increase in various small-geometry and quantum effects. This work describes both an approach to device simulator development and a physical model which advance the effort to meet the tremendous electronic device simulation challenge described above. The device simulation approach is to specify the physical model at a high level to a general-purpose (but highly efficient) partial differential equation solver (in this case PROPHET, developed by Lucent Technologies), which then simulates the model in 1-D, 2-D, or 3-D for a specified device and test regime. This approach allows for the rapid investigation of a wide range of device models and effects, which is certainly essential for device simulation to catch up with, and then stay ahead of, electronic device technology of the present and future. The physical device model used in this work is the density-gradient (DG) quantum correction to the drift-diffusion model [Ancona, Phys. Rev. B 35(5), 7959 (1987)]. This model adds tunneling and quantum smoothing of carrier density profiles to the drift-diffusion model. We used the DG model in 1-D and 2-D (for the first time) to simulate both bipolar and unipolar devices. Simulations of heavily-doped, short-base diodes indicated that the DG quantum

  17. Restricted ADP movement in cardiomyocytes: Cytosolic diffusion obstacles are complemented with a small number of open mitochondrial voltage-dependent anion channels.

    PubMed

    Simson, Päivo; Jepihhina, Natalja; Laasmaa, Martin; Peterson, Pearu; Birkedal, Rikke; Vendelin, Marko

    2016-08-01

    Adequate intracellular energy transfer is crucial for proper cardiac function. In energy starved failing hearts, partial restoration of energy transfer can rescue mechanical performance. There are two types of diffusion obstacles that interfere with energy transfer from mitochondria to ATPases: mitochondrial outer membrane (MOM) with voltage-dependent anion channel (VDAC) permeable to small hydrophilic molecules and cytoplasmatic diffusion barriers grouping ATP-producers and -consumers. So far, there is no method developed to clearly distinguish the contributions of cytoplasmatic barriers and MOM to the overall diffusion restriction. Furthermore, the number of open VDACs in vivo remains unknown. The aim of this work was to establish the partitioning of intracellular diffusion obstacles in cardiomyocytes. We studied the response of mitochondrial oxidative phosphorylation of permeabilized rat cardiomyocytes to changes in extracellular ADP by recording 3D image stacks of NADH autofluorescence. Using cell-specific mathematical models, we determined the permeability of MOM and cytoplasmatic barriers. We found that only ~2% of VDACs are accessible to cytosolic ADP and cytoplasmatic diffusion barriers reduce the apparent diffusion coefficient by 6-10×. In cardiomyocytes, diffusion barriers in the cytoplasm and by the MOM restrict ADP/ATP diffusion to similar extents suggesting a major role of both barriers in energy transfer and other intracellular processes. PMID:27261153

  18. Diffusion Tensor and Volumetric Magnetic Resonance Measures as Biomarkers of Brain Damage in a Small Animal Model of HIV

    PubMed Central

    Lentz, Margaret R.; Peterson, Kristin L.; Ibrahim, Wael G.; Lee, Dianne E.; Sarlls, Joelle; Lizak, Martin J.; Maric, Dragan; Reid, William C.; Hammoud, Dima A.

    2014-01-01

    Background There are currently no widely accepted neuro-HIV small animal models. We wanted to validate the HIV-1 Transgenic rat (Tg) as an appropriate neuro-HIV model and then establish in vivo imaging biomarkers of neuropathology, within this model, using MR structural and diffusion tensor imaging (DTI). Methods Young and middle-aged Tg and control rats were imaged using MRI. A subset of middle-aged animals underwent longitudinal repeat imaging six months later. Total brain volume (TBV), ventricular volume (VV) and parenchymal volume (PV = TBV–VV) were measured. Fractional anisotropy (FA) and mean diffusivity (MD) values of the corpus callosum (CC) were calculated from DTI data. Results TBV and PV were smaller in Tg compared to control rats in young and middle-aged cohorts (p<0.0001). VV increased significantly (p = 0.005) over time in the longitudinal Tg cohort. There were lower FA (p<0.002) and higher MD (p<0.003) values in the CC of middle-aged Tg rats compared to age-matched controls. Longitudinally, MD significantly decreased over time in Tg rats (p<0.03) while it did not change significantly in the control cohort over the same period of time (p>0.05). Conclusions We detected brain volume loss in the Tg rat, probably due to astrocytic dysfunction/loss, loss of structural/axonal matrix and striatal neuronal loss as suggested by immunofluorescence. Increased MD and decreased FA in the CC probably reflect microstructural differences between the Tg and Control rats which could include increased extracellular space between white matter tracts, demyelination and axonal degeneration, among other pathologies. We believe that the Tg rat is an adequate model of neuropathology in HIV and that volumetric MR and DTI measures can be potentially used as biomarkers of disease progression. PMID:25144656

  19. Creating social spaces to tackle AIDS-related stigma: reviewing the role of church groups in Sub-Saharan Africa.

    PubMed

    Campbell, C; Skovdal, M; Gibbs, A

    2011-08-01

    An expanding body of literature explores the role of African church groups in facilitating or hindering the support of people living with AIDS and challenging or contributing to HIV/AIDS-related stigma. Treating church groups as social spaces in which HIV/AIDS-related stigma may potentially be challenged, we systematically review this literature, identifying five themes that highlight the complex and contradictory role of the church as a potential agent of health-enhancing social change. In many ways the church perpetuates HIV/AIDS-related stigma through (i) moralistic attitudes and (ii) its reinforcement of conservative gender ideologies. However some churches have managed move towards action that makes a more positive contribution to HIV/AIDS management through (iii) promoting various forms of social control for HIV prevention, (iv) contributing to the care and support of the AIDS-affected and (v) providing social spaces for challenging stigmatising ideas and practices. We conclude that church groups, including church leadership, can play a key role in facilitating or hindering the creation of supportive social spaces to challenge stigma. Much work remains to be done in developing deeper understandings of the multi-layered factors that enable some churches, but not others, to respond effectively to HIV/AIDS. PMID:20668927

  20. Creating Social Spaces to Tackle AIDS-Related Stigma: Reviewing the Role of Church Groups in Sub-Saharan Africa

    PubMed Central

    Skovdal, M.; Gibbs, A.

    2012-01-01

    An expanding body of literature explores the role of African church groups in facilitating or hindering the support of people living with AIDS and challenging or contributing to HIV/AIDS-related stigma. Treating church groups as social spaces in which HIV/AIDS-related stigma may potentially be challenged, we systematically review this literature, identifying five themes that highlight the complex and contradictory role of the church as a potential agent of health-enhancing social change. In many ways the church perpetuates HIV/AIDS-related stigma through (i) moralistic attitudes and (ii) its reinforcement of conservative gender ideologies. However some churches have managed move towards action that makes a more positive contribution to HIV/AIDS management through (iii) promoting various forms of social control for HIV prevention, (iv) contributing to the care and support of the AIDS-affected and (v) providing social spaces for challenging stigmatising ideas and practices. We conclude that church groups, including church leadership, can play a key role in facilitating or hindering the creation of supportive social spaces to challenge stigma. Much work remains to be done in developing deeper understandings of the multi-layered factors that enable some churches, but not others, to respond effectively to HIV/AIDS. PMID:20668927

  1. Self-Diffusion of small Ag and Ni islands on Ag(111) and Ni(111) using the self-learning kinetic Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Islamuddin Shah, Syed; Nandipati, Giridhar; Kara, Abdelkader; Rahman, Talat S.

    2012-02-01

    We have applied a modified Self-Learning Kinetic Monte Carlo (SLKMC) method [1] to examine the self-diffusion of small Ag and Ni islands, containing up to 10 atom, on the (111) surface of the respective metal. The pattern recognition scheme in this new SLKMC method allows occupancy of the fcc, hcp and top sites on the fcc(111) surface and employs them to identify the local neighborhood around a central atom. Molecular static calculations with semi empirical interatomic potential and reliable techniques for saddle point search revealed several new diffusion mechanisms that contribute to the diffusion of small islands. For comparison we have also evaluated the diffusion characteristics of Cu clusters on Cu(111) and compared results with previous findings [2]. Our results show a linear increase in effective energy barriers scaling almost as 0.043, 0.051 and 0.064 eV/atom for the Cu/Cu(111), Ag/Ag(111), and Ni/Ni(111) systems, respectively. For all three systems, diffusion of small islands proceeds mainly through concerted motion, although several multiple and single atom processes also contribute. [1] Oleg Trushin et al. Phys. Rev. B 72, 115401 (2005) [2] Altaf Karim et al. Phys. Rev. B 73, 165411 (2006)

  2. Simulation of Ultra-Small MOSFETs Using a 2-D Quantum-Corrected Drift-Diffusion Model

    NASA Technical Reports Server (NTRS)

    Biegel, Bryan A.; Rafferty, Conor S.; Yu, Zhiping; Dutton, Robert W.; Ancona, Mario G.; Saini, Subhash (Technical Monitor)

    1998-01-01

    We describe an electronic transport model and an implementation approach that respond to the challenges of device modeling for gigascale integration. We use the density-gradient (DG) transport model, which adds tunneling and quantum smoothing of carrier density profiles to the drift-diffusion model. We present the current implementation of the DG model in PROPHET, a partial differential equation solver developed by Lucent Technologies. This implementation approach permits rapid development and enhancement of models, as well as run-time modifications and model switching. We show that even in typical bulk transport devices such as P-N diodes and BJTs, DG quantum effects can significantly modify the I-V characteristics. Quantum effects are shown to be even more significant in small, surface transport devices, such as sub-0.1 micron MOSFETs. In thin-oxide MOS capacitors, we find that quantum effects may reduce gate capacitance by 25% or more. The inclusion of quantum effects in simulations dramatically improves the match between C-V simulations and measurements. Significant quantum corrections also occur in the I-V characteristics of short-channel MOSFETs due to the gate capacitance correction.

  3. Performance investigation of SP3 and diffusion approximation for three-dimensional whole-body optical imaging of small animals.

    PubMed

    Yang, Defu; Chen, Xueli; Cao, Xu; Wang, Jing; Liang, Jimin; Tian, Jie

    2015-09-01

    The third-order simplified harmonic spherical approximation (SP3) and diffusion approximation (DA) equations have been widely used in the three-dimensional (3D) whole-body optical imaging of small animals. With different types of tissues, which were classified by the ratio of µ s'/µ ɑ, the two equations have their own application scopes. However, the classification criterion was blurring and unreasonable, and the scope has not been systematically investigated until now. In this study, a new criterion for classifying tissues was established based on the absolute value of absorption and reduced scattering coefficients. Using the newly defined classification criterion, the performance and applicability of the SP3 and DA equations were evaluated with a series of investigation experiments. Extensive investigation results showed that the SP3 equation exhibited a better performance and wider applicability than the DA one in most of the observed cases, especially in tissues of low-scattering-low-absorption and low-scattering-high-absorption range. For the case of tissues with the high-scattering-low-absorption properties, a similar performance was observed for both the SP3 and the DA equations, in which case the DA was the preferred option for 3D whole-body optical imaging. Results of this study would provide significant reference for the study of hybrid light transport models. PMID:25850985

  4. Thymoma of the left thymic lobe with a contralateral small pleural implant successfully detected with diffusion-weighted MRI.

    PubMed

    Priola, Adriano Massimiliano; Priola, Sandro Massimo

    2015-01-01

    Thymoma is the most common primary neoplasm of the anterior mediastinum. At diagnosis, up to 40% of patients present with advanced disease. Because advanced thymomas receive neoadjuvant chemotherapy, diagnostic imaging is crucial to plan the correct treatment. For characterizing thymomas, CT is the first choice modality, whereas 18F-FDG/PET is reserved for questionable cases and MRI is not routinely employed. Hereby, we describe a case of thymoma with a single contralateral pleural implant in a 30-year-old woman. The small pleural thickening detected at CT was correctly interpreted as pleural seeding related to thymoma at diffusion-weighted (DW)-MRI after a negative 18F-FDG/PET scan, and was subsequently confirmed at surgery. Precise diagnosis and accurate preoperative staging are crucial in managing thymic epithelial tumours in order to design the appropriate treatment and improve prognosis. Indeed, when stage IVa for pleural seeding is diagnosed preoperatively, a multimodality approach including primary chemotherapy followed by surgery and postoperative radiotherapy/chemotherapy is recommended. This is the first report that used DW-MRI for the characterization of pleural seeding in thymoma and demonstrates that DW-MRI could be useful for the correct pre-operatory staging in thymoma patients, especially in cases with indeterminate pleural thickenings at CT, in order to define the correct management. PMID:25702681

  5. Computed tomography-guided time-domain diffuse fluorescence tomography in small animals for localization of cancer biomarkers.

    PubMed

    Tichauer, Kenneth M; Holt, Robert W; Samkoe, Kimberley S; El-Ghussein, Fadi; Gunn, Jason R; Jermyn, Michael; Dehghani, Hamid; Leblond, Frederic; Pogue, Brian W

    2012-01-01

    Small animal fluorescence molecular imaging (FMI) can be a powerful tool for preclinical drug discovery and development studies. However, light absorption by tissue chromophores (e.g., hemoglobin, water, lipids, melanin) typically limits optical signal propagation through thicknesses larger than a few millimeters. Compared to other visible wavelengths, tissue absorption for red and near-infrared (near-IR) light absorption dramatically decreases and non-elastic scattering becomes the dominant light-tissue interaction mechanism. The relatively recent development of fluorescent agents that absorb and emit light in the near-IR range (600-1000 nm), has driven the development of imaging systems and light propagation models that can achieve whole body three-dimensional imaging in small animals. Despite great strides in this area, the ill-posed nature of diffuse fluorescence tomography remains a significant problem for the stability, contrast recovery and spatial resolution of image reconstruction techniques and the optimal approach to FMI in small animals has yet to be agreed on. The majority of research groups have invested in charge-coupled device (CCD)-based systems that provide abundant tissue-sampling but suboptimal sensitivity, while our group and a few others have pursued systems based on very high sensitivity detectors, that at this time allow dense tissue sampling to be achieved only at the cost of low imaging throughput. Here we demonstrate the methodology for applying single-photon detection technology in a fluorescence tomography system to localize a cancerous brain lesion in a mouse model. The fluorescence tomography (FT) system employed single photon counting using photomultiplier tubes (PMT) and information-rich time-domain light detection in a non-contact conformation. This provides a simultaneous collection of transmitted excitation and emission light, and includes automatic fluorescence excitation exposure control, laser referencing, and co

  6. With and without: the bereavement experiences of gay men who have lost a partner to non-AIDS-related causes.

    PubMed

    Hornjatkevyc, Nina L

    2011-10-01

    This study gives voice to the experiences of gay men who have lost a partner to non-AIDS-related causes, a subject that has received little attention in the psychological literature. Interviews were conducted with 8 gay men. An analysis informed by hermeneutic phenomenology generated themes and contexualized meanings regarding the participants' diverse experiences. The themes identified areas of similarity and difference between the bereavement of these participants from those who have participated in general bereavement studies and from those who have lost a partner to AIDS. Implications for counseling practice and further research are discussed. PMID:24501836

  7. Recruiting Chinese American adolescents to HIV/AIDS-related research: a lesson learned from a cross-sectional study.

    PubMed

    Lee, Yi-Hui; Salman, Ali; Wang, Fan

    2012-02-01

    The purpose of this article was to report identified barriers and challenges experienced in the recruiting process of Chinese American adolescents to a cross-sectional HIV/AIDS-related study. Snowball sampling method was used to recruit Chinese American adolescents from Chinese American communities in a U.S. Midwestern state. Barriers and challenges to recruitment were reviewed and analyzed from Chinese cultural perspectives in the hope of aiding researchers and health care providers understand and facilitate future recruitment of Chinese Americans for HIV/AIDS prevention studies. Barriers to recruitment were found related to the taboo topic of sexual issues in Chinese culture, unawareness and denial of HIV/AIDS risks, authoritarian parenting style in Chinese culture, and the required active consents. Facilitating factors of recruiting Chinese American adolescents to future HIV/AIDS prevention research or intervention programs are discussed. Information provided in this article may increase nurses' awareness of various barriers that they might encounter when they conduct research or address HIV/AIDS-related topics of Chinese American adolescents. PMID:20974090

  8. Ethnobotanical Study of Plants Used in the Management of HIV/AIDS-Related Diseases in Livingstone, Southern Province, Zambia

    PubMed Central

    Chinsembu, Kazhila C.

    2016-01-01

    Faced with critical shortages of staff, long queues, and stigma at public health facilities in Livingstone, Zambia, persons who suffer from HIV/AIDS-related diseases use medicinal plants to manage skin infections, diarrhoea, sexually transmitted infections, tuberculosis, cough, malaria, and oral infections. In all, 94 medicinal plant species were used to manage HIV/AIDS-related diseases. Most remedies are prepared from plants of various families such as Combretaceae, Euphorbiaceae, Fabaceae, and Lamiaceae. More than two-thirds of the plants (mostly leaves and roots) are utilized to treat two or more diseases related to HIV infection. Eighteen plants, namely, Achyranthes aspera L., Lannea discolor (Sond.) Engl., Hyphaene petersiana Klotzsch ex Mart., Asparagus racemosus Willd., Capparis tomentosa Lam., Cleome hirta Oliv., Garcinia livingstonei T. Anderson, Euclea divinorum Hiern, Bridelia cathartica G. Bertol., Acacia nilotica Delile, Piliostigma thonningii (Schumach.) Milne-Redh., Dichrostachys cinerea (L.) Wight and Arn., Abrus precatorius L., Hoslundia opposita Vahl., Clerodendrum capitatum (Willd.) Schumach., Ficus sycomorus L., Ximenia americana L., and Ziziphus mucronata Willd., were used to treat four or more disease conditions. About 31% of the plants in this study were administered as monotherapies. Multiuse medicinal plants may contain broad-spectrum antimicrobial agents. However, since widely used plants easily succumb to the threats of overharvesting, they need special protocols and guidelines for their genetic conservation. There is still need to confirm the antimicrobial efficacies, pharmacological parameters, cytotoxicity, and active chemical ingredients of the discovered plants. PMID:27069489

  9. Ethnobotanical Study of Plants Used in the Management of HIV/AIDS-Related Diseases in Livingstone, Southern Province, Zambia.

    PubMed

    Chinsembu, Kazhila C

    2016-01-01

    Faced with critical shortages of staff, long queues, and stigma at public health facilities in Livingstone, Zambia, persons who suffer from HIV/AIDS-related diseases use medicinal plants to manage skin infections, diarrhoea, sexually transmitted infections, tuberculosis, cough, malaria, and oral infections. In all, 94 medicinal plant species were used to manage HIV/AIDS-related diseases. Most remedies are prepared from plants of various families such as Combretaceae, Euphorbiaceae, Fabaceae, and Lamiaceae. More than two-thirds of the plants (mostly leaves and roots) are utilized to treat two or more diseases related to HIV infection. Eighteen plants, namely, Achyranthes aspera L., Lannea discolor (Sond.) Engl., Hyphaene petersiana Klotzsch ex Mart., Asparagus racemosus Willd., Capparis tomentosa Lam., Cleome hirta Oliv., Garcinia livingstonei T. Anderson, Euclea divinorum Hiern, Bridelia cathartica G. Bertol., Acacia nilotica Delile, Piliostigma thonningii (Schumach.) Milne-Redh., Dichrostachys cinerea (L.) Wight and Arn., Abrus precatorius L., Hoslundia opposita Vahl., Clerodendrum capitatum (Willd.) Schumach., Ficus sycomorus L., Ximenia americana L., and Ziziphus mucronata Willd., were used to treat four or more disease conditions. About 31% of the plants in this study were administered as monotherapies. Multiuse medicinal plants may contain broad-spectrum antimicrobial agents. However, since widely used plants easily succumb to the threats of overharvesting, they need special protocols and guidelines for their genetic conservation. There is still need to confirm the antimicrobial efficacies, pharmacological parameters, cytotoxicity, and active chemical ingredients of the discovered plants. PMID:27069489

  10. Soot formation and temperature structure in small methane-oxygen diffusion flames at subcritical and supercritical pressures

    SciTech Connect

    Joo, Hyun I.; Guelder, Oemer L.

    2010-06-15

    An experimental study was conducted to examine the characteristics of laminar methane-oxygen diffusion flames up to 100 atmospheres. The influence of pressure on soot formation and on the structure of the temperature field was investigated over the pressure range of 10-90 atmospheres in a high-pressure combustion chamber using a non-intrusive, line-of-sight spectral soot emission diagnostic technique. Two distinct zones characterized the appearance of a methane and pure oxygen diffusion flame: an inner luminous zone similar to the methane-air diffusion flames, and an outer diffusion flame zone which is mostly blue. The flame height, marked by the visible soot radiation emission, was reduced by over 50% over the pressure range of 10-100 atmospheres. Between 10 and 40 atmospheres, the soot levels increased with increasing pressure; however, above 40 atmospheres the soot concentrations decreased with increasing pressure. (author)

  11. Diffusion and adsorption of methane confined in nanoporous carbon aerogel: a combined quasi-elastic and small-angle neutron scattering study

    SciTech Connect

    Mavila Chathoth, Suresh; Mamontov, Eugene; Melnichenko, Yuri B; Zamponi, Michaela M

    2010-01-01

    The diffusion of methane confined in nano-porous carbon aerogel with the average pore size 48 {angstrom} and porosity 60% was investigated as a function of pressure at T = 298 K using quasi-elastic neutron scattering (QENS). The diffusivity of methane shows a clear effect of confinement: it is about two orders of magnitude lower than in bulk at the same thermodynamic conditions and is close to the diffusivity of liquid methane at 100 K (i.e. {approx} 90 K below the liquid-gas critical temperature T{sub C} {approx} 191 K). The diffusion coefficient (D) of methane initially increases with pressure by a factor of {approx}2.5 from 3.47 {+-} 0.41 x 10{sup -10} m{sup 2} s{sup -1} at 0.482 MPa to D = 8.55 {+-} 0.33 x 10{sup -10} m{sup 2} s{sup -1} at 2.75 MPa and starts to decrease at higher pressures. An explanation of the observed non-monotonic behavior of the diffusivity in the confined fluid is based on the results of small-angle neutron scattering experiments of the phase behavior of methane in a similar carbon aerogel sample. The initial increase of the diffusion coefficient with pressure is explained as due to progressive filling of bigger pores in which molecular mobility in the internal pore volume is less affected by the sluggish liquid-like molecular mobility in the adsorbed phase. Subsequent decrease of D, is associated with the effect of intermolecular collisions, which result in a lower total molecular mobility with pressure, as in the bulk state. The results are compared with the available QENS data on the methane diffusivity in zeolites, metal organic frameworks, and porous silica as well as with the molecular dynamics simulations of methane in nano-porous carbons and silica zeolites.

  12. Slow-down or speed-up of inter- and intra-cluster diffusion of controversial knowledge in stubborn communities based on a small world network

    NASA Astrophysics Data System (ADS)

    Ausloos, Marcel

    2015-06-01

    Diffusion of knowledge is expected to be huge when agents are open minded. The report concerns a more difficult diffusion case when communities are made of stubborn agents. Communities having markedly different opinions are for example the Neocreationist and Intelligent Design Proponents (IDP), on one hand, and the Darwinian Evolution Defenders (DED), on the other hand. The case of knowledge diffusion within such communities is studied here on a network based on an adjacency matrix built from time ordered selected quotations of agents, whence for inter- and intra-communities. The network is intrinsically directed and not necessarily reciprocal. Thus, the adjacency matrices have complex eigenvalues; the eigenvectors present complex components. A quantification of the slow-down or speed-up effects of information diffusion in such temporal networks, with non-Markovian contact sequences, can be made by comparing the real time dependent (directed) network to its counterpart, the time aggregated (undirected) network, - which has real eigenvalues. In order to do so, small world networks which both contain an odd number of nodes are studied and compared to similar networks with an even number of nodes. It is found that (i) the diffusion of knowledge is more difficult on the largest networks; (ii) the network size influences the slowing-down or speeding-up diffusion process. Interestingly, it is observed that (iii) the diffusion of knowledge is slower in IDP and faster in DED communities. It is suggested that the finding can be "rationalized", if some "scientific quality" and "publication habit" is attributed to the agents, as common sense would guess. This finding offers some opening discussion toward tying scientific knowledge to belief.

  13. Understanding the relationships among HIV/AIDS-related stigma, health service utilization, and HIV prevalence and incidence in Sub-Saharan Africa: a multi-level theoretical perspective.

    PubMed

    Williams, Leslie D

    2014-03-01

    HIV-positive individuals often face community-wide discrimination or public shame and humiliation as a result of their HIV-status. In Sub-Saharan Africa, high HIV incidence coupled with unique cultural contexts make HIV-positive individuals particularly likely to experience this kind of HIV/AIDS-related (HAR) stigma. To date, there is a relatively small amount of high-quality empirical literature specific to HAR stigma in this context, supporting the notion that a better understanding of this phenomenon is needed to inform potential interventions. This paper provides a thorough review of the literature specific to HAR stigma in Sub-Saharan Africa, finding (a) qualitative support for the existence of important relationships between HAR stigma and health service utilization and barriers; (b) a need for more quantitative study of stigma and its relationships both to health service utilization and to HIV outcomes directly; and (c) a disconnect between methodological techniques used in this context-specific literature and well-known theories about stigma as a general phenomenon. This paper then draws from its empirical literature review, as well as from well-known theoretical frameworks from multiple disciplines, to propose a theoretical framework for the ecological and multilevel relationships among HAR stigma, health service utilization, and HIV outcomes in this context. PMID:24477769

  14. Human Exportin-1 is a Target for Combined Therapy of HIV and AIDS Related Lymphoma.

    PubMed

    Boons, Eline; Vanstreels, Els; Jacquemyn, Maarten; Nogueira, Tatiane C; Neggers, Jasper E; Vercruysse, Thomas; van den Oord, Joost; Tamir, Sharon; Shacham, Sharon; Landesman, Yosef; Snoeck, Robert; Pannecouque, Christophe; Andrei, Graciela; Daelemans, Dirk

    2015-09-01

    Infection with HIV ultimately leads to advanced immunodeficiency resulting in an increased incidence of cancer. For example primary effusion lymphoma (PEL) is an aggressive non-Hodgkin lymphoma with very poor prognosis that typically affects HIV infected individuals in advanced stages of immunodeficiency. Here we report on the dual anti-HIV and anti-PEL effect of targeting a single process common in both diseases. Inhibition of the exportin-1 (XPO1) mediated nuclear transport by clinical stage orally bioavailable small molecule inhibitors (SINE) prevented the nuclear export of the late intron-containing HIV RNA species and consequently potently suppressed viral replication. In contrast, in CRISPR-Cas9 genome edited cells expressing mutant C528S XPO1, viral replication was unaffected upon treatment, clearly demonstrating the anti-XPO1 mechanism of action. At the same time, SINE caused the nuclear accumulation of p53 tumor suppressor protein as well as inhibition of NF-κB activity in PEL cells resulting in cell cycle arrest and effective apoptosis induction. In vivo, oral administration arrested PEL tumor growth in engrafted mice. Our findings provide strong rationale for inhibiting XPO1 as an innovative strategy for the combined anti-retroviral and anti-neoplastic treatment of HIV and PEL and offer perspectives for the treatment of other AIDS-associated cancers and potentially other virus-related malignancies. PMID:26501108

  15. Human Exportin-1 is a Target for Combined Therapy of HIV and AIDS Related Lymphoma

    PubMed Central

    Boons, Eline; Vanstreels, Els; Jacquemyn, Maarten; Nogueira, Tatiane C.; Neggers, Jasper E.; Vercruysse, Thomas; van den Oord, Joost; Tamir, Sharon; Shacham, Sharon; Landesman, Yosef; Snoeck, Robert; Pannecouque, Christophe; Andrei, Graciela; Daelemans, Dirk

    2015-01-01

    Infection with HIV ultimately leads to advanced immunodeficiency resulting in an increased incidence of cancer. For example primary effusion lymphoma (PEL) is an aggressive non-Hodgkin lymphoma with very poor prognosis that typically affects HIV infected individuals in advanced stages of immunodeficiency. Here we report on the dual anti-HIV and anti-PEL effect of targeting a single process common in both diseases. Inhibition of the exportin-1 (XPO1) mediated nuclear transport by clinical stage orally bioavailable small molecule inhibitors (SINE) prevented the nuclear export of the late intron-containing HIV RNA species and consequently potently suppressed viral replication. In contrast, in CRISPR-Cas9 genome edited cells expressing mutant C528S XPO1, viral replication was unaffected upon treatment, clearly demonstrating the anti-XPO1 mechanism of action. At the same time, SINE caused the nuclear accumulation of p53 tumor suppressor protein as well as inhibition of NF-κB activity in PEL cells resulting in cell cycle arrest and effective apoptosis induction. In vivo, oral administration arrested PEL tumor growth in engrafted mice. Our findings provide strong rationale for inhibiting XPO1 as an innovative strategy for the combined anti-retroviral and anti-neoplastic treatment of HIV and PEL and offer perspectives for the treatment of other AIDS-associated cancers and potentially other virus-related malignancies. PMID:26501108

  16. AIDS-Related Stigma and Mental Disorders among People Living with HIV: A Cross-Sectional Study in Cambodia

    PubMed Central

    Yi, Siyan; Chhoun, Pheak; Suong, Samedy; Thin, Kouland; Brody, Carinne; Tuot, Sovannary

    2015-01-01

    Background AIDS-related stigma and mental disorders are the most common conditions in people living with HIV (PLHIV). We therefore conducted this study to examine the association of AIDS-related stigma and discrimination with mental disorders among PLHIV in Cambodia. Methods A two-stage cluster sampling method was used to select 1,003 adult PLHIV from six provinces. The People Living with HIV Stigma Index was used to measure stigma and discrimination, and a short version of general health questionnaire (GHQ-12) was used to measure mental disorders. Multivariate logistic regression analysis was conducted. Results The reported experiences of discrimination in communities in the past 12 months ranged from 0.8% for reports of being denied health services to 42.3% for being aware of being gossiped about. Internal stigma was also common ranging from 2.8% for avoiding going to a local clinic and/or hospital to 59.6% for deciding not to have (more) children. The proportions of PLHIV who reported fear of stigma and discrimination ranged from 13.9% for fear of being physically assaulted to 34.5% for fear of being gossiped about. The mean score of GHQ-12 was 3.2 (SD = 2.4). After controlling for several potential confounders, higher levels of mental disorders (GHQ-12≥ 4) remained significantly associated with higher levels of experiences of stigma and discrimination in family and communities (AOR = 1.9, 95% CI = 1.4–2.6), higher levels of internal stigma (AOR = 1.7, 95% CI = 1.2–2.3), and higher levels of fear of stigma and discrimination in family and communities (AOR = 1.5, 95% CI = 1.1–2.2). Conclusions AIDS-related stigma and discrimination among PLHIV in Cambodia are common and may have potential impacts on their mental health conditions. These findings indicate a need for community-based interventions to reduce stigma and discrimination in the general public and to help PLHIV to cope with this situation. PMID:25806534

  17. Modelling non-homogeneous stochastic reaction-diffusion systems: the case study of gemcitabine-treated non-small cell lung cancer growth

    PubMed Central

    2012-01-01

    Background Reaction-diffusion based models have been widely used in the literature for modeling the growth of solid tumors. Many of the current models treat both diffusion/consumption of nutrients and cell proliferation. The majority of these models use classical transport/mass conservation equations for describing the distribution of molecular species in tumor spheroids, and the Fick's law for describing the flux of uncharged molecules (i.e oxygen, glucose). Commonly, the equations for the cell movement and proliferation are first order differential equations describing the rate of change of the velocity of the cells with respect to the spatial coordinates as a function of the nutrient's gradient. Several modifications of these equations have been developed in the last decade to explicitly indicate that the tumor includes cells, interstitial fluids and extracellular matrix: these variants provided a model of tumor as a multiphase material with these as the different phases. Most of the current reaction-diffusion tumor models are deterministic and do not model the diffusion as a local state-dependent process in a non-homogeneous medium at the micro- and meso-scale of the intra- and inter-cellular processes, respectively. Furthermore, a stochastic reaction-diffusion model in which diffusive transport of the molecular species of nutrients and chemotherapy drugs as well as the interactions of the tumor cells with these species is a novel approach. The application of this approach to he scase of non-small cell lung cancer treated with gemcitabine is also novel. Methods We present a stochastic reaction-diffusion model of non-small cell lung cancer growth in the specification formalism of the tool Redi, we recently developed for simulating reaction-diffusion systems. We also describe how a spatial gradient of nutrients and oncological drugs affects the tumor progression. Our model is based on a generalization of the Fick's first diffusion law that allows to model

  18. Specificity of anti-lymphocyte antibodies in sera from patients with AIDS-related complex (ARC) and healthy homosexuals.

    PubMed Central

    Warren, R Q; Johnson, E A; Donnelly, R P; Lavia, M F; Tsang, K Y

    1988-01-01

    The presence and specificity of anti-lymphocyte antibodies (ALA) was investigated in sera from male homosexuals with AIDS-Related Complex (ARC) as well as healthy homosexuals. Individuals in the healthy homosexual group had no detectable antibodies to human immunodeficiency virus (HIV). Antibodies reactive with normal peripheral blood mononuclear cells were detected by Western blot analysis in sera from both groups of homosexuals. Of those individuals whose sera contained ALA, 71% of ARC patients and 83% of healthy homosexuals had antibodies recognizing a 73 kilodalton (kD) molecule. ALA present in ARC sera reacted with CD3+, CD4+ and CD8+ lymphocytes while little reactivity with B cells was observed. Our results indicate that ALA appear in homosexuals prior to HIV infection and are reactive primarily with T lymphocytes. A 73 kD structure associated with the T cell membrane is frequently the target for these antibodies. Images Fig. 1 Fig. 2 Fig. 3 PMID:3052941

  19. Help-seeking for AIDS-related concerns: a comparison of gay men with various HIV diagnoses.

    PubMed

    Hays, R B; Catania, J A; McKusick, L; Coates, T J

    1990-10-01

    Examined help-seeking and psychological distress among four groups of gay men (30 AIDS-diagnosed, 107 HIV-seropositive, 149 HIV-seronegative, 244 untested) in the AIDS Behavioral Research Project, a longitudinal survey of San Francisco gay men. The men reported high levels of anxiety, depression, and help-seeking from their social networks. AIDS-diagnosed and HIV-positives reported the most AIDS worry and were the most likely to seek help. High percentages of AIDS-diagnosed men sought help from all sources (peers, professionals, family), whereas nondiagnosed men were more likely to seek help from peers. Regardless of the men's HIV status, peers were perceived to be the most helpful source. Family members were less likely sought and perceived as least helpful. The strengths and limitations of peers as social support providers for AIDS-related concerns are discussed, including implications for the design of community programs to enhance the abilities of peer helpers. PMID:2075900

  20. Professionalisation and social attitudes: a protocol for measuring changes in HIV/AIDS-related stigma among healthcare students

    PubMed Central

    Ahmadi, Keivan; Reidpath, Daniel D; Allotey, Pascale; Hassali, Mohamed Azmi Ahmad

    2013-01-01

    Introduction HIV/AIDS-related stigma affects the access and utilisation of health services. Although HIV/AIDS-related stigma in the health services has been studied, little work has attended to the relationship between professional development and stigmatising attitudes. Hence, in this study, we will extend earlier research by examining the relationship between the stage of professional development and the kinds of stigmatising attitudes held about people living with HIV/AIDS. Methods and analysis A serial cross-sectional design will be combined with a two-point in time longitudinal design to measure the levels of stigma among healthcare students from each year of undergraduate and graduate courses in Malaysia and Australia. In the absence of suitable measures, we will carry out a sequential mixed methods design to develop such a tool. The questionnaire data will be analysed using mixed effects linear models to manage the repeated measures. Ethics and dissemination We have received ethical approval from the Monash MBBS executive committee as well as the Monash University Human Research Ethics Committee. We will keep the data in a locked filing cabinet in the Monash University (Sunway campus) premises for 5 years, after which the information will be shredded and disposed of in secure bins, and digital recordings will be erased in accordance with Monash University's regulations. Only the principal investigator and the researcher will have access to the filing cabinet. We aim to present and publish the results of this study in national and international conferences and peer-reviewed journals, respectively. PMID:23793653

  1. Altered natural history of AIDS-related opportunistic infections in the era of potent combination antiretroviral therapy.

    PubMed

    Jacobson, M A; French, M

    1998-01-01

    Since potent HIV protease inhibitor drugs became widely available in early 1996, many HIV clinical specialists have noted a marked decrease in the occurrence of AIDS-related opportunistic infections, and some specialists have reported unusual clinical presentations and manifestations of previously common opportunistic infections. In this article, we will review (1) the available data regarding recent trends in AIDS-related opportunistic infections incidence and manifestations, (2) clinical and immunologic evidence that potent combination antiretroviral therapy can alter the natural history of these opportunistic infections, and (3) the implications of these findings for current patient management practice and future clinical and immunologic research. As a preface to this review, however, it is important to acknowledge that any evaluation of the potential benefit of potent combination antiretroviral therapy in reducing the risk of serious opportunistic infections can be confounded by the concomitant use of prophylactic antimicrobial agents co-administered to prevent specific opportunistic infections. For example, it is standard clinical practice to administer trimethoprim-sulfamethoxazole (or another agent if trimethoprim-sulfamethoxazole cannot be tolerated) to patients with an absolute CD4 lymphocyte count < 200 cells/microliters, unexplained chronic fever or a history of oropharyngeal candidiasis. Similarly, specific antimicrobial prophylaxis to prevent disseminated Mycobacterium avium complex (MAC) infection in patients with absolute CD4 counts < 50 cells/microliters is also a widely recommended guideline. Although the relative efficacies of specific antimicrobial prophylaxis regimens in preventing the most common life- and sight-threatening opportunistic infectious complications of AIDS [Pneumocystis carinii pneumonia (PCP), disseminated MAC infection, and cytomegalovirus (CMV) retinitis] are now well established, these relative efficacies were established in

  2. Vaneless diffusers

    NASA Astrophysics Data System (ADS)

    Senoo, Y.

    The influence of vaneless diffusers on flow in centrifugal compressors, particularly on surge, is discussed. A vaneless diffuser can demonstrate stable operation in a wide flow range only if it is installed with a backward leaning blade impeller. The circumferential distortion of flow in the impeller disappears quickly in the vaneless diffuser. The axial distortion of flow at the diffuser inlet does not decay easily. In large specific speed compressors, flow out of the impeller is distorted axially. Pressure recovery of diffusers at distorted inlet flow is considerably improved by half guide vanes. The best height of the vanes is a little 1/2 diffuser width. In small specific speed compressors, flow out of the impeller is not much distorted and pressure recovery can be predicted with one-dimensional flow analysis. Wall friction loss is significant in narrow diffusers. The large pressure drop at a small flow rate can cause the positive gradient of the pressure-flow rate characteristic curve, which may cause surging.

  3. HIV/AIDS-related stigmatizing and discriminatory attitudes and recent HIV testing among men who have sex with men in Beijing.

    PubMed

    Li, Xuefeng; Lu, Hongyan; Ma, Xiaoyan; Sun, Yanming; He, Xiong; Li, Chunmei; Raymond, H F; McFarland, Willi; Pan, Stephen W; Shao, Yiming; Vermund, Sten H; Xiao, Yan; Ruan, Yuhua; Jia, Yujiang

    2012-04-01

    This study assessed the correlates of recent HIV testing and HIV/AIDS-related stigmatizing and discriminatory attitudes among men who have sex with men (MSM) in Beijing, China. A cross-sectional study probed demographics, sexual and drug use behaviors, HIV testing, and prevention services. Of 500 participants, 39.3% recently received a test for HIV. Recent testing was independently associated with expressing lower levels of HIV/AIDS-related stigmatizing and discriminatory attitudes, more male sex partners, no female sexual partners and knowing HIV status of their last male partner. Expressing lower levels of HIV/AIDS-related stigmatizing and discriminatory attitudes was independently associated with recent testing, younger age, and knowing HIV status of their last male partner. This study revealed that HIV/AIDS-related stigmatizing and discriminatory attitudes were common and inversely associated with recent HIV testing. Low levels of testing highlighted the urgent needs to reduce HIV/AIDS-related stigma and discrimination and expand HIV testing among MSM in Beijing. PMID:22350831

  4. Topotecan Hydrochloride in Treating Children With Meningeal Cancer That Has Not Responded to Previous Treatment

    ClinicalTrials.gov

    2013-02-20

    AIDS-related Diffuse Large Cell Lymphoma; AIDS-related Diffuse Mixed Cell Lymphoma; AIDS-related Diffuse Small Cleaved Cell Lymphoma; AIDS-related Immunoblastic Large Cell Lymphoma; AIDS-related Lymphoblastic Lymphoma; AIDS-related Peripheral/Systemic Lymphoma; AIDS-related Primary CNS Lymphoma; AIDS-related Small Noncleaved Cell Lymphoma; Childhood Diffuse Large Cell Lymphoma; Childhood Immunoblastic Large Cell Lymphoma; HIV-associated Hodgkin Lymphoma; Leptomeningeal Metastases; Recurrent Childhood Acute Lymphoblastic Leukemia; Recurrent Childhood Acute Myeloid Leukemia; Recurrent Childhood Large Cell Lymphoma; Recurrent Childhood Lymphoblastic Lymphoma; Recurrent Childhood Medulloblastoma; Recurrent Childhood Small Noncleaved Cell Lymphoma; Recurrent/Refractory Childhood Hodgkin Lymphoma; Unspecified Childhood Solid Tumor, Protocol Specific

  5. AIDS-related myopathy.

    PubMed

    Sheikh, Rafiq A.; Yasmeen, Shagufta; Munn, Robert; Ruebner, Boris H.; Ellis, William G.

    1999-09-01

    Infection with the human immunodeficiency virus (HIV) is often associated with the acquired immunodeficiency syndrome (AIDS), and wasting is one of the defining clinical features of AIDS. Muscular weakness due to myopathy may develop at any stage of HIV infection. We report two illustrative cases of HIV-associated myopathies. One was due to inflammatory myosits most likely directly related to the HIV infection, and the other was most likely the result of mitochondrial damage due to zidovudine, a nucleoside analogue commonly used in treating HIV infection. Biopsies from both patients showed alterations of myofiber structures, of varying severity, culminating in necrosis, lipid droplets, and lymphoplasmocytic inflammatory response. The zidovudine-treated patient also showed distinctive mitochondrial changes, predominantly enlargement, variation in shape and size, and disorganization of the cristae. These two types of HIV-associated inflammatory myopathies are reviewed, along with other HIV-associated myopathies, including HIV wasting syndrome, nemaline rod myopathy, pyomyositis, rhabdomyolysis, cardiomyopathy, and other miscellaneous myopathies associated with HIV infection. PMID:11810429

  6. HIV/AIDS - Related Knowledge, Attitudes, and Sexual Practices among Migrant Wives in Rural Anhui Province, China

    PubMed Central

    Zou, Huachun; Dai, Xin; Meng, Xiaojun; Wang, Huadong; Jiang, Chao; Wang, Yanchun; Zhang, Lin; Gao, Yongqing; Tang, Song; Xu, Tan; Sun, Wenjie; Wen, Yufeng

    2015-01-01

    Background Migrant wives have been increasing in some poor rural regions of China and they may bridge HIV transmission across regions. This study aimed to assess HIV/AIDS-related knowledge, attitudes and sexual practices among this population in rural Anhui Province, China. Methods A cross-sectional survey was conducted with questionnaire of HIV/AIDS-related knowledge, attitudes, and sexual practices between June 2011 and May 2012. A total of 730 migrant wives and 207 local women were enrolled in this study. Unpaired T-test, Chi-square was utilized to compare the difference of HIV/AIDS knowledge, attitudes and sexual practices between migrant wives and local women. Results Around 80% of the migrant wives were from Yunnan, Guizhou, or Sichuan Provinces. The main sources of HIV/AIDS information were TV/radio, posters, and newspapers/periodicals. HIV/AIDS knowledge level among migrant wives was significantly lower than that among local women (e.g. 47.1% vs 57.0% (p<0.001) answered “Yes” for the question “Can an apparently healthy person be HIV-infected?”), and stigma and prejudice towards HIV/AIDS among migrant wives were more common than those among local women (e.g. 73.2% vs 65.7% (p=0.006) answered “No” for the question “If a shopkeeper or food seller had the HIV, would you buy food from them?”). Compared to local women, migrant wives were more likely to have ever had sex during menstruation (6.8% vs 3.4%, p=0.065) and extramarital sex (17.5% vs 10.1%, p=0.01), and were less likely to consistently use condoms with their husbands (45.8% vs 57.5%, p<0.001) or extramarital sex partners (48.8% vs 58.95, p<0.001). Conclusions Migrant wives in rural China had a low HIV/AIDS knowledge level and high prevalence of stigma and prejudice and risky sexual behaviors. Local HIV/AIDS prevention programs should target this neglected population. PMID:25844269

  7. Toxoplasma gondii Infection in Kyrgyzstan: Seroprevalence, Risk Factor Analysis, and Estimate of Congenital and AIDS-Related Toxoplasmosis

    PubMed Central

    Bodosheva, Aigerim; Kuttubaev, Omurbek; Hehl, Adrian B.; Tanner, Isabelle; Ziadinov, Iskender; Torgerson, Paul R.; Deplazes, Peter

    2013-01-01

    Background HIV-prevalence, as well as incidence of zoonotic parasitic diseases like cystic echinococcosis, has increased in the Kyrgyz Republic due to fundamental socio-economic changes after the breakdown of the Soviet Union. The possible impact on morbidity and mortality caused by Toxoplasma gondii infection in congenital toxoplasmosis or as an opportunistic infection in the emerging AIDS pandemic has not been reported from Kyrgyzstan. Methodology/Principal Findings We screened 1,061 rural and 899 urban people to determine the seroprevalence of T. gondii infection in 2 representative but epidemiologically distinct populations in Kyrgyzstan. The rural population was from a typical agricultural district where sheep husbandry is a major occupation. The urban population was selected in collaboration with several diagnostic laboratories in Bishkek, the largest city in Kyrgyzstan. We designed a questionnaire that was used on all rural subjects so a risk-factor analysis could be undertaken. The samples from the urban population were anonymous and only data with regard to age and gender was available. Estimates of putative cases of congenital and AIDS-related toxoplasmosis in the whole country were made from the results of the serology. Specific antibodies (IgG) against Triton X-100 extracted antigens of T. gondii tachyzoites from in vitro cultures were determined by ELISA. Overall seroprevalence of infection with T. gondii in people living in rural vs. urban areas was 6.2% (95%CI: 4.8–7.8) (adjusted seroprevalence based on census figures 5.1%, 95% CI 3.9–6.5), and 19.0% (95%CI: 16.5–21.7) (adjusted 16.4%, 95% CI 14.1–19.3), respectively, without significant gender-specific differences. The seroprevalence increased with age. Independently low social status increased the risk of Toxoplasma seropositivity while increasing numbers of sheep owned decreased the risk of seropositivity. Water supply, consumption of unpasteurized milk products or undercooked meat, as

  8. Apparent diffusion coefficient of hyperpolarized (3)He with minimal influence of the residual gas in small animals.

    PubMed

    Carrero-González, L; Kaulisch, T; Ruiz-Cabello, J; Pérez-Sánchez, J M; Peces-Barba, G; Stiller, D; Rodríguez, I

    2012-09-01

    The apparent diffusion coefficient (ADC) of hyperpolarized (HP) gases is a parameter that reflects changes in lung microstructure. However, ADC is dependent on many physiological and experimental variables that need to be controlled or specified in order to ensure the reliability and reproducibility of this parameter. A single breath-hold experiment is desirable in order to reduce the amount of consumed HP gas. The application of a positive end-expiratory pressure (PEEP) causes an increase in the residual gas volume. Depending on the applied PEEP, the ratio between the incoming and residual gas volumes will change and the ADC will vary, as long as both gases do not have the same diffusion coefficient. The most standard method for human applications uses air for breathing and a bolus of pure HP (3)He for MRI data acquisition. By applying this method in rats, we have demonstrated that ADC values are strongly dependent on the applied PEEP, and therefore on the residual gas volume in the lung. This outcome will play an important role in studies concerning certain diseases, such as emphysema, which is characterized by an increase in the residual volume. Ventilation with an oxygen-helium mixture (VOHeM) is a proposed single breath-hold method that uses two different gas mixtures (O(2)-(4)He for ventilation and HP (3)He-N(2) for imaging). The concentration of each gas in its respective mixture was calculated in order to obtain the same diffusion coefficient in both mixtures. ADCs obtained from VOHeM are independent of PEEP, thus minimizing the effect of the different residual volumes. PMID:22275333

  9. Fast Water Diffusion and Long-Term Polymer Reorganization during Nafion Membrane Hydration Evidenced by Time-Resolved Small-Angle Neutron Scattering.

    PubMed

    Fumagalli, M; Lyonnard, S; Prajapati, G; Berrod, Q; Porcar, L; Guillermo, A; Gebel, G

    2015-06-11

    We report a small-angle neutron scattering study of liquid water sorption in Nafion membranes. The swelling of hydrophilic domains was measured on the nanoscale by combining in situ time-resolved and long-term static experiments, yielding kinetic curves recorded over an unprecedented time scale, from hundreds of milliseconds to several years. At low water content, typically below 5 water molecules per ionic group, a limited subdiffusive regime was observed and ascribed to nanoconfinement and local interactions between charged species and water molecules. Further ultrafast and thermally activated swelling due to massive liquid water sorption was observed and analyzed by using Fick's equation. The extracted mutual water diffusion coefficients are in good agreement with pulsed field gradient NMR self-diffusion coefficient values, evidencing a water diffusion-driven process due to concentration gradients within the Nafion membrane. Finally, after completion of the ultrafast regime, the kinetic swelling curves exhibit a remarkable long-term behavior scaling as the logarithm of time, showing that the polymer membrane can continuously accommodate additional water molecules upon hydration stress. The present nanoscale kinetics results provide insights into the vapor-versus-liquid sorption mechanisms, the nanostructure of Nafion, and the role of polymer reorganization modes, highlighting that the membrane can never reach a steady state. PMID:25971732

  10. Insights into Surface Interactions between Metal Organic Frameworks and Gases during Transient Adsorption and Diffusion by In-Situ Small Angle X-ray Scattering.

    PubMed

    Dumée, Ludovic F; He, Li; Hodgson, Peter; Kong, Lingxue

    2016-01-01

    The fabrication of molecular gas sieving materials with specific affinities for a single gas species and able to store large quantities of materials at a low or atmospheric pressure is desperately required to reduce the adverse effects of coal and oil usage in carbon capture. Fundamental understanding of the dynamic adsorption of gas, the diffusion mechanisms across thin film membranes, and the impact of interfaces play a vital role in developing these materials. In this work, single gas permeation tests across micro-porous membrane materials, based on metal organic framework crystals grown on the surface of carbon nanotubes (ZiF-8@CNT), were performed for the first time in-situ at the Australian Synchrotron on the small angle X-ray scattering beamline in order to reveal molecular sieving mechanisms and gas adsorption within the material. The results show that specific chemi-sorption of CO₂ across the ZiF-8 crystal lattices affected the morphology and unit cell parameters, while the sieving of other noble or noble like gases across the ZiF-8@CNT membranes was found to largely follow Knudsen diffusion. This work demonstrates for the first time a novel and effective technique to assess molecular diffusion at the nano-scale across sub-nano-porous materials by probing molecular flexibility across crystal lattice and single cell units. PMID:27598211

  11. AIDS-related knowledge, attitudes and behaviour among South African street youth: reflections on power, sexuality and the autonomous self.

    PubMed

    Swart-Kruger, J; Richter, L M

    1997-09-01

    Street children in South Africa are, in the main, between the ages of 11 and 17 years. Rape, prostitution, sexual bartering and exchange, casual sex and romantic sexual relationships all occur in the experiences of young people who live and work on inner-city streets. In this study, the AIDS-related knowledge, attitudes and behaviour of 141 street youth, living in seven large cities in South Africa, were elicited in focus group discussions. At the time of the study, 79 boys (56%) were living in shelters run by nongovernmental and welfare organisations, while 62 boys (44%) were sleeping "rough". The results, both qualitative and quantitative, indicated that the AIDS knowledge of South African street children was comparable to levels reported for groups of "hard-to-reach" youth in other parts of the world. Fear of HIV infection did not appear in a list of day-to-day priorities constructed by the children, a list dominated by survival concerns with food, money and clothes. However, more than half of the boys conceded that they engaged in sex for money, goods or protection, several boys indicated that they had been raped, and most reported being sexually active with "girlfriends", who themselves frequently engaged in transactional sex. The findings are interpreted in terms of the relationships between power dynamics surrounding race and age, and how they affect self-initiated controls over sexuality and sexual protection. PMID:9255928

  12. HIV/AIDS-related knowledge and behaviors among rural married migrant women in Shandong Province, China: a comparison study.

    PubMed

    Song, Yapei; Kang, Dianmin; Wang, Guoyong; Wei, Chongyi; Tao, Xiaorun; Huang, Tao; Qian, Yuesheng; Zhu, Tiwen; Yang, Shan; Yu, Shaoqi; Wang, Hong; Ma, Wei

    2015-02-01

    Migrant women in China are disproportionately affected by HIV/AIDS. This study described HIV/AIDS-related knowledge and behaviors among married migrant women in Shandong province in comparison to non-migrant local women and identified factors associated with HIV testing history and extramarital sex among married migrant women. A probability-based sample of 1,076 migrant and 1,195 local women were included in the analyses. Compared to local women, married migrant women had lower levels of HIV/AIDS knowledge and were more likely to have had premarital sex, extramarital sex, history of sexually transmitted diseases, and drug use. Less than a quarter of migrant women used condoms consistently in extramarital sex. Only 31.0 % of married migrant women had ever tested for HIV, and the rate of premarital HIV testing was very low. Multivariable analysis showed that married migrant women with a history of extramarital sex were more likely to be from Yunnan province, be living in Yantai city, be in their first marriage, have lower family income, have poor relationship with spouses, use drug, have a history of sexually transmitted diseases, and have lower social support. Our findings provide further evidence that married migrant women are at higher risk for HIV infection and that targeted interventions need to be developed for this population. PMID:25323941

  13. A systematic review of HIV/AIDS-related stigma and discrimination in India: current understanding and future needs.

    PubMed

    Bharat, Shalini

    2011-01-01

    HIV/AIDS-related stigma is recognised as a major barrier to HIV prevention efforts and an impediment to mitigating its impact on individuals and communities. This paper reviews the existing research literature on AIDS stigma in India with the objective of documenting the current status of research, highlighting major findings and identifying key gaps remaining. Thirty publications were identified through a careful search of which a majority focused on stigma assessment and very few on stigma measurement, conceptual aspects of stigma or stigma reduction interventions. A few standardised stigma measures are available but more are required to assess causes of stigma among general population and compounded and internalised stigma among positive people. Research exploring linkages between stigma and HIV services uptake or the effect of HIV care and treatment programs on stigma levels are largely missing and need to be prioritised. In addition, more research is needed to advance conceptual understanding of stigma within the cultural context of the country including research on the neglected groups such as, transgender people. Context-specific (health care, community) interventions are needed to address various forms of stigma - enacted, perceived, internalised and layered - including structural approaches besides inter-personal and information-based approaches. A major gap relates to meager research on developing and evaluating stigma reduction interventions and needs priority focus. Overall, the review recommends developing a national agenda on AIDS stigma research and interventions to help realise the government's goal of stigma reduction. PMID:23237728

  14. Longitudinal Effects of Coping on Outcome in a Randomized Controlled Trial of a Group Intervention for HIV-Positive Adults with AIDS-Related Bereavement

    ERIC Educational Resources Information Center

    Hansen, Nathan B.; Tarakeshwar, Nalini; Ghebremichael, Musie; Zhang, Heping; Kochman, Arlene; Sikkema, Kathleen J.

    2006-01-01

    This study examined the longitudinal effects of coping on outcome one year following completion of a randomized, controlled trial of a group coping intervention for AIDS-related bereavement. Bereaved HIV-positive participants (N = 267) were administered measures of grief, psychiatric distress, quality of life, and coping at baseline,…

  15. With and With"out": The Bereavement Experiences of Gay Men Who Have Lost a Partner to Non-AIDS-Related Causes

    ERIC Educational Resources Information Center

    Hornjatkevyc, Nina L.; Alderson, Kevin G.

    2011-01-01

    This study gives voice to the experiences of gay men who have lost a partner to non-AIDS-related causes, a subject that has received little attention in the psychological literature. Interviews were conducted with 8 gay men. An analysis informed by hermeneutic phenomenology generated themes and contextualized meanings regarding the participants'…

  16. The Unfinished Nature of Rights-Informed HIV- and AIDS-Related Education: An Analysis of Three School-Based Initiatives

    ERIC Educational Resources Information Center

    Miedema, Esther; Maxwell, Claire; Aggleton, Peter

    2015-01-01

    Over the past 25 years, there has been growing investment in concepts of rights in the areas of HIV prevention, care and treatment, including HIV- and AIDS-related education delivered in schools. Despite this increasing commitment to the notion of rights, few efforts appear to have been made to understand the varying conceptions of rights that…

  17. Autograft HIV-DNA Load Predicts HIV-1 Peripheral Reservoir After Stem Cell Transplantation for AIDS-Related Lymphoma Patients

    PubMed Central

    Bortolin, Maria Teresa; Pratesi, Chiara; Tedeschi, Rosamaria; Basaglia, Giancarlo; Abbruzzese, Luciano; Mazzucato, Mario; Spina, Michele; Vaccher, Emanuela; Tirelli, Umberto; Rupolo, Maurizio; Michieli, Mariagrazia; Di Mascio, Michele; De Paoli, Paolo

    2015-01-01

    Abstract Autologous stem cell transplantation (ASCT) is a widely used procedure for AIDS-related lymphomas, and it represents an opportunity to evaluate strategies curing HIV-1 infection. The association of autograft HIV-DNA load with peripheral blood HIV-1 reservoir before ASCT and its contribution in predicting HIV-1 reservoir size and stability during combination antiretroviral therapy (cART) after transplantation are unknown. Aiming to obtain information suggesting new functional cure strategies by ASCT, we retrospectively evaluated HIV-DNA load in autograft and in peripheral blood before and after transplantation in 13 cART-treated HIV-1 relapse/refractoring lymphoma patients. Among them seven discontinued cART after autograft infusion. HIV-DNA was evaluated by a sensitive quantitative real-time polymerase chain reaction (PCR). After debulking chemotherapy/mobilization, the autograft HIV-1 reservoir was higher than and not associated with the peripheral HIV-1 reservoir at baseline [median 215 HIV-DNA copies/106 autograft mononuclear cells, range 13–706 vs. 82 HIV-DNA copies/106 peripheral blood mononuclear cells (PBMCs), range 13–479, p=0.03]. After high dose chemotherapy and autograft infusion, HIV-DNA levels reached a plateau between month 6 and 12 of follow-up. No association was found between peripheral HIV-DNA levels at baseline and after infusion in both cART interrupting and not interrupting patients. Only in the last subgroup, a stable significant linear association between autograft and peripheral blood HIV-1 reservoir emerged from month 1 (R2=0.84, p=0.01) to month 12 follow-up (R2=0.99, p=0.0005). In summary, autograft HIV-1 reservoir size could be influenced by the mobilization phase and predicts posttransplant peripheral HIV-1 reservoir size in patients on continuous cART. These findings could promote new research on strategies reducing the HIV-1 reservoir by using the ASCT procedure. PMID:25581618

  18. Risk factors for HIV infection in male sexual contacts of men with AIDS or an AIDS-related condition.

    PubMed

    Coates, R A; Calzavara, L M; Read, S E; Fanning, M M; Shepherd, F A; Klein, M H; Johnson, J K; Soskolne, C L

    1988-10-01

    A total of 246 healthy male sexual contacts of men with either acquired immunodeficiency syndrome (AIDS) or an AIDS-related condition were recruited into a prospective study in Toronto, Canada between July 1984 and July 1985. At induction, data were collected on the sexual relationship between the contact and his primary case, sexual activities with other men, history of sexually transmitted diseases and other diseases, and use of recreational drugs. At recruitment, 144 sexual contacts had antibodies to human immunodeficiency virus (HIV); 102 of the contacts were seronegative at induction and at three months following recruitment. No association between HIV seropositivity and total number of sexual partners could be demonstrated. In univariate and multivariate analyses, receptive and insertive anal intercourse with the primary cases, and activities which either indicated or potentially caused anorectal mucosal injury (rectal douching, perianal bleeding, receipt of objects in ano, and receptive fisting) were strongly associated with HIV seropositivity. In the final multiple logistic regression model, two significant interaction effects were observed: the interaction between receptive anal intercourse and insertive anal intercourse and that between receptive anal intercourse and the anorectal mucosal injury index. These two interaction terms had negative regression coefficients which suggested that change in one sexual activity would not decrementally reduce risk of HIV infection without a comparable modification in the other activity. No association could be demonstrated between oral-genital and oral-anal sexual contact and odds ratios for these sexual activities declined to levels below 1.0 when adjusted for frequency of receptive anal intercourse. PMID:3421239

  19. Fulminant inflammatory leukoencephalopathy associated with HAART-induced immune restoration in AIDS-related progressive multifocal leukoencephalopathy.

    PubMed

    Vendrely, Aurélie; Bienvenu, Boris; Gasnault, Jacques; Thiebault, Jean Baptiste; Salmon, Dominique; Gray, Françoise

    2005-04-01

    HAART-induced immune restoration is beneficial for patients with AIDS-related progressive multifocal leukoencephalopathy (PML). However, in rare instances, an immune-reconstitution inflammatory syndrome (IRIS) may cause paradoxical clinical deterioration. We report the neuropathological study of an AIDS patient who presented with progressive cognitive deterioration; CD4(+) count was 117 and the HIV viral load >10(4); imaging showed non-enhancing lesions consistent with PML. Following initiation of HAART, CD4(+) was 300 and HIV viral load <10(3), but his neurological symptoms continued to deteriorate. Imaging revealed an increase in the size and number of lesions and enhancement of all the lesions. A stereotactic biopsy showed severe inflammatory and demyelinating lesions with marked infiltration by macrophages and T lymphocytes in the absence of a detectable infectious agent. Despite high doses of steroids, the patient died 3 months after admission. Autopsy showed two types of lesions: (1) active inflammatory PML changes with abundant JC virus, and intraparenchymal and perivascular infiltration by T lymphocytes, and (2) acute perivenous leukoencephalitis devoid of JC virus. Most lymphocytes were CD8(+) lymphocytes; CD4(+) lymphocytes were virtually absent. Two pathological reactions were associated with the paradoxical clinical deterioration related to dysregulation of the immune response characteristic of IRIS in PML: (1) an accentuation of JCV infection, and (2) a nonspecific acute perivenous leukoencephalitis. We suggest that both these types of lesions are due to an imbalance of CD8(+)/CD4(+) T cells, with massive infiltration of the cerebral parenchyma by CD8(+) cytotoxic T lymphocytes in the absence of sufficient CD4(+) response. Better understanding of the mechanisms of the IRIS may enable prevention or cure of this severe, sometimes fatal complication of HAART. PMID:15739098

  20. Diffuse X-ray emission from the NGC 2300 group of galaxies - Implications for dark matter and galaxy evolution in small groups

    NASA Technical Reports Server (NTRS)

    Mulchaey, John S.; Davis, David S.; Mushotzky, Richard F.; Burstein, David

    1993-01-01

    The discovery of diffuse X-ray emission from the NGC 2300 group of galaxies using the ROSAT Position Sensitive Proportional Counter is reported. The gas distributions is roughly symmetric and extends to a radius of at least 0.2/h(50) Mpc. A Raymond-Smith hot plasma model provides an excellent fit the X-ray spectrum with a best-fit value temperature of 0.9 + -/15 or - 0.14 keV and abundance 0.06 + 0/.12 or - 0.05 solar. The assumption of gravitational confinement leads to a total mass of the group of 3.0 + 0.4 or - 0.5 x 10 exp 13 solar. Baryons can reasonably account for 4 percent of this mass, and errors could push this number not higher than 10-15 percent. This is one of the strongest pieces of evidence that dark matter dominates small groups such as this one. The intragroup medium in this system has the lowest metal abundance yet found in diffuse gas in a group or cluster.

  1. Severe Left Ventricular Hypertrophy, Small Pericardial Effusion, and Diffuse Late Gadolinium Enhancement by Cardiac Magnetic Resonance Suspecting Cardiac Amyloidosis: Endomyocardial Biopsy Reveals an Unexpected Diagnosis

    PubMed Central

    Hofmann, Nina P.; Giusca, Sorin; Klingel, Karin; Nunninger, Peter; Korosoglou, Grigorios

    2016-01-01

    Left ventricular (LV) hypertrophy can be related to a multitude of cardiac disorders, such as hypertrophic cardiomyopathy (HCM), cardiac amyloidosis, and hypertensive heart disease. Although the presence of LV hypertrophy is generally associated with poorer cardiac outcomes, the early differentiation between these pathologies is crucial due to the presence of specific treatment options. The diagnostic process with LV hypertrophy requires the integration of clinical evaluation, electrocardiography (ECG), echocardiography, biochemical markers, and if required CMR and endomyocardial biopsy in order to reach the correct diagnosis. Here, we present a case of a patient with severe LV hypertrophy (septal wall thickness of 23 mm, LV mass of 264 g, and LV mass index of 147 g/m2), severely impaired longitudinal function, and preserved radial contractility (ejection fraction = 55%), accompanied by small pericardial effusion and diffuse late gadolinium enhancement (LGE) by cardiac magnetic resonance (CMR). Due to the imaging findings, an infiltrative cardiomyopathy, such as cardiac amyloidosis, was suspected. However, amyloid accumulation was excluded by endomyocardial biopsy, which revealed the presence of diffuse myocardial fibrosis in an advanced hypertensive heart disease. PMID:27247807

  2. Autograft HIV-DNA load predicts HIV-1 peripheral reservoir after stem cell transplantation for AIDS-related lymphoma patients.

    PubMed

    Zanussi, Stefania; Bortolin, Maria Teresa; Pratesi, Chiara; Tedeschi, Rosamaria; Basaglia, Giancarlo; Abbruzzese, Luciano; Mazzucato, Mario; Spina, Michele; Vaccher, Emanuela; Tirelli, Umberto; Rupolo, Maurizio; Michieli, Mariagrazia; Di Mascio, Michele; De Paoli, Paolo

    2015-01-01

    Autologous stem cell transplantation (ASCT) is a widely used procedure for AIDS-related lymphomas, and it represents an opportunity to evaluate strategies curing HIV-1 infection. The association of autograft HIV-DNA load with peripheral blood HIV-1 reservoir before ASCT and its contribution in predicting HIV-1 reservoir size and stability during combination antiretroviral therapy (cART) after transplantation are unknown. Aiming to obtain information suggesting new functional cure strategies by ASCT, we retrospectively evaluated HIV-DNA load in autograft and in peripheral blood before and after transplantation in 13 cART-treated HIV-1 relapse/refractoring lymphoma patients. Among them seven discontinued cART after autograft infusion. HIV-DNA was evaluated by a sensitive quantitative real-time polymerase chain reaction (PCR). After debulking chemotherapy/mobilization, the autograft HIV-1 reservoir was higher than and not associated with the peripheral HIV-1 reservoir at baseline [median 215 HIV-DNA copies/10(6) autograft mononuclear cells, range 13-706 vs. 82 HIV-DNA copies/10(6) peripheral blood mononuclear cells (PBMCs), range 13-479, p = 0.03]. After high dose chemotherapy and autograft infusion, HIV-DNA levels reached a plateau between month 6 and 12 of follow-up. No association was found between peripheral HIV-DNA levels at baseline and after infusion in both cART interrupting and not interrupting patients. Only in the last subgroup, a stable significant linear association between autograft and peripheral blood HIV-1 reservoir emerged from month 1 (R(2) = 0.84, p = 0.01) to month 12 follow-up (R(2) = 0.99, p = 0.0005). In summary, autograft HIV-1 reservoir size could be influenced by the mobilization phase and predicts posttransplant peripheral HIV-1 reservoir size in patients on continuous cART. These findings could promote new research on strategies reducing the HIV-1 reservoir by using the ASCT procedure. PMID:25581618

  3. Noise characteristics of centrifugal blower with low solidity cascade diffuser (Noise reduction by means of small groove located at LSD blade leading tip)

    NASA Astrophysics Data System (ADS)

    Murakami, Tengen; Ishida, Masahiro; Sakaguchi, Daisaku; Koba, Yu

    2009-12-01

    This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blower characteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near the leading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reduce the noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondary flow formed additionally by the tip-groove were investigated experimentally as well as numerically, especially analyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD blade and the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of the LSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, the noise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove located only at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced without deteriorations of the LSD performance and the blower characteristics as well.

  4. The influence of personality disorder indication, social support, and grief on alcohol and cocaine use among HIV-positive adults coping with AIDS-related bereavement.

    PubMed

    Hansen, Nathan B; Cavanaugh, Courtenay E; Vaughan, Ellen L; Connell, Christian M; Tate, David C; Sikkema, Kathleen J

    2009-04-01

    Substance use is prevalent among HIV-positive adults and linked to a number of adverse health consequences; however little is known about risk and protective factors that influence substance use among HIV-positive adults coping with AIDS-related bereavement. Using structural equation modeling (SEM), male gender, diagnostic indications of antisocial and borderline personality disorders (PD), and grief severity were tested as risk factors, and social support as a protective factor, for alcohol and cocaine use among a diverse sample of 268 HIV-positive adults enrolled in an intervention for AIDS-related bereavement. Results indicated that the hypothesized model fit the study data. Male gender, PD indication, and social support had direct effects on substance use. PD had significant indirect effects on both alcohol and cocaine use, mediated by social support, but not by grief. Finally, both PD and social support had significant, but opposite, effects on grief. Implications for intervention and prevention efforts are discussed. PMID:17846878

  5. Diagnostic Utility of Diffusion-weighted Magnetic Resonance Imaging in Differentiating Small Solid Renal Tumors (≤4 cm) at 3.0T Magnetic Resonance Imaging

    PubMed Central

    Zhang, Han-Mei; Wu, Ying-Hua; Gan, Qi; Lyu, Xiao; Zhu, Xiang-Lan; Kuang, Min; Liu, Rong-Bo; Huang, Zi-Xing; Yuan, Fang; Liu, Xi-Jiao; Song, Bin

    2015-01-01

    Background: The aim of this study was to assess the performance of apparent diffusion coefficient (ADC) measurement obtained with diffusion-weighted magnetic resonance imaging (DW-MRI) to distinguish renal cell carcinomas (RCCs) from small benign solid renal tumors (≤4 cm). Methods: In this cross-sectional study, 49 consecutive patients with histopathologically confirmed small solid renal tumors, and seven healthy volunteers were imaged using nonenhanced MRI and DW-MRI. The ADC map was calculated using the b values of 0, 50, 400, and 600 s/mm2 and values compared via the Kruskal–Wallis and Mann–Whitney tests. The utility of ADC for differentiating RCCs and benign lesions was assessed using a receiver operating characteristic curve. Multiple nonenhanced MRI features were analyzed by Logistic regression. Results: The tumors consisted of 33 cases of clear-cell RCCs (ccRCCs) and 16 cases of benign tumors, including 14 cases of minimal fat angiomyolipomas and 2 cases of oncocytomas. The ADCs showed significant differences among benign tumors ([0.90 ± 0.52] × 10−3 mm2/s), ccRCCs ([1.53 ± 0.31] × 10−3 mm2/s) and the normal renal parenchyma ([2.22 ± 0.12] × 10−3 mm2/s) (P < 0.001). Moreover, there was statistically significant difference between high and low-grade ccRCCs (P = 0.004). Using a cut-off ADC of 1.36 × 10−3 mm2/s, DW-MRI resulted in an area under the curve (AUC), sensitivity, and specificity equal to 0.839, 75.8%, and 87.5%, respectively. Nonenhanced MRI alone and the combination of imaging methods led to an AUC, sensitivity and specificity equal to 0.919, 93.9%, and 81.2%, 0.998, 97%, and 100%, respectively. The Logistic regression showed that the location of the center of the tumor (inside the contour of the kidney) and appearance of stiff blood vessel were significantly helpful for diagnosing ccRCCs. Conclusions: DW-MRI has potential in distinguishing ccRCCs from benign lesions in human small solid renal tumors (≤4 cm), and in

  6. A comparison of HIV/AIDS-related stigma in four countries: Negative attitudes and perceived acts of discrimination towards people living with HIV/AIDS☆

    PubMed Central

    Genberg, Becky L.; Hlavka, Zdenek; Konda, Kelika A.; Maman, Suzanne; Chariyalertsak, Suwat; Chingono, Alfred; Mbwambo, Jessie; Modiba, Precious; Van Rooyen, Heidi; Celentano, David D.

    2010-01-01

    HIV/AIDS-related stigma and discrimination have a substantial impact on people living with HIV/AIDS (PLHA). The objectives of this study were: (1) to determine the associations of two constructs of HIV/AIDS-related stigma and discrimination (negative attitudes towards PLHA and perceived acts of discrimination towards PLHA) with previous history of HIV testing, knowledge of antiretroviral therapies (ARVs) and communication regarding HIV/AIDS and (2) to compare these two constructs across the five research sites with respect to differing levels of HIV prevalence and ARV coverage, using data presented from the baseline survey of U.S. National Institute of Mental Health (NIMH) Project Accept, a four-country HIV prevention trial in Sub-Saharan Africa (Tanzania, Zimbabwe and South Africa) and northern Thailand. A household probability sample of 14,203 participants completed a survey including a scale measuring HIV/AIDS-related stigma and discrimination. Logistic regression models determined the associations between negative attitudes and perceived discrimination with individual history of HIV testing, knowledge of ARVs and communication regarding HIV/AIDS. Spearman's correlation coefficients determined the relationships between negative attitudes and perceived discrimination and HIV prevalence and ARV coverage at the site-level. Negative attitudes were related to never having tested for HIV, lacking knowledge of ARVs, and never having discussed HIV/AIDS. More negative attitudes were found in sites with the lowest HIV prevalence (i.e., Tanzania and Thailand) and more perceived discrimination against PLHA was found in sites with the lowest ARV coverage (i.e., Tanzania and Zimbabwe). Programs that promote widespread HIV testing and discussion of HIV/AIDS, as well as education regarding and universal access to ARVs, may reduce HIV/AIDS-related stigma and discrimination. PMID:19427086

  7. Validity and Reliability of Persian Version of HIV/AIDS Related Stigma Scale for People Living With HIV/AIDS in Iran

    PubMed Central

    Pourmarzi, Davoud; Khoramirad, Ashraf; Ahmari Tehran, Hoda; Abedini, Zahra

    2015-01-01

    Objective: To assess the perceived HIV/AIDS related stigma a comprehensive and well developed stigma instrument is necessary. This study aimed to assess validity and reliability of the Persian version of HIV/AIDS related stigma scale which was developed by Kang et al for people living with HIV/AIDS in Iran. Materials and methods: Thescale was forward translatedby two bilingual academic members then both translations were discussed by expert team. Back-translation was done by two other bilingual translators then we carried out discussion with both of them. To evaluate understandability the scale was administered to 10 Persons Living with HIV/AIDS (PLWHA). Final Persian version was administered to 80 PLWHA in Qom, Iran in 2014. Test–retest reliability was assessed in a sample of 20 PLWHA after a week by intra-class correlation coefficient (ICC). Results: Cronbach’s alpha coefficient for overall scale was 0.85. Also Cronbach’s alpha coefficients for the five subscales were as follows: social rejection (9 items, α = 0.84), negative self-worth (4 items, α = 0.70), perceived interpersonal insecurity (2 items, α = 0.57), financial insecurity (3 items, α = 0.70), discretionary disclosure (2 items, α = 0.83). Test–retest reliability was also approved with ICC = 0.78. Correlation between items and their hypothesized subscale is greater than 0.5. Correlation between an item and its own subscale was significantly higher than its correlation with other subscales. Conclusion: This study demonstrate that the Persian version of HIV/AIDS related stigma scale is valid and reliable to assess HIV/AIDS related stigma perceived by people living whit HIV/AIDS in Iran. PMID:27047562

  8. A comparison of HIV/AIDS-related stigma in four countries: negative attitudes and perceived acts of discrimination towards people living with HIV/AIDS.

    PubMed

    Genberg, Becky L; Hlavka, Zdenek; Konda, Kelika A; Maman, Suzanne; Chariyalertsak, Suwat; Chingono, Alfred; Mbwambo, Jessie; Modiba, Precious; Van Rooyen, Heidi; Celentano, David D

    2009-06-01

    HIV/AIDS-related stigma and discrimination have a substantial impact on people living with HIV/AIDS (PLHA). The objectives of this study were: (1) to determine the associations of two constructs of HIV/AIDS-related stigma and discrimination (negative attitudes towards PLHA and perceived acts of discrimination towards PLHA) with previous history of HIV testing, knowledge of antiretroviral therapies (ARVs) and communication regarding HIV/AIDS and (2) to compare these two constructs across the five research sites with respect to differing levels of HIV prevalence and ARV coverage, using data presented from the baseline survey of U.S. National Institute of Mental Health (NIMH) Project Accept, a four-country HIV prevention trial in Sub-Saharan Africa (Tanzania, Zimbabwe and South Africa) and northern Thailand. A household probability sample of 14,203 participants completed a survey including a scale measuring HIV/AIDS-related stigma and discrimination. Logistic regression models determined the associations between negative attitudes and perceived discrimination with individual history of HIV testing, knowledge of ARVs and communication regarding HIV/AIDS. Spearman's correlation coefficients determined the relationships between negative attitudes and perceived discrimination and HIV prevalence and ARV coverage at the site-level. Negative attitudes were related to never having tested for HIV, lacking knowledge of ARVs, and never having discussed HIV/AIDS. More negative attitudes were found in sites with the lowest HIV prevalence (i.e., Tanzania and Thailand) and more perceived discrimination against PLHA was found in sites with the lowest ARV coverage (i.e., Tanzania and Zimbabwe). Programs that promote widespread HIV testing and discussion of HIV/AIDS, as well as education regarding and universal access to ARVs, may reduce HIV/AIDS-related stigma and discrimination. PMID:19427086

  9. A qualitative analysis of barriers to accessing HIV/AIDS-related services among newly diagnosed HIV-positive men who have sex with men in China.

    PubMed

    Li, Haochu Howard; Holroyd, Eleanor; Li, Xiaoming; Lau, Joseph

    2015-01-01

    In China, specific HIV/AIDS-related services have been in place since 2004. However, utilisation of these services remains limited among people living with HIV. We explored barriers to accessing HIV/AIDS-related services from the perspective of newly diagnosed HIV-positive men who have sex with men. We conducted repeated in-depth interviews with 31 newly diagnosed HIV-positive men who have sex with men, using the socio-ecological framework and thematic content analysis. Multiple barriers for utilisation of HIV/AIDS-related services were identified, including perceptions of subjective health and poor quality of services, mental and emotional health problems, lack of trust and understanding of the services on offer, low economic status, lack of insurance, and high medical fees, being refused access to services, and restrictive attendance policies. The findings provide information on potential multi-level obstacles preventing newly diagnosed HIV-positive men who have sex with men to use services that they need. It is recommended that policy makers should create a trustful and non-discriminating environment and services integrating physical and mental healthcare. PMID:24626063

  10. Structure and phase diagram of an adhesive colloidal dispersion under high pressure: A small angle neutron scattering, diffusing wave spectroscopy, and light scattering study

    NASA Astrophysics Data System (ADS)

    Vavrin, R.; Kohlbrecher, J.; Wilk, A.; Ratajczyk, M.; Lettinga, M. P.; Buitenhuis, J.; Meier, G.

    2009-04-01

    We have applied small angle neutron scattering (SANS), diffusing wave spectroscopy (DWS), and dynamic light scattering (DLS) to investigate the phase diagram of a sterically stabilized colloidal system consisting of octadecyl grafted silica particles dispersed in toluene. This system is known to exhibit gas-liquid phase separation and percolation, depending on temperature T, pressure P, and concentration φ. We have determined by DLS the pressure dependence of the coexistence temperature and the spinodal temperature to be dP /dT=77 bar/K. The gel line or percolation limit was measured by DWS under high pressure using the condition that the system became nonergodic when crossing it and we determined the coexistence line at higher volume fractions from the DWS limit of turbid samples. From SANS measurements we determined the stickiness parameter τB(P,T,φ) of the Baxter model, characterizing a polydisperse adhesive hard sphere, using a global fit routine on all curves in the homogenous regime at various temperatures, pressures, and concentrations. The phase coexistence and percolation line as predicted from τB(P,T,φ) correspond with the determinations by DWS and were used to construct an experimental phase diagram for a polydisperse sticky hard sphere model system. A comparison with theory shows good agreement especially concerning the predictions for the percolation threshold. From the analysis of the forward scattering we find a critical scaling law for the susceptibility corresponding to mean field behavior. This finding is also supported by the critical scaling properties of the collective diffusion.

  11. Vorinostat and Combination Chemotherapy With Rituximab in Treating Patients With HIV-Related Diffuse Large B-Cell Non-Hodgkin Lymphoma or Other Aggressive B-Cell Lymphomas

    ClinicalTrials.gov

    2016-09-08

    AIDS-Related Diffuse Large Cell Lymphoma; AIDS-Related Plasmablastic Lymphoma; AIDS-Related Primary Effusion Lymphoma; Grade 3b Follicular Lymphoma; HIV Infection; Plasmablastic Lymphoma; Primary Effusion Lymphoma; Recurrent Adult Diffuse Large Cell Lymphoma; Recurrent Grade 3 Follicular Lymphoma; Stage I Adult Diffuse Large Cell Lymphoma; Stage I Grade 3 Follicular Lymphoma; Stage II Contiguous Adult Diffuse Large Cell Lymphoma; Stage II Grade 3 Contiguous Follicular Lymphoma; Stage II Grade 3 Non-Contiguous Follicular Lymphoma; Stage II Non-Contiguous Adult Diffuse Large Cell Lymphoma; Stage III Adult Diffuse Large Cell Lymphoma; Stage III Grade 3 Follicular Lymphoma; Stage IV Adult Diffuse Large Cell Lymphoma; Stage IV Grade 3 Follicular Lymphoma

  12. Individual attitudes and perceived social norms: Reports on HIV/AIDS-related stigma among service providers in China

    PubMed Central

    Li, Li; Liang, Li-Jung; Wu, Zunyou; Lin, Chunqing; Wen, Yi

    2009-01-01

    This study examined HIV/AIDS-related stigma among Chinese service providers by comparing their personal attitudes toward people living with HIV/AIDS with their perception of social norms related to people living with HIV/AIDS. We randomly selected three provincial hospitals, four city/prefecture hospitals, 10 county hospitals, 18 township health clinics, and 54 village clinics from Yunnan, China. Doctors and nurses were randomly sampled proportionally to the doctor-nurse ratio of each hospital or clinic. Lab technicians were over-sampled in order to include an adequate representation in the analysis. A total of 1,101 service providers participated in a voluntary, anonymous survey where demographic characteristics, individual attitude and perceived social norms toward people living with HIV/AIDS, discrimination intent at work, general prejudicial attitude and knowledge on HIV/AIDS were measured. A majority of the sample demonstrated a similarity between their personal views and what they thought most people in society believe. Multiple logistic regressions revealed that participants who were younger or reported personal contact with people living with HIV/AIDS were significantly more likely to report personal attitudes toward the population that were more liberal than their perceived social norms. Holding a more liberal personal attitude toward people living with HIV/AIDS than perceived social norms was significantly and negatively related to the level of discrimination intent at work, perceived discrimination at interpersonal level and the level of general prejudicial attitude toward people living with HIV/AIDS. Results underscored the importance of understanding social norms and personal attitudes in studying HIV-related stigma and called for the incorporation of existing human capital into future HIV stigma reduction programs. Cette étude a examiné le VIH/SIDA lié à stigmatisation parmi les agences chinoises fournissant des soins en comparant leurs attitudes

  13. Closed-form solution for the Wigner phase-space distribution function for diffuse reflection and small-angle scattering in a random medium.

    PubMed

    Yura, H T; Thrane, L; Andersen, P E

    2000-12-01

    Within the paraxial approximation, a closed-form solution for the Wigner phase-space distribution function is derived for diffuse reflection and small-angle scattering in a random medium. This solution is based on the extended Huygens-Fresnel principle for the optical field, which is widely used in studies of wave propagation through random media. The results are general in that they apply to both an arbitrary small-angle volume scattering function, and arbitrary (real) ABCD optical systems. Furthermore, they are valid in both the single- and multiple-scattering regimes. Some general features of the Wigner phase-space distribution function are discussed, and analytic results are obtained for various types of scattering functions in the asymptotic limit s > 1, where s is the optical depth. In particular, explicit results are presented for optical coherence tomography (OCT) systems. On this basis, a novel way of creating OCT images based on measurements of the momentum width of the Wigner phase-space distribution is suggested, and the advantage over conventional OCT images is discussed. Because all previous published studies regarding the Wigner function are carried out in the transmission geometry, it is important to note that the extended Huygens-Fresnel principle and the ABCD matrix formalism may be used successfully to describe this geometry (within the paraxial approximation). Therefore for completeness we present in an appendix the general closed-form solution for the Wigner phase-space distribution function in ABCD paraxial optical systems for direct propagation through random media, and in a second appendix absorption effects are included. PMID:11140505

  14. A multi-view time-domain non-contact diffuse optical tomography scanner with dual wavelength detection for intrinsic and fluorescence small animal imaging

    NASA Astrophysics Data System (ADS)

    Lapointe, Eric; Pichette, Julien; Bérubé-Lauzière, Yves

    2012-06-01

    We present a non-contact diffuse optical tomography (DOT) scanner with multi-view detection (over 360°) for localizing fluorescent markers in scattering and absorbing media, in particular small animals. It relies on time-domain detection after short pulse laser excitation. Ultrafast time-correlated single photon counting and photomultiplier tubes are used for time-domain measurements. For light collection, seven free-space optics non-contact dual wavelength detection channels comprising 14 detectors overall are placed around the subject, allowing the measurement of time point-spread functions at both excitation and fluorescence wavelengths. The scanner is endowed with a stereo camera pair for measuring the outer shape of the subject in 3D. Surface and DOT measurements are acquired simultaneously with the same laser beam. The hardware and software architecture of the scanner are discussed. Phantoms are used to validate the instrument. Results on the localization of fluorescent point-like inclusions immersed in a scattering and absorbing object are presented. The localization algorithm relies on distance ranging based on the measurement of early photons arrival times at different positions around the subject. This requires exquisite timing accuracy from the scanner. Further exploiting this capability, we show results on the effect of a scattering hetereogenity on the arrival time of early photons. These results demonstrate that our scanner provides all that is necessary for reconstructing images of small animals using full tomographic reconstruction algorithms, which will be the next step. Through its free-space optics design and the short pulse laser used, our scanner shows unprecedented timing resolution compared to other multi-view time-domain scanners.

  15. A multi-view time-domain non-contact diffuse optical tomography scanner with dual wavelength detection for intrinsic and fluorescence small animal imaging.

    PubMed

    Lapointe, Eric; Pichette, Julien; Bérubé-Lauzière, Yves

    2012-06-01

    We present a non-contact diffuse optical tomography (DOT) scanner with multi-view detection (over 360°) for localizing fluorescent markers in scattering and absorbing media, in particular small animals. It relies on time-domain detection after short pulse laser excitation. Ultrafast time-correlated single photon counting and photomultiplier tubes are used for time-domain measurements. For light collection, seven free-space optics non-contact dual wavelength detection channels comprising 14 detectors overall are placed around the subject, allowing the measurement of time point-spread functions at both excitation and fluorescence wavelengths. The scanner is endowed with a stereo camera pair for measuring the outer shape of the subject in 3D. Surface and DOT measurements are acquired simultaneously with the same laser beam. The hardware and software architecture of the scanner are discussed. Phantoms are used to validate the instrument. Results on the localization of fluorescent point-like inclusions immersed in a scattering and absorbing object are presented. The localization algorithm relies on distance ranging based on the measurement of early photons arrival times at different positions around the subject. This requires exquisite timing accuracy from the scanner. Further exploiting this capability, we show results on the effect of a scattering hetereogenity on the arrival time of early photons. These results demonstrate that our scanner provides all that is necessary for reconstructing images of small animals using full tomographic reconstruction algorithms, which will be the next step. Through its free-space optics design and the short pulse laser used, our scanner shows unprecedented timing resolution compared to other multi-view time-domain scanners. PMID:22755630

  16. NOTCH1, TP53, and MAP2K1 Mutations in Splenic Diffuse Red Pulp Small B-cell Lymphoma Are Associated With Progressive Disease.

    PubMed

    Martinez, Daniel; Navarro, Alba; Martinez-Trillos, Alejandra; Molina-Urra, Ricardo; Gonzalez-Farre, Blanca; Salaverria, Itziar; Nadeu, Ferran; Enjuanes, Anna; Clot, Guillem; Costa, Dolors; Carrio, Ana; Villamor, Neus; Colomer, Dolors; Martinez, Antonio; Bens, Susanne; Siebert, Reiner; Wotherspoon, Andrew; Beà, Sílvia; Matutes, Estella; Campo, Elias

    2016-02-01

    Splenic diffuse red pulp small B-cell lymphoma (SDRPL) is considered an indolent neoplasm and its pathogenesis is not well known. We investigated the molecular characteristics of 19 SDRPL patients, 5 of them with progressive disease. IGHV genes were mutated in 9/13 (69%). Cytogenetic and molecular studies identified complex karyotypes in 2 cases, and IGH rearrangements in 3, with PAX5 and potentially TCL1 as partners in each one of them. Copy number arrays showed aberrations in 69% of the tumors, including recurrent losses of 10q23, 14q31-q32, and 17p13 in 3, and 9p21 in 2 cases. Deletion of 7q31.3-q32.3 was present in only 1 case and no trisomies 3 or 18 were detected. NOTCH1 and MAP2K1 were mutated in 2 cases each, whereas BRAF, TP53, and SF3B1 were mutated each in single cases. No mutations were found in NOTCH2 or MYD88. Four of the 5 patients with aggressive disease had mutations in NOTCH1 (2 cases), TP53 (1 case), and MAP2K1 (1 case). The progression-free survival of patients with mutated genes was significantly shorter than in the unmutated (P=0.011). These findings show that SDRPL share some mutated genes but not chromosomal alterations, with other splenic lymphomas, that may confer a more aggressive behavior. PMID:26426381

  17. Six minute walking test and carbon monoxide diffusing capacity for non-small cell lung cancer: easy performed tests in every day practice

    PubMed Central

    Kerenidi, Theodora; Huang, Haidong; Kontakiotis, Theodoros; Tremma, Ourania; Porpodis, Konstantinos; Kalianos, Anastasios; Rapti, Ageliki; Foroulis, Christoforos; Zissimopoulos, Athanasios; Courcoutsakis, Nikolaos; Zarogoulidis, Konstantinos

    2012-01-01

    Background Several studies have demonstrated that reduced lung function is a significant risk factor for lung cancer and increased surgical risk in patients with operable stages of lung cancer. The aim of the study was to perform pulmonary function tests and investigate which is a favorable respiratory function test for overall survival between lung cancer stages. Methods Lung function tests were performed to lung cancer patients with non-small cell lung cancer of stage I, II, III and IV (241 patients in total). They had the last follow-up consecutively between December 2006 and July 2008. The staging was decided according to the sixth edition of TNM classification of NSCLC. The Forced Expiratory Volume in 1sec (FEV1), Forced Vital Capacity (FVC) and Carbon Monoxide Diffusing Capacity (DLCO) were measured according to American Thoracic Society/European Respiratory Society guidelines. The 6 Minute Walking Test (6MWT) was measured according to the American Thoracic Society. Results There was a significant association of the DLCO upon diagnosis and overall survival for stage II (P<0.007) and IV (P<0.003). Furthermore, there was a significant association between 6MWT and overall survival for stage III (P<0.001) and stage IV (P<0.010). Conclusions The significance for each lung function test is different among the stages of NSCLC. DLCO and 6MWT upon admission are the most valuable prognostic factors for overall survival of NSCLC. PMID:23205280

  18. Erratum for the Appendix of "Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo (NOGSE) NMR" [J. Magn. Reson. 247 (2014) 110

    NASA Astrophysics Data System (ADS)

    Shemesh, Noam; Álvarez, Gonzalo A.; Frydman, Lucio

    2015-05-01

    This corrects a typo of Eq. (A4) in the Erratum [J. Magn. Reson. 247 (2014) 110] for the Appendix of "Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo (NOGSE) NMR". The Erratum should have read as follow:

  19. Estimation of optimal b-value sets for obtaining apparent diffusion coefficient free from perfusion in non-small cell lung cancer

    NASA Astrophysics Data System (ADS)

    Karki, Kishor; Hugo, Geoffrey D.; Ford, John C.; Olsen, Kathryn M.; Saraiya, Siddharth; Groves, Robert; Weiss, Elisabeth

    2015-10-01

    The purpose of this study was to determine optimal sets of b-values in diffusion-weighted MRI (DW-MRI) for obtaining monoexponential apparent diffusion coefficient (ADC) close to perfusion-insensitive intravoxel incoherent motion (IVIM) model ADC (ADCIVIM) in non-small cell lung cancer. Ten subjects had 40 DW-MRI scans before and during radiotherapy in a 1.5 T MRI scanner. Respiratory triggering was applied to the echo-planar DW-MRI with \\text{TR}≈ 4500 ms, TE  =  74 ms, eight b-values of 0-1000 μs μm-2, pixel size  =  1.98× 1.98 mm2, slice thickness  =  6 mm, interslice gap  =  1.2 mm, 7 axial slices and total acquisition time ≈6 min. One or more DW-MRI scans together covered the whole tumour volume. Monoexponential model ADC values using various b-value sets were compared to reference-standard ADCIVIM values using all eight b-values. Intra-scan coefficient of variation (CV) of active tumour volumes was computed to compare the relative noise in ADC maps. ADC values for one pre-treatment DW-MRI scan of each of the 10 subjects were computed using b-value pairs from DW-MRI images synthesized for b-values of 0-2000 μs μm-2 from the estimated IVIM parametric maps and corrupted by various Rician noise levels. The square root of mean of squared error percentage (RMSE) of the ADC value relative to the corresponding ADCIVIM for the tumour volume of the scan was computed. Monoexponential ADC values for the b-value sets of 250 and 1000; 250, 500 and 1000; 250, 650 and 1000; 250, 800 and 1000; and 250-1000 μs μm-2 were not significantly different from ADCIVIM values (p>0.05 , paired t-test). Mean error in ADC values for these sets relative to ADCIVIM were within 3.5%. Intra-scan CVs for these sets were comparable to that for ADCIVIM. The monoexponential ADC values for other sets—0-1000 50-1000 100-1000 500-1000 and 250 and 800 μs μm-2 were significantly different from the ADCIVIM values. From Rician noise simulation

  20. Effect of media use on HIV/AIDS-related knowledge and condom use in sub-Saharan Africa: a cross-sectional study.

    PubMed

    Jung, Minsoo; Arya, Monisha; Viswanath, Kasisomayajula

    2013-01-01

    It is known that the level of HIV/AIDS-related knowledge and the degree of condom use varies by socioeconomic status (SES). However, there is limited research on the effect of mass media use on HIV/AIDS-related cognitive and behavioral outcomes in low-income countries and how it might influence the association between SES and HIV-related outcomes. We investigated the moderating effect of media use on the relationship between SES and HIV/AIDS-related knowledge and condom use in sub-Saharan Africa in terms of communication inequalities. Cross-sectional data from the Demographic Health Surveys from 13 sub-Saharan countries (2004-10) were pooled. Gender-stratified multivariable poisson regression of 151,209 women and 68,890 men were used to calculate adjusted relative ratios and 95% confidence intervals for the associations between SES, media use, HIV-related outcomes, and condom use. We found significant disparities in mass media use among people from different SES groups as well as among countries. Education and wealth are strongly and positively associated with awareness of HIV/AIDS and knowledge about transmission and prevention of HIV/AIDS and are significantly associated with condom use. These associations are attenuated when the use of various types of mass media is added to the models, with newspapers showing the strongest effect. The findings of this study suggest that media use has the potential to blunt the impact of socioeconomic status though not completely eliminate it. Thus, we need to pay attention to reducing communication inequalities among social groups and countries to moderate the effect of wealth and SES on HIV/AIDS. PMID:23874598

  1. Joint derivation method for determining optical properties based on steady-state spatially resolved diffuse reflectance measurement at small source-detector separations and large reduced albedo range: theory and simulation.

    PubMed

    Shi, Zhenzhi; Fan, Ying; Zhao, Huijuan; Xu, Kexin

    2012-06-01

    Accurate determination of the optical properties (the absorption coefficient μ(a) and the reduced scattering coefficient μ(s) (')) of tissues is very important in a variety of diagnostic and therapeutic procedures. Optical diffusion theory is frequently used as the forward model for describing the photon transfer in media with large reduced albedos (a(')) and in large source-detector separations (SDS). Several other methods (PN approximation, hybrid diffusion-P3 approximation) have also been published that describe photon transfer in media with low a(') or small SDSs. We studied the theoretical models for the steady-state spatially resolved diffuse reflectance measurement to accurately determine μ(a) and μ(s) (') at large a(') range but small SDSs. Instead of using a single model, a joint derivation method is proposed. The developed method uses one of the best aforementioned theoretical methods separately in five ranges of a(') determined from several forward models. In the region of small SDSs (the range between 0.4 and 8 mm) and large a(') range (between 0.5 and 0.99), the best theoretical derivation model was determined. The results indicate that the joint derivation method can improve the derivation accuracy and that a(') range can be determined by the steady-state spatially resolved diffuse reflectance measurement. PMID:22734782

  2. Development of EBV-encoded small RNA targeted PCR to classify EBV positive diffuse large B-cell lymphoma (DLBCL) of the elderly

    PubMed Central

    Lee, Jaewang; Park, Min; Lee, Min Ho; Woo, Hyun Jun; Kim, Hyun-Woo; Yang, Ji Yeong; Eom, Yong-Bin; Kim, Sa-Hyun; Yoo, Changyoung; Kim, Jong-Bae

    2015-01-01

    Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma (DLBCL) of the elderly has been included in the 2008 WHO classification of lymphoma as a new provisional entity. EBV-positive DLBCL of the elderly is newly classified due to the main occurrence usually in patients of older than 50-year-old. This study was performed in 91 DLBCL patients from January 2002 to December 2012 in Catholic university of St. Vincent Hospital. Age distribution of the patients was 14~87-year-old. Specimens were collected from lymph nodes (n = 45) and extra-lymph nodes (n = 46). EBV encoded small RNA1 in situ hybridization (EBER1-ISH) known as a standard method for the diagnosis of DLBCL. In this study, nested PCR of DNA polymerase gene and EBER PCR were conducted to detect EBV. Presence of EBV was indicated in 3 samples (3.30%) by EBER-ISH, 26 samples (28.57%) by nPCR, and 3 samples (3.30%) by EBER PCR. The concordant results were obtained from EBER1-ISH and EBER PCR. Two samples were classified as EBV-positive DLBCL of the elderly among 91 DLBCL patients. Previously, the incidence rate of DLBCL of the elderly in Asia has been reported as 5~11%, but the result in this study showed a slightly lower incidence rate. To our knowledge, this is the first report on EBV-positive DLBCL of the elderly in Suwon area, Korea. EBER1-ISH and EBER PCR developed in this study may be helpful in classification of EBV-positive DLBCL of the elderly in future. PMID:26339350

  3. Change in Diffusing Capacity After Radiation as an Objective Measure for Grading Radiation Pneumonitis in Patients Treated for Non-Small-Cell Lung Cancer

    SciTech Connect

    Lopez Guerra, Jose Luis; Gomez, Daniel; Zhuang Yan; Levy, Lawrence B.; Eapen, George; Liu Hongmei; Mohan, Radhe; Komaki, Ritsuko; Cox, James D.; Liao Zhongxing

    2012-08-01

    Purpose: Scoring of radiation pneumonitis (RP), a dose-limiting toxicity after thoracic radiochemotherapy, is subjective and thus inconsistent among studies. Here we investigated whether the extent of change in diffusing capacity of the lung for carbon monoxide (DLCO) after radiation therapy (RT) for non-small-cell lung cancer (NSCLC) could be used as an objective means of quantifying RP. Patients and Methods: We analyzed potential correlations between DLCO and RP in 140 patients who received definitive RT ({>=}60 Gy) with or without chemotherapy for primary NSCLC. All underwent DLCO analysis before and after RT. Post-RT DLCO values within 1 week of the RP diagnosis (Grade 0, 1, 2, or 3) were selected and compared with that individual's preradiation values. Percent reductions in DLCO and RP grade were compared by point biserial correlation in the entire patient group and in subgroups stratified according to various clinical factors. Results: Patients experiencing Grade 0, 1, 2, or 3 RP had median percentage changes in DLCO after RT of 10.7%, 13%, 22.1%, or 35.2%. Percent reduction in DLCO correlated with RP Grade {<=}1 vs. {>=}2 (p = 0.0004). This association held for the following subgroups: age {>=}65 years, advanced stage, smokers, use of chemotherapy, volume of normal lung receiving at least 20 Gy {>=}30%, and baseline DLCO or forced expiratory volume in 1 second {>=}60%. Conclusions: By correlating percent change in DLCO from pretreatment values at the time of diagnosis of RP with RP grade, we were able to identify categories of RP based on the change in DLCO. These criteria provide a basis for an objective scoring system for RP based on change in DLCO.

  4. Multinomial Diffusion Equation

    SciTech Connect

    Balter, Ariel I.; Tartakovsky, Alexandre M.

    2011-06-01

    We have developed a novel stochastic, space/time discrete representation of particle diffusion (e.g. Brownian motion) based on discrete probability distributions. We show that in the limit of both very small time step and large concentration, our description is equivalent to the space/time continuous stochastic diffusion equation. Being discrete in both time and space, our model can be used as an extremely accurate, efficient, and stable stochastic finite-difference diffusion algorithm when concentrations are so small that computationally expensive particle-based methods are usually needed. Through numerical simulations, we show that our method can generate realizations that capture the statistical properties of particle simulations. While our method converges converges to both the correct ensemble mean and ensemble variance very quickly with decreasing time step, but for small concentration, the stochastic diffusion PDE does not, even for very small time steps.

  5. Effect of plasticizers (water and glycerol) on the diffusion of a small molecule in iota-carrageenan biopolymer films for edible coating application.

    PubMed

    Karbowiak, Thomas; Hervet, Hubert; Léger, Liliane; Champion, Dominique; Debeaufort, Frédéric; Voilley, Andrée

    2006-06-01

    Translational diffusion of a fluorescein probe has been measured in iota-carrageenan edible films containing different amounts of glycerol (0, 15, 30, and 45%), using fluorescence recovery after photobleaching (FRAP) experiments. The effects of this plasticizer as well as the plasticizing effect of water on the diffusion of fluorescein have been studied in this edible coating mainly composed of natural biopolymer. Diffusion coefficients of about 10(-13) m2 s(-1) have been measured in these films for water activity (aw) lower than 0.7. Above this water content threshold, fluorescein translational diffusion coefficient increases up to 10(-12) m2 s(-1). Another interesting information obtained from FRAP experiments on this system is the ratio of the diffusing molecules which are immobilized in the carrageenan matrix at aw lower than 0.98. Moreover, films containing more than 30% glycerol (w/w carrageenan) present a huge increase of the diffusion coefficient of fluorescein at high water activity (about 2 orders of magnitude), this effect being less pronounced at low water activity. The increase of diffusion seems to be only related to the water content, and glycerol only acts through the enhancement of water adsorption. Therefore, in biopolymer films containing polyol plasticizers, the gain in mobility could be devoted to the effect of the ubiquitous plasticizing molecule, water, whose adsorption is increased by the plasticizer. PMID:16768427

  6. In-situ small angle x-ray scattering studies of continuous nano-particle synthesis in premixed and diffusion flames

    NASA Astrophysics Data System (ADS)

    Agashe, Nikhil

    Flame technology has proven to be an extremely effective method to synthesize nano-particles of ceramic oxides. The single-step chemistry, the ability to control shape and size and to produce millions of tons of nano-powders per annum with relative ease have made it popular with industry. Although this process primarily focused on oxides of silicon and titanium, it has now been adopted for manufacture of several other oxides of bismuth, vanadium, aluminum, iron, germanium and zirconium. There has been extraordinary progress in the application of flame burner to synthesize new oxides having wide range of particle size, polydispersity, composition and aggregation. But the fundamentals behind the mechanisms for particle formation and growth are still not well understood. Due to the extremely fast rates of reaction, high temperatures and low concentrations associated with this process, it is difficult to accurately observe the formation of nuclei and their growth to form aggregated nano-particles. Entire particle growth from inception to aggregation takes place in a few milliseconds! Light scattering and thermophoretic sampling have been used extensively to study such flames. But light scattering suffers from the brightness of the flame and the limitation on the range of size-scale it can probe. It can only detect aggregates, and information about primary particles needs to be obtained by thermophoretic sampling. However thermophoretic sampling is an intrusive technique and sample collection in the flame involves disturbance of flow dynamics of the gases and the particles in the flame. It is necessary to find a single non-intrusive technique that can give complete information for the flame and handle the fast rates of growth. In-situ small angle x-ray scattering (iSAXS), which utilizes high energy x-rays from synchrotron sources fits such a role perfectly. iSAXS of particles in the flame provides full information from nano-scale to micron-scale and about the evolution

  7. AIDS-related lymphoma. Histopathology, immunophenotype, and association with Epstein-Barr virus as demonstrated by in situ nucleic acid hybridization.

    PubMed Central

    Hamilton-Dutoit, S. J.; Pallesen, G.; Franzmann, M. B.; Karkov, J.; Black, F.; Skinhøj, P.; Pedersen, C.

    1991-01-01

    To investigate the range of pathology shown by acquired immune deficiency syndrome (AIDS)-related lymphomas arising in an epidemiologically well-defined group of patients, all cases of lymphoma recognized in Danish human immunodeficiency virus (HIV)-infected individuals up to the end of 1988 were studied. Twenty-seven cases (26 high-grade non-Hodgkin's lymphoma [NHL], 1 Hodgkin's disease) were found, to give a cumulative incidence rate of 8% among Danish AIDS patients. Morphologically most NHL patients were classified into two groups: 1) high-grade tumors with a predominant population of immunoblasts, either monomorphic or more often polymorphic with plasmacytic differentiation; 2) Burkitt-type. Of 26 NHLs, 22 had a B-cell paraffin-section immunophenotype and 4 were non-B, non-T. Epstein-Barr virus (EBV) DNA was demonstrated in tumor cells of 12 of 24 cases (50%) using in situ nucleic acid hybridization with a 35S-labeled probe in paraffin sections. Epstein-Barr virus DNA was found in 65% of group 1 and 20% of group 2 tumors. This study suggests the existence of two main groups of AIDS-related lymphoma with different pathogeneses. First there are immunoblast-rich lesions, which usually are associated with EBV and morphologically resemble lymphomas described in immunosuppressed organ-transplantation patients. Second there are Burkitt-type tumors in which EBV sequences are less common and that may be pathogenetically analogous to sporadic Burkitt's lymphoma. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 PMID:1846263

  8. Belief in AIDS-Related Conspiracy Theories and Mistrust in the Government: Relationship With HIV Testing Among At-Risk Older Adults

    PubMed Central

    Ford, Chandra L.

    2013-01-01

    Purpose: One in 4 persons living with HIV/AIDS is an older adult (age 50 or older); unfortunately, older adults are disproportionately diagnosed in late stages of HIV disease. Psychological barriers, including belief in AIDS-related conspiracy theories (e.g., HIV was created to eliminate certain groups) and mistrust in the government, may influence whether adults undergo HIV testing. We examined relationships between these factors and recent HIV testing among at-risk, older adults. Design and Methods: This was a cross-sectional study among older adults enrolled in a large venue–based study. None had a previous diagnosis of HIV/AIDS; all were seeking care at venues with high HIV prevalence. We used multiple logistic regression to estimate the associations between self-reported belief in AIDS-related conspiracy theories, mistrust in the government, and HIV testing performed within the past 12 months. Results: Among the 226 participants, 30% reported belief in AIDS conspiracy theories, 72% reported government mistrust, and 45% reported not undergoing HIV testing within the past 12 months. Belief in conspiracy theories was positively associated with recent HIV testing (adjusted odds ratio [OR] = 1.94, 95% confidence interval [CI] = 1.05–3.60), whereas mistrust in the government was negatively associated with testing (OR = 0.43, 95% CI = 0.26–0.73). Implications: Psychological barriers are prevalent among at-risk older adults seeking services at venues with high HIV prevalences and may influence HIV testing. Identifying particular sources of misinformation and mistrust would appear useful for appropriate targeting of HIV testing strategies. PMID:23362210

  9. HIV and/or AIDS-related deaths and modifiable risk factors: A descriptive study of medical admissions at Oshakati Intermediate Hospital in Northern Namibia

    PubMed Central

    Mgori, N.K.

    2015-01-01

    Background High rates of HIV infection have decreased life expectancy in many African countries. Regardless of worldwide efforts to escalate treatment, care and prevention strategies, the number of deaths due to AIDS-related disorders is still high. Local healthcare workers suspect that there are modifiable factors in the care of HIV and/or AIDS patients which can be identified and improved. Aim To describe the HIV and/or AIDS-related causes of adult mortality and identify modifiable factors amongst patients admitted to Oshakati Intermediate Hospital, northern Namibia. Methods Data was extracted retrospectively and coded using the modified CoDe protocol for AIDS. Modifiable factors relating to the patient, health system or clinical care were identified using a standardised data collection tool. Results A total of 177 HIV and/or AIDS patients were identified, 94 (53.1%) were male and 120 (68%) had a CD4 count of less than 200 cells/mL. The common HIV-related causes of death were tuberculosis (25.9%), renal failure (15.8%), Pneumocystis jirovecii pneumonia (11.3%), cryptococcal meningitis (9%), HIV wasting syndrome (7.9%) and AIDS-defining malignancy (7.9%). The analysis revealed 281 modifiable factors; patient-related factors were the most common (153 [54.4%]), followed by health system factors (97 [34.5%]) and healthcare personnel factors (31 [11%]). Conclusion Our findings have highlighted the challenges in overall HIV and/or AIDS inpatient care and surrounding primary care facilities. The identification of specific modifiable factors can be used to reduce mortality by providing training as well as rational monitoring, planning and resource allocation.

  10. Combining Land Use Information and Small Stream Sampling with PCR-Based Methods for Better Characterization of Diffuse Sources of Human Fecal Pollution

    EPA Science Inventory

    Diffuse sources of human fecal pollution allow for the direct discharge of waste into receiving waters with minimal or no treatment. Traditional culture-based methods are commonly used to characterize fecal pollution in ambient waters, however these methods do not discern between...

  11. A Study of the Relative Importance of Communication and Economic Variables in Diffusion: Dwarf Wheats on Unirrigated Small Holdings in Pakistan.

    ERIC Educational Resources Information Center

    Rochin, Refugio I.

    The purpose of this paper is twofold: (1) it presents some empirical findings of the relative importance of both "economic" and "communication" variables in the diffusion of an innovation (dwarf wheats) in an unirrigated region of Pakistan which is densely populated by smallholders. The sample of farmers reported are representative of a class of…

  12. Diffusion on strained surfaces

    NASA Astrophysics Data System (ADS)

    Schroeder, M.; Wolf, D. E.

    1997-03-01

    The change of diffusion kinetics when elastic fields are present is discussed for diffusion on (001) surfaces of simple cubic, fcc and bcc lattices. All particles interact pairwise with a Lennard-Jones potential. The simple cubic lattice was stabilized by an anisotropic prefactor. It is found that generically compressive strain enhances diffusion whereas tensile strain increases the activation barrier. An approximately linear dependence of the barrier in a wide range of misfits is found. In heteroepitaxy, diffusion on top of large clusters is inhomogeneous and anisotropic. The kinetics close to edges and centers of islands are remarkably different. In many cases changes of binding energies are small compared to those of saddle point energies. Thermodynamic arguments (minimization of free energy) are not appropriate to describe diffusion on strained surfaces in these cases.

  13. Holographic diffusers

    NASA Astrophysics Data System (ADS)

    Wadle, Stephen; Wuest, Daniel; Cantalupo, John; Lakes, Roderic S.

    1994-01-01

    Holographic diffusers are prepared using silver halide (Agfa 8E75 and Kodak 649F) and photopolymer (Polaroid DMP 128 and DuPont 600, 705, and 150 series) media. It is possible to control the diffusion angle in three ways: by selection of the properties of the source diffuser, by control of its subtended angle, and by selection of the holographic medium. Several conventional diffusers based on refraction or scattering of light are examined for comparison.

  14. Diffusion MRI

    NASA Astrophysics Data System (ADS)

    Fukuyama, Hidenao

    Recent advances of magnetic resonance imaging have been described, especially stressed on the diffusion sequences. We have recently applied the diffusion sequence to functional brain imaging, and found the appropriate results. In addition to the neurosciences fields, diffusion weighted images have improved the accuracies of clinical diagnosis depending upon magnetic resonance images in stroke as well as inflammations.

  15. Outcome of Patients with Relapsed/Refractory AIDS-Related Lymphoma Diagnosed 1999–2008 and Treated with Curative Intent in the AIDS Malignancy Consortium

    PubMed Central

    Bayraktar, U. D.; Ramos, J. C.; Petrich, A.; Gupta, N.; Lensing, S.; Moore, Page; Reid, E. G.; Aboulafia, D. M.; Ratner, L.; Mitsuyasu, R.; Cooley, Timothy; Henry, D. H.; Barr, P.; Noy, A.

    2012-01-01

    No comparative studies exist for relapsed/refractory (rel/rfr) AIDS-related lymphomas (ARLs). To determine practices over the last decade and to assess the outcomes of salvage chemotherapy with curative intent and autologous stem cell transplantation (ASCT), we retrospectively evaluated treatment outcomes in patients with rel/rfr ARL who were treated in 13 national AIDS Malignancy Consortium (AMC) sites between 1999 and 2008 (N=88). The most commonly used second line therapies were ICE (n=34), dose adjusted EPOCH (n=17), and ESHAP (n=11). The odds of achieving a response were lower for those with non-Hodgkin lymphoma (NHL) than those with HL and for those with primary refractory disease than those with relapse. Overall survival (OS) was significantly longer for those with relapsed disease compared to those with refractory disease and for those with non-Burkitt NHL compared to those with Burkitt. OS was longer in patients who underwent ASCT compared to those who did not (1-year OS: 63.2% vs. 37.2%). However, among 32 patients (36%) who achieved CR/PR after second-line therapy 1-year OS was not different between the 2 groups (87.5% for ASCT vs. 81.8% for non-ASCT). Long-term survival in some patients with rel/rfr ARL may be possible without transplant, although transplant remains the standard of care for chemotherapy sensitive disease. PMID:22642936

  16. IgM, IgG and IgA rheumatoid factors and circulating immune complexes in patients with AIDS and AIDS-related complex with serological abnormalities.

    PubMed Central

    Procaccia, S; Lazzarin, A; Colucci, A; Gasparini, A; Forcellini, P; Lanzanova, D; Foppa, C U; Novati, R; Zanussi, C

    1987-01-01

    To investigate some humoral aspects which may reflect the involvement of B lymphocytes in the acquired immunodeficiency syndrome (AIDS), we used an enzyme-linked immunoassay (ELISA) to determine the levels of IgM, IgG and IgA rheumatoid factors (RF) in 16 patients suffering from full-blown AIDS and 32 patients with AIDS-related complex (ARC), in the clinical form of lymphoadenopathy syndrome (LAS), compared with 40 healthy, young heterosexual subjects. Both AIDS and ARC patients showed a greater incidence of high IgM RF levels, with mean values significantly higher than controls, but with no differences between the two pathological groups. IgG RF behaviour was similar in the two patient populations and the healthy subjects. IgA RF were significantly raised in AIDS and ARC. Further information on RF was obtained by determination of the immunoglobulin levels of the respective isotypes in the same patients. Mean IgG levels were above normal in AIDS and ARC patients, but the latter group showed a higher incidence of increased values and higher mean levels. The IgA isotype was significantly increased mainly in AIDS patients. The behaviour of IgM was virtually the same in the three groups studied. A difference between AIDS and ARC patients was established by the detection of circulating immune-complexes (IC) by the C1q-binding and CIC-conglutinin assays. IC were significantly high, by both methods, only in the ARC group, but normal or very low in AIDS. These overall findings suggest once again the impairment of B cell function in AIDS, with prevalent hyperactivation in ARC and exhaustion in full-blown AIDS, and apparent preservation, in the latter group, of the antibody responses which are more closely related to the activity of subsets of T helper cells. PMID:3608224

  17. High-dose cytosine-arabinoside and cisplatin regimens as salvage therapy for refractory or relapsed AIDS-related non-Hodgkin's lymphoma.

    PubMed

    Bi, J; Espina, B M; Tulpule, A; Boswell, W; Levine, A M

    2001-12-15

    No effective salvage regimen has been defined for patients with AIDS-related non-Hodgkin's lymphoma (AIDS-NHL) who do not respond to first-line chemotherapy that contains anthracycline. Combined dexamethasone, cytosine arabinoside, and cisplatin (DHAP) and etoposide, methylprednisolone, cytosine arabinoside, and cisplatin (ESHAP) have shown good response rates in HIV-negative patients with relapsed lymphomas. We retrospectively analyzed patients with refractory or relapsed AIDS-NHL who had been treated with either DHAP or ESHAP to evaluate the feasibility and efficacy of these regimens. Twenty-six patients with refractory or relapsed AIDS-NHL were treated between 1990 and 1999 either with DHAP ( n = 13) or with ESHAP ( n = 13). Only 1 patient from each group (8%) had achieved complete remission with any previous therapy, and most had progressive disease after the regimen immediately preceding DHAP or ESHAP. In the ESHAP group, 4 patients (31%) achieved complete remission (CR) and 3 patients (23%) attained partial remission (PR) for an overall response rate of 54%. The median survival was 7.1 months (range, 1-58.9+ months) from the time ESHAP was begun. Among the 3 patients with primary refractory lymphoma, there was 1 CR, 1 PR, and one patient with stable disease. In contrast, only 1 PR (7%) was observed with DHAP; the median survival was 3 months. Myelosuppression was the most significant toxicity with grade 4 neutropenia occurring in all who received ESHAP and in 54% of patients treated with DHAP. Neutropenic fever occurred in 8 (62%) ESHAP-treated and 6 (46%) DHAP-treated patients. Although hematologic toxicity is profound, ESHAP appears to be an active salvage regimen for patients with relapsed or refractory AIDS-NHL. PMID:11744828

  18. WE-G-18C-02: Estimation of Optimal B-Value Set for Obtaining Apparent Diffusion Coefficient Free From Perfusion in Non-Small Cell Lung Cancer

    SciTech Connect

    Karki, K; Hugo, G; Ford, J; Saraiya, S; Weiss, E; Olsen, K; Groves, R

    2014-06-15

    Purpose: Diffusion-weighted MRI (DW-MRI) is increasingly being investigated for radiotherapy planning and response assessment. Selection of a limited number of b-values in DW-MRI is important to keep geometrical variations low and imaging time short. We investigated various b-value sets to determine an optimal set for obtaining monoexponential apparent diffusion coefficient (ADC) close to perfusion-insensitive intravoxel incoherent motion (IVIM) model ADC (ADCIVIM) in nonsmall cell lung cancer. Methods: Seven patients had 27 DW-MRI scans before and during radiotherapy in a 1.5T scanner. Respiratory triggering was applied to the echo-planar DW-MRI with TR=4500ms approximately, TE=74ms, pixel size=1.98X1.98mm{sub 2}, slice thickness=4–6mm and 7 axial slices. Diffusion gradients were applied to all three axes producing traceweighted images with eight b-values of 0–1000μs/μm{sup 2}. Monoexponential model ADC values using various b-value sets were compared to ADCIVIM using all b-values. To compare the relative noise in ADC maps, intra-scan coefficient of variation (CV) of active tumor volumes was computed. Results: ADCIVIM, perfusion coefficient and perfusion fraction for tumor volumes were in the range of 880-1622 μm{sup 2}/s, 8119-33834 μm{sup 2}/s and 0.104–0.349, respectively. ADC values using sets of 250, 800 and 1000; 250, 650 and 1000; and 250–1000μs/μm{sup 2} only were not significantly different from ADCIVIM(p>0.05, paired t-test). Error in ADC values for 0–1000, 50–1000, 100–1000, 250–1000, 500–1000, and three b-value sets- 250, 500 and 1000; 250, 650 and 1000; and 250, 800 and 1000μs/μm{sup 2} were 15.0, 9.4, 5.6, 1.4, 11.7, 3.7, 2.0 and 0.2% relative to the reference-standard ADCIVIM, respectively. Mean intrascan CV was 20.2, 20.9, 21.9, 24.9, 32.6, 25.8, 25.4 and 24.8%, respectively, whereas that for ADCIVIM was 23.3%. Conclusion: ADC values of two 3 b-value sets

  19. Random walk in a two-dimensional self-affine random potential: Properties of the anomalous diffusion phase at small external force

    NASA Astrophysics Data System (ADS)

    Monthus, Cécile; Garel, Thomas

    2010-08-01

    We study the dynamical response to an external force F for a particle performing a random walk in a two-dimensional quenched random potential of Hurst exponent H=1/2 . We present numerical results on the statistics of first-passage times that satisfy closed backward master equations. We find that there exists a zero-velocity phase in a finite region of the external force 0diffusion law x(t)˜ξ(F)tμ(F) . The anomalous exponent 0<μ(F)<1 and the correlation length ξ(F) vary continuously with F . In the limit of vanishing force F→0 , we measure the following power laws: the anomalous exponent vanishes as μ(F)∝Fa with a≃0.6 (instead of a=1 in dimension d=1 ), and the correlation length diverges as ξ(F)∝F-ν with ν≃1.29 (instead of ν=2 in dimension d=1 ). Our main conclusion is thus that the dynamics renormalizes onto an effective directed trap model, where the traps are characterized by a typical length ξ(F) along the direction of the force, and by a typical barrier 1/μ(F) . The fact that these traps are “smaller” in linear size and in depth than in dimension d=1 , means that the particle uses the transverse direction to find lower barriers.

  20. Diffusion barriers

    NASA Technical Reports Server (NTRS)

    Nicolet, M. A.

    1983-01-01

    The choice of the metallic film for the contact to a semiconductor device is discussed. One way to try to stabilize a contact is by interposing a thin film of a material that has low diffusivity for the atoms in question. This thin film application is known as a diffusion barrier. Three types of barriers can be distinguished. The stuffed barrier derives its low atomic diffusivity to impurities that concentrate along the extended defects of a polycrystalline layer. Sacrificial barriers exploit the fact that some (elemental) thin films react in a laterally uniform and reproducible fashion. Sacrificial barriers have the advantage that the point of their failure is predictable. Passive barriers are those most closely approximating an ideal barrier. The most-studied case is that of sputtered TiN films. Stuffed barriers may be viewed as passive barriers whose low diffusivity material extends along the defects of the polycrystalline host.

  1. Diffuse radiation

    NASA Technical Reports Server (NTRS)

    1981-01-01

    A diffuse celestial radiation which is isotropic at least on a course scale were measured from the soft X-ray region to about 150 MeV, at which energy the intensity falls below that of the galactic emission for most galactic latitudes. The spectral shape, the intensity, and the established degree of isotropy of this diffuse radiation already place severe constraints on the possible explanations for this radiation. Among the extragalactic theories, the more promising explanations of the isotropic diffuse emission appear to be radiation from exceptional galaxies from matter antimatter annihilation at the boundaries of superclusters of galaxies of matter and antimatter in baryon symmetric big bang models. Other possible sources for extragalactic diffuse gamma radiation are discussed and include normal galaxies, clusters of galaxies, primordial cosmic rays interacting with intergalactic matter, primordial black holes, and cosmic ray leakage from galaxies.

  2. Diffusion of innovative agricultural production systems for sustainable development of small islands: A methodological approach based on the science of complexity

    NASA Astrophysics Data System (ADS)

    Barbera, Guiseppe; Butera, Federico M.

    1992-09-01

    In order to develop small islands, not only must a vital agricultural system be maintained, but the range of opportunities for tourism must be increased with respect to both the seaside and the environmental features of the rural landscape. As an alternative to the traditional and economically declining ones, many innovative production processes can be identified, but their success depends on their interaction with the physical, biological, economic and social environment. In order to identify the main nodes and the most critical interactions, so as to increase the probability of success of a new productive process, a methodological approach based on the science of complexity is proposed for the cultivation of capers ( Capparis spinosa L.) on the island of Pantelleria. The methodology encompasses the identification of actors and factors involved. the quantitative evaluation of their interactions with the different stages of the productive process, and a quasiquantitative evaluation of the probability that the particular action will be performed successfully. The study of “traditional,” “modernized,” and “modernized-sustainable” processes, shows that the modernized-sustainable process offers mutually reinforcing opportunities in terms of an integrated development of high-quality agricultural products and the enhancement of environmental features, in conjunction with high-efficiency production techniques, in conjunction with high-efficiency production techniques, in a way that suits the development of Pantelleria. There is a high probability of failure, however, as a result of the large number of critical factors. Nevertheless, the present study indicates which activities will enhance the probability of successful innovation in the production process.

  3. Romidepsin in Treating Patients With Lymphoma, Chronic Lymphocytic Leukemia, or Solid Tumors With Liver Dysfunction

    ClinicalTrials.gov

    2016-09-09

    Adult Mixed Glioma; Adult Pineal Gland Astrocytoma; Adult Solid Neoplasm; AIDS Related Immunoblastic Lymphoma; AIDS-Related Burkitt Lymphoma; AIDS-Related Diffuse Large Cell Lymphoma; AIDS-Related Diffuse Mixed Cell Lymphoma; AIDS-Related Diffuse Small Cleaved Cell Lymphoma; AIDS-Related Hodgkin Lymphoma; AIDS-Related Lymphoblastic Lymphoma; AIDS-Related Lymphoma; AIDS-Related Primary Central Nervous System Lymphoma; Glioma; Lymphoma; Recurrent Adult Brain Neoplasm; Recurrent Adult Soft Tissue Sarcoma; Recurrent Bladder Carcinoma; Recurrent Breast Carcinoma; Recurrent Chronic Lymphocytic Leukemia; Recurrent Colorectal Carcinoma; Recurrent Cutaneous T-Cell Non-Hodgkin Lymphoma; Recurrent Head and Neck Carcinoma; Recurrent Lung Carcinoma; Recurrent Mature T- and NK-Cell Non-Hodgkin Lymphoma; Recurrent Melanoma; Recurrent Pancreatic Carcinoma; Recurrent Prostate Carcinoma; Recurrent Renal Cell Carcinoma; Recurrent Thyroid Gland Carcinoma; Refractory Chronic Lymphocytic Leukemia; Refractory Cutaneous T-Cell Non-Hodgkin Lymphoma; Refractory Mature T-Cell and NK-Cell Non-Hodgkin Lymphoma

  4. Defusing Diffusion

    ERIC Educational Resources Information Center

    Dou, Remy; Hogan, DaNel; Kossover, Mark; Spuck, Timothy; Young, Sarah

    2013-01-01

    Diffusion has often been taught in science courses as one of the primary ways by which molecules travel, particularly within organisms. For years, classroom teachers have used the same common demonstrations to illustrate this concept (e.g., placing drops of food coloring in a beaker of water). Most of the time, the main contributor to the motion…

  5. Relativistic diffusion

    NASA Astrophysics Data System (ADS)

    Haba, Z.

    2009-02-01

    We discuss relativistic diffusion in proper time in the approach of Schay (Ph.D. thesis, Princeton University, Princeton, NJ, 1961) and Dudley [Ark. Mat. 6, 241 (1965)]. We derive (Langevin) stochastic differential equations in various coordinates. We show that in some coordinates the stochastic differential equations become linear. We obtain momentum probability distribution in an explicit form. We discuss a relativistic particle diffusing in an external electromagnetic field. We solve the Langevin equations in the case of parallel electric and magnetic fields. We derive a kinetic equation for the evolution of the probability distribution. We discuss drag terms leading to an equilibrium distribution. The relativistic analog of the Ornstein-Uhlenbeck process is not unique. We show that if the drag comes from a diffusion approximation to the master equation then its form is strongly restricted. The drag leading to the Tsallis equilibrium distribution satisfies this restriction whereas the one of the Jüttner distribution does not. We show that any function of the relativistic energy can be the equilibrium distribution for a particle in a static electric field. A preliminary study of the time evolution with friction is presented. It is shown that the problem is equivalent to quantum mechanics of a particle moving on a hyperboloid with a potential determined by the drag. A relation to diffusions appearing in heavy ion collisions is briefly discussed.

  6. Demonstrating Diffusion

    ERIC Educational Resources Information Center

    Foy, Barry G.

    1977-01-01

    Two demonstrations are described. Materials and instructions for demonstrating movement of molecules into cytoplasm using agar blocks, phenolphthalein, and sodium hydroxide are given. A simple method for demonstrating that the rate of diffusion of a gas is inversely proportional to its molecular weight is also presented. (AJ)

  7. Relativistic diffusion.

    PubMed

    Haba, Z

    2009-02-01

    We discuss relativistic diffusion in proper time in the approach of Schay (Ph.D. thesis, Princeton University, Princeton, NJ, 1961) and Dudley [Ark. Mat. 6, 241 (1965)]. We derive (Langevin) stochastic differential equations in various coordinates. We show that in some coordinates the stochastic differential equations become linear. We obtain momentum probability distribution in an explicit form. We discuss a relativistic particle diffusing in an external electromagnetic field. We solve the Langevin equations in the case of parallel electric and magnetic fields. We derive a kinetic equation for the evolution of the probability distribution. We discuss drag terms leading to an equilibrium distribution. The relativistic analog of the Ornstein-Uhlenbeck process is not unique. We show that if the drag comes from a diffusion approximation to the master equation then its form is strongly restricted. The drag leading to the Tsallis equilibrium distribution satisfies this restriction whereas the one of the Jüttner distribution does not. We show that any function of the relativistic energy can be the equilibrium distribution for a particle in a static electric field. A preliminary study of the time evolution with friction is presented. It is shown that the problem is equivalent to quantum mechanics of a particle moving on a hyperboloid with a potential determined by the drag. A relation to diffusions appearing in heavy ion collisions is briefly discussed. PMID:19391727

  8. Correlation between viral load, plasma levels of CD4 - CD8 T lymphocytes and AIDS-related oral diseases: a multicentre study on 30 HIV+ children in the HAART era.

    PubMed

    Nesti, M; Carli, E; Giaquinto, C; Rampon, O; Nastasio, S; Giuca, M R

    2012-01-01

    This experimental retrospective multicenter study carried out on 30 seropositive children treated with Highly Active Antiretroviral Therapy (HAART), between the ages of 18 months and 14 years, in the clinical categories Centers for Disease Control (CDC) classification 1993 A (mildly symptomatic), B (moderately symptomatic) and C (severely symptomatic) aims to: 1) clinically and immunologically demonstrate the therapeutic benefits of HAART; 2) monitor the frequency of AIDS-related oral diseases in seropositive children with HAART therapy; 3) monitor the plasma levels of total CD4, CD4 percent, CD8 percent, CD4-CD8 lymphocytes and viral load from 1997 to 30 April, 2011. The statistic methods used are the analysis of covariance and the Bonferroni Test. More than 100 AIDS-related oral diseases were found in the study samples, the most frequent being: oral candidiasis, oropharyngeal candidiasis, HSV-1 herpetic esophagyitis, herpetic gingivolstomatitis (RHOG), recurrent aphthous stomatitis (RAS), parotid swelling, oral hairy leukoplakia (OHL), Herpes simplex 1 (HSV-1), linear gingival erythema (LGE), necrotizing gingivitis (NUG), facial lipodistrophy, facial-cervical lymphadenopathy (FCL), xerostomia, dysgeusia, hyposmia, oral mucosa hyperpigmentation (OMP). The Bonferroni test showed a significant difference between the mean plasma values (mpVTL) of total CD4, CD4 percentage, CD4-CD8 T lymphocytes and Viral Load (VL) of the various oral diseases found in the study samples. The therapeutic benefits of HAART are: immune reconstitution; reduction of the HIV/AIDS-related stomatology diseases; prevention and cure of the AIDS correlated neoplasias; reduction in maternal-fetal transmission of the HIV virus. The negative effects of HAART in relation to odontostomatolgy are: increase in oral lesions from HPV; xerostomia; dysgeusia/ageusia, hyposmia, perioral paresthesia; hyperpigmentation of oral mucosa; facial lipodystrophy, recurrent aphthous stomatitis (RAS). No case of

  9. Genetically Modified Peripheral Blood Stem Cell Transplant in Treating Patients With HIV-Associated Non-Hodgkin or Hodgkin Lymphoma

    ClinicalTrials.gov

    2015-05-06

    Adult Nasal Type Extranodal NK/T-cell Lymphoma; AIDS-related Diffuse Large Cell Lymphoma; AIDS-related Diffuse Mixed Cell Lymphoma; AIDS-related Diffuse Small Cleaved Cell Lymphoma; AIDS-related Immunoblastic Large Cell Lymphoma; AIDS-related Lymphoblastic Lymphoma; AIDS-related Peripheral/Systemic Lymphoma; AIDS-related Small Noncleaved Cell Lymphoma; Anaplastic Large Cell Lymphoma; Angioimmunoblastic T-cell Lymphoma; Cutaneous B-cell Non-Hodgkin Lymphoma; Extranodal Marginal Zone B-cell Lymphoma of Mucosa-associated Lymphoid Tissue; Hepatosplenic T-cell Lymphoma; HIV-associated Hodgkin Lymphoma; Intraocular Lymphoma; Nodal Marginal Zone B-cell Lymphoma; Noncutaneous Extranodal Lymphoma; Peripheral T-cell Lymphoma; Recurrent Adult Burkitt Lymphoma; Recurrent Adult Diffuse Large Cell Lymphoma; Recurrent Adult Diffuse Mixed Cell Lymphoma; Recurrent Adult Diffuse Small Cleaved Cell Lymphoma; Recurrent Adult Grade III Lymphomatoid Granulomatosis; Recurrent Adult Hodgkin Lymphoma; Recurrent Adult Immunoblastic Large Cell Lymphoma; Recurrent Adult Lymphoblastic Lymphoma; Recurrent Adult T-cell Leukemia/Lymphoma; Recurrent Cutaneous T-cell Non-Hodgkin Lymphoma; Recurrent Grade 1 Follicular Lymphoma; Recurrent Grade 2 Follicular Lymphoma; Recurrent Grade 3 Follicular Lymphoma; Recurrent Mantle Cell Lymphoma; Recurrent Marginal Zone Lymphoma; Recurrent Mycosis Fungoides/Sezary Syndrome; Recurrent Small Lymphocytic Lymphoma; Refractory Hairy Cell Leukemia; Small Intestine Lymphoma; Splenic Marginal Zone Lymphoma; Stage I AIDS-related Lymphoma; Stage II AIDS-related Lymphoma; Stage III AIDS-related Lymphoma; Stage IV AIDS-related Lymphoma; T-cell Large Granular Lymphocyte Leukemia; Testicular Lymphoma; Waldenström Macroglobulinemia

  10. Diffusion bonding

    DOEpatents

    Anderson, Robert C.

    1976-06-22

    1. A method for joining beryllium to beryllium by diffusion bonding, comprising the steps of coating at least one surface portion of at least two beryllium pieces with nickel, positioning a coated surface portion in a contiguous relationship with an other surface portion, subjecting the contiguously disposed surface portions to an environment having an atmosphere at a pressure lower than ambient pressure, applying a force upon the beryllium pieces for causing the contiguous surface portions to abut against each other, heating the contiguous surface portions to a maximum temperature less than the melting temperature of the beryllium, substantially uniformly decreasing the applied force while increasing the temperature after attaining a temperature substantially above room temperature, and maintaining a portion of the applied force at a temperature corresponding to about maximum temperature for a duration sufficient to effect the diffusion bond between the contiguous surface portions.

  11. Quantum diffusion

    SciTech Connect

    Habib, S.

    1994-10-01

    We consider a simple quantum system subjected to a classical random force. Under certain conditions it is shown that the noise-averaged Wigner function of the system follows an integro-differential stochastic Liouville equation. In the simple case of polynomial noise-couplings this equation reduces to a generalized Fokker-Planck form. With nonlinear noise injection new ``quantum diffusion`` terms rise that have no counterpart in the classical case. Two special examples that are not of a Fokker-Planck form are discussed: the first with a localized noise source and the other with a spatially modulated noise source.

  12. DIFFUSION PUMP

    DOEpatents

    Levenson, L.

    1963-09-01

    A high-vacuum diffusion pump is described, featuring a novel housing geometry for enhancing pumping speed. An upright, cylindrical lower housing portion is surmounted by a concentric, upright, cylindrical upper housing portion of substantially larger diameter; an uppermost nozzle, disposed concentrically within the upper portion, is adapted to eject downwardly a conical sheet of liquid outwardly to impinge upon the uppermost extremity of the interior wall of the lower portion. Preferably this nozzle is mounted upon a pedestal rising coaxially from within the lower portion and projecting up into said upper portion. (AEC)

  13. Diffusion of monochromatic classical waves.

    PubMed

    Gerritsen, Sijmen; Bauer, Gerrit E W

    2006-01-01

    We study the diffusion of monochromatic classical waves in a disordered acoustic medium by scattering theory. In order to avoid artifacts associated with mathematical point scatterers, we model the randomness by small but finite insertions. We derive expressions for the configuration-averaged energy flux, energy density, and intensity for one-, two-, and three-dimensional (3D) systems with an embedded monochromatic source using the ladder approximation to the Bethe-Salpeter equation. We study the transition from ballistic to diffusive wave propagation and obtain results for the frequency dependence of the medium properties such as mean free path and diffusion coefficient as a function of the scattering parameters. We discover characteristic differences of the diffusion in 2D as compared to the conventional 3D case, such as an explicit dependence of the energy flux on the mean free path and quite different expressions for the effective transport velocity. PMID:16486306

  14. Geometry-induced asymmetric diffusion

    PubMed Central

    Shaw, Robert S.; Packard, Norman; Schröter, Matthias; Swinney, Harry L.

    2007-01-01

    Past work has shown that ions can pass through a membrane more readily in one direction than the other. We demonstrate here in a model and an experiment that for a mixture of small and large particles such asymmetric diffusion can arise solely from an asymmetry in the geometry of the pores of the membrane. Our deterministic simulation considers a two-dimensional gas of elastic disks of two sizes diffusing through a membrane, and our laboratory experiment examines the diffusion of glass beads of two sizes through a metal membrane. In both experiment and simulation, the membrane is permeable only to the smaller particles, and the asymmetric pores lead to an asymmetry in the diffusion rates of these particles. The presence of even a small percentage of large particles can clog a membrane, preventing passage of the small particles in one direction while permitting free flow of the small particles in the other direction. The purely geometric kinetic constraints may play a role in common biological contexts such as membrane ion channels. PMID:17522257

  15. Changes in "thermal lens" measure diffusivity

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Hong, S. D.; Moacanin, J.

    1980-01-01

    In an extension of "thermal lens" effect to new applications and better resolution, two laser beams combine to rapidly measure thermal diffusivity and other molecular dynamic properties. New double-beam technique handles very small samples unlike classical techniques for measuring diffusivity. It can be used for measurements on samples undergoing stress, making it applicable to data collection for structural engineering.

  16. Molecular Diffusion Coefficients: Experimental Determination and Demonstration.

    ERIC Educational Resources Information Center

    Fate, Gwendolyn; Lynn, David G.

    1990-01-01

    Presented are laboratory methods which allow the demonstration and determination of the diffusion coefficients of compounds ranging in size from water to small proteins. Included are the procedures involving the use of a spectrometer, UV cell, triterated agar, and oxygen diffusion. Results including quantification are described. (CW)

  17. Acid diffusion through polymer films

    NASA Astrophysics Data System (ADS)

    Zhang, P. Linda; Eckert, Andrew R.; Willson, C. Grant; Webber, Stephen E.; Byers, Jeffrey D.

    1997-07-01

    In order to perform 0.2 micrometer processes, one needs to study the diffusion of photoacid generators within the photoresist system, since diffusion during post exposure bake time has an influence on the critical dimension (CD). We have developed a new method to study the diffusion of photoacid generators within a polymer film. This new method is based on monitoring the change of the fluorescence intensity of a pH- sensitive fluorescent dye caused by the reaction with photoacid. A simplified version of this experiment has been conducted by introducing acid vapor to quench the fluorescence intensity of this pH sensor. A thin polymer film is spin cast onto the sensor to create a barrier to the acid diffusion process. During the acid diffusion process, the fluorescence intensity of this pH sensor is measured in situ, using excitation and emission wavelengths at 466 nm and 516 nm, respectively. Fluoresceinamine, the pH sensitive fluorescent dye, is covalently bonded onto the treated quartz substrate to form a single dye layer. Poly(hydroxystyrene) (Mn equals 13k, Tg equals 180 degrees Celsius) in PGMEA (5% - 18% by weight) is spin cast onto this quartz substrate to form films with varying thickness. The soft bake time is 60 seconds at 90 degrees Celsius and a typical film has a thickness of 1.4 micrometers. Trifluoroacetic acid is introduced into a small chamber while the fluorescence from this quartz window is observed. Our study focuses on finding the diffusion constant of the vaporized acid (trifluoroacetic acid) in the poly(hydroxystyrene) polymer film. By applying the Fick's second law, (It - Io)/(I(infinity ) - Io) equals erfc [L/(Dt)1/2] is obtained. The change of fluorescence intensity with respect to the diffusion time is monitored. The above equation is used for the data analysis, where L represents the film thickness and t represents the average time for the acid to diffuse through the film. The diffusion constant is calculated to be at the order of 10

  18. Solventless supramolecular chemistry via vapor diffusion of volatile small molecules upon a new trinuclear silver(I)-nitrated pyrazolate macrometallocyclic solid: an experimental/theoretical investigation of the dipole/quadrupole chemisorption phenomena.

    PubMed

    Galassi, Rossana; Ricci, Simone; Burini, Alfredo; Macchioni, Alceo; Rocchigiani, Luca; Marmottini, Fabio; Tekarli, Sammer M; Nesterov, Vladimir N; Omary, Mohammad A

    2013-12-16

    A comparative study on the tendency of a new trinuclear silver(I) pyrazolate, namely, [N,N-(3,5-dinitropyrazolate)Ag]3 (1), and a similar compound known previously, [N,N-[3,5-bis(trifluoromethyl)pyrazolate]Ag]3 (2), to adsorb small volatile molecules was performed. It was found that 1 has a remarkable tendency to form adducts, at room temperature and atmospheric pressure, with acetone, acetylacetone, ammonia, pyridine, acetonitrile, triethylamine, dimethyl sulfide, and tetrahydrothiophene, while carbon monoxide, tetrahydrofuran, alcohols, and diethyl ether were not adsorbed. On the contrary, 2 did not undergo adsorption of any of the aforementioned volatile molecules. Adducts of 1 were characterized by elemental analysis, IR, thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) surface area, and diffusion NMR measurements. The crystal structures of 1·2CH3CN and compound 3, derived from an attempt to crystallize the adduct of 1 with ammonia, were determined by single-crystal X-ray diffractometric studies. The former shows a sandwich structure with a 1:2 stoichiometric [Ag3]/[CH3CN] ratio in which one acetonitrile molecule points above and the other below the centroid of the Ag3N6 metallocycle. Compound 3 formed via rearrangement of the ammonia adduct to yield an anionic trinuclear silver(I) derivative with an additional bridging 3,5-dinitropyrazolate and having [Ag(NH3)2](+) as the counterion, [Ag(NH3)2][N,N-(3,5-dinitropyrazolate)4Ag3]. Irreversible sorption and/or decomposition upon vapor exposure are desirable advantages toward toxic gas filtration applications, including ammonia inhalation. TGA confirms the analytical data for all of the samples, showing weight loss for each adsorbed molecule at temperatures significantly higher than the corresponding boiling temperature, which suggests a chemical-bonding nature for adsorption as opposed to physisorption. BET surface measurements of the "naked" compound 1 excluded physical adsorption in its porous

  19. Parallel flow diffusion battery

    DOEpatents

    Yeh, H.C.; Cheng, Y.S.

    1984-01-01

    A parallel flow diffusion battery for determining the mass distribution of an aerosol has a plurality of diffusion cells mounted in parallel to an aerosol stream, each diffusion cell including a stack of mesh wire screens of different density.

  20. Parallel flow diffusion battery

    DOEpatents

    Yeh, Hsu-Chi; Cheng, Yung-Sung

    1984-08-07

    A parallel flow diffusion battery for determining the mass distribution of an aerosol has a plurality of diffusion cells mounted in parallel to an aerosol stream, each diffusion cell including a stack of mesh wire screens of different density.

  1. NIST Diffusion Data Center

    National Institute of Standards and Technology Data Gateway

    NIST Diffusion Data Center (Web, free access)   The NIST Diffusion Data Center is a collection of over 14,100 international papers, theses, and government reports on diffusion published before 1980.

  2. FRACTIONAL PEARSON DIFFUSIONS

    PubMed Central

    Leonenko, Nikolai N.; Meerschaert, Mark M.

    2013-01-01

    Pearson diffusions are governed by diffusion equations with polynomial coefficients. Fractional Pearson diffusions are governed by the corresponding time-fractional diffusion equation. They are useful for modeling sub-diffusive phenomena, caused by particle sticking and trapping. This paper provides explicit strong solutions for fractional Pearson diffusions, using spectral methods. It also presents stochastic solutions, using a non-Markovian inverse stable time change. PMID:23626377

  3. A diffusion-diffusion model for percutaneous drug absorption.

    PubMed

    Kubota, K; Ishizaki, T

    1986-08-01

    Several theories describing percutaneous drug absorption have been proposed, incorporating the mathematical solutions of differential equations describing percutaneous drug absorption processes where the vehicle and skin are regarded as simple diffusion membranes. By a solution derived from Laplace transforms, the mean residence time MRT and the variance of the residence time VRT in the vehicle are expressed as simple elementary functions of the following five pharmacokinetic parameters characterizing the percutaneous drug absorption: kd, which is defined as the normalized diffusion coefficient of the skin, kc, which is defined as the normalized skin-capillary boundary clearance, the apparent length of diffusion of the skin 1d, the effective length of the vehicle lv, and the diffusion coefficient of the vehicle Dv. All five parameters can be obtained by the methods proposed here. Results of numerical computation indicate that: concentration-distance curves in the vehicle and skin approximate two curves which are simply expressed using trigonometric functions when sufficient time elapses after an ointment application; the most suitable condition for the assumption that the concentration of a drug in the uppermost epidermis can be considered unchanged is the case where the partition coefficient between vehicle and skin is small, and the constancy of drug concentration is even more valid when the effective length of the vehicle is large; and the amount of a drug in the vehicle or skin and the flow rate of the drug from vehicle into skin or from skin into blood becomes linear on a semilogarithmic scale, and the slopes of those lines are small when Dv is small, when the partition coefficient between vehicle and skin is small, when lv is large, or when kc is small. A simple simulation method is also proposed using a biexponential for the concentration-time curve for the skin near the skin-capillary boundary, that is, the flow rate-time curve for drug passing from skin

  4. Particle and tracer diffusion in complex liquids

    NASA Astrophysics Data System (ADS)

    Koynov, Kaloian; Butt, Hans-Jürgen

    2013-02-01

    The diffusion of fluorescent tracers can be studied using fluorescence correlation spectroscopy (FCS). This powerful method offers the possibility to monitor very small tracers at low concentrations, down to single molecules. Furthermore it possesses a sub-femtoliter detection volume that can be precisely positioned in a heterogeneous environment to probe the local dynamics. Despite its great potential and high versatility in addressing the diffusion and transport properties in complex systems, FCS has been predominantly applied in molecular and cell biology. Here we present some applications that are more relevant for material and soft matter science. First, we study the diffusion of single tracers with molecular sizes in undiluted polymer systems. Next, the diffusion of small molecules and semiconductor nanoparticles (quantum dots) in silica inverse opals is studied and correlated to the size and morphology of the inverse opals. Finally, we show how FCS can be used to measure the diffusion coefficient of nanoparticles at water-oil interfaces.

  5. Treatment Options for AIDS-Related Lymphoma

    MedlinePlus

    ... the picture. This procedure is also called nuclear magnetic resonance imaging (NMRI). Lumbar puncture : A procedure used to collect cerebrospinal fluid (CSF) from the spinal column . This is done ...

  6. Treatment Option Overview (AIDS Related-Lymphoma)

    MedlinePlus

    ... the picture. This procedure is also called nuclear magnetic resonance imaging (NMRI). Lumbar puncture : A procedure used to collect cerebrospinal fluid (CSF) from the spinal column . This is done ...

  7. Stages of AIDS-Related Lymphoma

    MedlinePlus

    ... the picture. This procedure is also called nuclear magnetic resonance imaging (NMRI). Lumbar puncture : A procedure used to collect cerebrospinal fluid (CSF) from the spinal column . This is done ...

  8. Dentistry and HIV/AIDS related stigma

    PubMed Central

    Elizondo, Jesus Eduardo; Treviño, Ana Cecilia; Violant, Deborah

    2015-01-01

    OBJECTIVE To analyze HIV/AIDS positive individual’s perception and attitudes regarding dental services. METHODS One hundred and thirty-four subjects (30.0% of women and 70.0% of men) from Nuevo León, Mexico, took part in the study (2014). They filled out structured, analytical, self-administered, anonymous questionnaires. Besides the sociodemographic variables, the perception regarding public and private dental services and related professionals was evaluated, as well as the perceived stigma associated with HIV/AIDS, through a Likert-type scale. The statistical evaluation included a factorial and a non-hierarchical cluster analysis. RESULTS Social inequalities were found regarding the search for public and private dental professionals and services. Most subjects reported omitting their HIV serodiagnosis and agreed that dentists must be trained and qualified to treat patients with HIV/AIDS. The factorial analysis revealed two elements: experiences of stigma and discrimination in dental appointments and feelings of concern regarding the attitudes of professionals or their teams concerning patients’ HIV serodiagnosis. The cluster analysis identified three groups: users who have not experienced stigma or discrimination (85.0%); the ones who have not had those experiences, but feel somewhat concerned (12.7%); and the ones who underwent stigma and discrimination and feel concerned (2.3%). CONCLUSIONS We observed a low percentage of stigma and discrimination in dental appointments; however, most HIV/AIDS patients do not reveal their serodiagnosis to dentists out of fear of being rejected. Such fact implies a workplace hazard to dental professionals, but especially to the very own health of HIV/AIDS patients, as dentists will not be able to provide them a proper clinical and pharmaceutical treatment. PMID:26538100

  9. Women and AIDS-Related Concerns

    PubMed Central

    Cochran, Susan D.; Mays, Vickie M.

    2014-01-01

    Acquired Immunodeficiency Syndrome (AIDS) has important implications for the practice of psychology. As the epidemic continues, the role of behavior change and psychosocial factors in the spread and transmission of Human Immunodeficiency Virus (HIV) infections assumes increasing significance. Psychologists, as behavior change experts, have a special and challenging role to play in educating the public, particularly women, about AIDS. This article examines AIDS- and HIV-related concerns in women with a focus on the personal dilemmas for the practicing psychologist, problems in health behavior advocacy, and methods and pitfalls in modifying sexual behaviors. PMID:2930055

  10. Transverse Diffusion in Bedload Transport

    NASA Astrophysics Data System (ADS)

    Devauchelle, Olivier; Abramian, Anais; Seizilles, Gregoire; Lajeunesse, Eric

    2015-11-01

    When a fluid flows over a granular bed, it entrains the grains as bedload. This interaction produces a beautiful variety of shapes and landscapes, such as dunes, ripples and meanders. In this context, Coulomb's law of friction translates into a threshold shear stress, above which the grains are entrained. When the flow-induced stress is barely above this threshold, only a small proportion of the superficial grains move. Their trajectory is then strongly influenced by the layer of static grains below them. They mostly move in the flow direction, but the roughness of the underlying bed causes their velocity to fluctuate, and turns their trajectory into a random walk. As a consequence, bedload diffuses in the direction orthogonal to the flow. Laboratory experiments suggest that this diffusion opposes gravity to maintain the banks of a river. However, quantifying the terms of this balance remains an experimental challenge. We propose to use an instability generated by bedload diffusion to do so.

  11. Microfabricated diffusion source

    DOEpatents

    Oborny, Michael C.; Frye-Mason, Gregory C.; Manginell, Ronald P.

    2008-07-15

    A microfabricated diffusion source to provide for a controlled diffusion rate of a vapor comprises a porous reservoir formed in a substrate that can be filled with a liquid, a headspace cavity for evaporation of the vapor therein, a diffusion channel to provide a controlled diffusion of the vapor, and an outlet to release the vapor into a gas stream. The microfabricated diffusion source can provide a calibration standard for a microanalytical system. The microanalytical system with an integral diffusion source can be fabricated with microelectromechanical systems technologies.

  12. Diffusion on spatial network

    NASA Astrophysics Data System (ADS)

    Hui, Zi; Tang, Xiaoyue; Li, Wei; Greneche, Jean-Marc; Wang, Qiuping A.

    2015-04-01

    In this work, we study the problem of diffusing a product (idea, opinion, disease etc.) among agents on spatial network. The network is constructed by random addition of nodes on the planar. The probability for a previous node to be connected to the new one is inversely proportional to their spatial distance to the power of α. The diffusion rate between two connected nodes is inversely proportional to their spatial distance to the power of β as well. Inspired from the Fick's first law, we introduce the diffusion coefficient to measure the diffusion ability of the spatial network. Using both theoretical analysis and Monte Carlo simulation, we get the fact that the diffusion coefficient always decreases with the increasing of parameter α and β, and the diffusion sub-coefficient follows the power-law of the spatial distance with exponent equals to -α-β+2. Since both short-range diffusion and long-range diffusion exist, we use anomalous diffusion method in diffusion process. We get the fact that the slope index δ in anomalous diffusion is always smaller that 1. The diffusion process in our model is sub-diffusion.

  13. Diffusion in Brain Extracellular Space

    PubMed Central

    Syková, Eva; Nicholson, Charles

    2009-01-01

    Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecules in the brain. Deviations from the equation reveal loss of molecules across the blood-brain barrier, through cellular uptake, binding or other mechanisms. Early diffusion measurements used radiolabeled sucrose and other tracers. Presently, the real-time iontophoresis (RTI) method is employed for small ions and the integrative optical imaging (IOI) method for fluorescent macromolecules, including dextrans or proteins. Theoretical models and simulations of the ECS have explored the influence of ECS geometry, effects of dead-space microdomains, extracellular matrix and interaction of macromolecules with ECS channels. Extensive experimental studies with the RTI method employing the cation tetramethylammonium (TMA) in normal brain tissue show that the volume fraction of the ECS typically is about 20% and the tortuosity about 1.6 (i.e. free diffusion coefficient of TMA is reduced by 2.6), although there are regional variations. These parameters change during development and aging. Diffusion properties have been characterized in several interventions, including brain stimulation, osmotic challenge and knockout of extracellular matrix components. Measurements have also been made during ischemia, in models of Alzheimer's and Parkinson's diseases and in human gliomas. Overall, these studies improve our conception of ECS structure and the roles of glia and extracellular matrix in modulating the ECS microenvironment. Knowledge of ECS diffusion properties are valuable in contexts ranging from understanding extrasynaptic volume transmission to the development of paradigms for drug delivery to the brain. PMID:18923183

  14. UPDATING APPLIED DIFFUSION MODELS

    EPA Science Inventory

    Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Socie...

  15. Diffusion bonding aeroengine components

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, G. A.; Broughton, T.

    1988-10-01

    The use of diffusion bonding processes at Rolls-Royce for the manufacture of titanium-alloy aircraft engine components and structures is described. A liquid-phase diffusion bonding process called activated diffusion bonding has been developed for the manufacture of the hollow titanium wide chord fan blade. In addition, solid-state diffusion bonding is being used in the manufacture of hollow vane/blade airfoil constructions mainly in conjunction with superplastic forming and hot forming techniques.

  16. Diffusion and transport coefficients in synthetic opals

    SciTech Connect

    Sofo, J. O.; Mahan, G. D.

    2000-07-15

    Opals are structures composed of close-packed spheres in the size range of nano to micrometers. They are sintered to create small necks at the points of contact. We have solved the diffusion problem in such structures. The relation between the diffusion coefficient and the thermal and electrical conductivity is used to estimate the transport coefficients of opal structures as a function of the neck size and the mean free path of the carriers. The theory presented is also applicable to the diffusion problem in other periodic structures. (c) 2000 The American Physical Society.

  17. Analytical study of diffusive relativistic shock acceleration.

    PubMed

    Keshet, Uri

    2006-12-01

    Particle acceleration in relativistic shocks is studied analytically in the test-particle, small-angle scattering limit, for an arbitrary velocity-angle diffusion function D. The particle spectral index s is found to be sensitive to D, particularly downstream and at certain angles. The analysis, confirmed numerically, justifies and generalizes previous results for isotropic diffusion. It can be used to test collisionless shock models and to observationally constrain D. For example, strongly forward- or backward-enhanced diffusion downstream is ruled out by gamma-ray burst afterglow observations. PMID:17155790

  18. ANALYTIC FORMS OF THE PERPENDICULAR DIFFUSION COEFFICIENT IN NRMHD TURBULENCE

    SciTech Connect

    Shalchi, A.

    2015-02-01

    In the past different analytic limits for the perpendicular diffusion coefficient of energetic particles interacting with magnetic turbulence were discussed. These different limits or cases correspond to different transport modes describing how the particles are diffusing across the large-scale magnetic field. In the current paper we describe a new transport regime by considering the model of noisy reduced magnetohydrodynamic turbulence. We derive different analytic forms of the perpendicular diffusion coefficient, and while we do this, we focus on the aforementioned new transport mode. We show that for this turbulence model a small perpendicular diffusion coefficient can be obtained so that the latter diffusion coefficient is more than hundred times smaller than the parallel diffusion coefficient. This result is relevant to explain observations in the solar system where such small perpendicular diffusion coefficients have been reported.

  19. Handbook on atmospheric diffusion

    SciTech Connect

    Hanna, S.R.; Briggs, G.A.; Hosker, R.P. Jr.

    1982-01-01

    Basic meteorological concepts are covered as well as plume rise, source effects, and diffusion models. Chapters are included on cooling tower plumes and urban diffusion. Suggestions are given for calculating diffusion in special situations, such as for instantaneous releases over complex terrain, over long distances, and during times when chemical reactions or dry or wet deposition are important. (PSB)

  20. Reduce Confusion about Diffusion.

    ERIC Educational Resources Information Center

    Hebrank, Mary R.

    1997-01-01

    Presents activities that allow students to explore the fundamental but poorly understood concept of diffusion by appealing to their kinesthetic senses first, then challenging their analytical skills as they try to deduce the mathematical principle involved. Presents a computer simulation of diffusion and discusses diffusion's limitations and…

  1. Diffusion of uranium hexafluoride

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of uranium hexafluoride

  2. Diffusion Strategy Guide.

    ERIC Educational Resources Information Center

    McCutcheon, James R.; Sanders, John R.

    A methodology is presented for planning and managing the spread of educational innovations. The first portion of the guide develops a theoretical framework for diffusion which summarizes and capitalizes on the latest marketing and on the latest marketing and diffusion research findings. Major stages in the diffusion paradigm discussed include…

  3. Self diffusion of interacting membrane proteins.

    PubMed Central

    Abney, J R; Scalettar, B A; Owicki, J C

    1989-01-01

    A two-dimensional version of the generalized Smoluchowski equation is used to analyze the time (or distance) dependent self diffusion of interacting membrane proteins in concentrated membrane systems. This equation provides a well established starting point for descriptions of the diffusion of particles that interact through both direct and hydrodynamic forces; in this initial work only the effects of direct interactions are explicitly considered. Data describing diffusion in the presence of hard-core repulsions, soft repulsions, and soft repulsions with weak attractions are presented. The effect that interactions have on the self-diffusion coefficient of a real protein molecule from mouse liver gap junctions is also calculated. The results indicate that self diffusion is always inhibited by direct interactions; this observation is interpreted in terms of the caging that will exist at finite protein concentration. It is also noted that, over small distance scales, the diffusion coefficient is determined entirely by the very strong Brownian forces; therefore, as a function of displacement the self-diffusion coefficient decays (rapidly) from its value at infinite dilution to its steady-state interaction-averaged value. The steady-state self-diffusion coefficient describes motion over distance scales that range from approximately 10 nm to cellular dimensions and is the quantity measured in fluorescence recovery after photobleaching experiments. The short-ranged behavior of the diffusion coefficient is important on the interparticle-distance scale and may therefore influence the rate at which nearest-neighbor collisional processes take place. The hard-disk theoretical results presented here are in excellent agreement with lattice Monte-Carlo results obtained by other workers. The concentration dependence of experimentally measured diffusion coefficients of antibody-hapten complexes bound to the membrane surface is consistent with that predicted by the theory. The

  4. Proton diffusion along biological membranes

    NASA Astrophysics Data System (ADS)

    Medvedev, E. S.; Stuchebrukhov, A. A.

    2011-06-01

    Biological surfaces are known to be capable of retaining protons and facilitating their lateral diffusion. Since the surface dynamically exchanges protons with the bulk, the proton movement from a source to a target at the surface acquires a complicated pattern of coupled surface and bulk (2D + 3D) diffusion of which the main feature is that the surface acts as a proton-collecting antenna enhancing the proton flux from the bulk. A phenomenological model of this process is reviewed and its applications to recent experiments on lipid bilayers and small unilaminar vesicles are discussed. The model (i) introduces the important notions of the fast and slow regimes of proton exchange between the surface and the bulk, (ii) permits evaluation of the antenna radius and amplification coefficient in both regimes, (iii) explains the observed macroscopically large distances (in the micrometer range; Antonenko and Pohl 1998 FEBS Lett. 429 197) that the proton can travel along lipid membranes embedded into pure aqueous solutions, and (iv) predicts the dependence of the steady-state proton flux and the kinetics of the non-stationary diffusion upon the buffer concentration in buffered solutions. The surface diffusion coefficient for small unilaminar vesicles is calculated from experimental data (Sandén et al 2010 Proc. Natl Acad. Sci. USA 107 4129) to be 1 × 10 - 5 cm2 s - 1. The dependence of the shape of the kinetic curves representing protonation/deprotonation of a lipid-bound pH-sensitive dye attached to a planar bilayer lipid membrane upon the buffer concentration (Serowy et al 2003 Biophys. J. 84 1031) and the effect of changing the membrane composition (Antonenko and Pohl 2008 Eur. Biophys. J. 37 865) are explained.

  5. Proton diffusion along biological membranes.

    PubMed

    Medvedev, E S; Stuchebrukhov, A A

    2011-06-15

    Biological surfaces are known to be capable of retaining protons and facilitating their lateral diffusion. Since the surface dynamically exchanges protons with the bulk, the proton movement from a source to a target at the surface acquires a complicated pattern of coupled surface and bulk (2D + 3D) diffusion of which the main feature is that the surface acts as a proton-collecting antenna enhancing the proton flux from the bulk. A phenomenological model of this process is reviewed and its applications to recent experiments on lipid bilayers and small unilaminar vesicles are discussed. The model (i) introduces the important notions of the fast and slow regimes of proton exchange between the surface and the bulk, (ii) permits evaluation of the antenna radius and amplification coefficient in both regimes, (iii) explains the observed macroscopically large distances (in the micrometer range; Antonenko and Pohl 1998 FEBS Lett. 429 197) that the proton can travel along lipid membranes embedded into pure aqueous solutions, and (iv) predicts the dependence of the steady-state proton flux and the kinetics of the non-stationary diffusion upon the buffer concentration in buffered solutions. The surface diffusion coefficient for small unilaminar vesicles is calculated from experimental data (Sandén et al 2010 Proc. Natl Acad. Sci. USA 107 4129) to be 1 × 10(-5) cm(2) s(-1). The dependence of the shape of the kinetic curves representing protonation/deprotonation of a lipid-bound pH-sensitive dye attached to a planar bilayer lipid membrane upon the buffer concentration (Serowy et al 2003 Biophys. J. 84 1031) and the effect of changing the membrane composition (Antonenko and Pohl 2008 Eur. Biophys. J. 37 865) are explained. PMID:21613715

  6. A fluorescent laser-diffuser arrangement for uniform backlighting

    NASA Astrophysics Data System (ADS)

    Jain, Saransh; Somasundaram, S.; Anand, T. N. C.

    2016-02-01

    Laser-light diffusers are used in conjunction with pulsed lasers to generate bright, spatially uniform background illumination for imaging and particle sizing applications. The present paper describes a cost effective way of fabricating a fluorescent laser-light diffuser. The procedure to obtain a uniform background using laser illumination is explained. To characterize the diffuser, images are acquired using a CCD camera with the illumination provided using the diffuser and the variations of pixel intensity values along the centerline of the images are plotted. It is observed that the standard deviation of pixel intensity values is fairly small. Hence, these diffusers are suitable for experiments that need a uniform background.

  7. Handheld Diffusion Test Cells

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This photo shows an individual cell from the Handheld Diffusion Test Cell (HH-DTC) apparatus flown on the Space Shuttle. Similar cells will be used in the Observable Protein Crystal Growth Apparatus (OPCGA) to be operated aboard the International Space Station (ISS). The principal investigator is Dr. Alex McPherson of the University of California, Irvine. Each individual cell comprises two sample chambers with a rotating center section that isolates the two from each other until the start of the experiment and after it is completed. The cells are made from optical-quality quartz glass to allow photography and interferometric observations. Each cell has a small light-emitting diode and lens to back-light the solution. In protein crystal growth experiments, a precipitating agent such as a salt solution is used to absorb and hold water but repel the protein molecules. This increases the concentration of protein until the molecules nucleate to form crystals. This cell is one of 96 that make up the experiment module portion of the OPCGA.

  8. Handheld Diffusion Test Cells

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This photo shows the Handheld Diffusion Test Cell (HH-DTC) apparatus flown on the Space Shuttle. Similar cells (inside the plastic box) will be used in the Observable Protein Crystal Growth Apparatus (OPCGA) to be operated aboard the International Space Station (ISS). The principal investigator is Dr. Alex McPherson of the University of California, Irvine. Each individual cell comprises two sample chambers with a rotating center section that isolates the two from each other until the start of the experiment and after it is completed. The cells are made from optical-quality quartz glass to allow photography and interferometric observations. Each cell has a small light-emitting diode and lens to back-light the solution. In protein crystal growth experiments, a precipitating agent such as a salt solution is used to absorb and hold water but repel the protein molecules. This increases the concentration of protein until the molecules nucleate to form crystals. This cell is one of 96 that make up the experiment module portion of the OPCGA.

  9. Grain boundary diffusion in olivine (Invited)

    NASA Astrophysics Data System (ADS)

    Marquardt, K.; Dohmen, R.

    2013-12-01

    . Grain boundary diffusion perpendicular to the dislocation lines of the small angle grain boundaries proved to be about an order of magnitude faster than volume diffusion, whereas diffusion in high angle grain boundaries is several orders of magnitude faster. We will discuss the variation of element diffusion rates with grain boundary orientation and the temperature- and/or time-induced transition from one diffusion regime to the next regime. This is done using time series experiments and two-dimensional grain boundary diffusion simulations. Finally, we will debate the differences between our data and other data sets that result from different experimental setups, conditions and analyses.

  10. Diffusion in disordered media

    NASA Astrophysics Data System (ADS)

    Havlin, Shlomo; Ben-Avraham, Daniel

    2002-01-01

    Diffusion in disordered systems does not follow the classical laws which describe transport in ordered crystalline media, and this leads to many anomalous physical properties. Since the application of percolation theory, the main advances in the understanding of these processes have come from fractal theory. Scaling theories and numerical simulations are important tools to describe diffusion processes (random walks: the 'ant in the labyrinth') on percolation systems and fractals. Different types of disordered systems exhibiting anomalous diffusion are presented (the incipient infinite percolation cluster, diffusion-limited aggregation clusters, lattice animals, and random combs), and scaling theories as well as numerical simulations of greater sophistication are described. Also, diffusion in the presence of singular distributions of transition rates is discussed and related to anomalous diffusion on disordered structures.

  11. Hereditary Diffuse Infiltrating Retinoblastoma.

    PubMed

    Schedler, Katharina J E; Traine, Peter G; Lohmann, Dietmar R; Haritoglou, Christos; Metz, Klaus A; Rodrigues, Eduardo B

    2016-03-01

    Retinoblastoma is one of the most common childhood cancers. The diffuse infiltrating retinoblastoma is a rare subtype of this neoplasm. The majority of cases of diffuse infiltrating retinoblastoma are unilateral and occur sporadically. Herein we report on a family with three children affected by retinoblastoma, among them one girl with diffuse infiltrating retinoblastoma. This girl was diagnosed at the age of 8 years with a unilateral diffuse infiltrating retinoblastoma. By contrast, the two brothers became clinically apparent in the first 2 years of life with bilateral retinoblastoma. The parents were clinically unremarkable. Genetic analysis of RB1 gene was performed. The girl with diffuse infiltrating RB was found to be heterozygous for an oncogenic mutation in the RB1 gene that was also carried by both brothers and the father of the family. These results show that diffuse infiltrating retinoblastoma can develop on the background of a hereditary predisposition to retinoblastoma. PMID:24892564

  12. Multinomial diffusion equation

    NASA Astrophysics Data System (ADS)

    Balter, Ariel; Tartakovsky, Alexandre M.

    2011-06-01

    We describe a new, microscopic model for diffusion that captures diffusion induced fluctuations at scales where the concept of concentration gives way to discrete particles. We show that in the limit as the number of particles N→∞, our model is equivalent to the classical stochastic diffusion equation (SDE). We test our new model and the SDE against Langevin dynamics in numerical simulations, and show that our model successfully reproduces the correct ensemble statistics, while the classical model fails.

  13. Multinomial diffusion equation

    SciTech Connect

    Balter, Ariel I.; Tartakovsky, Alexandre M.

    2011-06-24

    We describe a new, microscopic model for diffusion that captures diffusion induced uctuations at scales where the concept of concentration gives way to discrete par- ticles. We show that in the limit as the number of particles N ! 1, our model is equivalent to the classical stochastic diffusion equation (SDE). We test our new model and the SDE against Langevin dynamics in numerical simulations, and show that our model successfully reproduces the correct ensemble statistics, while the classical model fails.

  14. Gaseous diffusion system

    DOEpatents

    Garrett, George A.; Shacter, John

    1978-01-01

    1. A gaseous diffusion system comprising a plurality of diffusers connected in cascade to form a series of stages, each of said diffusers having a porous partition dividing it into a high pressure chamber and a low pressure chamber, and means for combining a portion of the enriched gas from a succeeding stage with a portion of the enriched gas from the low pressure chamber of each stage and feeding it into one extremity of the high pressure chamber thereof.

  15. Inpainting using airy diffusion

    NASA Astrophysics Data System (ADS)

    Lorduy Hernandez, Sara

    2015-09-01

    One inpainting procedure based on Airy diffusion is proposed, implemented via Maple and applied to some digital images. Airy diffusion is a partial differential equation with spatial derivatives of third order in contrast with the usual diffusion with spatial derivatives of second order. Airy diffusion generates the Airy semigroup in terms of the Airy functions which can be rewritten in terms of Bessel functions. The Airy diffusion can be used to smooth an image with the corresponding noise elimination via convolution. Also the Airy diffusion can be used to erase objects from an image. We build an algorithm using the Maple package ImageTools and such algorithm is tested using some images. Our results using Airy diffusion are compared with the similar results using standard diffusion. We observe that Airy diffusion generates powerful filters for image processing which could be incorporated in the usual packages for image processing such as ImageJ and Photoshop. Also is interesting to consider the possibility to incorporate the Airy filters as applications for smartphones and smart-glasses.

  16. Mutual diffusion in a binary isotopic mixture.

    PubMed

    Sharma, Raman; Tankeshwar, K

    2010-11-17

    The mass dependence of the mutual diffusion coefficient, in a binary equimolar mixture of Lennard-Jones fluids, is studied within Mori's memory function formalism. A phenomenological form of the memory function is used to study the time evolution of the self- and relative velocity correlation functions. The diffusion coefficients are calculated from the relevant velocity correlation functions using the Green-Kubo integral formula. Like the self-diffusion coefficient, the mutual diffusion coefficient is also found to be weakly dependent on the mass ratio. The present study shows that the minimum value that the mutual diffusion coefficient in an equimolar mixture of isotopic fluids can have is √(1/2) times the self-diffusion coefficient of any of the species when in isolation. Further, the contribution of the dynamic/distinct cross correlations to the mutual diffusion coefficient is found to be small and positive for the whole range of the mass ratio which is consistent with earlier molecular dynamics results. PMID:21339621

  17. Brain Extracellular Space as a Diffusion Barrier

    PubMed Central

    Nicholson, Charles; Kamali-Zare, Padideh; Tao, Lian

    2012-01-01

    The extracellular space (ECS) consists of the narrow channels between brain cells together with their geometrical configuration and contents. Despite being only 20–60 nm in width, the ECS typically occupies 20% of the brain volume. Numerous experiments over the last 50 years have established that molecules moving through the ECS obey the laws of diffusion but with an effective diffusion coefficient reduced by a factor of about 2.6 compared to free diffusion. This review considers the origins of the diffusion barrier arising from the ECS and its properties. The paper presents a brief overview of software for implementing two point-source paradigms for measurements of localized diffusion properties: the real-time iontophoresis or pressure method for small ions and the integrative optical imaging method for macromolecules. Selected results are presented. This is followed by a discussion of the application of the MCell Monte Carlo simulation program to determining the importance of geometrical constraints, especially dead-space microdomains, and the possible role of interaction with the extracellular matrix. It is concluded that we can predict the impediment to diffusion of many molecules of practical importance and also use studies of the diffusion of selected molecular probes to reveal the barrier properties of the ECS. PMID:23172993

  18. Aqueous diffusion in repository and backfill environments

    SciTech Connect

    Conca, J.L.; Apted, M.; Arthur, R.

    1993-12-31

    Aqueous diffusion coefficients have been experimentally determined in a variety of porous/fractured geologic and engineered media. For performance assessment applications, the purely diffusive flux must be separated from retardation effects. The simple diffusion coefficient, D, does not include any transient chemical effects, e.g., sorption, which lower the diffusion coefficient for some finite time period until equilibrium is reached. D is primarily a function of volumetric water content, {theta}, and not material characteristics. At high water contents, D gradually declines as water content decreases, from 10{sup -5} cm{sup 2}/sec at {theta} {approximately}0.5%. Although surface diffusion has a strong experimental basis in the transport of gases along metal surfaces experimental evidence for aqueous geologic/backfill/engineered systems strongly indicates that surface diffusion is not important, even in bentonite, because of the extremely poor connectivity among electric double-layers and the extremely low diffusivities and high {partial_derivative}C/{partial_derivative}x at small area/point contacts which more than negate the increased flux along intragrain surfaces.

  19. Experimental study of vortex diffusers

    SciTech Connect

    Shakerin, S.; Miller, P.L.

    1995-11-01

    This report documents experimental research performed on vortex diffusers used in ventilation and air-conditioning systems. The main objectives of the research were (1) to study the flow characteristics of isothermal jets issuing from vortex diffusers, (2) to compare the vortex diffuser`s performance with that of a conventional diffuser, and (3) to prepare a report that disseminates the results to the designers of ventilation and air-conditioning systems. The researchers considered three diffusers: a conventional round ceiling diffuser and two different styles of vortex diffusers. Overall, the vortex diffusers create slightly more induction of ambient air in comparison to the conventional diffuser.

  20. On the behavior of Kazhikov-Smagulov mass diffusion model for vanishing diffusion and viscosity coefficients

    NASA Astrophysics Data System (ADS)

    Araruna, F. D.; Braz e Silva, P.; Carvalho, R. R.; Rojas-Medar, M. A.

    2015-06-01

    We consider the motion of a viscous incompressible fluid consisting of two components with a diffusion effect obeying Fick's law in ℝ3. We prove that there exists a small time interval where the fluid variables converge uniformly as the viscosity and the diffusion coefficient tend to zero. In the limit, we find a non-homogeneous, non-viscous, incompressible fluid governed by an Euler-like system.

  1. Fujita phenomenon in inhomogeneous fast diffusion system

    NASA Astrophysics Data System (ADS)

    Yang, Jinge; Zheng, Sining; Qu, Chengyuan

    2013-04-01

    This paper deals with the Fujita phenomenon for the Cauchy problem of an inhomogeneous fast diffusion system. Both the critical exponent and the second exponent are obtained. We observe that the inhomogeneous terms in the system substantially contribute to the critical exponent, in that the blow-up exponent region is obviously enlarged, with keeping the second critical exponent unchanged for small inhomogeneous sources.

  2. Galactic Diffuse Emissions

    SciTech Connect

    Digel, Seth W.; /SLAC

    2007-10-25

    Interactions of cosmic rays with interstellar nucleons and photons make the Milky Way a bright, diffuse source of high-energy {gamma}-rays. Observationally, the results from EGRET, COMPTEL, and OSSE have now been extended to higher energies by ground-based experiments, with detections of diffuse emission in the Galactic center reported by H.E.S.S. in the range above 100 GeV and of diffuse emission in Cygnus by MILAGRO in the TeV range. In the range above 100 keV, INTEGRAL SPI has found that diffuse emission remains after point sources are accounted for. I will summarize current knowledge of diffuse {gamma}-ray emission from the Milky Way and review some open issues related to the diffuse emission -- some old, like the distribution of cosmic-ray sources and the origin of the 'excess' of GeV emission observed by EGRET, and some recently recognized, like the amount and distribution of molecular hydrogen not traced by CO emission -- and anticipate some of the advances that will be possible with the Large Area Telescope on GLAST. We plan to develop an accurate physical model for the diffuse emission, which will be useful for detecting and accurately characterizing emission from Galactic point sources as well as any Galactic diffuse emission from exotic processes, and for studying the unresolved extragalactic emission.

  3. The Diffusion of Innovation

    NASA Technical Reports Server (NTRS)

    Earabino, Gerard J.; Heyl, G. Christopher; Percorini, Thomas J.

    1987-01-01

    New ideas encounter obstacles on way to becoming products. Report examines process by which new ideas become products, processes, or accepted standards. Sequence of events called "the diffusion of innovation." Focuses on development of material processing in low gravity as case study in diffusion of innovation.

  4. Investigating Diffusion with Technology

    ERIC Educational Resources Information Center

    Miller, Jon S.; Windelborn, Augden F.

    2013-01-01

    The activities described here allow students to explore the concept of diffusion with the use of common equipment such as computers, webcams and analysis software. The procedure includes taking a series of digital pictures of a container of water with a webcam as a dye slowly diffuses. At known time points, measurements of the pixel densities…

  5. Anatomy of Particle Diffusion

    ERIC Educational Resources Information Center

    Bringuier, E.

    2009-01-01

    The paper analyses particle diffusion from a thermodynamic standpoint. The main goal of the paper is to highlight the conceptual connection between particle diffusion, which belongs to non-equilibrium statistical physics, and mechanics, which deals with particle motion, at the level of third-year university courses. We start out from the fact…

  6. Cosmology with matter diffusion

    SciTech Connect

    Calogero, Simone; Velten, Hermano E-mail: velten@cce.ufes.br

    2013-11-01

    We construct a viable cosmological model based on velocity diffusion of matter particles. In order to ensure the conservation of the total energy-momentum tensor in the presence of diffusion, we include a cosmological scalar field φ which we identify with the dark energy component of the universe. The model is characterized by only one new degree of freedom, the diffusion parameter σ. The standard ΛCDM model can be recovered by setting σ = 0. If diffusion takes place (σ > 0) the dynamics of the matter and of the dark energy fields are coupled. We argue that the existence of a diffusion mechanism in the universe may serve as a theoretical motivation for interacting models. We constrain the background dynamics of the diffusion model with Supernovae, H(z) and BAO data. We also perform a perturbative analysis of this model in order to understand structure formation in the universe. We calculate the impact of diffusion both on the CMB spectrum, with particular attention to the integrated Sachs-Wolfe signal, and on the matter power spectrum P(k). The latter analysis places strong constraints on the magnitude of the diffusion mechanism but does not rule out the model.

  7. A Simple Refraction Experiment for Probing Diffusion in Ternary Mixtures

    ERIC Educational Resources Information Center

    Coutinho, Cecil A.; Mankidy, Bijith D.; Gupta, Vinay K.

    2010-01-01

    Diffusion is a fundamental phenomenon that is vital in many chemical processes such as mass transport in living cells, corrosion, and separations. We describe a simple undergraduate-level experiment based on Weiner's Method to probe diffusion in a ternary aqueous mixture of small molecular-weight molecules. As an illustration, the experiment…

  8. Diffusion in Coulomb crystals.

    PubMed

    Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

    2011-07-01

    Diffusion in Coulomb crystals can be important for the structure of neutron star crusts. We determine diffusion constants D from molecular dynamics simulations. We find that D for Coulomb crystals with relatively soft-core 1/r interactions may be larger than D for Lennard-Jones or other solids with harder-core interactions. Diffusion, for simulations of nearly perfect body-centered-cubic lattices, involves the exchange of ions in ringlike configurations. Here ions "hop" in unison without the formation of long lived vacancies. Diffusion, for imperfect crystals, involves the motion of defects. Finally, we find that diffusion, for an amorphous system rapidly quenched from Coulomb parameter Γ=175 to Coulomb parameters up to Γ=1750, is fast enough that the system starts to crystalize during long simulation runs. These results strongly suggest that Coulomb solids in cold white dwarf stars, and the crust of neutron stars, will be crystalline and not amorphous. PMID:21867316

  9. Combustor diffuser interaction program

    NASA Technical Reports Server (NTRS)

    Srinivasan, Ram; Thorp, Daniel

    1986-01-01

    Advances in gas turbine engine performance are achieved by using compressor systems with high stage loading and low part count, which result in high exit Mach numbers. The diffuser and combustor systems in such engines should be optimized to reduce system pressure loss and to maximize the engine thrust-to-weight ratio and minimize length. The state-of-the-art combustor-diffuser systems do not meet these requirements. Detailed understanding of the combustor-diffuser flow field interaction is required for designing advanced gas turbine engines. An experimental study of the combustor-diffuser interaction (CDI) is being conducted to obtain data for the evaluation and improvement of analytical models applicable to a wide variety of diffuser designs. The CDI program consists of four technical phases: Literature Search; Baseline Configuration; Parametric Configurations; and Performance Configurations. Phase 2 of the program is in progress.

  10. Diffusion filter eliminates fringe effects of coherent laser light source

    NASA Technical Reports Server (NTRS)

    Olsasky, M. J.

    1970-01-01

    Diffusion filter comprised of small particles in colloidal suspension reduces the coherence of a laser beam used as a photographic light source. Interference patterns which obscure details in photographic film are eliminated, the intensity and collimation are moderately affected.

  11. Thorium Diffusion in Monazite

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    2006-05-01

    Diffusion of thorium has been characterized in synthetic monazite under dry conditions. The synthetic monazites (either pure CePO4, NdPO4, or a mixed LREE phosphate containing Ce, Nd, and Sm) were grown via a Na2CO3-MoO3 flux method. The source of diffusant for the experiments were either synthesized ThSiO4 or CaTh(PO4)2 powders. Experiments were performed by placing source and monazite in Pt capsules and annealing capsules in 1 atm furnaces for times ranging from 10 days to a few hours, at temperatures from 1400 to 1550C. The Th distributions in the monazite were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation was obtained for diffusion in monazite: DSm = 7.2x103 exp(-814 kJ mol-1/RT) m2sec-1 The diffusivity of Th was similar for monazites containing a single REE and the mixed LREE phosphates. Th diffusion was also similar for experiments run using the Th silicate and Ca-Th phosphate sources, suggesting that the substitutional mechanism for Th in monazite, i.e, Th+4 + Si+4 for REE+3 + P+5 with the ThSiO4 source, and Th+4 + Ca+2 for 2REE+3 with the CaTh(PO4)2 source, does not significantly affect Th diffusivities, and that Th is likely the rate-limiting species. Th diffusion in monazite is about 4 orders of magnitude slower than Pb diffusion (Cherniak et al., 2004). This contrasts with findings of Gardes et al. (2005) who determined that Pb, Th and REE diffusivities in monazite are similar. Th diffusion in zircon (Cherniak et al., 1997) is about an order of magnitude slower than in monazite, but with similar activation energy for diffusion. The smaller diffusivities in zircon may be a consequence of the larger disparity in size between Th and the Zr site in zircon as compared with Th and the REE site in monazite. Nonetheless, Th is essentially immobile in monazite with respect to exchange by volume diffusion under most geologic conditions; these findings may have implications for containment of high- level actinide

  12. Spatial dilemmas of diffusible public goods.

    PubMed

    Allen, Benjamin; Gore, Jeff; Nowak, Martin A

    2013-01-01

    The emergence of cooperation is a central question in evolutionary biology. Microorganisms often cooperate by producing a chemical resource (a public good) that benefits other cells. The sharing of public goods depends on their diffusion through space. Previous theory suggests that spatial structure can promote evolution of cooperation, but the diffusion of public goods introduces new phenomena that must be modeled explicitly. We develop an approach where colony geometry and public good diffusion are described by graphs. We find that the success of cooperation depends on a simple relation between the benefits and costs of the public good, the amount retained by a producer, and the average amount retained by each of the producer's neighbors. These quantities are derived as analytic functions of the graph topology and diffusion rate. In general, cooperation is favored for small diffusion rates, low colony dimensionality, and small rates of decay of the public good. DOI: http://dx.doi.org/10.7554/eLife.01169.001. PMID:24347543

  13. Isotope effect of mercury diffusion in air

    PubMed Central

    Koster van Groos, Paul G.; Esser, Bradley K.; Williams, Ross W.; Hunt, James R.

    2014-01-01

    Identifying and reducing impacts from mercury sources in the environment remains a considerable challenge and requires process based models to quantify mercury stocks and flows. The stable isotope composition of mercury in environmental samples can help address this challenge by serving as a tracer of specific sources and processes. Mercury isotope variations are small and result only from isotope fractionation during transport, equilibrium, and transformation processes. Because these processes occur in both industrial and environmental settings, knowledge of their associated isotope effects is required to interpret mercury isotope data. To improve the mechanistic modeling of mercury isotope effects during gas phase diffusion, an experimental program tested the applicability of kinetic gas theory. Gas-phase elemental mercury diffusion through small bore needles from finite sources demonstrated mass dependent diffusivities leading to isotope fractionation described by a Rayleigh distillation model. The measured relative atomic diffusivities among mercury isotopes in air are large and in agreement with kinetic gas theory. Mercury diffusion in air offers a reasonable explanation of recent field results reported in the literature. PMID:24364380

  14. Tungsten diffusion in silicon

    SciTech Connect

    De Luca, A.; Texier, M.; Burle, N.; Oison, V.; Pichaud, B.; Portavoce, A.; Grosjean, C.

    2014-01-07

    Two doses (10{sup 13} and 10{sup 15} cm{sup −2}) of tungsten (W) atoms were implanted in different Si(001) wafers in order to study W diffusion in Si. The samples were annealed or oxidized at temperatures between 776 and 960 °C. The diffusion profiles were measured by secondary ion mass spectrometry, and defect formation was studied by transmission electron microscopy and atom probe tomography. W is shown to reduce Si recrystallization after implantation and to exhibit, in the temperature range investigated, a solubility limit close to 0.15%–0.2%, which is higher than the solubility limit of usual metallic impurities in Si. W diffusion exhibits unusual linear diffusion profiles with a maximum concentration always located at the Si surface, slower kinetics than other metals in Si, and promotes vacancy accumulation close to the Si surface, with the formation of hollow cavities in the case of the higher W dose. In addition, Si self-interstitial injection during oxidation is shown to promote W-Si clustering. Taking into account these observations, a diffusion model based on the simultaneous diffusion of interstitial W atoms and W-Si atomic pairs is proposed since usual models used to model diffusion of metallic impurities and dopants in Si cannot reproduce experimental observations.

  15. Tungsten diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Van Orman, J. A.

    2014-03-01

    Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1 atm furnaces for times ranging from 45 min to several weeks, at temperatures from 1050 to 1450 °C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for W diffusion in forsterite: D=1.0×10-8exp(-365±28 kJ mol/RT) m s Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity. The slow diffusivities measured for W in olivine indicate that Hf-W ages in olivine-metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

  16. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, V. R.

    2006-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated. A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  17. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.

    2007-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm) (Fig. 1, left). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated (Fig. 1, right). A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  18. Impurity diffusion in transition-metal oxides

    SciTech Connect

    Peterson, N.L.

    1982-06-01

    Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe/sub 3/O/sub 4/. Tracer impurity diffusion in these materials and TiO/sub 2/, together with measurements of the effect of impurities on tracer diffusion (Co in NiO and Cr in CoO), are reviewed and discussed in terms of impurity-defect interactions and mechanisms of diffusion. Divalent impurities in divalent solvents seem to have a weak interaction with vacancies whereas trivalent impurities in divalent solvents strongly influence the vacancy concentrations and significantly reduce solvent jump frequencies near a trivalent impurity. Impurities with small ionic radii diffuse more slowly with a larger activation energy than impurities with larger ionic radii for all systems considered in this review. Cobalt ions (a moderate size impurity) diffuse rapidly along the open channels parallel to the c-axis in TiO/sub 2/ whereas chromium ions (a smaller-sized impurity) do not. 60 references, 11 figures.

  19. Size of diffusion pore of Alcaligenes faecalis.

    PubMed

    Ishii, J; Nakae, T

    1988-03-01

    The diffusion pore of the outer membrane of Alcaligenes faecalis was shown to be substantially smaller than the Escherichia coli porin pore. In experiments with intact cells, pentoses and hexoses penetrated into the NaCl-expanded periplasm, whereas saccharides of Mr greater than 342 did not. Cells treated with 0.5 M saccharides of Mr greater than 342 weighed 33 to 38% less than cells treated with isotonic solution, suggesting that these saccharides do not permeate through the outer membrane. The diffusion rates of various solutes through the liposome membranes reconstituted from the Mr-43,000 outer membrane protein showed the following characteristics. (i) The relative diffusion rates of pentoses, hexoses, and methylhexoses appeared to be about 1.0, 0.6, and negligibly small, respectively. (ii) The diffusion rate of glucose appeared to be about 1/10th that with the E. coli B porin. (iii) The diffusion rate of gluconic acid was five to seven times higher than that of glucose. (iv) The diffusion rates of beta-lactam antibiotics appeared to be 40 to less than 10% of those with the E. coli B porin. PMID:2835003

  20. Size of diffusion pore of Alcaligenes faecalis.

    PubMed Central

    Ishii, J; Nakae, T

    1988-01-01

    The diffusion pore of the outer membrane of Alcaligenes faecalis was shown to be substantially smaller than the Escherichia coli porin pore. In experiments with intact cells, pentoses and hexoses penetrated into the NaCl-expanded periplasm, whereas saccharides of Mr greater than 342 did not. Cells treated with 0.5 M saccharides of Mr greater than 342 weighed 33 to 38% less than cells treated with isotonic solution, suggesting that these saccharides do not permeate through the outer membrane. The diffusion rates of various solutes through the liposome membranes reconstituted from the Mr-43,000 outer membrane protein showed the following characteristics. (i) The relative diffusion rates of pentoses, hexoses, and methylhexoses appeared to be about 1.0, 0.6, and negligibly small, respectively. (ii) The diffusion rate of glucose appeared to be about 1/10th that with the E. coli B porin. (iii) The diffusion rate of gluconic acid was five to seven times higher than that of glucose. (iv) The diffusion rates of beta-lactam antibiotics appeared to be 40 to less than 10% of those with the E. coli B porin. Images PMID:2835003

  1. 'LTE-diffusion approximation' for arc calculations

    NASA Astrophysics Data System (ADS)

    Lowke, J. J.; Tanaka, M.

    2006-08-01

    This paper proposes the use of the 'LTE-diffusion approximation' for predicting the properties of electric arcs. Under this approximation, local thermodynamic equilibrium (LTE) is assumed, with a particular mesh size near the electrodes chosen to be equal to the 'diffusion length', based on De/W, where De is the electron diffusion coefficient and W is the electron drift velocity. This approximation overcomes the problem that the equilibrium electrical conductivity in the arc near the electrodes is almost zero, which makes accurate calculations using LTE impossible in the limit of small mesh size, as then voltages would tend towards infinity. Use of the LTE-diffusion approximation for a 200 A arc with a thermionic cathode gives predictions of total arc voltage, electrode temperatures, arc temperatures and radial profiles of heat flux density and current density at the anode that are in approximate agreement with more accurate calculations which include an account of the diffusion of electric charges to the electrodes, and also with experimental results. Calculations, which include diffusion of charges, agree with experimental results of current and heat flux density as a function of radius if the Milne boundary condition is used at the anode surface rather than imposing zero charge density at the anode.

  2. Hydrogen diffusion and trapping in nickel

    NASA Technical Reports Server (NTRS)

    Louthan, M. R., Jr.; Donovan, J. A.; Caskey, G. R., Jr.

    1975-01-01

    An analysis of hydrogen transport in pure polycrystalline nickel foils and rods at 300-550 K shows that both trapping and short-circuit diffusion are present and have small yet significant effects on permeation, evolution, and absorption. Both effects appear to be associated primarily with the dislocation substructure of nickel. Relations describing hydrogen transport in nickel are obtained using the data on deuterium permeation, tritium absorption, and outgassing in pure polycrystalline nickel together with earlier measurements of diffusivity and solubility of hydrogen isotopes.

  3. Simulations of singlet exciton diffusion in organic semiconductors: a review

    SciTech Connect

    Bjorgaard, Josiah A.; Kose, Muhammet Erkan

    2014-12-22

    Our review describes the various aspects of simulation strategies for exciton diffusion in condensed phase thin films of organic semiconductors. Several methods for calculating energy transfer rate constants are discussed along with procedures for how to account for energetic disorder. Exciton diffusion can be modelled by using kinetic Monte-Carlo methods or master equations. Recent literature on simulation efforts for estimating exciton diffusion lengths of various conjugated polymers and small molecules are introduced. Moreover, these studies are discussed in the context of the effects of morphology on exciton diffusion and the necessity of accurate treatment of disorder for comparison of simulation results with those of experiment.

  4. Hereditary Diffuse Gastric Cancer

    MedlinePlus

    ... with the syndrome is recommended. What are the estimated cancer risks associated with HDGC? Not everyone who ... the lifetime risk for diffuse gastric cancer is estimated to be 70% to 80% for men and ...

  5. Investigating diffusion with technology

    NASA Astrophysics Data System (ADS)

    Miller, Jon S.; Windelborn, Augden F.

    2013-07-01

    The activities described here allow students to explore the concept of diffusion with the use of common equipment such as computers, webcams and analysis software. The procedure includes taking a series of digital pictures of a container of water with a webcam as a dye slowly diffuses. At known time points, measurements of the pixel densities (darkness) of the digital pictures are recorded and then plotted on a graph. The resulting graph of darkness versus time allows students to see the results of diffusion of the dye over time. Through modification of the basic lesson plan, students are able to investigate the influence of a variety of variables on diffusion. Furthermore, students are able to expand the boundaries of their thinking by formulating hypotheses and testing their hypotheses through experimentation. As a result, students acquire a relevant science experience through taking measurements, organizing data into tables, analysing data and drawing conclusions.

  6. Mastocytosis, diffuse cutaneous (image)

    MedlinePlus

    This is a picture of diffuse, cutaneous mastocytosis. Abnormal collections of cells in the skin (mast cells) produce this rash. Unlike bullous mastocytosis, rubbing will not lead to formation of blisters ( ...

  7. Lung diffusion testing

    MedlinePlus

    Lung diffusion testing measures how well the lungs exchange gases. This is an important part of lung testing , because ... Gender Height Hemoglobin (the protein in red blood cells that carries oxygen) level

  8. Hydrogen Diffusion in Forsterite

    NASA Astrophysics Data System (ADS)

    Demouchy, S.; Mackwell, S.

    2002-12-01

    Physical and chemical properties of Earth's mantle are readily modified by interaction with volatiles, such as water. Thus, characterization of solubility and kinetics of incorporation for water in nominally anhydrous minerals is important in order to understand the behavior of Earth's interior under hydrous conditions. Experimental studies on the olivine-water system indicate that significant amounts of OH can dissolve within olivine as point defects (Bell and Rossman, 1992; Kohlstedt et al. 1996). Extending Kohlstedt and Mackwell's (1998) work, our study concerns the kinetics of hydrogen transport in the iron-free olivine-water system. This study is based on hydrogenation of forsterite samples during piston-cylinder and TZM cold-seal vessel experiments. We use infrared analyses in order to constrain the speciation of the mobile water-derived defects in forsterite single-crystal sample, and the rates of diffusion of such species under uppermost mantle conditions (0.2 to 1.5 GPa, 900 to 1100° C). Hydrogen defect transport in single crystals of forsterite is investigated for diffusion parallel to each crystallographic axis. Defect diffusivities are obtained by fitting a diffusion law to the OH content as a function of position in the sample. Our current results indicate that incorporation of hydroxyl species into iron-free olivine is a one-stage process with hydrogen diffusion linked to magnesium vacancy self-diffusion DV, such that DV = D~/3 = 10-12 m2/s at 1000° C parallel to [001], where D~ represents the chemical diffusivity. Those diffusion rates are slightly lower than in iron-bearing olivine for the same incorporation mechanism. The different concentration profiles show a clear anisotropy of diffusion, with fastest diffusion parallel to [001] as in iron-bearing olivine. Thus, while hydrogen solubilities are dependent on iron content, the rate of incorporation of water-derived species in olivine is not strongly coupled to the concentration of iron. This

  9. Diffusion and isotope effects in the diffusion of homovalent cations in cesium iodide

    NASA Astrophysics Data System (ADS)

    Klotsman, S. M.; Polikarpova, I. P.; Tatarinova, G. N.; Timofeev, A. N.

    1988-10-01

    Preexponentials D0 and activation energies Q for self-diffusion and diffusion of homovalent cations of small radius in single crystals of CsI measured by the tracer sectioning method are as follows: for 137Cs, 19+/-1.5 cm2 s-1 and 35.59+/-0.18 kcal/mol; for 86Rb, 30.7+/-3.0 cm2 s-1 and 35.13+/-0.22 kcal/mol; for 42K, 47+/-6 cm2 s-1 and 35.30+/-0.30 kcal/mol; for 22Na, 34.94+/-0.20 kcal/mol, respectively. The temperature dependence of the isotope effect for diffusion of 22,24Na in CsI is described by a simple exponent: E=126 exp[-(13.3+/-1.5 kcal/mol)/RT]. Calculations based on these experimental results and the ``five-frequency model'' of diffusion are provided to obtain the main diffusion parameters for all homovalent cations in CsI. The diffusion behavior of these cations in CsI is in good agreement with the model of ``displaced homovalent cations of small radius.''

  10. Computational simulations of vorticity enhanced diffusion

    NASA Astrophysics Data System (ADS)

    Vold, Erik L.

    1999-11-01

    Computer simulations are used to investigate a phenomenon of vorticity enhanced diffusion (VED), a net transport and mixing of a passive scalar across a prescribed vortex flow field driven by a background gradient in the scalar quantity. The central issue under study here is the increase in scalar flux down the gradient and across the vortex field. The numerical scheme uses cylindrical coordinates centered with the vortex flow which allows an exact advective solution and 1D or 2D diffusion using simple numerical methods. In the results, the ratio of transport across a localized vortex region in the presence of the vortex flow over that expected for diffusion alone is evaluated as a measure of VED. This ratio is seen to increase dramatically while the absolute flux across the vortex decreases slowly as the diffusion coefficient is decreased. Similar results are found and compared for varying diffusion coefficient, D, or vortex rotation time, τv, for a constant background gradient in the transported scalar vs an interface in the transported quantity, and for vortex flow fields constant in time vs flow which evolves in time from an initial state and with a Schmidt number of order unity. A simple analysis shows that for a small diffusion coefficient, the flux ratio measure of VED scales as the vortex radius over the thickness for mass diffusion in a viscous shear layer within the vortex characterized by (Dτv)1/2. The phenomenon is linear as investigated here and suggests that a significant enhancement of mixing in fluids may be a relatively simple linear process. Discussion touches on how this vorticity enhanced diffusion may be related to mixing in nonlinear turbulent flows.

  11. Nodal Diffusion & Transport Theory

    1992-02-19

    DIF3D solves multigroup diffusion theory eigenvalue, adjoint, fixed source, and criticality (concentration, buckling, and dimension search) problems in 1, 2, and 3-space dimensions for orthogonal (rectangular or cylindrical), triangular, and hexagonal geometries. Anisotropic diffusion theory coefficients are permitted. Flux and power density maps by mesh cell and regionwise balance integrals are provided. Although primarily designed for fast reactor problems, upscattering and internal black boundary conditions are also treated.

  12. Advanced manufacturing: Technology diffusion

    SciTech Connect

    Tesar, A.

    1995-12-01

    In this paper we examine how manufacturing technology diffuses rom the developers of technology across national borders to those who do not have the capability or resources to develop advanced technology on their own. None of the wide variety of technology diffusion mechanisms discussed in this paper are new, yet the opportunities to apply these mechanisms are growing. A dramatic increase in technology diffusion occurred over the last decade. The two major trends which probably drive this increase are a worldwide inclination towards ``freer`` markets and diminishing isolation. Technology is most rapidly diffusing from the US In fact, the US is supplying technology for the rest of the world. The value of the technology supplied by the US more than doubled from 1985 to 1992 (see the Introduction for details). History shows us that technology diffusion is inevitable. It is the rates at which technologies diffuse to other countries which can vary considerably. Manufacturers in these countries are increasingly able to absorb technology. Their manufacturing efficiency is expected to progress as technology becomes increasingly available and utilized.

  13. Derivation of anisotropic diffusion coefficients in a large annular cavity

    SciTech Connect

    Eiichi Suetomi; Hiroshi Sekimoto )

    1993-06-01

    A small reactor for a spacecraft or a small liquid-metal reactor for urban siting, decentralized electrical units, or seawater desalination is designed for a large leakage of neutrons from the reactor core. In these reactors, a movable annular reflector is used for reactivity control. Therefore, a large annular cavity exists between the core and the shielding materials. In this paper, anisotropic diffusion coefficients for a large annular cavity are derived by equating the neutron currents obtained by the diffusion equation and by the transport equation. These diffusion coefficients depend only on the geometrical configuration of the cavity. A numerical comparison of diffusion calculations using these diffusion coefficients and transport calculations shows good agreement.

  14. Small Wins.

    ERIC Educational Resources Information Center

    Rhatigan, James J.; Schuh, John H.

    2003-01-01

    Examines how it easy for people to overlook small successes when they are overwhelmed by and preoccupied with large projects and goals. Explores the concept of "small wins" in organizational theory, which have the potential to become a prominent part of institutional culture and impact organizational behavior and change. (GCP)

  15. Chemical effect on diffusion in intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Ting

    With the trend of big data and the Internet of things, we live in a world full of personal electronic devices and small electronic devices. In order to make the devices more powerful, advanced electronic packaging such as wafer level packaging or 3D IC packaging play an important role. Furthermore, ?-bumps, which connect silicon dies together with dimension less than 10 ?m, are crucial parts in advanced packaging. Owing to the dimension of ?-bumps, they transform into intermetallic compound from tin based solder after the liquid state bonding process. Moreover, many new reliability issues will occur in electronic packaging when the bonding materials change; in this case, we no longer have tin based solder joint, instead, we have intermetallic compound ?-bumps. Most of the potential reliability issues in intermetallic compounds are caused by the chemical reactions driven by atomic diffusion in the material; thus, to know the diffusivities of atoms inside a material is significant and can help us to further analyze the reliability issues. However, we are lacking these kinds of data in intermetallic compound because there are some problems if used traditional Darken's analysis. Therefore, we considered Wagner diffusivity in our system to solve the problems and applied the concept of chemical effect on diffusion by taking the advantage that large amount of energy will release when compounds formed. Moreover, by inventing the holes markers made by Focus ion beam (FIB), we can conduct the diffusion experiment and obtain the tracer diffusivities of atoms inside the intermetallic compound. We applied the technique on Ni3Sn4 and Cu3Sn, which are two of the most common materials in electronic packaging, and the tracer diffusivities are measured under several different temperatures; moreover, microstructure of the intermetallic compounds are investigated to ensure the diffusion environment. Additionally, the detail diffusion mechanism was also discussed in aspect of diffusion

  16. Cation Diffusion in Xenotime

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    2004-05-01

    Xenotime is an important mineral in metamorphic paragenesis, and useful in isotopic dating, garnet-xenotime thermometry, and monazite-xenotime thermometry, so diffusion data for xenotime of cations of geochronological and geochemical importance are of some interest. We report here on diffusion of the rare earth elements Sm, Dy and Yb in synthetic xenotime under dry conditions. The synthetic xenotime was grown via a Na2}CO{3}-MoO_{3 flux method. The source of diffusant for the experiments were REE phosphate powders, with experiments run with sources containing a single REE. Experiments were performed by placing source and xenotime in Pt capsules, and annealing capsules in 1 atm furnaces for times ranging from thirty minutes to a month, at temperatures from 1000 to 1400C. The REE distributions in the xenotime were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relations are obtained for diffusion in xenotime, normal to (101): DSm = 1.7x10-4 exp(-442 kJ mol-1/RT) m2}sec{-1 DDy = 3.5x10-7 exp(-365 kJ mol-1/RT) m2}sec{-1 DYb = 7.4x10-7 exp(-371 kJ mol-1/RT) m2}sec{-1. Diffusivities of these REE do not differ greatly in xenotime, in contrast to the findings noted for the REE in zircon (Cherniak et al., 1997), where the LREE diffuse more slowly, and with higher activation energies for diffusion, than the heavier rare earths. In zircon, these differences among diffusion of the rare earths are attributed to the relatively large size of the REE with respect to Zr, for which they substitute in the zircon lattice. With the systematic increase in ionic radius from the heavy to lighter REE, this size mismatch becomes more pronounced and diffusivities of the LREE are as consequence slower. Although xenotime is isostructural with zircon, the REE are more closely matched in size to Y, so in xenotime this effect appears much smaller and the REE diffuse at similar rates. In addition, the process of diffusion in xenotime likely involves simple REE+3

  17. Ti Diffusion in Pyroxene

    NASA Astrophysics Data System (ADS)

    Cherniak, D.; Liang, Y.

    2008-12-01

    Diffusion of titanium has been characterized in natural enstatite and diopside under buffered conditions and in air. The sources of diffusant for the enstatite experiments were mixtures of Mg, Si and Ti oxide powders, which were combined and heated at 1300°C overnight, and then thoroughly mixed with synthesized enstatite powder and heated for an additional day at 1300°C. Sources for diopside experiments were prepared similarly, using Ca, Mg, Si, and Ti oxide powders combined with synthesized diopside powder, with heating of source materials at 1200°C. Buffered experiments were prepared by enclosing source material and pyroxene (polished and pre-annealed under conditions comparable to those to be experienced in the experiment) in AgPd or platinum capsules, placing the metal capsule in a silica glass capsule with a solid buffer (to buffer at NNO or IW) and sealing the assembly under vacuum. Some experiments on enstatite were run in air; sample and source were placed in Pt capsules and crimped shut. Prepared capsules were then annealed in 1 atm furnaces for times ranging from 8 hours to a few months, at temperatures from 950 to 1200°C. The Ti distributions in the pyroxene were profiled with Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for Ti diffusion in a natural enstatite, for diffusion normal to the (210) cleavage face (950 - 1150°C, experiments run in air): DTi = 1.9×10-10 exp(-300 ± 44 kJ mol-1/RT) m2 sec-1. Diffusion under NNO and IW-buffered conditions is similar to that for experiments run in air, suggesting little dependence of Ti diffusion on oxygen fugacity. There is also little evidence of anisotropy, as diffusion normal to (001) does not differ significantly from diffusion for the other orientation. Preliminary findings for Ti diffusion in diopside suggest diffusivities similar to those for enstatite. Ti diffusivities in enstatite are similar to those of the trivalent REEs (Cherniak and Liang, 2007

  18. Restricted Transport in Small Pores

    PubMed Central

    Anderson, John L.; Quinn, John A.

    1974-01-01

    The basic hydrodynamic equations governing transport in submicron pores are reexamined. Conditions necessary for a simplified, one-dimensional treatment of the diffusion/convection process are established. Steric restrictions and Brownian motion are incorporated directly into the resulting model. Currently available fluid mechanical results are used to evaluate an upper limit on hindered diffusion; this limit is valid for small particle-to-pore ratios. Extensions of the analysis are shown to depend on numerical solutions of the related hydrodynamic problem, that of asymmetrical particle motion in a bounded fluid. PMID:4813157

  19. Numerical discretization for nonlinear diffusion filter

    NASA Astrophysics Data System (ADS)

    Mustaffa, I.; Mizuar, I.; Aminuddin, M. M. M.; Dasril, Y.

    2015-05-01

    Nonlinear diffusion filters are famously used in machine vision for image denoising and restoration. This paper presents a study on the effects of different numerical discretization of nonlinear diffusion filter. Several numerical discretization schemes are presented; namely semi-implicit, AOS, and fully implicit schemes. The results of these schemes are compared by visual results, objective measurement e.g. PSNR and MSE. The results are also compared to a Daubechies wavelet denoising method. It is acknowledged that the two preceding scheme have already been discussed in literature, however comparison to the latter scheme has not been made. The semi-implicit scheme uses an additive operator splitting (AOS) developed to overcome the shortcoming of the explicit scheme i.e., stability for very small time steps. Although AOS has proven to be efficient, from the nonlinear diffusion filter results with different discretization schemes, examples shows that implicit schemes are worth pursuing.

  20. MODIS Solar Diffuser: Modelled and Actual Performance

    NASA Technical Reports Server (NTRS)

    Waluschka, Eugene; Xiong, Xiao-Xiong; Esposito, Joe; Wang, Xin-Dong; Krebs, Carolyn (Technical Monitor)

    2001-01-01

    The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument's solar diffuser is used in its radiometric calibration for the reflective solar bands (VIS, NTR, and SWIR) ranging from 0.41 to 2.1 micron. The sun illuminates the solar diffuser either directly or through a attenuation screen. The attenuation screen consists of a regular array of pin holes. The attenuated illumination pattern on the solar diffuser is not uniform, but consists of a multitude of pin-hole images of the sun. This non-uniform illumination produces small, but noticeable radiometric effects. A description of the computer model used to simulate the effects of the attenuation screen is given and the predictions of the model are compared with actual, on-orbit, calibration measurements.

  1. Various diffusion magnetic resonance imaging techniques for pancreatic cancer

    PubMed Central

    Tang, Meng-Yue; Zhang, Xiao-Ming; Chen, Tian-Wu; Huang, Xiao-Hua

    2015-01-01

    Pancreatic cancer is one of the most common malignant tumors and remains a treatment-refractory cancer with a poor prognosis. Currently, the diagnosis of pancreatic neoplasm depends mainly on imaging and which methods are conducive to detecting small lesions. Compared to the other techniques, magnetic resonance imaging (MRI) has irreplaceable advantages and can provide valuable information unattainable with other noninvasive or minimally invasive imaging techniques. Advances in MR hardware and pulse sequence design have particularly improved the quality and robustness of MRI of the pancreas. Diffusion MR imaging serves as one of the common functional MRI techniques and is the only technique that can be used to reflect the diffusion movement of water molecules in vivo. It is generally known that diffusion properties depend on the characterization of intrinsic features of tissue microdynamics and microstructure. With the improvement of the diffusion models, diffusion MR imaging techniques are increasingly varied, from the simplest and most commonly used technique to the more complex. In this review, the various diffusion MRI techniques for pancreatic cancer are discussed, including conventional diffusion weighted imaging (DWI), multi-b DWI based on intra-voxel incoherent motion theory, diffusion tensor imaging and diffusion kurtosis imaging. The principles, main parameters, advantages and limitations of these techniques, as well as future directions for pancreatic diffusion imaging are also discussed. PMID:26753059

  2. Counterion Diffusion in Ionomers

    NASA Astrophysics Data System (ADS)

    Walter, Russell; Winey, Karen; Kim, Joon-Seop; Composto, Russell

    2004-03-01

    Diffusion of Cs counterions to the air/ionomer film interface is followed using Rutherford backscattering spectrometry and results compared with the "sticky reptation" model[1]. The ionomer system is poly(styrene-ran-methacrylic acid) (Cs-SMAA) neutralized at 100% by Cs. The concentration profiles exhibit a surface excess, z*, of Cs followed by a depletion of Cs. The z* and depletion layer thickness grow as t1/2, consistent with diffusion limited growth. Annealing studies at 130 °C, 145 °C and 208 °C were used to extract the diffusion coefficient, D. In all cases, D is greater than that of the matrix chains. These results suggest that the diffusion rate is controlled by the fraction of counterions that disassociate from the acid groups and migrate through the matrix. Moreover, the "sticky reptation" model doesn't appear to predict the diffusion behavior in the Cs-SMAA system. [1] Leibler, L, Ludwick, L., Rubinstein, M., Colby, R.H., Macromolecules 24 (1991) 4701.

  3. NMR measurements of solvent self-diffusion coefficients in polymer solutions

    NASA Astrophysics Data System (ADS)

    Blum, Frank D.; Pickup, Stephen; Waggoner, R. Allen

    1989-11-01

    The transport of solvents and other small molecules in polymer solutions is important in many areas such as reaction rates, drying of coatings, plasticizer loss, curing of resins, elimination of residual monomer, and controlled drug release. Some of the work done in our laboratory on the diffusion of small molecules in polymer solutions and dispersions is reviewed. The diffusion data was used to test the Vrentas and Duda's free-volume theory for self-diffusion coefficients; test the independence of the normalized solvent self-diffusion for several polymer-solvent systems; and predict the solvent loss curves for drying of coatings based on solvent self-diffusion coefficients.

  4. Position Displacement of Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Galazutdinov, G.; Krełowski, J.; Beletsky, Y.; Valyavin, G.

    2015-04-01

    We reconsider the already published phenomenon of the blue shift of diffuse interstellar bands, observed in spectra of HD34078 (AE Aur) and members of the Sco OB1 association, in particular HD152233. We have analyzed 29 diffuse bands. Some of them, already proven as blue-shifted in our earlier study, are now confirmed using another instrument: the 6.5 m Clay telescope equipped with the MIKE spectrograph. The high signal-to-noise ratio (over 600) of our spectra allowed us to reveal even small small-scale displacements of positions (both blue and redshifts) of diffuse bands along the considered lines of sight. In some cases, the magnitude of deviation exceeds 10 km s-1. Also, we prove that profiles of many diffuse bands in spectra of HD34078 suffer significant broadening. The origin of the observed phenomena is discussed. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory (Chile).

  5. Cesium diffusion in graphite

    SciTech Connect

    Evans, R.B. III; Davis, W. Jr.; Sutton, A.L. Jr.

    1980-05-01

    Experiments on diffusion of /sup 137/Cs in five types of graphite were performed. The document provides a completion of the report that was started and includes a presentation of all of the diffusion data, previously unpublished. Except for data on mass transfer of /sup 137/Cs in the Hawker-Siddeley graphite, analyses of experimental results were initiated but not completed. The mass transfer process of cesium in HS-1-1 graphite at 600 to 1000/sup 0/C in a helium atmosphere is essentially pure diffusion wherein values of (E/epsilon) and ..delta..E of the equation D/epsilon = (D/epsilon)/sub 0/ exp (-..delta..E/RT) are about 4 x 10/sup -2/ cm/sup 2//s and 30 kcal/mole, respectively.

  6. Apparatus for diffusion separation

    DOEpatents

    Nierenberg, William A.; Pontius, Rex B.

    1976-08-10

    1. The method of testing the separation efficiency of porous permeable membranes which comprises causing a stream of a gaseous mixture to flow into contact with one face of a finely porous permeable membrane under such conditions that a major fraction of the mixture diffuses through the membrane, maintaining a rectangular cross section of the gaseous stream so flowing past said membrane, continuously recirculating the gas that diffuses through said membrane and continuously withdrawing the gas that does not diffuse through said membrane and maintaining the volume of said recirculating gas constant by continuously introducing into said continuously recirculating gas stream a mass of gas equivalent to that which is continuously withdrawn from said gas stream and comparing the concentrations of the light component in the entering gas, the withdrawn gas and the recirculated gas in order to determine the efficiency of said membrane.

  7. Complex hydrogen diffusion in forsterite

    NASA Astrophysics Data System (ADS)

    Padron-Navarta, J.

    2013-12-01

    The singular geodynamic and chemical evolution of the Earth seems to be dictated by the influence of 'water' (more specifically hydrogen structurally bonded to oxygen forming hydroxyl groups, OH-) on the physical properties of the nominally minerals of the Earth's mantle. In the most abundant upper mantle phase, olivine, the presence of hydrogen has been shown to significantly modify the timescale of chemical diffusion, plastic deformation, electrical conductivity and the attenuation of seismic waves. In olivine there are four different hydrogen substitution mechanisms, associated with Mg vacancies, Si vacancies, trivalent cations and titanium substitution, hereafter referred to as H[Mg], H[Si], H[triv] and H[Ti] respectively. It seems possible that hydrogen diffusion rates vary with the type of defect. We addressed this hypothesis by an experimental investigation of the dehydroxylation of synthetic forsterite with two contrasting hydrous defect populations: (1) Ti4+-doped forsterite with H[Si], and H[Ti] dominant and H[Mg] and H[triv] subsidiary; and (2) MgO-buffered forsterite with only H[Si] hydrous defects. The experiments were conducted by annealing the hydroxylated forsterites at atmospheric pressure and 1073 to 1273 K, with OH- contents monitored at intervals by room-temperature FTIR spectroscopy. For the Ti4+-doped forsterite, four stages were observed during dehydoxylation. Firstly, the small amounts of H[Mg] and H[triv] disappear very quickly. Secondly, Ti is removed from the forsterite lattice by precipitation of a new phase; thirdly, the dehydroxylation of H[Ti] as monitored by the 3525 cm-1 peak proceeds at the same rate as H[Si] monitored by the 3613 cm-1 peak; and fourthly, once H[Ti] reaches zero, the dehydroxylation of H[Si] slows drastically, to rates that are unobservable in the duration of our experiments (1073-1273 K). Whereas the rates of loss of H[Mg] and H[triv] are in agreement with previous measurements of bulk hydrogen diffusion in

  8. Diffusion imaging concepts for clinicians.

    PubMed

    Neil, Jeffrey J

    2008-01-01

    This review covers the fundamentals of diffusion tensor imaging. It is written with the clinician in mind and assumes the reader has a passing familiarity with magnetic resonance imaging (MRI). Topics covered include comparison of diffusion MRI with conventional MRI, water apparent diffusion coefficient (ADC), diffusion anisotropy, tract tracing, and changes of water apparent diffusion in response to injury. The discussion centers primarily on applications to the central nervous system, but examples from other tissues are included. PMID:18050325

  9. Hydrogen diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Ingrin, Jannick; Zhang, Peipei

    2016-04-01

    Hydrogen mobility in gem quality zircon single crystals from Madagascar was investigated through H-D exchange experiments. Thin slices were annealed in a horizontal furnace flushed with a gas mixture of Ar/D2(10%) under ambient pressure between 900 ° C to 1150 ° C. FTIR analyses were performed on oriented slices before and after each annealing run. H diffusion along [100] and [010] follow the same diffusion law D = D0exp[-E /RT], with log D0 = 2.24 ± 1.57 (in m2/s) and E = 374 ± 39 kJ/mol. H diffusion along [001] follows a slightly more rapid diffusion law, with log D0 = 1.11 ± 0.22 (in m2/s) and E = 334 ± 49 kJ/mol. H diffusion in zircon has much higher activation energy and slower diffusivity than other NAMs below 1150 ° C even iron-poor garnets which are known to be among the slowest (Blanchard and Ingrin, 2004; Kurka et al. 2005). During H-D exchange zircon incorporates also deuterium. This hydration reaction involves uranium reduction as it is shown from the exchange of U5+ and U4+ characteristic bands in the near infrared region during annealing. It is the first time that a hydration reaction U5+ + OH‑ = U4+ + O2‑ + 1/2H2, is experimentally reported. The kinetics of deuterium incorporation is slightly slower than hydrogen diffusion, suggesting that the reaction is limited by hydrogen mobility. Hydrogen isotopic memory of zircon is higher than other NAMs. Zircons will be moderately retentive of H signatures at mid-crustal metamorphic temperatures. At 500 ° C, a zircon with a radius of 300 μm would retain its H isotopic signature over more than a million years. However, a zircon is unable to retain this information for geologically significant times under high-grade metamorphism unless the grain size is large enough. Refrences Blanchard, M. and Ingrin, J. (2004) Hydrogen diffusion in Dora Maira pyrope. Physics and Chemistry of Minerals, 31, 593-605. Kurka, A., Blanchard, M. and Ingrin, J. (2005) Kinetics of hydrogen extraction and deuteration in

  10. Radon diffusion modelling.

    PubMed

    Wilkinson, P; Dimbylow, P J

    1985-10-01

    A mathematical model has been developed that examines the ingress of radon into houses, through a vertical crack in an otherwise impervious concrete floor. Initially, the model considered the diffusive flow of radon from its soil source and this simulation has highlighted the dependency of the flux of radon into the house on the magnitude of various parameters, such as the diffusion coefficient of radon in soil. A preliminary investigation of the modelling of pressure-driven flow into a building is presented, and the potential of this type of analysis is discussed. PMID:4081719

  11. Evolution of error diffusion

    NASA Astrophysics Data System (ADS)

    Knox, Keith T.

    1999-10-01

    As we approach the new millennium, error diffusion is approaching the 25th anniversary of its invention. Because of its exceptionally high image quality, it continues to be a popular choice among digital halftoning algorithms. Over the last 24 years, many attempts have been made to modify and improve the algorithm--to eliminate unwanted textures and to extend it to printing media and color. Some of these modifications have been very successful and are in use today. This paper will review the history of the algorithm and its modifications. Three watershed events in the development of error diffusion will be described, together with the lessons learned along the way.

  12. Evolution of error diffusion

    NASA Astrophysics Data System (ADS)

    Knox, Keith T.

    1998-12-01

    As we approach the new millennium, error diffusion is approaching the 25th anniversary of its invention. Because of its exceptionally high image quality, it continues to be a popular choice among digital halftoning algorithms. Over the last 24 years, many attempts have been made to modify and improve the algorithm - to eliminate unwanted textures and to extend it to printing media and color. Some of these modifications have been very successful and are in use today. This paper will review the history of the algorithm and its modifications. Three watershed events in the development of error diffusion will be described, together with the lesions learned along the way.

  13. Mass diffusion in liquids

    NASA Astrophysics Data System (ADS)

    Walter, H. U.

    Dimensionless number analysis indicates that diffusion-controlled conditions with liquid samples having characteristic dimensions larger than one millimetre can only be established under microgravity conditions.Consequently, heat and mass transport properties of fluids can only be quantitatively investigated in space.Results obtained from experiments on selfdiffusion, interdiffusion and thermodiffusion carried out during the SL-1 and D-1 Spacelab missions clearly demonstrate the potential of space platforms to determine such properties with a precision unattainable on earth. These results imply also that crystal growth from solutions, vapours and melts in the diffusive regime can be realised in space only.

  14. Diffusion impact on atmospheric moisture transport

    NASA Astrophysics Data System (ADS)

    Moseley, C.; Haerter, J.; Göttel, H.; Hagemann, S.; Jacob, D.

    2009-04-01

    To ensure numerical stability, many global and regional climate models employ numerical diffusion to dampen short wavelength modes. Terrain following sigma diffusion is known to cause unphysical effects near the surface in orographically structured regions. They can be reduced by applying z-diffusion on geopotential height levels. We investigate the effect of the diffusion scheme on atmospheric moisture transport and precipitation formation at different resolutions in the European region. With respect to a better understanding of diffusion in current and future grid-space global models, current day regional models may serve as the appropriate tool for studies of the impact of diffusion schemes: Results can easily be constrained to a small test region and checked against reliable observations, which often are unavailable on a global scale. Special attention is drawn to the Alps - a region of strong topographic gradients and good observational coverage. Our study is further motivated by the appearance of the "summer drying problem" in South Eastern Europe. This too warm and too dry simulation of climate is common to many regional climate models and also to some global climate models, and remains a permanent unsolved problem in the community. We perform a systematic comparison of the two diffusion-schemes with respect to the hydrological cycle. In particular, we investigate how local meteorological quantities - such as the atmospheric moisture in the region east of the Alps - depend on the spatial model resolution. Higher model resolution would lead to a more accurate representation of the topography and entail larger gradients in the Alps. This could lead to consecutively stronger transport of moisture along the slopes in the case of sigma-diffusion with subsequent orographic precipitation, whereas the effect could be qualitatively different in the case of z-diffusion. For our study, we analyse a sequence of simulations of the regional climate model REMO employing

  15. Multispecies diffusion models: A study of uranyl species diffusion

    NASA Astrophysics Data System (ADS)

    Liu, Chongxuan; Shang, Jianying; Zachara, John M.

    2011-12-01

    Rigorous numerical description of multispecies diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication in imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multispecies diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multispecies diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multispecies U(VI) diffusion under a steady state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that for multispecies U(VI) diffusion under transient chemical conditions, a fully coupled diffusion model could be well approximated by a component-based diffusion model when the diffusion coefficient for each chemical component was properly selected. The component-based diffusion model considers the difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be enforced, if necessary, by adding a secondary migration term resulting from model simplification. The effect of ion activity coefficient gradients on multispecies diffusion is also discussed. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from U.S. Department of Energy's Hanford 300A

  16. Irradiance calibration with solar diffuser

    NASA Technical Reports Server (NTRS)

    Haring, Robert E. (Inventor); Roeder, Herbert A. (Inventor); Hartmann, Ulli G. (Inventor)

    1993-01-01

    The sun's energy is used in combination of movable and fixed diffuser plates, windows and apertures which are positioned in a series of test sequences (modes) for reflectance monitoring and calibration without the use of man-made sources. There are three embodiments, or implementations, of the invention--one embodiment uses two diffusers--a working diffuser and a secondary diffuser--the second embodiment uses three diffusers, a working diffuser, a secondary diffuser and a reference diffuser--and the third embodiment uses two diffusers--a working diffuser and a secondary diffuser, the latter also functioning as a cover for the working diffuser. The movable diffusers are mounted on rotatable cones and, in all embodiments, the sun is blocked from reaching the diffusers when not in use. Thus, the sun is used as a stable source for calibration and monitoring and the sun/diffuser combination is used in such a way that the response of all elements of the optical subsystem of the TOMS can be unambiguously and efficiently characterized with high accuracy and precision.

  17. Improved Thermal-Diffusivity-Measuring Apparatus

    NASA Technical Reports Server (NTRS)

    Wood, C.; Zoltan, A.

    1985-01-01

    Accuracy at high temperature improved. Furnace heats specimen to experimental temperature, and flash tube raises specimen temperature by small amount and for short time so diffusivity (composite property of heat capacity and conductivity) determined. Specimen mount ensures minimum heat loss during temperature-rise measurement. Measurement temperatures up to 1,000 degrees C realized with fused-quartz light pipe and up to 1,600 degrees C with sapphire light pipe.

  18. Small ethics.

    PubMed

    Chambers, David W

    2007-01-01

    Traditionally, ethics in the professions has focused on big problems that could be found on other peoples' back porches. Small, habitual, frequent, and personal lapses get little attention. In this essay, the literature on opportunism is applied to dentistry with a view toward bringing matters of "near ethics" within reach. Examples of small lapses are discussed under the headings of shirking, free riding, shrinkage, pressing, adverse selection, moral hazard, and risk shifting. The conditions that support opportunism include relationships with small numbers of transactions and uneven access to information. Practical limits on understanding all the consequences of agreements and the costs of supervising others and enforcing corrections of breaches are inescapable aspects of opportunism. Opportunism may not be accepted by all as the subject matter of ethical, but curbing it is a worthy goal and understanding the causes and management of opportunism casts some light on the ethical enterprise. Four suggestions are offered for addressing issue of opportunism. PMID:17691498

  19. Diffusion in random networks

    NASA Astrophysics Data System (ADS)

    Padrino, Juan C.; Zhang, Duan Z.

    2015-11-01

    The ensemble phase averaging technique is applied to model mass transport in a porous medium. The porous material is idealized as an ensemble of random networks, where each network consists of a set of junction points representing the pores and tortuous channels connecting them. Inside a channel, fluid transport is assumed to be governed by the one-dimensional diffusion equation. Mass balance leads to an integro-differential equation for the pores mass density. Instead of attempting to solve this equation, and equivalent set of partial differential equations is derived whose solution is sought numerically. As a test problem, we consider the one-dimensional diffusion of a substance from one end to the other in a bounded domain. For a statistically homogeneous and isotropic material, results show that for relatively large times the pore mass density evolution from the new theory is significantly delayed in comparison with the solution from the classical diffusion equation. In the short-time case, when the solution evolves with time as if the domain were semi-infinite, numerical results indicate that the pore mass density becomes a function of the similarity variable xt- 1 / 4 rather than xt- 1 / 2 characteristic of classical diffusion. This result was verified analytically. Possible applications of this framework include flow in gas shales. Work supported by LDRD project of LANL.

  20. Osmosis and Diffusion

    ERIC Educational Resources Information Center

    Sack, Jeff

    2005-01-01

    OsmoBeaker is a CD-ROM designed to enhance the learning of diffusion and osmosis by presenting interactive experimentation to the student. The software provides several computer simulations that take the student through different scenarios with cells, having different concentrations of solutes in them.

  1. Thermodynamics of diffusion

    NASA Astrophysics Data System (ADS)

    Matuszak, Daniel

    Diffusion is the migration of molecules in the reference frame of a system's center of mass and it is a physical process that occurs in all chemical and biological systems. Diffusion generally involves intermolecular interactions that lead to clustering, adsorption, and phase transitions; as such, it is difficult to describe theoretically on a molecular level in systems containing both intermolecular repulsions and attractions. This work describes a simple thermodynamic approach that accounts for intermolecular attractions and repulsions (much like how the van der Waals equation does) to model and help provide an understanding of diffusion. The approach is an extension of the equilibrium Lattice Density Functional Theory of Aranovich and Donohue; it was developed with Mason and Lonsdale's guidelines on how to construct and test a transport theory. In the framework of lattice fluids, this new approach gives (a) correct equilibrium limits, (b) Fickian behavior for non-interacting systems, (c) correct departures from Fickian behavior in non-ideal systems, (d) the correct Maxwell-Stefan formulation, (e) symmetry behavior upon re-labeling species, (f) reasonable non-equilibrium phase behavior, (g) agreement with Molecular Dynamics simulations, (h) agreement with the theory of non-equilibrium thermodynamics, (i) a vanishing diffusive flux at the critical point, and (j) other qualitatively-correct behaviors when applied to problems in porous membranes and in packed beds.

  2. Diffuse sorption modeling.

    PubMed

    Pivovarov, Sergey

    2009-04-01

    This work presents a simple solution for the diffuse double layer model, applicable to calculation of surface speciation as well as to simulation of ionic adsorption within the diffuse layer of solution in arbitrary salt media. Based on Poisson-Boltzmann equation, the Gaines-Thomas selectivity coefficient for uni-bivalent exchange on clay, K(GT)(Me(2+)/M(+))=(Q(Me)(0.5)/Q(M)){M(+)}/{Me(2+)}(0.5), (Q is the equivalent fraction of cation in the exchange capacity, and {M(+)} and {Me(2+)} are the ionic activities in solution) may be calculated as [surface charge, mueq/m(2)]/0.61. The obtained solution of the Poisson-Boltzmann equation was applied to calculation of ionic exchange on clays and to simulation of the surface charge of ferrihydrite in 0.01-6 M NaCl solutions. In addition, a new model of acid-base properties was developed. This model is based on assumption that the net proton charge is not located on the mathematical surface plane but diffusely distributed within the subsurface layer of the lattice. It is shown that the obtained solution of the Poisson-Boltzmann equation makes such calculations possible, and that this approach is more efficient than the original diffuse double layer model. PMID:19159896

  3. Diffusion welding tool

    NASA Technical Reports Server (NTRS)

    Milam, T. B.

    1973-01-01

    Tool allows flat plate diffusion welding to be done in standard brazing furnace. Weld is achieved using high water pressure applied by hand-operated positive-displacement pump. Good welds have been obtained between nickel and nickel-base alloy plates at temperature of 1200 K and water pressure of 13.8 million N/sq m.

  4. Water vapor diffusion membranes

    NASA Technical Reports Server (NTRS)

    Holland, F. F., Jr.; Smith, J. K.

    1974-01-01

    The program is reported, which was designed to define the membrane technology of the vapor diffusion water recovery process and to test this technology using commercially available or experimental membranes. One membrane was selected, on the basis of the defined technology, and was subjected to a 30-day demonstration trial.

  5. Ti Diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2006-12-01

    Diffusion of Ti under anhydrous conditions at 1 atmosphere and under fluid-present conditions at 1.1-1.2 GPa has been measured in natural zircon. The source of diffusant for 1-atm experiments was a ZrO2- TiO2-ZrSiO4 mixture, with experiments run in Pt capsules. Diffusion experiments conducted in the presence of H2O-CO2 fluid were run in a piston-cylinder apparatus, using a source of ground TiO2, ZrSiO4 and SiO2, with oxalic acid added to produce H2O-CO2 vapor and partially melt the solid source material, yielding an assemblage of rutile + zircon + melt + vapor. Resonant nuclear reaction analysis (NRA) with the nuclear reaction ^{48}Ti(p,Γ)^{49}V was used to measure diffusion profiles for both sets of experiments. The following Arrhenius relation was obtained for Ti diffusion normal to c over the temperature range 1350-1550C at one atmosphere: DTi = 3.3x102 exp(-754 ± 56 kJ mol-1 /RT) m2sec-1 Ti diffusivities were found to be similar for experiments run under fluid-present conditions. A fit to all of the data yields the Arrhenius relation D = 1.3x103 exp(-741 ± 46 kJ mol-1 /RT) m2sec-1. These data suggest that zircon should be extremely retentive of Ti chemical signatures, indicating that the recently developed Ti-in-zircon crystallization geothermometer (Watson and Harrison, 2005; Watson et al., 2006) will be quite robust in preserving temperatures of zircon crystallization. Titanium diffuses somewhat faster in zircon than larger tetravalent cations U, Th, and Hf, but considerably more slowly than Pb, the REE, and oxygen; hence Ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost. Watson EB, Harrison TM (2005) Science 308, 841-844. Watson EB, Wark DA, Thomas JB (2006) CMP(in press).

  6. A Mathematical Model of Diffusion-Limited Gas Bubble Dynamics in Tissue with Varying Diffusion Region Thickness

    NASA Technical Reports Server (NTRS)

    Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.; Paloski, William H. (Technical Monitor)

    2000-01-01

    A three-region mathematical model of gas bubble dynamics has been shown suitable for describing diffusion-limited dynamics of more than one bubble in a given volume of extravascular tissue. The model is based on the dynamics of gas exchange between a bubble and a well-stirred tissue region through an intervening unperfused diffusion region previously assumed to have constant thickness and uniform gas diffusivity. As a result, the gas content of the diffusion region remains constant as the volume of the region increases with bubble growth, causing dissolved gas in the region to violate Henry's law. Earlier work also neglected the relationship between the varying diffusion region volume and the fixed total tissue volume, because only cases in which the diffusion region volume is a small fraction of the overall tissue volume were considered. We herein extend the three-region model to correct these theoretical inconsistencies by allowing both the thickness and gas content of the diffusion region to vary during bubble evolution. A postulated difference in gas diffusivity between an infinitesimally thin layer at the bubble surface and the remainder of the diffusion region leads to variation in diffusion region gas content and thickness during bubble growth and resolution. This variable thickness, differential diffusivity (VTDD) model can yield bubble lifetimes considerably longer than those yielded by earlier three-region models for given model and decompression parameters, and meets a need for theoretically consistent but relatively simple bubble dynamics models for use in studies of decompression sickness (DCS) in human subjects, Keywords: decompression sickness, gas diffusion in tissue, diffusivity

  7. Diffusion on Cu surfaces

    NASA Technical Reports Server (NTRS)

    Karimi, Majid

    1993-01-01

    Understanding surface diffusion is essential in understanding surface phenomena, such as crystal growth, thin film growth, corrosion, physisorption, and chemisorption. Because of its importance, various experimental and theoretical efforts have been directed to understand this phenomena. The Field Ion Microscope (FIM) has been the major experimental tool for studying surface diffusion. FIM have been employed by various research groups to study surface diffusion of adatoms. Because of limitations of the FIM, such studies are only limited to a few surfaces: nickel, platinum, aluminum, iridium, tungsten, and rhodium. From the theoretical standpoint, various atomistic simulations are performed to study surface diffusion. In most of these calculations the Embedded Atom Method (EAM) along with the molecular static (MS) simulation are utilized. The EAM is a semi-empirical approach for modeling the interatomic interactions. The MS simulation is a technique for minimizing the total energy of a system of particles with respect to the positions of its particles. One of the objectives of this work is to develop the EAM functions for Cu and use them in conjunction with the molecular static (MS) simulation to study diffusion of a Cu atom on a perfect as well as stepped Cu(100) surfaces. This will provide a test of the validity of the EAM functions on Cu(100) surface and near the stepped environments. In particular, we construct a terrace-ledge-kink (TLK) model and calculate the migration energies of an atom on a terrace, near a ledge site, near a kink site, and going over a descending step. We have also calculated formation energies of an atom on the bare surface, a vacancy in the surface, a stepped surface, and a stepped-kink surface. Our results are compared with the available experimental and theoretical results.

  8. Least-squares streamline diffusion finite element approximations to singularly perturbed convection-diffusion problems

    SciTech Connect

    Lazarov, R D; Vassilevski, P S

    1999-05-06

    In this paper we introduce and study a least-squares finite element approximation for singularly perturbed convection-diffusion equations of second order. By introducing the flux (diffusive plus convective) as a new unknown, the problem is written in a mixed form as a first order system. Further, the flux is augmented by adding the lower order terms with a small parameter. The new first order system is approximated by the least-squares finite element method using the minus one norm approach of Bramble, Lazarov, and Pasciak [2]. Further, we estimate the error of the method and discuss its implementation and the numerical solution of some test problems.

  9. Small Magnetometer

    NASA Technical Reports Server (NTRS)

    Kuhnke, Falko; Musmann, Gunter; Glassmeier, K. H.; Tsurutani, Bruce

    1995-01-01

    Small, lightweight, low-power magnetometer measures three-dimensional magnetic field. Includes three toroidal cores - one for each dimension. Exhibits high sensitivity, low zero-point drift, and low noise. Magnetometer circuit includes driver circuit and three analog signal-processing circuits. Output of analog signal-processing circuit proportional to one of components of external magnetic field.

  10. Hydrodynamic theory of diffusion in two-temperature multicomponent plasmas

    SciTech Connect

    Ramshaw, J.D.; Chang, C.H.

    1995-12-31

    Detailed numerical simulations of multicomponent plasmas require tractable expressions for species diffusion fluxes, which must be consistent with the given plasma current density J{sub q} to preserve local charge neutrality. The common situation in which J{sub q} = 0 is referred to as ambipolar diffusion. The use of formal kinetic theory in this context leads to results of formidable complexity. We derive simple tractable approximations for the diffusion fluxes in two-temperature multicomponent plasmas by means of a generalization of the hydrodynamical approach used by Maxwell, Stefan, Furry, and Williams. The resulting diffusion fluxes obey generalized Stefan-Maxwell equations that contain driving forces corresponding to ordinary, forced, pressure, and thermal diffusion. The ordinary diffusion fluxes are driven by gradients in pressure fractions rather than mole fractions. Simplifications due to the small electron mass are systematically exploited and lead to a general expression for the ambipolar electric field in the limit of infinite electrical conductivity. We present a self-consistent effective binary diffusion approximation for the diffusion fluxes. This approximation is well suited to numerical implementation and is currently in use in our LAVA computer code for simulating multicomponent thermal plasmas. Applications to date include a successful simulation of demixing effects in an argon-helium plasma jet, for which selected computational results are presented. Generalizations of the diffusion theory to finite electrical conductivity and nonzero magnetic field are currently in progress.

  11. Er3+ diffusion in LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Zhang, De-Long; Zhang, Qun; Wong, Wing-Han; Pun, Edwin Yue-Bun

    2015-12-01

    Some Er3+-doped LiTaO3 plates were prepared by in-diffusion of Er-metal film locally coated onto congruent Z-cut substrate in air at a wide temperature range from 1000 to 1500 °C. After diffusion, Er3+-doping effect on LiTaO3 refractive index and Li2O out-diffusion arising from Er3+ in-diffusion were studied at first. Refractive indices at the doped and undoped surface parts were measured by prism coupling technique and the surface composition was estimated. The results show that Er3+ dopant has small contribution to the LiTaO3 index. Li2O out-diffusion is slight (Li2O content loss <0.3 mol%) for the temperature below 1300 °C while is moderate (Li2O content loss <0.6 mol%) for the temperature above 1400 °C. The Er3+ profile was studied by secondary ion mass spectrometry. The study shows that the diffused Er3+ ions follow either a complementary error function or a Gaussian profile. Characteristic parameters including diffusivity, diffusion constant, activation energy, solubility, solubility constant and heat of solution were obtained and compared with the LiNbO3 case. The comparison shows that the diffusivity and solubility in LiTaO3 are considerably smaller than in LiNbO3 because of the difference of Ta and Nb in atomic weight.

  12. Instrumentation in Diffuse Optical Imaging

    PubMed Central

    Zhang, Xiaofeng

    2014-01-01

    Diffuse optical imaging is highly versatile and has a very broad range of applications in biology and medicine. It covers diffuse optical tomography, fluorescence diffuse optical tomography, bioluminescence, and a number of other new imaging methods. These methods of diffuse optical imaging have diversified instrument configurations but share the same core physical principle – light propagation in highly diffusive media, i.e., the biological tissue. In this review, the author summarizes the latest development in instrumentation and methodology available to diffuse optical imaging in terms of system architecture, light source, photo-detection, spectral separation, signal modulation, and lastly imaging contrast. PMID:24860804

  13. Erbium diffusion in silicon dioxide

    SciTech Connect

    Lu Yingwei; Julsgaard, B.; Petersen, M. Christian; Jensen, R. V. Skougaard; Pedersen, T. Garm; Pedersen, K.; Larsen, A. Nylandsted

    2010-10-04

    Erbium diffusion in silicon dioxide layers prepared by magnetron sputtering, chemical vapor deposition, and thermal growth has been investigated by secondary ion mass spectrometry, and diffusion coefficients have been extracted from simulations based on Fick's second law of diffusion. Erbium diffusion in magnetron sputtered silicon dioxide from buried erbium distributions has in particular been studied, and in this case a simple Arrhenius law can describe the diffusivity with an activation energy of 5.3{+-}0.1 eV. Within a factor of two, the erbium diffusion coefficients at a given temperature are identical for all investigated matrices.

  14. Spring 2014 Internship Diffuser Data Analysis

    NASA Technical Reports Server (NTRS)

    Laigaie, Robert T.; Ryan, Harry M.

    2014-01-01

    showed different data dependent on section. Section 1 strains were small, and were in the range of 50 to 150 microstrain, which would result in stresses from 1.45 to 4.35 ksi. The yield stress of the material, A-285 Grade C Steel, is 29.7 ksi. Section 4 strain gages showed much higher values with strains peaking at 1600 microstrain. This strain corresponds to a stress of 46.41 ksi, which is in excess of the yield stress, but below the ultimate stress of 55 to 75 ksi. The decreased accelerations and strain in Section 1, and the increased accelerations and strain in Sections 3 and 4 verified the computer simulation prediction of increased plume oscillations in the lower sections of the diffuser. Hot-Fire Test 2 ran for a duration of 125 seconds. The engine operated at a slightly higher power level than Hot-Fire Test 1 for the initial 35 seconds of the test. After 35 seconds the power level was lowered to Hot-Fire Test 1 levels. The acceleration and strain data for Hot-Fire Test 2 was similar during the initial part of the test. However, just prior to the engine being lowered to the Hot-Fire Test 1 power level, the strain gage data in Section 4 showed a large decrease to strains near zero microstrain from their peak at 1500 microstrain. Future work includes further strain and acceleration data analysis and evaluation.

  15. Light-element diffusion in Mg using first-principles calculations: Anisotropy and elastodiffusion

    NASA Astrophysics Data System (ADS)

    Agarwal, Ravi; Trinkle, Dallas R.

    2016-08-01

    The light-elemental solutes B, C, N, and O can penetrate the surface of Mg alloys and diffuse during heat treatment or high temperature application, forming undesirable compounds. We investigate the diffusion of these solutes by determining their stable interstitial sites and the interpenetrating network formed by these sites. We use density functional theory (DFT) to calculate the site energies, migration barriers, and attempt frequencies for these networks to inform our analytical model for bulk diffusion. Due to the nature of the networks, O diffuses isotropically, while B, C, and N diffuse anisotropically. We compute the elastodiffusion tensor which quantifies changes in diffusivity due to small strains that perturb the diffusion network geometry and the migration barriers. The DFT-computed elastic dipole tensor which quantifies the change in site energies and migration barriers due to small strains is used as an input to determine the elastodiffusion tensor. We employ the elastodiffusion tensor to determine the effect of thermal strains on interstitial diffusion and find that B, C, and N diffusivity increases on crystal expansion, while O diffusivity decreases. From the elastodiffusion and compliance tensors we calculate the activation volume of diffusion and find that it is positive and anisotropic for B, C, and N diffusion, whereas it is negative and isotropic for O diffusion.

  16. Unsteady planar diffusion flames: Ignition, travel, burnout

    NASA Technical Reports Server (NTRS)

    Fendell, F.; Wu, F.

    1995-01-01

    In microgravity, a thin planar diffusion flame is created and thenceforth travels so that the flame is situated at all times at an interface at which the hydrogen and oxygen meet in stoichiometric proportion. If the initial amount of hydrogen is deficient relative to the initial amount of oxygen, then the planar flame will travel further and further into the half volume initially containing hydrogen, until the hydrogen is (virtually) fully depleted. Of course, when the amount of residual hydrogen becomes small, the diffusion flame is neither vigorous nor thin; in practice, the flame is extinguished before the hydrogen is fully depleted, owing to the finite rate of the actual chemical-kinetic mechanism. The rate of travel of the hydrogen-air diffusion flame is much slower than the rate of laminar flame propagation through a hydrogen-air mixture. This slow travel facilitates diagnostic detection of the flame position as a function of time, but the slow travel also means that the time to burnout (extinction) probably far exceeds the testing time (typically, a few seconds) available in earth-sited facilities for microgravity-environment experiments. We undertake an analysis to predict (1) the position and temperature of the diffusion flame as a function of time, (2) the time at which extinction of the diffusion flame occurs, and (3) the thickness of quench layers formed on side walls (i.e., on lateral boundaries, with normal vectors parallel to the diffusion-flame plane), and whether, prior to extinction, water vapor formed by burning will condense on these cold walls.

  17. The faint galaxy contribution to the diffuse extragalactic background light

    NASA Technical Reports Server (NTRS)

    Cole, Shaun; Treyer, Marie-Agnes; Silk, Joseph

    1992-01-01

    Models of the faint galaxy contribution to the diffuse extragalactic background light are presented, which are consistent with current data on faint galaxy number counts and redshifts. The autocorrelation function of surface brightness fluctuations in the extragalactic diffuse light is predicted, and the way in which these predictions depend on the cosmological model and assumptions of biasing is determined. It is confirmed that the recent deep infrared number counts are most compatible with a high density universe (Omega-0 is approximately equal to 1) and that the steep blue counts then require an extra population of rapidly evolving blue galaxies. The faintest presently detectable galaxies produce an interesting contribution to the extragalactic diffuse light, and still fainter galaxies may also produce a significant contribution. These faint galaxies still only produce a small fraction of the total optical diffuse background light, but on scales of a few arcminutes to a few degrees, they produce a substantial fraction of the fluctuations in the diffuse light.

  18. Enhancement of diffuse reflectance using air tunnel structure.

    PubMed

    Jang, Jae Eun; Lee, Gae Hwang; Song, Byoung Gwon; Cha, Seung Nam; Jung, Jae Eun

    2013-02-01

    Submicrometer air gap structure has formed on diffuse reflection structure to improve light reflectance. Covering polymer or liquid on a diffuse reflector to make optical components induces the severe decrease of the total reflectance, since the diffuse reflected angle of some light rays is larger than the critical angle and the rays travel to the medium until meeting a proper small incident angle. The reflectance drops to 68% of the original value with just a polymer coating on the diffuse reflector. The formation of an air tunnel structure between the polymer layer and the diffuse reflector makes a symmetrical reflective index matching state and recovers 95% of the original reflectance. Due to the simple fabrication process and the chemical stability, the structure can be applied to various optical components and reflective display devices. PMID:23381414

  19. Giant diffusion of underdamped particles in a biased periodic potential

    NASA Astrophysics Data System (ADS)

    Lindner, Benjamin; Sokolov, Igor M.

    2016-04-01

    We consider the diffusive properties of Brownian motion in a biased periodic potential. We relate the effective diffusion coefficient to the solution of two coupled time-independent partial differential equations and solve these equations numerically by the matrix-continued-fraction (MCF) method for intermediate values of the temperature and friction coefficient. The weak-noise limit is explored by numerical simulations of the Langevin equations. Here, we identify the regions of parameters for which the diffusion coefficient exponentially grows with inverse temperature. In particular, we demonstrate that there is a finite range of bias forces for which such a growth is observed (region of giant enhancement of diffusion). We also show that at small forces close to the critical range, the diffusion coefficient possesses a pronounced maximum as a function of temperature. All results can be interpreted in the framework of a simple two-state theory incorporating the transition rates between the locked and running solutions.

  20. Cation self-diffusion in Fe2O3

    NASA Astrophysics Data System (ADS)

    Hoshino, K.; Peterson, N. L.

    Self-diffusion of Fe(59) in single crystals of Fe2O3 parallel to the c-axis has been measured as a function of temperature (1150 to 1340 C) and oxygen partial pressure 0.002 less than or equal to Po2 less than or equal to 1 atm). The oxygen partial pressure dependence of the diffusivity indicates that cation self-diffusion occurs by an interstitial-type mechanism. The simultaneous diffusion of Fe(52) and Fe(59) was measured in Fe2O3 at 1251 C and Po2 = .0191 atm. The small value of the isotope effect (f(DELTA)K = 0.067 + or - 0.016) is consistent with diffusion of Fe ions by an interstitially mechanism.

  1. Magma zonation - Effects of chemical buoyancy and diffusion

    NASA Technical Reports Server (NTRS)

    Spera, Frank J.; Oldenburg, Curtis M.; Yuen, David A.

    1989-01-01

    Numerical simulations and scale analysis are used to assess the viability of the marginal box-filling mechanism for producing compositional zonation in magma bodies. Scale analysis and two-dimensional numerical experiments both show that box-filling occurs provided a critical ratio of compositional-to-thermal buoyancy is exceeded. This critical ratio depends on the ratio of thermal-to-chemical diffusivity; application of this result to magma bodies suggests that box-filling may occur for components with relatively high-chemical diffusivities such as water. However, box-filling will not produce significant zonation for components with small chemical diffusivities, such as silica, unless diffusive coupling increases silica diffusivity.

  2. Nonlocalized modulation of periodic reaction diffusion waves: The Whitham equation

    NASA Astrophysics Data System (ADS)

    Johnson, Mathew A.; Noble, Pascal; Rodrigues, L. Miguel; Zumbrun, Kevin

    2013-02-01

    In a companion paper, we established nonlinear stability with detailed diffusive rates of decay of spectrally stable periodic traveling-wave solutions of reaction diffusion systems under small perturbations consisting of a nonlocalized modulation plus a localized ( L 1) perturbation. Here, we determine time-asymptotic behavior under such perturbations, showing that solutions consist of a leading order of a modulation whose parameter evolution is governed by an associated Whitham averaged equation.

  3. [Diffuse Pulmonary Ossification].

    PubMed

    Avsar, K; Behr, J; Morresi-Hauf, A

    2016-04-01

    Diffuse pulmonary ossification (DPO) represents an uncommon condition usually associated with different underlying pulmonary and extrapulmonary diseases. In this work, we discuss eleven patients of our clinic with the diagnosis of a diffuse pulmonary ossification. We focus on histological changes in the surrounding lung tissue. Clinical and radiological findings were analysed. The aim of the study is to collect data for a better understanding of this condition, especially in association with interstitial lung disease.Three patients with interstitial lung disease had histological findings of UIP. The follow-up data of these patients showed a benign course of the disease.The analysis of the clinical data yielded a very heterogenous group. Regarding these fact we assume, that DPO is not an own entity, but a pathological epiphenomenon in the context of different conditions, possibly with pathogenetic overlap. PMID:26829606

  4. Diffusion dans les liquides

    NASA Astrophysics Data System (ADS)

    Dianoux, A. J.

    2003-09-01

    Après une brève introduction qui rappelle les concepts détaillés dans le cours de M. Bée, nous présentons un aperçu de trois de nos travaux sur l'étude de la diffusion. Tout d'abord la dynamique de l'eau, dans son état normal ou surfondu, révèle la complexité apportée par le réseau de liaisons hydrogène. Ensuite l'effet du confinement sur la dynamique de l'eau sera étudié dans le cas de la membrane Nafion. Enfin la diffusion dans les phases nématique et smectique A d'un cristal liquide permet d'obtenir la valeur du potentiel qui maintient les couches dans la phase smectique.

  5. Galactic Diffuse Polarized Emission

    NASA Astrophysics Data System (ADS)

    Carretti, Ettore

    2011-12-01

    Diffuse polarized emission by synchrotron is a key tool to investigate magnetic fields in the Milky Way, particularly the ordered component of the large scale structure. Key observables are the synchrotron emission itself and the RM is by Faraday rotation. In this paper the main properties of the radio polarized diffuse emission and its use to investigate magnetic fields will be reviewed along with our current understanding of the galactic magnetic field and the data sets available. We will then focus on the future perspective discussing RM-synthesis - the new powerful instrument devised to unlock the information encoded in such an emission - and the surveys currently in progress like S-PASS and GMIMS.

  6. Thermal diffusivity imaging

    NASA Astrophysics Data System (ADS)

    Gfroerer, Tim; Phillips, Ryan; Rossi, Peter

    2015-11-01

    The tip of a rod is heated with a torch and brought into contact with the center of a metal sheet. A thermal camera is then used to image the temperature profile of the surface as a function of time. The infrared camera is capable of recording radiometric data with 1 mK resolution in nearly 105 pixels, so thermal diffusion can be monitored with unprecedented precision. With a frame rate of approximately 10 Hz, the pace of the data acquisition minimizes the loss of accuracy due to inevitable cooling mechanisms. We report diffusivity constants equal to 1.23 ± 0.06 cm2/s in copper and 0.70 ± 0.05 cm2/s in aluminum. The behavior is modeled with a straightforward but oddly under-utilized one-dimensional finite difference method.

  7. Nonlocal electrical diffusion equation

    NASA Astrophysics Data System (ADS)

    Gómez-Aguilar, J. F.; Escobar-Jiménez, R. F.; Olivares-Peregrino, V. H.; Benavides-Cruz, M.; Calderón-Ramón, C.

    2016-07-01

    In this paper, we present an analysis and modeling of the electrical diffusion equation using the fractional calculus approach. This alternative representation for the current density is expressed in terms of the Caputo derivatives, the order for the space domain is 0<β≤1 and for the time domain is 0<γ≤2. We present solutions for the full fractional equation involving space and time fractional derivatives using numerical methods based on Fourier variable separation. The case with spatial fractional derivatives leads to Levy flight type phenomena, while the time fractional equation is related to sub- or super diffusion. We show that the mathematical concept of fractional derivatives can be useful to understand the behavior of semiconductors, the design of solar panels, electrochemical phenomena and the description of anomalous complex processes.

  8. Small satellites

    NASA Technical Reports Server (NTRS)

    Thomas, P.; Veverka, J.; Dermott, S.

    1986-01-01

    Satellites smaller than Mimas (r = 195 km) are distinguished by irregular overall shapes and by rough limb topography. Material properties and impact cratering dominate the shaping of these objects. Long fragmentation histories can produce a variety of internal structures, but so far there is no direct evidence that any small satellite is an equilibrium ellipsoid made up of noncohesive gravitationally bound rubble. One many bodies that orbit close to their primary the tidal and rotational components of surface gravity strongly affect the directions of local g and thereby affect the redistribution of regolith by mass wasting. Downslope movement of regolith is extensive on Deimos, and is probably effective on many other small satellites. It is shown that in some cases observed patterns of downslope mass wasting cold produce useful constraints on the satellite's mean density. The diversity of features seen in the few high-resolution images of small satellites currently available suggests that these objects have undergone complex histories of cratering, fragmentation, and regolith evolution.

  9. Turbo fluid machinery and diffusers

    NASA Technical Reports Server (NTRS)

    Sakurai, T.

    1984-01-01

    The general theory behind turbo devices and diffusers is explained. Problems and the state of research on basic equations of flow and experimental and measuring methods are discussed. Conventional centrifugation-type compressor and fan diffusers are considered in detail.

  10. Modeling the role of diffusion coefficients on Turing instability in a reaction-diffusion prey-predator system.

    PubMed

    Mukhopadhyay, B; Bhattacharyya, R

    2006-02-01

    The paper is concerned with the effect of variable dispersal rates on Turing instability of a non-Lotka-Volterra reaction-diffusion system. In ecological applications, the dispersal rates of different species tends to oscillate in time. This oscillation is modeled by temporal variation in the diffusion coefficient with large as well as small periodicity. The case of large periodicity is analyzed using the theory of Floquet multipliers and that of the small periodicity by using Hill's equation. The effect of such variation on the resulting Turing space is studied. A comparative analysis of the Turing spaces with constant diffusivity and variable diffusivities is performed. Numerical simulations are carried out to support analytical findings. PMID:16794932

  11. Diffusive Shock Acceleration

    NASA Astrophysics Data System (ADS)

    Baring, Matthew

    2003-04-01

    The process of diffusive acceleration of charged particles in shocked plasmas is widely invoked in astrophysics to account for the ubiquitous presence of signatures of non-thermal relativistic electrons and ions in the universe. This statistical energization mechanism, manifested in turbulent media, was first posited by Enrico Fermi in 1949 to explain the observed cosmic ray population, which exhibits an almost power-law distribution in rigidity. The absence of a momentum scale is a key characteristic of diffusive shock acceleration, and astrophysical systems generally only impose scales at the injection (low energy) and loss (high energy) ends of the particle spectrum. The existence of structure in the cosmic ray spectrum (the "knee") at around 3000 TeV has promoted contentions that there are at least two origins for cosmic rays, a galactic one supplying those up to the knee, and perhaps an extragalactic one that can explain even the ultra-high energy cosmic rays (UHECRs) seen at 1-300 EeV. Accounting for the UHECRs with familiar astrophysical sites of acceleration has historically proven difficult due to the need to assume high magnetic fields in order to reduce the shortest diffusive acceleration timescale, the ion gyroperiod, to meaningful values. Yet active galaxies and gamma-ray bursts remain strong and interesting candidate sources for UHECRs, turning the theoretical focus to relativistic shocks. This review summarizes properties of diffusive shock acceleration that are salient to the issue of UHECR generation. These include spectral indices, anisotropies, acceleration efficencies and timescales, as functions of the shock speed and mean field orientation, and also the degree of field turbulence. Astrophysical sites for UHECR production are also critiqued.

  12. Peridynamic thermal diffusion

    NASA Astrophysics Data System (ADS)

    Oterkus, Selda; Madenci, Erdogan; Agwai, Abigail

    2014-05-01

    This study presents the derivation of ordinary state-based peridynamic heat conduction equation based on the Lagrangian formalism. The peridynamic heat conduction parameters are related to those of the classical theory. An explicit time stepping scheme is adopted for numerical solution of various benchmark problems with known solutions. It paves the way for applying the peridynamic theory to other physical fields such as neutronic diffusion and electrical potential distribution.

  13. Peridynamic thermal diffusion

    SciTech Connect

    Oterkus, Selda; Madenci, Erdogan; Agwai, Abigail

    2014-05-15

    This study presents the derivation of ordinary state-based peridynamic heat conduction equation based on the Lagrangian formalism. The peridynamic heat conduction parameters are related to those of the classical theory. An explicit time stepping scheme is adopted for numerical solution of various benchmark problems with known solutions. It paves the way for applying the peridynamic theory to other physical fields such as neutronic diffusion and electrical potential distribution.

  14. Mass transport by diffusion

    NASA Technical Reports Server (NTRS)

    Baird, James K.

    1987-01-01

    For the purpose of determining diffusion coefficients as required for electrodeposition studies and other applications, a diaphragm cell and an isothermal water bath were constructed. the calibration of the system is discussed. On the basis of three calibration runs on the diaphram cell, researchers concluded that the cell constant beta equals 0.12 cm -2 . Other calibration runs in progress should permit the cell constant to be determined with an accuracy of one percent.

  15. [Diffuse Lewy body disease].

    PubMed

    Kosaka, K

    1995-12-01

    Diffuse Lewy body disease (DLBD), which we have proposed since 1976, has received great attention among both researchers and clinicians. Recently, it was reported by some English and American research groups that DLBD is the second most frequent dementing illness in the elderly, following Alzheimer-type dementia (ATD). Our recent research of 79 autopsied dementia cases in a hospital disclosed that DLBD (15.4%) was the second most common degenerative dementia, following ATD (43.6%). In 1980 we proposed Lewy body disease, and classified it into three types: brain stem type, transitional type, and diffuse type. Diffuse type of LBD is now called DLBD. In 1990 we divided DLBD into two forms: common form and pure form. The common form of DLBD has more or less Alzheimer pathology, and pure form has none. Very recently, we proposed the cerebral type of LBD, in which numerous Lewy bodies are found in the cerebral cortex and amygdala, but no PD pathology is present in the brain stem. Therefore, LBD is now classified as follows: [table: see text] PMID:8752428

  16. Solute diffusion in liquid metals

    NASA Technical Reports Server (NTRS)

    Bhat, B. N.

    1973-01-01

    A gas model of diffusion in liquid metals is presented. In this model, ions of liquid metals are assumed to behave like the molecules in a dense gas. Diffusion coefficient of solute is discussed with reference to its mass, ionic size, and pair potential. The model is applied to the case of solute diffusion in liquid silver. An attempt was made to predict diffusion coefficients of solutes with reasonable accuracy.

  17. A novel method to evaluate spin diffusion length of Pt

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-qing; Sun, Niu-yi; Che, Wen-ru; Shan, Rong; Zhu, Zhen-gang

    2016-05-01

    Spin diffusion length of Pt is evaluated via proximity effect of spin orbit coupling (SOC) and anomalous Hall effect (AHE) in Pt/Co2FeAl bilayers. By varying the thicknesses of Pt and Co2FeAl layer, the thickness dependences of AHE parameters can be obtained, which are theoretically predicted to be proportional to the square of the SOC strength. According to the physical image of the SOC proximity effect, the spin diffusion length of Pt can easily be identified from these thickness dependences. This work provides a novel method to evaluate spin diffusion length in a material with a small value.

  18. Partial volume effect of cingulum tract in diffusion-tensor MRI

    NASA Astrophysics Data System (ADS)

    Cao, Ning; Gold, Brian T.; Zhang, Jun

    2008-03-01

    Diffusion tensor imaging (DTI) represents a promising tool for the early diagnosis of certain brain diseases. Many DTI studies have compared differences in local diffusivity in specific region-of- interest (ROI) between patient and control groups to find possible disease markers. However, local diffusivity results may be influenced by partial volume effects (PVE), particularly in small white matter tracts that border grey matter tissue. Here, we investigated the influence of PVE on local diffusivity measurements in a small but critical white matter tract, the cingulum. Results demonstrated significant variability in PVE that contribute to local diffusivity in the cingulum. Our results highlight the need for careful consideration of PVE when computing diffusivity of small tissues.

  19. Percolation of interaction diffusing particles

    NASA Technical Reports Server (NTRS)

    Selinger, Robin Blumberg; Stanley, H. Eugene

    1990-01-01

    The connectivity properties of systems of diffusing interacting particles with the blind and myopic diffusion rules are studied. It is found that the blind rule case is equivalent to the lattice gas with J = 0 in all dimensions. The connectivity properties of blind rule diffusion are described by random site percolation due to the fact that the density on neighboring sites is uncorrelated.

  20. Diffusion of Zonal Variables Using Node-Centered Diffusion Solver

    SciTech Connect

    Yang, T B

    2007-08-06

    Tom Kaiser [1] has done some preliminary work to use the node-centered diffusion solver (originally developed by T. Palmer [2]) in Kull for diffusion of zonal variables such as electron temperature. To avoid numerical diffusion, Tom used a scheme developed by Shestakov et al. [3] and found their scheme could, in the vicinity of steep gradients, decouple nearest-neighbor zonal sub-meshes leading to 'alternating-zone' (red-black mode) errors. Tom extended their scheme to couple the sub-meshes with appropriate chosen artificial diffusion and thereby solved the 'alternating-zone' problem. Because the choice of the artificial diffusion coefficient could be very delicate, it is desirable to use a scheme that does not require the artificial diffusion but still able to avoid both numerical diffusion and the 'alternating-zone' problem. In this document we present such a scheme.

  1. Diffuse-charge dynamics in electrochemical systems

    NASA Astrophysics Data System (ADS)

    Bazant, Martin Z.; Thornton, Katsuyo; Ajdari, Armand

    2004-08-01

    The response of a model microelectrochemical system to a time-dependent applied voltage is analyzed. The article begins with a fresh historical review including electrochemistry, colloidal science, and microfluidics. The model problem consists of a symmetric binary electrolyte between parallel-plate blocking electrodes, which suddenly apply a voltage. Compact Stern layers on the electrodes are also taken into account. The Nernst-Planck-Poisson equations are first linearized and solved by Laplace transforms for small voltages, and numerical solutions are obtained for large voltages. The “weakly nonlinear” limit of thin double layers is then analyzed by matched asymptotic expansions in the small parameter ɛ=λD/L , where λD is the screening length and L the electrode separation. At leading order, the system initially behaves like an RC circuit with a response time of λDL/D (not λD2/D ), where D is the ionic diffusivity, but nonlinearity violates this common picture and introduces multiple time scales. The charging process slows down, and neutral-salt adsorption by the diffuse part of the double layer couples to bulk diffusion at the time scale, L2/D . In the “strongly nonlinear” regime (controlled by a dimensionless parameter resembling the Dukhin number), this effect produces bulk concentration gradients, and, at very large voltages, transient space charge. The article concludes with an overview of more general situations involving surface conduction, multicomponent electrolytes, and Faradaic processes.

  2. Anisotropic fractional diffusion tensor imaging

    PubMed Central

    Meerschaert, Mark M; Magin, Richard L; Ye, Allen Q

    2015-01-01

    Traditional diffusion tensor imaging (DTI) maps brain structure by fitting a diffusion model to the magnitude of the electrical signal acquired in magnetic resonance imaging (MRI). Fractional DTI employs anomalous diffusion models to obtain a better fit to real MRI data, which can exhibit anomalous diffusion in both time and space. In this paper, we describe the challenge of developing and employing anisotropic fractional diffusion models for DTI. Since anisotropy is clearly present in the three-dimensional MRI signal response, such models hold great promise for improving brain imaging. We then propose some candidate models, based on stochastic theory.

  3. Diffusion tensor MR microscopy of tissues with low diffusional anisotropy

    PubMed Central

    Bajd, Franci; Mattea, Carlos; Stapf, Siegfried

    2016-01-01

    Abstract Background Diffusion tensor imaging exploits preferential diffusional motion of water molecules residing within tissue compartments for assessment of tissue structural anisotropy. However, instrumentation and post-processing errors play an important role in determination of diffusion tensor elements. In the study, several experimental factors affecting accuracy of diffusion tensor determination were analyzed. Materials and methods Effects of signal-to-noise ratio and configuration of the applied diffusion-sensitizing gradients on fractional anisotropy bias were analyzed by means of numerical simulations. In addition, diffusion tensor magnetic resonance microscopy experiments were performed on a tap water phantom and bovine articular cartilage-on-bone samples to verify the simulation results. Results In both, the simulations and the experiments, the multivariate linear regression of the diffusion-tensor analysis yielded overestimated fractional anisotropy with low SNRs and with low numbers of applied diffusion-sensitizing gradients. Conclusions An increase of the apparent fractional anisotropy due to unfavorable experimental conditions can be overcome by applying a larger number of diffusion sensitizing gradients with small values of the condition number of the transformation matrix. This is in particular relevant in magnetic resonance microscopy, where imaging gradients are high and the signal-to-noise ratio is low. PMID:27247550

  4. Comments on the Diffusive Behavior of Two Upwind Schemes

    NASA Technical Reports Server (NTRS)

    Wood, William A.; Kleb, William L.

    1998-01-01

    The diffusive characteristics of two upwind schemes, multi-dimensional fluctuation splitting and locally one-dimensional finite volume, are compared for scalar advection-diffusion problems. Algorithms for the two schemes are developed for node-based data representation on median-dual meshes associated with unstructured triangulations in two spatial dimensions. Four model equations are considered: linear advection, non-linear advection, diffusion, and advection-diffusion. Modular coding is employed to isolate the effects of the two approaches for upwind flux evaluation, allowing for head-to-head accuracy and efficiency comparisons. Both the stability of compressive limiters and the amount of artificial diffusion generated by the schemes is found to be grid-orientation dependent, with the fluctuation splitting scheme producing less artificial diffusion than the finite volume scheme. Convergence rates are compared for the combined advection-diffusion problem, with a speedup of 2.5 seen for fluctuation splitting versus finite volume when solved on the same mesh. However, accurate solutions to problems with small diffusion coefficients can be achieved on coarser meshes using fluctuation splitting rather than finite volume, so that when comparing convergence rates to reach a given accuracy, fluctuation splitting shows a speedup of 29 over finite volume.

  5. Diffusion Characteristics of Upwind Schemes on Unstructured Triangulations

    NASA Technical Reports Server (NTRS)

    Wood, William A.; Kleb, William L.

    1998-01-01

    The diffusive characteristics of two upwind schemes, multi-dimensional fluctuation splitting and dimensionally-split finite volume, are compared for scalar advection-diffusion problems. Algorithms for the two schemes are developed for node-based data representation on median-dual meshes associated with unstructured triangulations in two spatial dimensions. Four model equations are considered: linear advection, non-linear advection, diffusion, and advection-diffusion. Modular coding is employed to isolate the effects of the two approaches for upwind flux evaluation, allowing for head-to-head accuracy and efficiency comparisons. Both the stability of compressive limiters and the amount of artificial diffusion generated by the schemes is found to be grid-orientation dependent, with the fluctuation splitting scheme producing less artificial diffusion than the dimensionally-split finite volume scheme. Convergence rates are compared for the combined advection-diffusion problem, with a speedup of 2-3 seen for fluctuation splitting versus finite volume when solved on the same mesh. However, accurate solutions to problems with small diffusion coefficients can be achieved on coarser meshes using fluctuation splitting rather than finite volume, so that when comparing convergence rates to reach a given accuracy, fluctuation splitting shows a 20-25 speedup over finite volume.

  6. Diffusion of radiotracers in normal and ischemic brain slices.

    PubMed

    Patlak, C S; Hospod, F E; Trowbridge, S D; Newman, G C

    1998-07-01

    Diffusion in the extracellular space (ECS) is important in physiologic and pathologic brain processes but remains poorly understood. To learn more about factors influencing tissue diffusion and the role of diffusion in solute-tissue interactions, particularly during cerebral ischemia, we have studied the kinetics of several radiotracers in control and hypoxic 450-microm hippocampal slices and in 1,050-microm thick slices that model the ischemic penumbra. Kinetics were analyzed by nonlinear least squares methods using models that combine extracellular diffusion with tissue compartments in series or in parallel. Studies with 14C-polyethylene glycol confirmed prior measurements of extracellular volume and that ECS shrinks during ischemia. Separating diffusion from transport also revealed large amounts of 45Ca that bind to or enter brain as well as demonstrating a small, irreversibly bound compartment during ischemia. The rapidity of 3H2O entry into cells made it impossible for us to distinguish intracellular from extracellular diffusion. The diffusion-compartment analysis of 3-O-methylglucose data appears to indicate that 5 mmol/L glucose is inadequate to support glycolysis fully in thick slices. Unexpectedly, the diffusion coefficient for all four tracers rose in thick slices compared with thin slices, suggesting that ECS becomes less tortuous in the penumbra. PMID:9663508

  7. Nitric Oxide Diffusion Rate is Reduced in the Aortic Wall☆

    PubMed Central

    Liu, Xiaoping; Srinivasan, Parthasarathy; Collard, Eric; Grajdeanu, Paula; Zweier, Jay L.; Friedman, Avner

    2008-01-01

    Endogenous nitric oxide (NO) plays important physiological roles in the body. As a small diatomic molecule, NO has been assumed to freely diffuse in tissues with a diffusion rate similar to that in water. However, this assumption has not been tested experimentally. In this study, a modified Clark-type NO electrode attached with a customized aorta holder was used to directly measure the flux of NO diffusion across the aortic wall at 37°C. Experiments were carefully designed for accurate measurements of the apparent NO diffusion coefficient D and the partition coefficient α in the aortic wall. A mathematical model was presented for analyzing experimental data. It was determined that α = 1.15 ± 0.11 and D = 848 ± 45 μm2/s (n = 12). The NO diffusion coefficient in the aortic wall is nearly fourfold smaller than the reported diffusion coefficient in solution at 37°C, indicating that NO diffusion in the vascular wall is no longer free, but markedly dependent on the environment in the tissue where these NO molecules are. These results imply that the NO diffusion rate in the vascular wall may be upregulated and downregulated by certain physiological and/or pathophysiological processes affecting the composition of tissues. PMID:18032554

  8. A computational kinetic model of diffusion for molecular systems

    PubMed Central

    Teo, Ivan; Schulten, Klaus

    2013-01-01

    Regulation of biomolecular transport in cells involves intra-protein steps like gating and passage through channels, but these steps are preceded by extra-protein steps, namely, diffusive approach and admittance of solutes. The extra-protein steps develop over a 10–100 nm length scale typically in a highly particular environment, characterized through the protein's geometry, surrounding electrostatic field, and location. In order to account for solute energetics and mobility of solutes in this environment at a relevant resolution, we propose a particle-based kinetic model of diffusion based on a Markov State Model framework. Prerequisite input data consist of diffusion coefficient and potential of mean force maps generated from extensive molecular dynamics simulations of proteins and their environment that sample multi-nanosecond durations. The suggested diffusion model can describe transport processes beyond microsecond duration, relevant for biological function and beyond the realm of molecular dynamics simulation. For this purpose the systems are represented by a discrete set of states specified by the positions, volumes, and surface elements of Voronoi grid cells distributed according to a density function resolving the often intricate relevant diffusion space. Validation tests carried out for generic diffusion spaces show that the model and the associated Brownian motion algorithm are viable over a large range of parameter values such as time step, diffusion coefficient, and grid density. A concrete application of the method is demonstrated for ion diffusion around and through the Eschericia coli mechanosensitive channel of small conductance ecMscS. PMID:24089741

  9. A computational kinetic model of diffusion for molecular systems

    NASA Astrophysics Data System (ADS)

    Teo, Ivan; Schulten, Klaus

    2013-09-01

    Regulation of biomolecular transport in cells involves intra-protein steps like gating and passage through channels, but these steps are preceded by extra-protein steps, namely, diffusive approach and admittance of solutes. The extra-protein steps develop over a 10-100 nm length scale typically in a highly particular environment, characterized through the protein's geometry, surrounding electrostatic field, and location. In order to account for solute energetics and mobility of solutes in this environment at a relevant resolution, we propose a particle-based kinetic model of diffusion based on a Markov State Model framework. Prerequisite input data consist of diffusion coefficient and potential of mean force maps generated from extensive molecular dynamics simulations of proteins and their environment that sample multi-nanosecond durations. The suggested diffusion model can describe transport processes beyond microsecond duration, relevant for biological function and beyond the realm of molecular dynamics simulation. For this purpose the systems are represented by a discrete set of states specified by the positions, volumes, and surface elements of Voronoi grid cells distributed according to a density function resolving the often intricate relevant diffusion space. Validation tests carried out for generic diffusion spaces show that the model and the associated Brownian motion algorithm are viable over a large range of parameter values such as time step, diffusion coefficient, and grid density. A concrete application of the method is demonstrated for ion diffusion around and through the Eschericia coli mechanosensitive channel of small conductance ecMscS.

  10. DIOS: the diffuse intergalactic oxygen surveyor

    NASA Astrophysics Data System (ADS)

    Ohashi, T.; Ishida, M.; Sasaki, S.; Ishisaki, Y.; Mitsuda, K.; Yamasaki, N. Y.; Fujimoto, R.; Takei, Y.; Tawara, Y.; Furuzawa, A.; Suto, Y.; Yoshikawa, Y.; Kawayara, H.; Kawai, N.; Tsuru, T. G.; Matsushita, K.; Kitayama, T.

    2006-06-01

    We present our proposal for a small X-ray mission DIOS (Diffuse Intergalactic Oxygen Surveyor), consisting of a 4-stage X-ray telescope and an array of TES microcalorimeters, cooled with mechanical coolers, with a total weight of about 400 kg. The mission will perform survey observations of warm-hot intergalactic medium using OVII and OVIII emission lines, with the energy coverage up to 1.5 keV. The wide field of view of about 50' diameter, superior energy resolution close to 2 eV FWHM, and very low background will together enable us a wide range of science for diffuse X-ray sources. We briefly describe the design of the satellite, performance of the subsystems and the expected results.

  11. A Diffusive Strategic Dynamics for Social Systems

    NASA Astrophysics Data System (ADS)

    Agliari, Elena; Burioni, Raffaella; Contucci, Pierluigi

    2010-05-01

    We propose a model for the dynamics of a social system, which includes diffusive effects and a biased rule for spin-flips, reproducing the effect of strategic choices. This model is able to mimic some phenomena taking place during marketing or political campaigns. Using a cost function based on the Ising model defined on the typical quenched interaction environments for social systems (Erdös-Renyi graph, small-world and scale-free networks), we find, by numerical simulations, that a stable stationary state is reached, and we compare the final state to the one obtained with standard dynamics, by means of total magnetization and magnetic susceptibility. Our results show that the diffusive strategic dynamics features a critical interaction parameter strictly lower than the standard one. We discuss the relevance of our findings in social systems.

  12. Diffusion of Cu adatoms and dimers on Cu(111) and Ag(111) surfaces

    NASA Astrophysics Data System (ADS)

    Mińkowski, Marcin; Załuska-Kotur, Magdalena A.

    2015-12-01

    Diffusion of Cu adatoms and dimers on Cu(111) and Ag(111) surfaces is analyzed based on ab initio surface potentials. Single adatom diffusion is compared with dimer diffusion on both surfaces. Surface geometry makes the adatoms jump alternately between two states in the same way in both systems, whereas dimers undergo more complex diffusion process that combines translational and rotational motion. Small difference in the surface lattice constant between Cu and Ag crystals results in a completely different energy landscape for dimer jumps. As an effect the character of diffusion process changes. Homogeneous Cu dimer diffusion is more difficult and dimers rather rotate within single surface cell, whereas diffusion over Ag surface is faster and happens more smoothly. The temperature dependence of diffusion coefficient and its parameters: energy barrier and prefactor is calculated and compared for both surfaces.

  13. Accelerated stochastic diffusion processes

    NASA Astrophysics Data System (ADS)

    Garbaczewski, Piotr

    1990-07-01

    We give a purely probabilistic demonstration that all effects of non-random (external, conservative) forces on the diffusion process can be encoded in the Nelson ansatz for the second Newton law. Each random path of the process together with a probabilistic weight carries a phase accumulation (complex valued) weight. Random path summation (integration) of these weights leads to the transition probability density and transition amplitude respectively between two spatial points in a given time interval. The Bohm-Vigier, Fenyes-Nelson-Guerra and Feynman descriptions of the quantum particle behaviours are in fact equivalent.

  14. Diffusion in silicon isotope heterostructures

    SciTech Connect

    Silvestri, Hughes Howland

    2004-05-14

    The simultaneous diffusion of Si and the dopants B, P, and As has been studied by the use of a multilayer structure of isotopically enriched Si. This structure, consisting of 5 pairs of 120 nm thick natural Si and {sup 28}Si enriched layers, enables the observation of {sup 30}Si self-diffusion from the natural layers into the {sup 28}Si enriched layers, as well as dopant diffusion from an implanted source in an amorphous Si cap layer, via Secondary Ion Mass Spectrometry (SIMS). The dopant diffusion created regions of the multilayer structure that were extrinsic at the diffusion temperatures. In these regions, the Fermi level shift due to the extrinsic condition altered the concentration and charge state of the native defects involved in the diffusion process, which affected the dopant and self-diffusion. The simultaneously recorded diffusion profiles enabled the modeling of the coupled dopant and self-diffusion. From the modeling of the simultaneous diffusion, the dopant diffusion mechanisms, the native defect charge states, and the self- and dopant diffusion coefficients can be determined. This information is necessary to enhance the physical modeling of dopant diffusion in Si. It is of particular interest to the modeling of future electronic Si devices, where the nanometer-scale features have created the need for precise physical models of atomic diffusion in Si. The modeling of the experimental profiles of simultaneous diffusion of B and Si under p-type extrinsic conditions revealed that both species are mediated by neutral and singly, positively charged Si self-interstitials. The diffusion of As and Si under extrinsic n-type conditions yielded a model consisting of the interstitialcy and vacancy mechanisms of diffusion via singly negatively charged self-interstitials and neutral vacancies. The simultaneous diffusion of P and Si has been modeled on the basis of neutral and singly negatively charged self-interstitials and neutral and singly positively charged P

  15. Attracted diffusion-limited aggregation.

    PubMed

    Rahbari, S H Ebrahimnazhad; Saberi, A A

    2012-07-01

    In this paper we present results of extensive Monte Carlo simulations of diffusion-limited aggregation (DLA) with a seed placed on an attractive plane as a simple model in connection with the electrical double layers. We compute the fractal dimension of the aggregated patterns as a function of the attraction strength α. For the patterns grown in both two and three dimensions, the fractal dimension shows a significant dependence on the attraction strength for small values of α and approaches that of the ordinary two-dimensional (2D) DLA in the limit of large α. For the nonattracting case with α = 1, our results in three dimensions reproduce the patterns of 3D ordinary DLA, while in two dimensions our model leads to the formation of a compact cluster with dimension 2. For intermediate α, the 3D clusters have a quasi-2D structure with a fractal dimension very close to that of the ordinary 2D DLA. This allows one to control the morphology of a growing cluster by tuning a single external parameter α. PMID:23005417

  16. Attracted diffusion-limited aggregation

    NASA Astrophysics Data System (ADS)

    Rahbari, S. H. Ebrahimnazhad; Saberi, A. A.

    2012-07-01

    In this paper we present results of extensive Monte Carlo simulations of diffusion-limited aggregation (DLA) with a seed placed on an attractive plane as a simple model in connection with the electrical double layers. We compute the fractal dimension of the aggregated patterns as a function of the attraction strength α. For the patterns grown in both two and three dimensions, the fractal dimension shows a significant dependence on the attraction strength for small values of α and approaches that of the ordinary two-dimensional (2D) DLA in the limit of large α. For the nonattracting case with α=1, our results in three dimensions reproduce the patterns of 3D ordinary DLA, while in two dimensions our model leads to the formation of a compact cluster with dimension 2. For intermediate α, the 3D clusters have a quasi-2D structure with a fractal dimension very close to that of the ordinary 2D DLA. This allows one to control the morphology of a growing cluster by tuning a single external parameter α.

  17. Anisotropic diffusion-limited aggregation.

    PubMed

    Popescu, M N; Hentschel, H G E; Family, F

    2004-06-01

    Using stochastic conformal mappings, we study the effects of anisotropic perturbations on diffusion-limited aggregation (DLA) in two dimensions. The harmonic measure of the growth probability for DLA can be conformally mapped onto a constant measure on a unit circle. Here we map m preferred directions for growth to a distribution on the unit circle, which is a periodic function with m peaks in [-pi,pi) such that the angular width sigma of the peak defines the "strength" of anisotropy kappa= sigma(-1) along any of the m chosen directions. The two parameters (m,kappa) map out a parameter space of perturbations that allows a continuous transition from DLA (for small enough kappa ) to m needlelike fingers as kappa--> infinity. We show that at fixed m the effective fractal dimension of the clusters D(m,kappa) obtained from mass-radius scaling decreases with increasing kappa from D(DLA) approximately 1.71 to a value bounded from below by D(min) = 3 / 2. Scaling arguments suggest a specific form for the dependence of the fractal dimension D(m,kappa) on kappa for large kappa which compares favorably with numerical results. PMID:15244564

  18. A simple flow analysis of diffuser-getter-diffuser systems

    SciTech Connect

    Klein, J. E.; Howard, D. W.

    2008-07-15

    Tritium clean-up systems typically deploy gas processing technologies between stages of palladium-silver (Pd/Ag) diffusers/permeators. The number of diffusers positioned before and after a gas clean-up process to obtain optimal system performance will vary with feed gas inert composition. A simple method to analyze optimal diffuser configuration is presented. The method assumes equilibrium across the Pd/Ag tubes and system flows are limited by diffuser vacuum pump speeds preceding or following the clean-up process. A plot of system feed as a function of inert feed gas composition for various diffuser configuration allows selection of a diffuser configuration for maximum throughput based on feed gas composition. (authors)

  19. FLOW ANALYSIS OF DIFFUSER-GETTER-DIFFUSER SYSTEMS

    SciTech Connect

    Klein, J; Dave W. Howard, D

    2007-07-24

    Tritium clean-up systems typically deploy gas processing technologies between stages of palladium-silver (Pd/Ag) diffusers/permeators. The number of diffusers positioned before and after a gas clean-up process to obtain optimal system performance will vary with feed gas inert composition. A simple method to analyze optimal diffuser configuration is presented. The method assumes equilibrium across the Pd/Ag tubes and system flows are limited by diffuser vacuum pump speeds preceding or following the clean-up process. A plot of system feed as a function of inert feed gas composition for various diffuser configuration allows selection of a diffuser configuration for maximum throughput based on feed gas composition.

  20. Sampling diffusive transition paths

    SciTech Connect

    F. Miller III, Thomas; Predescu, Cristian

    2006-10-12

    We address the problem of sampling double-ended diffusive paths. The ensemble of paths is expressed using a symmetric version of the Onsager-Machlup formula, which only requires evaluation of the force field and which, upon direct time discretization, gives rise to a symmetric integrator that is accurate to second order. Efficiently sampling this ensemble requires avoiding the well-known stiffness problem associated with sampling infinitesimal Brownian increments of the path, as well as a different type of stiffness associated with sampling the coarse features of long paths. The fine-features sampling stiffness is eliminated with the use of the fast sampling algorithm (FSA), and the coarse-feature sampling stiffness is avoided by introducing the sliding and sampling (S&S) algorithm. A key feature of the S&S algorithm is that it enables massively parallel computers to sample diffusive trajectories that are long in time. We use the algorithm to sample the transition path ensemble for the structural interconversion of the 38-atom Lennard-Jones cluster at low temperature.

  1. Sampling diffusive transition paths.

    PubMed

    Miller, Thomas F; Predescu, Cristian

    2007-04-14

    The authors address the problem of sampling double-ended diffusive paths. The ensemble of paths is expressed using a symmetric version of the Onsager-Machlup formula, which only requires evaluation of the force field and which, upon direct time discretization, gives rise to a symmetric integrator that is accurate to second order. Efficiently sampling this ensemble requires avoiding the well-known stiffness problem associated with the sampling of infinitesimal Brownian increments of the path, as well as a different type of stiffness associated with the sampling of the coarse features of long paths. The fine-feature sampling stiffness is eliminated with the use of the fast sampling algorithm, and the coarse-feature sampling stiffness is avoided by introducing the sliding and sampling (S&S) algorithm. A key feature of the S&S algorithm is that it enables massively parallel computers to sample diffusive trajectories that are long in time. The authors use the algorithm to sample the transition path ensemble for the structural interconversion of the 38-atom Lennard-Jones cluster at low temperature. PMID:17444696

  2. Anisotropic Thermal Diffusion

    NASA Astrophysics Data System (ADS)

    Gardiner, Thomas

    2013-10-01

    Anisotropic thermal diffusion in magnetized plasmas is an important physical phenomena for a diverse set of physical conditions ranging from astrophysical plasmas to MFE and ICF. Yet numerically simulating this phenomenon accurately poses significant challenges when the computational mesh is misaligned with respect to the magnetic field. Particularly when the temperature gradients are unresolved, one frequently finds entropy violating solutions with heat flowing from cold to hot zones for χ∥ /χ⊥ >=102 which is substantially smaller than the range of interest which can reach 1010 or higher. In this talk we present a new implicit algorithm for solving the anisotropic thermal diffusion equations and demonstrate its characteristics on what has become a fairly standard set of test problems in the literature. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2013-5687A.

  3. The diffusion of microfinance.

    PubMed

    Banerjee, Abhijit; Chandrasekhar, Arun G; Duflo, Esther; Jackson, Matthew O

    2013-07-26

    To study the impact of the choice of injection points in the diffusion of a new product in a society, we developed a model of word-of-mouth diffusion and then applied it to data on social networks and participation in a newly available microfinance loan program in 43 Indian villages. Our model allows us to distinguish information passing among neighbors from direct influence of neighbors' participation decisions, as well as information passing by participants versus nonparticipants. The model estimates suggest that participants are seven times as likely to pass information compared to informed nonparticipants, but information passed by nonparticipants still accounts for roughly one-third of eventual participation. An informed household is not more likely to participate if its informed friends participate. We then propose two new measures of how effective a given household would be as an injection point. We show that the centrality of the injection points according to these measures constitutes a strong and significant predictor of eventual village-level participation. PMID:23888042

  4. Apparatus for diffusion separation

    DOEpatents

    Nierenberg, William A.

    1976-08-10

    1. A diffuser separator apparatus which comprises a plurality of flow channels in a single stage, each of said channels having an inlet port and an outlet port and a constant cross sectional area between said ports, at least a portion of the defining surface of each of said channels being a diffusion separation membrane, and each of said channels having a different cross sectional area, means for connecting said channels in series so that each successive channel of said series has a smaller cross sectional area than the previous channel of said series, a source of gaseous mixture, individual means for flowing said gaseous mixture to the inlet port of each of said channels, gas receiving and analyzing means, individual means for flowing gas passing from each of said outlet ports and means for flowing gas passing through said membranes to said receiving and analyzing means, and individual means for connecting the outlet port of each channel with the inlet port of the channel having the next smaller cross sectional area.

  5. Sucrose diffusion in aqueous solution.

    PubMed

    Price, Hannah C; Mattsson, Johan; Murray, Benjamin J

    2016-07-28

    The diffusion of sugar in aqueous solution is important both in nature and in technological applications, yet measurements of diffusion coefficients at low water content are scarce. We report directly measured sucrose diffusion coefficients in aqueous solution. Our technique utilises a Raman isotope tracer method to monitor the diffusion of non-deuterated and deuterated sucrose across a boundary between the two aqueous solutions. At a water activity of 0.4 (equivalent to 90 wt% sucrose) at room temperature, the diffusion coefficient of sucrose was determined to be approximately four orders of magnitude smaller than that of water in the same material. Using literature viscosity data, we show that, although inappropriate for the prediction of water diffusion, the Stokes-Einstein equation works well for predicting sucrose diffusion under the conditions studied. As well as providing information of importance to the fundamental understanding of diffusion in binary solutions, these data have technological, pharmaceutical and medical implications, for example in cryopreservation. Moreover, in the atmosphere, slow organic diffusion may have important implications for aerosol growth, chemistry and evaporation, where processes may be limited by the inability of a molecule to diffuse between the bulk and the surface of a particle. PMID:27364512

  6. Diffusion limited aggregation. The role of surface diffusion

    NASA Astrophysics Data System (ADS)

    García-Ruiz, Juan M.; Otálora, Fermín

    1991-11-01

    We present a growth model in which the hitting particles are able to diffuse to more stable growth sites in the perimeter of a cluster growing by diffusion limited aggregation. By tuning the diffusion path Ls, the morphological output - from disordered fractal to perfect single crystals - can be controlled. Instabilities appear when the mean length of the crystal faces Lf are greater than 2 Ls.

  7. The Harrison Diffusion Kinetics Regimes in Solute Grain Boundary Diffusion

    SciTech Connect

    Belova, Irina; Fiedler, T; Kulkarni, Nagraj S; Murch, Prof. Graeme

    2012-01-01

    Knowledge of the limits of the principal Harrison kinetics regimes (Type-A, B and C) for grain boundary diffusion is very important for the correct analysis of the depth profiles in a tracer diffusion experiment. These regimes for self-diffusion have been extensively studied in the past by making use of the phenomenological Lattice Monte Carlo (LMC) method with the result that the limits are now well established. The relationship of those self-diffusion limits to the corresponding ones for solute diffusion in the presence of solute segregation to the grain boundaries remains unclear. In the present study, the influence of solute segregation on the limits is investigated with the LMC method for the well-known parallel grain boundary slab model by showing the equivalence of two diffusion models. It is shown which diffusion parameters are useful for identifying the limits of the Harrison kinetics regimes for solute grain boundary diffusion. It is also shown how the measured segregation factor from the diffusion experiment in the Harrison Type-B kinetics regime may differ from the global segregation factor.

  8. Diffusive evolution of experimental braided rivers

    NASA Astrophysics Data System (ADS)

    Reitz, M. D.; Lajeunesse, E.; Jerolmack, D. J.; Limare, A.; Metivier, F.; Devauchelle, O.

    2012-12-01

    Braided rivers are complex systems in which a network of ephemeral, interacting channels continually migrate to create a rapidly changing landscape, with activity on a range of scales from channel to network organization. A previously proposed formulation in the literature has described the macroscopic behavior of braided rivers with a relationship between sediment flux and system slope that has the form of diffusion. This deterministic relationship has yet to be shown to be a true expression of stastistical diffusion on the macroscopic scale that results from stochastic behavior at the unit scale. We present results of a set of ~1m-scale experiments of braided rivers forming over a bed of monodisperse glass beads, designed to quantify both the characteristics of individual channels and the statistics of the system, and to test the extent to which statistical diffusion is applicable to braided rivers. Our data consist of repeat high-resolution topography scans, which provide data on both topographic relief and water depth values. The experiments evolve from an initial flat bed, allowing us to study the approach of the system to a steady state. We find that, although channels migrate rapidly, they have stable, self-similar geometries organized to a critical Shields stress criterion, which suggests that the timescale of channel geometry organization is small compared to dynamic channel timescales. Analysis of the channel network through time shows a decorrelation that is random and memoryless, and which occurs over time and space scales that yield a diffusivity estimate consistent with the deterministic theoretical prediction. Further investigation shows that many aspects of the system dynamics can be directly described with this diffusional framework. The timescale to equilibrium slope and topographic steady state, the rate at which correlation lengthscales increase through time, and the dependence of the equilibrium slope on sediment flux can all be described with

  9. Numerical Computation of Diffusion on a Surface

    SciTech Connect

    Schwartz, Peter; Adalsteinsson, David; Colella, Phillip; Arkin, Adam Paul; Onsum, Matthew

    2005-02-24

    We present a numerical method for computing diffusive transport on a surface derived from image data. Our underlying discretization method uses a Cartesian grid embedded boundary method for computing the volume transport in region consisting of all points a small distance from the surface. We obtain a representation of this region from image data using a front propagation computation based on level set methods for solving the Hamilton-Jacobi and eikonal equations. We demonstrate that the method is second-order accurate in space and time, and is capable of computing solutions on complex surface geometries obtained from image data of cells.

  10. Surface modification by subsurface pressure induced diffusion

    SciTech Connect

    Zimmermann, Claus G.

    2012-01-23

    Polycrystalline Ag, covered with a nm thin siloxane layer, was irradiated with ultraviolet light in vacuum at 500 K. Ag particles of different aspect ratios, 50-1000 nm in size, formed on the surface, including a small fraction of nanorods. Pressurized water vapor bubbles are created in the subsurface region by hydrogen radicals photo-chemically released by the siloxane layer. They provide the driving force for a diffusive material flux along grain boundaries to the surface. This mechanism was modeled and found to agree with the experimental timescale: approximately 300 h are required for a 1000 nm particle to form.

  11. Apoplastic Diffusion Barriers in Arabidopsis

    PubMed Central

    Schreiber, Lukas; Franke, Rochus Benni; Geldner, Niko; Reina-Pinto, José J.; Kunst, Ljerka

    2013-01-01

    During the development of Arabidopsis and other land plants, diffusion barriers are formed in the apoplast of specialized tissues within a variety of plant organs. While the cuticle of the epidermis is the primary diffusion barrier in the shoot, the Casparian strips and suberin lamellae of the endodermis and the periderm represent the diffusion barriers in the root. Different classes of molecules contribute to the formation of extracellular diffusion barriers in an organ- and tissue-specific manner. Cutin and wax are the major components of the cuticle, lignin forms the early Casparian strip, and suberin is deposited in the stage II endodermis and the periderm. The current status of our understanding of the relationships between the chemical structure, ultrastructure and physiological functions of plant diffusion barriers is discussed. Specific aspects of the synthesis of diffusion barrier components and protocols that can be used for the assessment of barrier function and important barrier properties are also presented. PMID:24465172

  12. Small centrifugal pumps for low thrust rockets

    NASA Technical Reports Server (NTRS)

    Gulbrandsen, N. C.; Furst, R. B.; Burgess, R. M.; Scheer, D. D.

    1985-01-01

    This paper presents the results of a combined analytical and experimental investigation of low specific speed pumps for potential use as components of propellant feed systems for low thrust rocket engines. Shrouded impellers and open face impellers were tested in volute type and vaned diffuser type pumps. Full- and partial-emission diffusers and full- and partial-admission impellers were tested. Axial and radial loads, head and efficiency versus flow, and cavitation tests were conducted. Predicted performance of two pumps are compared when pumping water and liquid hydrogen. Detailed pressure loss and parasitic power values are presented for two pump configurations. Partial-emission diffusers were found to permit use of larger impeller and diffuser passages with a minimal performance penalty. Normal manufacturing tolerances were found to result in substantial power requirement variation with only a small pressure rise change. Impeller wear ring leakage was found to reduce pump pressure rise to an increasing degree as the pump flowrate was decreased.

  13. Fluorescence Correlation Spectroscopy and Nonlinear Stochastic Reaction-Diffusion

    SciTech Connect

    Del Razo, Mauricio; Pan, Wenxiao; Qian, Hong; Lin, Guang

    2014-05-30

    The currently existing theory of fluorescence correlation spectroscopy (FCS) is based on the linear fluctuation theory originally developed by Einstein, Onsager, Lax, and others as a phenomenological approach to equilibrium fluctuations in bulk solutions. For mesoscopic reaction-diffusion systems with nonlinear chemical reactions among a small number of molecules, a situation often encountered in single-cell biochemistry, it is expected that FCS time correlation functions of a reaction-diffusion system can deviate from the classic results of Elson and Magde [Biopolymers (1974) 13:1-27]. We first discuss this nonlinear effect for reaction systems without diffusion. For nonlinear stochastic reaction-diffusion systems there are no closed solutions; therefore, stochastic Monte-Carlo simulations are carried out. We show that the deviation is small for a simple bimolecular reaction; the most significant deviations occur when the number of molecules is small and of the same order. Extending Delbrück-Gillespie’s theory for stochastic nonlinear reactions with rapidly stirring to reaction-diffusion systems provides a mesoscopic model for chemical and biochemical reactions at nanometric and mesoscopic level such as a single biological cell.

  14. Light diffusing fiber optic chamber

    DOEpatents

    Maitland, Duncan J.

    2002-01-01

    A light diffusion system for transmitting light to a target area. The light is transmitted in a direction from a proximal end to a distal end by an optical fiber. A diffusing chamber is operatively connected to the optical fiber for transmitting the light from the proximal end to the distal end and transmitting said light to said target area. A plug is operatively connected to the diffusing chamber for increasing the light that is transmitted to the target area.

  15. Multilane driven diffusive systems

    NASA Astrophysics Data System (ADS)

    Curatolo, A. I.; Evans, M. R.; Kafri, Y.; Tailleur, J.

    2016-03-01

    We consider networks made of parallel lanes along which particles hop according to driven diffusive dynamics. The particles also hop transversely from lane to lane, hence indirectly coupling their longitudinal dynamics. We present a general method for constructing the phase diagram of these systems which reveals that in many cases their physics reduce to that of single-lane systems. The reduction to an effective single-lane description legitimizes, for instance, the use of a single TASEP to model the hopping of molecular motors along the many tracks of a single microtubule. Then, we show how, in quasi-2D settings, new phenomena emerge due to the presence of non-zero transverse currents, leading, for instance, to strong ‘shear localization’ along the network.

  16. Enthalpy Diffusion in Multicomponent Flows

    SciTech Connect

    Cook, A W

    2009-01-20

    The conclusions of this paper are: (1) Enthalpy diffusion preserves the second law. (2) Euler solvers will not produce correct temperatures in mixing regions. (3) Navier-Stokes solvers will only produce correct temperatures if q{sub d} is included. (4) Errors from neglecting enthalpy diffusion are most severe when differences in molecular weights are large. (5) In addition to temperature, enthalpy diffusion affects density, dilatation and other fields in subtle ways. (6) Reacting flow simulations that neglect the term are a dubious proposition. (7) Turbulence models for RANS and LES closures should preserve consistency between energy and species diffusion.

  17. Lateral Diffusion in an Archipelago

    PubMed Central

    Saxton, Michael J.

    1982-01-01

    Lateral diffusion of molecules in lipid bilayer membranes can be hindered by the presence of impermeable domains of gel-phase lipid or of proteins. Effective-medium theory and percolation theory are used to evaluate the effective lateral diffusion constant as a function of the area fraction of fluid-phase lipid and the permeability of the obstructions to the diffusing species. Applications include the estimation of the minimum fraction of fluid lipid needed for bacterial growth, and the enhancement of diffusion-controlled reactions by the channeling effect of solid patches of lipid. PMID:7052153

  18. Solvent diffusion into fluoropolymer membranes

    SciTech Connect

    Aminabhavi, T.M.; Munnolli, R.S.

    1993-12-31

    Solvent diffusion in polymers is important to the physical properties of the material from processing to end-use and shelf-life. Many aspects of diffusion in polymers have been studied using indirect and direct methods. Du Pont`s fluoropolymers are known for their excellent resistance to a variety of organic solvents. This paper describes the measurement of diffusion coefficients and the derived thermodynamic quantities on four different fluoropolymer membranes with several esters. This information is interpreted in terms of the molecular organization and phase structure. Diffusion coefficients are sensitive to structural changes as well as binding and association phenomena.

  19. Thermal diffusion in dilute nanofluids investigated by photothermal interferometry

    NASA Astrophysics Data System (ADS)

    Philip, J.; Nisha, M. R.

    2010-03-01

    We have carried out a theoretical analysis of the dependence of the particle mass fraction on the thermal diffusivity of dilute suspensions of nanoparticles in liquids (dilute nanofluids). The analysis takes in to account adsorption of an ordered layer of solvent molecules around the nanoparticles. It is found that thermal diffusivity decreases with mass fraction for sufficiently small particle sizes. Beyond a critical particle size thermal diffusivity begins to increase with mass fraction for the same system. The results have been verified experimentally by measuring the thermal diffusivity of dilute suspensions of TiO2 nanoparticles dispersed in polyvinyl alcohol (PVA) medium. The effect is attributed to Kapitza resistance of thermal waves in the medium.

  20. Diffusive Dynamics of Contact Formation in Disordered Polypeptides

    NASA Astrophysics Data System (ADS)

    Zerze, Gül H.; Mittal, Jeetain; Best, Robert B.

    2016-02-01

    Experiments measuring contact formation between probes in disordered chains provide information on the fundamental time scales relevant to protein folding. However, their interpretation usually relies on one-dimensional (1D) diffusion models, as do many experiments probing a single distance. Here, we use all-atom molecular simulations to capture both the time scales of contact formation, as well as the scaling with peptide length for tryptophan triplet quenching experiments, revealing the sensitivity of the experimental quenching times to the configurational space explored by the chain. We find a remarkable consistency between the results of the full calculation and from Szabo-Schulten-Schulten theory applied to a 1D diffusion model, supporting the validity of such models. The significant reduction in diffusion coefficient at the small probe separations which most influence quenching rate, suggests that contact formation and Förster resonance energy transfer correlation experiments provide complementary information on diffusivity.

  1. Diffusive Dynamics of Contact Formation in Disordered Polypeptides.

    PubMed

    Zerze, Gül H; Mittal, Jeetain; Best, Robert B

    2016-02-12

    Experiments measuring contact formation between probes in disordered chains provide information on the fundamental time scales relevant to protein folding. However, their interpretation usually relies on one-dimensional (1D) diffusion models, as do many experiments probing a single distance. Here, we use all-atom molecular simulations to capture both the time scales of contact formation, as well as the scaling with peptide length for tryptophan triplet quenching experiments, revealing the sensitivity of the experimental quenching times to the configurational space explored by the chain. We find a remarkable consistency between the results of the full calculation and from Szabo-Schulten-Schulten theory applied to a 1D diffusion model, supporting the validity of such models. The significant reduction in diffusion coefficient at the small probe separations which most influence quenching rate, suggests that contact formation and Förster resonance energy transfer correlation experiments provide complementary information on diffusivity. PMID:26919016

  2. Simulations of singlet exciton diffusion in organic semiconductors: a review

    DOE PAGESBeta

    Bjorgaard, Josiah A.; Kose, Muhammet Erkan

    2014-12-22

    Our review describes the various aspects of simulation strategies for exciton diffusion in condensed phase thin films of organic semiconductors. Several methods for calculating energy transfer rate constants are discussed along with procedures for how to account for energetic disorder. Exciton diffusion can be modelled by using kinetic Monte-Carlo methods or master equations. Recent literature on simulation efforts for estimating exciton diffusion lengths of various conjugated polymers and small molecules are introduced. Moreover, these studies are discussed in the context of the effects of morphology on exciton diffusion and the necessity of accurate treatment of disorder for comparison of simulationmore » results with those of experiment.« less

  3. Dynamics and pattern formation in a cancer network with diffusion

    NASA Astrophysics Data System (ADS)

    Zheng, Qianqian; Shen, Jianwei

    2015-10-01

    Diffusion is ubiquitous inside cells, and it is capable of inducing spontaneous pattern formation in reaction-diffusion systems on a spatially homogeneous domain. In this paper, we investigate the dynamics of a diffusive cancer network regulated by microRNA and obtain the condition that the network undergoes a Hopf bifurcation and a Turing pattern bifurcation. In addition, we also develop the amplitude equation of the network model by using Taylor series expansion, multi-scaling and further expansion in powers of a small parameter. As a result of these analyses, we obtain the explicit condition on how the dynamics of the diffusive cancer network evolve. These results reveal that this system has rich dynamics, such as spotted stripe and hexagon patterns. The bifurcation diagram helps us understand the biological mechanism in the cancer network. Finally, numerical simulations confirm our analytical results.

  4. Asymptotic neutron scattering laws for anomalously diffusing quantum particles

    NASA Astrophysics Data System (ADS)

    Kneller, Gerald R.

    2016-07-01

    The paper deals with a model-free approach to the analysis of quasielastic neutron scattering intensities from anomalously diffusing quantum particles. All quantities are inferred from the asymptotic form of their time-dependent mean square displacements which grow ∝tα, with 0 ≤ α < 2. Confined diffusion (α = 0) is here explicitly included. We discuss in particular the intermediate scattering function for long times and the Fourier spectrum of the velocity autocorrelation function for small frequencies. Quantum effects enter in both cases through the general symmetry properties of quantum time correlation functions. It is shown that the fractional diffusion constant can be expressed by a Green-Kubo type relation involving the real part of the velocity autocorrelation function. The theory is exact in the diffusive regime and at moderate momentum transfers.

  5. Asymptotic neutron scattering laws for anomalously diffusing quantum particles.

    PubMed

    Kneller, Gerald R

    2016-07-28

    The paper deals with a model-free approach to the analysis of quasielastic neutron scattering intensities from anomalously diffusing quantum particles. All quantities are inferred from the asymptotic form of their time-dependent mean square displacements which grow ∝t(α), with 0 ≤ α < 2. Confined diffusion (α = 0) is here explicitly included. We discuss in particular the intermediate scattering function for long times and the Fourier spectrum of the velocity autocorrelation function for small frequencies. Quantum effects enter in both cases through the general symmetry properties of quantum time correlation functions. It is shown that the fractional diffusion constant can be expressed by a Green-Kubo type relation involving the real part of the velocity autocorrelation function. The theory is exact in the diffusive regime and at moderate momentum transfers. PMID:27475344

  6. Diffusion inspires selection of pinning nodes in pinning control

    NASA Astrophysics Data System (ADS)

    Zhou, Ming-Yang; He, Xingsheng; Fu, Zhong-Qian; Liao, Hao; Cai, Shi-min; Zhuo, Zhao

    2016-03-01

    The outstanding problem of controlling a complex network via pinning is related to network dynamics and has the potential to master large-scale real-world systems as well. This paper addresses the heart issue about how to choose pinning nodes for pinning control, where pinning control aims to control a network to an identical state by injecting feedback control signals to a small fraction of nodes. We explore networks' controllability from not only mathematical analysis, but also the aspects of network topology and information diffusion. Then, the connection between pinning control and information diffusion is given, and pinning node selection is transferred into multi-spreader problem in information diffusion. Based on information diffusion, a heuristic method is proposed to select pinning nodes by optimizing the spreading ability of multiple spreaders. The proposed method greatly improves the controllability of large practical networks, and provides a new perspective to investigate pinning node selection.

  7. Perpendicular diffusion of energetic particles in collisionless plasmas

    SciTech Connect

    Shalchi, A.

    2015-01-15

    A fundamental problem in plasma and astrophysics is the interaction between energetic particles and magnetized plasmas. In the current paper, we focus on particle diffusion across the guide magnetic field. It is shown that the perpendicular diffusion coefficient depends only on the parallel diffusion coefficient and the Kubo number. Therefore, one can find four asymptotic limits depending on the values of these two parameters. These regimes are the quasilinear limit, the Kadomtsev and Pogutse limit, the scaling of Rechester and Rosenbluth, and the scaling found by Zybin and Istomin. In the current article, we focus on the Rechester and Rosenbluth scenario because this was not discovered before in the context of collisionless plasmas. Examples and applications are discussed as well. We show that an energy independent ratio of perpendicular and parallel diffusion coefficients can be found and that this ratio can be very small but also close to unity. This is exactly what one observes in the solar wind.

  8. Control of gold surface diffusion on si nanowires.

    PubMed

    den Hertog, Martien I; Rouviere, Jean-Luc; Dhalluin, Florian; Desré, Pierre J; Gentile, Pascal; Ferret, Pierre; Oehler, Fabrice; Baron, Thiery

    2008-05-01

    Silicon nanowires (NW) were grown by the vapor-liquid-solid mechanism using gold as the catalyst and silane as the precursor. Gold from the catalyst particle can diffuse over the wire sidewalls, resulting in gold clusters decorating the wire sidewalls. The presence or absence of gold clusters was observed either by high angle annular darkfield scanning transmission electron microscopy images or by scanning electron microscopy. We find that the gold surface diffusion can be controlled by two growth parameters, the silane partial pressure and the growth temperature, and that the wire diameter also affects gold diffusion. Gold clusters are not present on the NW side walls for high silane partial pressure, low temperature, and small NW diameters. The absence or presence of gold on the NW sidewall has an effect on the sidewall morphology. Different models are qualitatively discussed. The main physical effect governing gold diffusion seems to be the adsorption of silane on the NW sidewalls. PMID:18422363

  9. A refined model of water and CO2 membrane diffusion: Effects and contribution of sterols and proteins

    PubMed Central

    Kai, Lei; Kaldenhoff, Ralf

    2014-01-01

    Black lipid bilayers, a general model system for biomembranes were studied for diffusion rates of small molecules such as water or CO2 using advanced analysis techniques and cell free synthesized proteins. We provide evidence that by simple insertion of proteins or sterols the diffusion rates of water or those of CO2 decrease. Insertion of cell free synthesized water permeable aquaporins restored water diffusion rates as well as insertion of CO2-facilitating aquaporins the CO2 diffusion. Insertion of water or CO2 impermeable proteins decreased the respective diffusion rates. Therefore, for normal high cellular CO2 diffusion rates specific aquaporins are mandatory. PMID:25331164

  10. An integration factor method for stochastic and stiff reaction-diffusion systems

    NASA Astrophysics Data System (ADS)

    Ta, Catherine; Wang, Dongyong; Nie, Qing

    2015-08-01

    Stochastic effects are often present in the biochemical systems involving reactions and diffusions. When the reactions are stiff, existing numerical methods for stochastic reaction diffusion equations require either very small time steps for any explicit schemes or solving large nonlinear systems at each time step for the implicit schemes. Here we present a class of semi-implicit integration factor methods that treat the diffusion term exactly and reaction implicitly for a system of stochastic reaction-diffusion equations. Our linear stability analysis shows the advantage of such methods for both small and large amplitudes of noise. Direct use of the method to solving several linear and nonlinear stochastic reaction-diffusion equations demonstrates good accuracy, efficiency, and stability properties. This new class of methods, which are easy to implement, will have broader applications in solving stochastic reaction-diffusion equations arising from models in biology and physical sciences.

  11. An integration factor method for stochastic and stiff reaction–diffusion systems

    SciTech Connect

    Ta, Catherine; Wang, Dongyong; Nie, Qing

    2015-08-15

    Stochastic effects are often present in the biochemical systems involving reactions and diffusions. When the reactions are stiff, existing numerical methods for stochastic reaction diffusion equations require either very small time steps for any explicit schemes or solving large nonlinear systems at each time step for the implicit schemes. Here we present a class of semi-implicit integration factor methods that treat the diffusion term exactly and reaction implicitly for a system of stochastic reaction–diffusion equations. Our linear stability analysis shows the advantage of such methods for both small and large amplitudes of noise. Direct use of the method to solving several linear and nonlinear stochastic reaction–diffusion equations demonstrates good accuracy, efficiency, and stability properties. This new class of methods, which are easy to implement, will have broader applications in solving stochastic reaction–diffusion equations arising from models in biology and physical sciences.

  12. HINDERED DIFFUSION OF ASPHALTENES AT EVALUATED TEMPERATURE AND PRESSURE

    SciTech Connect

    James A. Guin; Surya Vadlamani

    1999-04-01

    During this time period, we performed experiments to examine the effects of solvent composition on the diffusion controlled uptake of quinoline into alumina catalyst pellets. Of particular interest was the effect of solvent aromaticity on the diffusive uptake process. The uptake experiments were performed at a temperature of 300 C for the adsorptive diffusion of quinoline in a solvent mixture of mineral oil and 1-methyl naphthalene onto alumina catalyst pellets. These experiments were conducted in a 40 cm{sup 3} microautoclave, the use of which is more economical from both a purchasing and waste disposal standpoint due to the small quantities of solvents and catalysts utilized, and is also significantly safer at the higher temperatures. In order to study the effect of aromaticity of the solvent on the hindered diffusion-adsorption process, the experiments were performed at different volume fractions of 1-methyl naphthalene. Detailed calculations were made to estimate the effects of aromaticity, i. e., as reflected by the percentage of 1-methyl naphthalene in the solvent, on the diffusive properties of the solute. Model simulation results were then performed which showed that the mathematical model incorporating diffusion and adsorption mechanisms satisfactorily fitted the adsorptive diffusion of quinoline onto the alumina catalyst at 300 C with various solvent aromaticities. The logarithm of the adsorption constant at a particular volume fraction of 1-methyl naphthalene, obtained by simulating the experimental data with the model solution, was found to be linearly dependent on an aromaticity factor.

  13. Diffusing proteins on a fluctuating membrane: Analytical theory and simulations

    NASA Astrophysics Data System (ADS)

    Reister-Gottfried, Ellen; Leitenberger, Stefan M.; Seifert, Udo

    2010-03-01

    Using analytical calculations and computer simulations, we consider both the lateral diffusion of a membrane protein and the fluctuation spectrum of the membrane in which the protein is embedded. The membrane protein interacts with the membrane shape through its spontaneous curvature and bending rigidity. The lateral motion of the protein may be viewed as diffusion in an effective potential, hence, the effective mobility is always reduced compared to the case of free diffusion. Using a rigorous path-integral approach, we derive an analytical expression for the effective diffusion coefficient for small ratios of temperature and bending rigidity, which is the biologically relevant limit. Simulations show very good quantitative agreement with our analytical result. The analysis of the correlation functions contributing to the diffusion coefficient shows that the correlations between the stochastic force of the protein and the response in the membrane shape are responsible for the reduction. Our quantitative analysis of the membrane height correlation spectrum shows an influence of the protein-membrane interaction causing a distinctly altered wave-vector dependence compared to a free membrane. Furthermore, the time correlations exhibit the two relevant time scales of the system: that of membrane fluctuations and that of lateral protein diffusion with the latter typically much longer than the former. We argue that the analysis of the long-time decay of membrane height correlations can thus provide a new means to determine the effective diffusion coefficient of proteins in the membrane.

  14. Multi-source information diffusion in online social networks

    NASA Astrophysics Data System (ADS)

    Xiong, Fei; Liu, Yun; Zhang, Hai-Feng

    2015-07-01

    Individual spreading behavior in online social networks is closely related to user activity, tie strength, and other user and network features. The results concentrate on personal spreading decisions; however, whether these features promote the global information diffusion and increase the macroscopic density of infected agents, remains unclear to us. In this paper, we propose a multi-source diffusion model in which agents may create new messages and spread other agents’ messages. Agents receive many messages, and each time they select a certain message preferentially to spread in consideration of different features. Simulation results show the density of infected agents for different messages follows a power-law distribution in both scale-free and small-world networks. Selecting the largest author degree, author activity and tie strength preferentially can advance the overall diffusion process. Weak tie bias is the least effective feature for multiple information diffusion, but it helps to diffuse a single message. Unexpectedly, the bias of interest similarity does not have an apparent effect. Integrated with the influence on individual diffusion behavior, strong tie bias is a significant feature both for local and global diffusion.

  15. Inlet free-stream turbulence effects on diffuser performance

    NASA Technical Reports Server (NTRS)

    Hoffman, J. A.; Gonzales, G.

    1983-01-01

    The performance of a subsonic two dimensional diffuser was experimentally evaluated as a function of inlet free-stream turbulence parameters. Anisotropic inlet free-stream turbulence with the eddy axis perpendicular to the flow and parallel to the diverging walls of the diffuser appears to be more effective at transmitting energy to the diverging walls of the diffuser, thereby improving diffuser performance, as compared to isotropic turbulence or anisotropic turbulence with the eddy axis perpendicular to the diverging walls of the diffuser. The pressure recovery of the diffuser was found to be strongly dependent upon the inlet free-stream total turbulence intensity, was independent of eddy size for large eddy dimensions, and was dependent upon eddy size for small eddy dimensions. The improvement in the diffuser's static pressure recovery coefficient at a total included divergence angle of 20 deg, compared to the low inlet turbulence case, was found to be as much as 21 times larger than the pressure loss across the turbulence generators.

  16. Determination of eddy diffusivity in the lowermost stratosphere

    NASA Astrophysics Data System (ADS)

    Hegglin, M. I.; Brunner, D.; Peter, T.; Staehelin, J.; Wirth, V.; Hoor, P.; Fischer, H.

    2005-07-01

    We present a 2D-advection-diffusion model that simulates the main transport pathways influencing tracer distributions in the lowermost stratosphere (LMS). The model describes slow diabatic descent of aged stratospheric air, vertical (cross-isentropic) and horizontal (along isentropes) diffusion within the LMS and across the tropopause using equivalent latitude and potential temperature coordinates. Eddy diffusion coefficients parameterize the integral effect of dynamical processes leading to small scale turbulence and mixing. They were specified by matching model simulations to observed CO distributions. Interestingly, the model suggests mixing across isentropes to be more important than horizontal mixing across surfaces of constant equivalent latitude, shining new light on the interplay between various transport mechanisms in the LMS. The model achieves a good description of the small scale tracer features at the tropopause with squared correlation coefficients R2 = 0.72...0.94.

  17. Atomic diffusion processes in heteroepitaxial metallic systems using SLKMC-II

    NASA Astrophysics Data System (ADS)

    Shah, Syed Islamuddin; Karim, Altaf

    We have examined the diffusion of small islands of Cu on Ag(111) surface using a self-learning kinetic Monte Carlo (SLKMC-II) method with an improved pattern recognition scheme. Due to strain generated at the interface between metals with different bulk lattice constants, interesting single atom, multi-atom and concerted diffusion processes are automatically revealed in the simulations. Here we will report various processes for small islands in the case of Cu/Ag(111) system. Key processes responsible for island diffusion and their energetics together with trends in effective energy barriers as well as diffusion constants for small islands will also be provided. In addition to 2-D diffusion processes, as an application of SLKMC-II to the 3-dimensional heteroepitaxial systems, we will also report energy barriers of some of the 3-dimensional processes including down the A- and B-steps and exchange processes

  18. Evaluating rotational diffusion from protein MD simulations.

    PubMed

    Wong, Vance; Case, David A

    2008-05-15

    It is now feasible to carry out molecular dynamics simulations of proteins in water that are long compared to the overall tumbling of the molecule. Here, we examine rotational diffusion in four small, globular proteins (ubiquitin, binase, lysozyme, and fragment B3 of protein G) with the TIP3P, TIP4P/EW, and SPC/E water models, in simulations that are 6 to 60 times as long as the mean rotational tumbling time. We describe a method for extracting diffusion tensors from such simulations and compare the results to experimental values extracted from NMR relaxation measurements. The simulation results accurately follow a diffusion equation, even for spherical harmonic correlation functions with l as large as 8. However, the best-fit tensors are significantly different from experiment, especially for the commonly used TIP3P water model. Simulations that are 20 to 100 times longer than the rotational tumbling times are needed for good statistics. A number of residues exhibit internal motions on the nanosecond time scale, but in all cases examined here, a product of internal and overall time-correlation functions matches the total time-correlation function well. PMID:18052365

  19. THE CHANDRA M101 MEGASECOND: DIFFUSE EMISSION

    SciTech Connect

    Kuntz, K. D.; Snowden, S. L. E-mail: snowden@milkyway.gsfc.nasa.go

    2010-05-15

    Because M101 is nearly face-on, it provides an excellent laboratory in which to study the distribution of X-ray-emitting gas in a typical late-type spiral galaxy. We obtained a Chandra observation with a cumulative exposure of roughly 1 Ms to study the diffuse X-ray emission in M101. The bulk of the X-ray emission is correlated with the star formation traced by the far-UV (FUV) emission. The global FUV/X-ray correlation is nonlinear (the X-ray surface brightness is roughly proportional to the square root of the FUV surface brightness) and the small-scale correlation is poor, probably due to the delay between the FUV emission and the X-ray production in star-forming regions. The X-ray emission contains only minor contributions from unresolved stars ({approx}<3%), unresolved X-ray point sources ({approx}<4%), and individual supernova remnants ({approx}3%). The global spectrum of the diffuse emission can be reasonably well fitted with a three-component thermal model, but the fitted temperatures are not unique; many distributions of emission measure can produce the same temperatures when observed with the current CCD energy resolution. The spectrum of the diffuse emission depends on the environment; regions with higher X-ray surface brightnesses have relatively stronger hard components, but there is no significant evidence that the temperatures of the emitting components increase with surface brightness.

  20. AIDS-Related Stigma and Health Professionals in Puerto Rico

    PubMed Central

    Ruiz-Torres, Yamilette; Cintrón-Bou, Francheska N.; Varas-Díaz, Nelson

    2009-01-01

    This study addresses an important issue in the AIDS epidemic in Puerto Rico: AIDS stigma among health professionals and health profession students. AIDS stigma has been documented among health services providers such as doctors, nurses, psychologists, and social workers. It has detrimental effects of the services provided and the lives of people living with HIV/AIDS (PLWHA). The main objective of this study was to explore AIDS stigma manifestations among a sample composed of eighty health professionals and health profession students who participated in in-depth qualitative interviews. Four thematic categories stemmed from the data analysis process. These addressed the following subjects: social manifestations of stigma, stigma manifestations in the workplace, use of sensitive information to control PLWHA, and surveillance of PLWHA. Participants manifested instances of stigmatization they had witnessed in their work and training scenarios. Furthermore, they elaborated on the need to place effective surveillance mechanism on PLWHA in order to control the epidemic. PMID:21423837

  1. Balancing engagement/detachment in AIDS-related multiple losses.

    PubMed

    Carmack, B J

    1992-01-01

    The process gay persons use to manage the multiple losses and cumulative grief from losing lovers, friends, colleagues and clients to AIDS was explored. Interviews with gay individuals (n = 19) in a large urban area in the West provided data for conceptual coding and comparative analysis. Balancing engagement and detachment was identified as the basic social-psychological process that described how gay individuals struggled to reach an optimal balance in their involvement in the needs of individuals and the community. Four conceptual categories were identified: dysfunctional engagement, functional engagement, functional detachment and dysfunctional detachment. These four categories occur within the contexts of previous life style and redefinition of personal values. PMID:1541482

  2. AIDS-related reasons for gay men's adoption of celibacy.

    PubMed

    Siegel, K; Raveis, V H

    1993-01-01

    Since it was first recognized that human immunodeficiency virus (HIV) infection could be sexually transmitted, celibacy has been advocated by some as the only unequivocally effective adaptation for avoiding the risk of infection. Others, however, have countered that few will be willing to be celibate and, further, that such behavior may have adverse psychosocial consequences. As part of a qualitative study of gay men's sexual decision-making in the context of the AIDS/HIV epidemic, we identified a subsample of respondents who had adopted celibacy for varying periods of time as an adaptation to the threat of AIDS/HIV infection. A content analysis of these men's interviews revealed 5 principal themes relating their reasons for choosing celibacy. PMID:8297710

  3. Diffuser for intravessels radiation based on plastic fiber

    NASA Astrophysics Data System (ADS)

    Pich, Justyna; Grobelny, Andrzej; Beres-Pawlik, Elzbieta

    2006-03-01

    Laser radiation is used in such contemporary medicine as: sport medicine, gynecology etc. Because of many radiations inside the system, there is a need of an element, which allows to supply the place of illness with energy. The dimensions of this element are often small and the one that meets these conditions is diffuser.

  4. INVESTIGATION OF PRODUCT-LAYER DIFFUSIVITY FOR CAO SULFATION

    EPA Science Inventory

    The paper gives results of comparisons of the sulfation rates of CaO prepared from Ca(OH)2 and CaCO3, using six types of each precursor derived from the same natural limestones. The particles were small enough to eliminate all transport resistances except diffusion through the Ca...

  5. Measurements of Transverse Beam Diffusion Rates in the Fermilab Tevatron Collider

    SciTech Connect

    Stancari, G.; Annala, G.; Johnson, T.R.; Still, D.A.; Valishev, A.; /Fermilab

    2011-08-01

    The transverse beam diffusion rate vs. particle oscillation amplitude was measured in the Tevatron using collimator scans. All collimator jaws except one were retracted. As the jaw of interest was moved in small steps, the local shower rates were recorded as a function of time. By using a diffusion model, the time evolution of losses could be related to the diffusion rate at the collimator position. Preliminary results of these measurements are presented.

  6. Fractional diffusion on bounded domains

    DOE PAGESBeta

    Defterli, Ozlem; D'Elia, Marta; Du, Qiang; Gunzburger, Max Donald; Lehoucq, Richard B.; Meerschaert, Mark M.

    2015-03-13

    We found that the mathematically correct specification of a fractional differential equation on a bounded domain requires specification of appropriate boundary conditions, or their fractional analogue. In this paper we discuss the application of nonlocal diffusion theory to specify well-posed fractional diffusion equations on bounded domains.

  7. Teaching Diffusion with a Coin

    ERIC Educational Resources Information Center

    Haddad, Hamilton; Baldo, Marcus Vinicius Chrysostomo

    2010-01-01

    In this article, the authors describe an inexpensive and simple way to make students intuitively experience the probabilistic nature and nonorientated motion of diffusing particles. This understanding allows students to realize why diffusion works so well over short distances and becomes increasingly and rapidly less effective as the distances…

  8. Demonstrating Diffusion: Why the Confusion?

    ERIC Educational Resources Information Center

    Panizzon, Debra Lee

    1998-01-01

    Examines the principles of diffusion and how it may be confused with convection. Suggests that educators may be misleading students and clouding their understanding of the process. Provides two contemporary examples to explain the process of diffusion and how it differs from convection. (Author/CCM)

  9. Osmosis and Diffusion Conceptual Assessment

    ERIC Educational Resources Information Center

    Fisher, Kathleen M.; Williams, Kathy S.; Lineback, Jennifer Evarts

    2011-01-01

    Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large public university, we developed and validated an 18-item Osmosis and Diffusion Conceptual Assessment (ODCA). This assessment includes two-tiered items, some adopted or modified…

  10. The Diffusion of New Math.

    ERIC Educational Resources Information Center

    Ready, Patricia M.

    The life cycle of "new math" is fertile ground for the study of the diffusion of an innovation. New math arrived in 1958 to save the day for America after the Soviet Union launched Sputnik, the first successful space flight in 1957. In a period of 16 years an entire diffusion cycle was completed throughout the entire educational system of the…

  11. Radiant Extinction Of Gaseous Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Berhan, S.; Chernovsky, M.; Atreya, A.; Baum, Howard R.; Sacksteder, Kurt R.

    2003-01-01

    one-dimensional. (ii) The spherical diffusion flame completely encloses the soot which is formed on the fuel rich side of the reaction zone. This increases the importance of flame radiation because now both soot and gaseous combustion products co-exist inside the high temperature spherical diffusion flame. (iii) For small fuel injection velocities, as is usually the case for a pyrolyzing solid, the diffusion flame in :g around the solid naturally develops spherical symmetry. Thus, spherical diffusion flames are of interest to fires in :g and identifying conditions that lead to radiation-induced extinction is important for spacecraft fire safety.

  12. Diffusion Driven Combustion Waves in Porous Media

    NASA Technical Reports Server (NTRS)

    Aldushin, A. P.; Matkowsky, B. J.

    2000-01-01

    Filtration of gas containing oxidizer, to the reaction zone in a porous medium, due, e.g., to a buoyancy force or to an external pressure gradient, leads to the propagation of Filtration combustion (FC) waves. The exothermic reaction occurs between the fuel component of the solid matrix and the oxidizer. In this paper, we analyze the ability of a reaction wave to propagate in a porous medium without the aid of filtration. We find that one possible mechanism of propagation is that the wave is driven by diffusion of oxidizer from the environment. The solution of the combustion problem describing diffusion driven waves is similar to the solution of the Stefan problem describing the propagation of phase transition waves, in that the temperature on the interface between the burned and unburned regions is constant, the combustion wave is described by a similarity solution which is a function of the similarity variable x/square root of(t) and the wave velocity decays as 1/square root of(t). The difference between the two problems is that in the combustion problem the temperature is not prescribed, but rather, is determined as part of the solution. We will show that the length of samples in which such self-sustained combustion waves can occur, must exceed a critical value which strongly depends on the combustion temperature T(sub b). Smaller values of T(sub b) require longer sample lengths for diffusion driven combustion waves to exist. Because of their relatively small velocity, diffusion driven waves are considered to be relevant for the case of low heat losses, which occur for large diameter samples or in microgravity conditions, Another possible mechanism of porous medium combustion describes waves which propagate by consuming the oxidizer initially stored in the pores of the sample. This occurs for abnormally high pressure and gas density. In this case, uniformly propagating planar waves, which are kinetically controlled, can propagate, Diffusion of oxidizer decreases

  13. Comparison of Student Learning about Diffusion and Osmosis in Constructivist and Traditional Classrooms.

    ERIC Educational Resources Information Center

    Christianson, Roger G.; Fisher, Kathleen M.

    1999-01-01

    Reports on the effects of constructivist versus traditional teaching approaches on university students' learning about osmosis and diffusion. Students understood diffusion and osmosis more deeply in the constructivist-informed classroom, which used small discussion groups rather than traditional large lecture groups. Suggests ways to improve…

  14. AEROSOL SIZE MEASUREMENT BY ELECTRICAL MOBILITY AND DIFFUSION ANALYSIS - A COMPARISON OF METHODS

    EPA Science Inventory

    The principle of the electrical aerosol analyzer method is reviewed and the diffusion battery method is described in detail. An appendix explains the basis of the calculations used. The diffusion battery method is complicated by counting losses of very small particles, inherent t...

  15. A Simple Educational Method for the Measurement of Liquid Binary Diffusivities

    ERIC Educational Resources Information Center

    Rice, Nicholas P.; de Beer, Martin P.; Williamson, Mark E.

    2014-01-01

    A simple low-cost experiment has been developed for the measurement of the binary diffusion coefficients of liquid substances. The experiment is suitable for demonstrating molecular diffusion to small or large undergraduate classes in chemistry or chemical engineering. Students use a cell phone camera in conjunction with open-source image…

  16. A Device to Emulate Diffusion and Thermal Conductivity Using Water Flow

    ERIC Educational Resources Information Center

    Blanck, Harvey F.

    2005-01-01

    A device designed to emulate diffusion and thermal conductivity using flowing water is reviewed. Water flowing through a series of cells connected by a small tube in each partition in this plastic model is capable of emulating diffusion and thermal conductivity that occurs in variety of systems described by several mathematical equations.

  17. Enthalpy Diffusion in Multicomponent Flows

    SciTech Connect

    Cook, A W

    2008-11-12

    The enthalpy diffusion flux in the multicomponent energy equation is a well known yet frequently neglected term. It accounts for energy changes, associated with compositional changes, resulting from species diffusion. Enthalpy diffusion is important in flows where significant mixing occurs between species of dissimilar molecular weight. The term plays a critical role in preventing local violations of the entropy condition. In simulations of nonpremixed combustion, omission of the enthalpy flux can lead to anomalous temperature gradients, which may cause mixing regions to exceed ignition conditions. The term can also play a role in generating acoustic noise in turbulent mixing layers. Euler solvers that rely on numerical diffusion to mix fluids cannot accurately predict the temperature in mixed regions. On the other hand, Navier-Stokes solvers that incorporate enthalpy diffusion can provide much more accurate results.

  18. Thermal diffusivity of diamond films

    NASA Technical Reports Server (NTRS)

    Albin, Sacharia; Winfree, William P.; Crews, B. Scott

    1990-01-01

    A laser pulse technique to measure the thermal diffusivity of diamond films deposited on a silicon substrate is developed. The effective thermal diffusivity of diamond film on silicon was measured by observing the phase and amplitude of the cyclic thermal waves generated by the laser pulses. An analytical model is developed to calculate the effective in-plane (face-parallel) diffusivity of a two layer system. The model is used to reduce the effective thermal diffusivity of the diamond/silicon sample to a value for the thermal diffusivity and conductivity of the diamond film. Phase and amplitude measurements give similar results. The thermal conductivity of the films is found to be better than that of type 1a natural diamond.

  19. Ammonia diffusion through Nalophan™ bags.

    PubMed

    Sironi, Selena; Eusebio, Lidia; Dentoni, Licinia; Capelli, Laura; Del Rosso, Renato

    2014-01-01

    The aim of the work is to verify the diffusion rate of ammonia through the Nalophan™ film that constitutes the sampling bag, considering storage times ranging from 1 to 26 h. The ammonia decay over time was evaluated using gas-chromatography for the quantification of ammonia concentration inside the bag. The research assesses the roles of both of ammonia and water concentration gradients at the polymeric film interface on the diffusion process. The results show that both the ammonia concentration gradient and, in a less pronounced way, the water concentration gradient are the main 'engines' of ammonia diffusion. Double bags seem to represent a simple solution for preventing ammonia losses during storage. Another interesting result concerns the role of the bag surface on the ammonia diffusion rate: the higher the surface/volume (S/V) ratio, the higher the ammonia diffusion rate through the polymeric film. PMID:24552718

  20. Portable vapor diffusion coefficient meter

    DOEpatents

    Ho, Clifford K.

    2007-06-12

    An apparatus for measuring the effective vapor diffusion coefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vapor that has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transient diffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

  1. Heat transfer, diffusion, and evaporation

    NASA Technical Reports Server (NTRS)

    Nusselt, Wilhelm

    1954-01-01

    Although it has long been known that the differential equations of the heat-transfer and diffusion processes are identical, application to technical problems has only recently been made. In 1916 it was shown that the speed of oxidation of the carbon in iron ore depends upon the speed with which the oxygen of the combustion air diffuses through the core of gas surrounding the carbon surface. The identity previously referred to was then used to calculate the amount of oxygen diffusing to the carbon surface on the basis of the heat transfer between the gas stream and the carbon surface. Then in 1921, H. Thoma reversed that procedure; he used diffusion experiments to determine heat-transfer coefficients. Recently Lohrisch has extended this work by experiment. A technically very important application of the identity of heat transfer and diffusion is that of the cooling tower, since in this case both processes occur simultaneously.

  2. Interfacial diffusion aided deformation during nanoindentation

    NASA Astrophysics Data System (ADS)

    Samanta, Amit; E, Weinan

    2016-07-01

    Nanoindentation is commonly used to quantify the mechanical response of material surfaces. Despite its widespread use, a detailed understanding of the deformation mechanisms responsible for plasticity during these experiments has remained elusive. Nanoindentation measurements often show stress values close to a material's ideal strength which suggests that dislocation nucleation and subsequent dislocation activity dominates the deformation. However, low strain-rate exponents and small activation volumes have also been reported which indicates high temperature sensitivity of the deformation processes. Using an order parameter aided temperature accelerated sampling technique called adiabatic free energy dynamics [J. B. Abrams and M. E. Tuckerman, J. Phys. Chem. B, 112, 15742 (2008)], and molecular dynamics we have probed the diffusive mode of deformation during nanoindentation. Localized processes such as surface vacancy and ad-atom pair formation, vacancy diffusion are found to play an important role during indentation. Our analysis suggests a change in the dominant deformation mode from dislocation mediated plasticity to diffusional flow at high temperatures, slow indentation rates and small indenter tip radii.

  3. STRAIN-DEPENDENT OXYGEN DIFFUSIVITY IN BOVINE ANNULUS FIBROSUS

    PubMed Central

    Yuan, T-Y; Jackson, AR; Huang, C-Y; Gu, W Y

    2009-01-01

    Background The intervertebral disc (IVD) is the largest avascular structure in human body. Transport of small molecules in IVD is mainly through diffusion from the endplates and the peripheral blood vessels surrounding IVD. Studies have investigated the structure, chemical components and water content in IVD, but to our knowledge no study has investigated the effect of mechanical loading on oxygen transport in IVD. The objective of this study was to determine the stain-dependent behavior of oxygen diffusivity in IVD tissue. Method of Approach A one-dimensional steady-state diffusion experiment was designed and performed to determine the oxygen diffusivity in bovine annulus fibrosus (AF). The oxygen diffusivity was calculated using equation derived from Fick’s law. A total of 20 AF specimens (d=6 mm, h~0.5 mm) from bovine coccygeal IVD were used to determine oxygen diffusivity at three levels of compressive strain. Results The average oxygen diffusivity (mean ± SD) of bovine AF in the axial direction was 1.43 ± 0.242×10−5 cm2/s (n=20) at 4.68 ± 1.67% compressive strain level, 1.05 ± 0.282×10−5 cm2/s (n=20) at 14.2 ± 1.50% strain level, and 7.71 ± 1.63×10−6 cm2/s (n=20) at 23.7±1.34% strain level. There was a significant decrease in oxygen diffusivity with increasing level of compressive strain (ANOVA, p<0.05). Conclusions Oxygen diffusivity of bovine AF in the axial direction has been determined. The mechanical loading has a significant effect on oxygen transport in IVD tissues. This study is important in understanding nutritional transport in IVD tissues and related disc degeneration. PMID:19640139

  4. Diffusion in membranes: Toward a two-dimensional diffusion map

    NASA Astrophysics Data System (ADS)

    Toppozini, Laura; Garcia-Sakai, Victoria; Bewley, Robert; Dalgliesh, Robert; Perring, Toby; Rheinstädter, Maikel C.

    2015-01-01

    For decades, quasi-elastic neutron scattering has been the prime tool for studying molecular diffusion in membranes over relevant nanometer distances. These experiments are essential to our current understanding of molecular dynamics of lipids, proteins and membrane-active molecules. Recently, we presented experimental evidence from X-ray diffraction and quasi-elastic neutron scattering demonstrating that ethanol enhances the permeability of membranes. At the QENS 2014/WINS 2014 conference we presented a novel technique to measure diffusion across membranes employing 2-dimensional quasi-elastic neutron scattering. We present results from our preliminary analysis of an experiment on the cold neutron multi-chopper spectrometer LET at ISIS, where we studied the self-diffusion of water molecules along lipid membranes and have the possibility of studying the diffusion in membranes. By preparing highly oriented membrane stacks and aligning them horizontally in the spectrometer, our aim is to distinguish between lateral and transmembrane diffusion. Diffusion may also be measured at different locations in the membranes, such as the water layer and the hydrocarbon membrane core. With a complete analysis of the data, 2-dimensional mapping will enable us to determine diffusion channels of water and ethanol molecules to quantitatively determine nanoscale membrane permeability.

  5. Diffuse Microwave Emission Survey

    NASA Astrophysics Data System (ADS)

    Shafer, R. A.; Mather, J.; Kogut, A.; Fixsen, D. J.; Seiffert, M.; Lubin, P. M.; Levin, S. M.

    1996-12-01

    The Diffuse Microwave Emission Survey (DIMES) is a mission concept selected by NASA in 1995 to answer fundamental questions about the content and history of the universe. DIMES will use a set of absolutely calibrated cryogenic radiometers from a space platform to measure the frequency spectrum of the cosmic microwave background (CMB) at wavelengths 15--0.3 cm (frequency 2--100 GHz) to precision 0.1 mK or better. Measurements at centimeter wavelengths probe different physical processes than the COBE-FIRAS spectra at shorter wavelengths, and complement the anisotropy measurements from DMR, balloon and ground-based instruments, and the planned MAP and COBRAS/SAMBA satellites. DIMES will observe the free-free signal from early photoionization to establish the precise epoch of structure formation, and will measure or limit energy release at redshift 10(4) < z < 10(7) by measuring the chemical potential distortion of the CMB spectrum. Both are likely under current cosmological theory and allowed by current measurement limits; even an upper limit at the expected sensitivity 10(-5) MJy/sr will place important constraints on the matter content, structure, and evolution of the universe. Detecting these distortions or showing that they do not exist constitutes the last frontier of CMB observations.

  6. Diffuse gamma radiation

    NASA Technical Reports Server (NTRS)

    Fichtel, C. E.; Simpson, G. A.; Thompson, D. J.

    1977-01-01

    An examination of the intensity, energy spectrum, and spatial distribution of the diffuse gamma-radiation observed by SAS-2 satellite away from the galactic plane in the energy range above 35 MeV has shown that it consists of two components. One component is generally correlated with galactic latitudes, the atomic hydrogen column density was deduced from 21 cm measurements, and the continuum radio emission, believed to be synchrotron emission. It has an energy spectrum similar to that in the plane and joins smoothly to the intense radiation from the plane. It is therefore presumed to be of galactic origin. The other component is apparently isotropic, at least on a coarse scale, and has a steep energy spectrum. No evidence is found for a cosmic ray halo surrounding the galaxy in the shape of a sphere or oblate spheroid with galactic dimensions. Constraints for a halo model with significantly larger dimensions are set on the basis of an upper limit to the gamma-ray anisotropy.

  7. Diffusion with optimal resetting

    NASA Astrophysics Data System (ADS)

    Evans, Martin R.; Majumdar, Satya N.

    2011-10-01

    We consider the mean time to absorption by an absorbing target of a diffusive particle with the addition of a process whereby the particle is reset to its initial position with rate r. We consider several generalizations of the model of Evans and Majumdar (2011 Phys. Rev. Lett.106 160601): (i) a space-dependent resetting rate r(x); (ii) resetting to a random position z drawn from a resetting distribution { P}(z); and (iii) a spatial distribution for the absorbing target PT(x). As an example of (i) we show that the introduction of a non-resetting window around the initial position can reduce the mean time to absorption provided that the initial position is sufficiently far from the target. We address the problem of optimal resetting, that is, minimizing the mean time to absorption for a given target distribution. For an exponentially decaying target distribution centred at the origin we show that a transition in the optimal resetting distribution occurs as the target distribution narrows.

  8. Disturbance-driven Hillslope Diffusion Scales and Values Clarified by Extant Surface Roughness

    NASA Astrophysics Data System (ADS)

    Doane, T.; Furbish, D. J.

    2015-12-01

    In low-relief landscapes, the hillslope diffusion equation approximates the rate of topographic evolution due to disturbance driven sediment transport. Whereas this expression is appealing and performs well, the physical meaning of a hillslope diffusivity remains unclear. Here, a study of the disturbances that redistribute sediment on hillslopes clarifies a physical interpretation. We conceptualize the cumulative hillslope diffusivity, which is a rate constant for topographic degradation at large scales, as the aggregate of all surface disturbing processes. A numerical model that generates pit and mound topography from tree throw events illustrates this idea. Using the diffusion equation, we model the degradation of pits and mounds by all smaller scale disturbances. However, when examined at a larger scale, the effective hillslope diffusivity is composed of the small scale diffusivity plus the effect of tree throw. We also present a method to determine the background hillslope diffusivity using the extant hillslope roughness and rates of roughness production. Numerical simulations show that the variance of the surface roughness of a hillslope as introduced by pit and mound topography reaches a steady state when the rate of variance production (tree throw) is constant. The magnitude of the steady state variance is a function of variance production and decay (small scale diffusivity), so there is an opportunity to determine hillslope diffusivity values if the rates of variance production are known. This method yields estimates of the modern hillslope diffusivity which are useful in problems involving the human and climate change time scales.

  9. Transdermal diffusion of xenon in vitro using diffusion cells

    NASA Astrophysics Data System (ADS)

    Verkhovsky, A.; Petrov, E.

    2015-11-01

    The aim of this research was to study the diffusion rate of xenon through guinea pig skin and how viscosity of cosmetic component capryl/capric triglyceride (CCT) facilitates to deliver xenon to surface of skin patches. They were placed in Franz cell for 24 hours and diffusion rate and permeability of xenon were calculated. Thus diffusion rate was 0.031 mg/hour*cm2 and permeability was 0.003 cm/hour. Using Brookfield viscometer it was shown that viscosity of CCT decreased upon increasing xenon concentration. Obtained results can be utilized in developing of new xenon containing drugs for topical administration.

  10. Diffusion of nitric oxide into low density lipoprotein.

    PubMed

    Denicola, Ana; Batthyány, Carlos; Lissi, Eduardo; Freeman, Bruce A; Rubbo, Homero; Radi, Rafael

    2002-01-11

    A key early event in the development of atherosclerosis is the oxidation of low density lipoprotein (LDL) via different mechanisms including free radical reactions with both protein and lipid components. Nitric oxide (( small middle dot)NO) is capable of inhibiting LDL oxidation by scavenging radical species involved in oxidative chain propagation reactions. Herein, the diffusion of ( small middle dot)NO into LDL is studied by fluorescence quenching of pyrene derivatives. Selected probes 1-(pyrenyl)methyltrimethylammonium (PMTMA) and 1-(pyrenyl)-methyl-3-(9-octadecenoyloxy)-22,23-bisnor-5-cholenate (PMChO) were chosen so that they could be incorporated at different depths of the LDL particle. Indeed, PMTMA and PMChO were located in the surface and core of LDL, respectively, as indicated by changes in fluorescence spectra, fluorescence quenching studies with water-soluble quenchers and the lifetime values (tau(o)) of the excited probes. The apparent second order rate quenching constants of ( small middle dot)NO (k(NO)) for both probes were 2.6-3.8 x 10(10) m(-1) s(-1) and 1.2 x 10(10) m(-1) s(-1) in solution and native LDL, respectively, indicating that there is no significant barrier to the diffusion of ( small middle dot)NO to the surface and core of LDL. Nitric oxide was also capable of diffusing through oxidized LDL. Considering the preferential partitioning of ( small middle dot)NO in apolar milieu (6-8 for n-octanol:water) and therefore a larger ( small middle dot)NO concentration in LDL with respect to the aqueous phase, a corrected k(NO) value of approximately 0.2 x 10(10) m(-1) s(-1) can be determined, which still is sufficiently large and consistent with a facile diffusion of ( small middle dot)NO through LDL. Applying the Einstein-Smoluchowsky treatment, the apparent diffusion coefficient (D(')NO) of ( small middle dot)NO in native LDL is on average 2 x 10(-5) cm(2) s(-1), six times larger than that previously reported for erythrocyte plasma membrane

  11. Design and performance of family of diffusing scrolls with mixed-flow impeller and vaneless diffuser

    NASA Technical Reports Server (NTRS)

    Brown, W Byron; Bradshaw, Guy R

    1949-01-01

    A family of diffusing scrolls was designed for use with a mixed-flow impeller and a small-diameter vaneless diffuser. The design theory, intended to maintain a uniform pressure around the scroll inlet, permits determination of the position of scroll cross sections of preassigned area by considering the radial variation in fluid density and the effects of friction along the scroll. Inasmuch as the design method leaves the cross-sectional shape undetermined, the effect of certain variations in scroll shape was investigated by studying scrolls having angles of divergence (of the scroll walls downstream of the entrance section) of 24 degrees, 40 degrees, and 80 degrees. A second 80 degree scroll was of asymmetrical construction and a third was plaster-cast instead of sand-cast. Each scroll was tested as a compressor component at actual impeller tip speeds of 700 to 1300 feet per second from full throttle to surge.

  12. Scanning, non-contact, hybrid broadband diffuse optical spectroscopy and diffuse correlation spectroscopy system.

    PubMed

    Johansson, Johannes D; Mireles, Miguel; Morales-Dalmau, Jordi; Farzam, Parisa; Martínez-Lozano, Mar; Casanovas, Oriol; Durduran, Turgut

    2016-02-01

    A scanning system for small animal imaging using non-contact, hybrid broadband diffuse optical spectroscopy (ncDOS) and diffuse correlation spectroscopy (ncDCS) is presented. The ncDOS uses a two-dimensional spectrophotometer retrieving broadband (610-900 nm) spectral information from up to fifty-seven source-detector distances between 2 and 5 mm. The ncDCS data is simultaneously acquired from four source-detector pairs. The sample is scanned in two dimensions while tracking variations in height. The system has been validated with liquid phantoms, demonstrated in vivo on a human fingertip during an arm cuff occlusion and on a group of mice with xenoimplanted renal cell carcinoma. PMID:26977357

  13. Scanning, non-contact, hybrid broadband diffuse optical spectroscopy and diffuse correlation spectroscopy system

    PubMed Central

    Johansson, Johannes D.; Mireles, Miguel; Morales-Dalmau, Jordi; Farzam, Parisa; Martínez-Lozano, Mar; Casanovas, Oriol; Durduran, Turgut

    2016-01-01

    A scanning system for small animal imaging using non-contact, hybrid broadband diffuse optical spectroscopy (ncDOS) and diffuse correlation spectroscopy (ncDCS) is presented. The ncDOS uses a two-dimensional spectrophotometer retrieving broadband (610-900 nm) spectral information from up to fifty-seven source-detector distances between 2 and 5 mm. The ncDCS data is simultaneously acquired from four source-detector pairs. The sample is scanned in two dimensions while tracking variations in height. The system has been validated with liquid phantoms, demonstrated in vivo on a human fingertip during an arm cuff occlusion and on a group of mice with xenoimplanted renal cell carcinoma. PMID:26977357

  14. Enhancement of gas-phase diffusion in the presence of liquid

    NASA Astrophysics Data System (ADS)

    Webb, S.; Angert, A.

    2003-04-01

    Gas diffusion in porous media occurs in both the gas and liquid phases. In many instances, gas diffusion in the liquid phase is ignored. However, under many conditions, gas diffusion in the liquid phase may be more important than gas diffusion in the gas phase. Two different cases will be examined in this work. The first case is a continuous liquid path between the gas concentrations of interest modeled after Jury et al. (1984). The second case is the situation at low liquid saturation where liquid islands exist. For the first case, Jury's model can be rewritten as a ratio of the total gas diffusion in the gas and liquid phases to that just in the gas phase. The liquid diffusion coefficient is approximately 10-4 times the gas diffusion coefficient consistent with Jury et al. (1984). The ratio of total diffusion to gas-phase diffusion is then only a function of Henry's constant and the liquid saturation. For higher values of Henry's constant, such as for CO2 and O2, the effect of diffusion in the liquid phase is small except at high liquid saturations. For small values of Henry's constant, such as for some VOCs and explosive compounds, diffusion in the liquid phase dominates for low and moderate liquid saturation values. The second case is the enhancement of diffusion caused by liquid islands at low liquid saturation. Enhanced vapor diffusion across liquid islands has been observed and modeled by Webb and Ho (1999), where condensation and evaporation occur on opposite ends of the liquid island. Vapor diffusion enhancement of up to a factor of 10 has been observed. Similarly, gas can diffuse through the liquid island. For high values of Henry's constant, gas diffusion through liquid islands is negligible and can be ignored. For small values of Henry's constant, diffusion through liquid islands may be much greater than diffusion through gas, so the rate is enhanced. The work was sponsored by the Geneva International Center for Humanitarian Demining (GICHD) under the

  15. Diffusion instability in a bimodal disc. [planetary rings

    NASA Technical Reports Server (NTRS)

    Ward, W. R.; Harris, A. W.

    1982-01-01

    A simplified model of radial diffusion in a planetary disk with a bimodal size distribution is presented. The large particle component excites the small particles' dispersion velocity via gravitational scattering. The resulting small particle viscous stress goes through a maximum near optical depth = sq root 3. Such a stress profile promotes the development of high and low optical depth zones. The resulting ringlet appearance is due primarily to the distribution of small particles, which produce most of the optical depth but may constitute only a minor portion of system mass.

  16. Fick's Insights on Liquid Diffusion

    SciTech Connect

    Narasimhan, T.N.

    2004-10-07

    In 1855, Adolph Fick published ''On Liquid Diffusion'', mathematically treating salt movements in liquids as a diffusion process, analogous to heat diffusion. Less recognized is the fact that Fick also provided a detailed account of the implications of salt diffusion to transport through membranes. A careful look at Fick (1855) shows that his conceptualization of molecular diffusion was more comprehensive than could be captured with the mathematical methods available to him, and therefore his expression, referred to as Fick's Law, dealt only with salt flux. He viewed salt diffusion in liquids as a binary process, with salt moving in one way and water moving in the other. Fick's analysis of the consequences of such a binary process operating in a hydrophilic pore in a membrane offers insights that are relevant to earth systems. This paper draws attention to Fick's rationale, and its implications to hydrogeological systems. Fick (1829-1901; Figure 1), a gifted scientist, published the first book on medical physics (Fick, 1858), discussing the application of optics, solid mechanics, gas diffusion, and heat budget to biological systems. Fick's paper is divisible into two parts. The first describes his experimental verification of the applicability of Fourier's equation to liquid diffusion. The second is a detailed discussion of diffusion through a membrane. Although Fick's Law specifically quantifies solute flux, Fick visualized a simultaneous movement of water and stated, ''It is evident that a volume of water equal to that of the salt passes simultaneously out of the upper stratum into the lower.'' (Fick, 1855, p.30). Fick drew upon Fourier's model purely by analogy. He assumed that concentration gradient impelled salt movement, without inquiring why concentration gradient should constitute a driving force. As for water movement, he stated intuitively, ''a force of suction comes into play on each side of the membrane, proportional to the difference of concentration

  17. Time scale of diffusion in molecular and cellular biology

    NASA Astrophysics Data System (ADS)

    Holcman, D.; Schuss, Z.

    2014-05-01

    Diffusion is the driver of critical biological processes in cellular and molecular biology. The diverse temporal scales of cellular function are determined by vastly diverse spatial scales in most biophysical processes. The latter are due, among others, to small binding sites inside or on the cell membrane or to narrow passages between large cellular compartments. The great disparity in scales is at the root of the difficulty in quantifying cell function from molecular dynamics and from simulations. The coarse-grained time scale of cellular function is determined from molecular diffusion by the mean first passage time of molecular Brownian motion to a small targets or through narrow passages. The narrow escape theory (NET) concerns this issue. The NET is ubiquitous in molecular and cellular biology and is manifested, among others, in chemical reactions, in the calculation of the effective diffusion coefficient of receptors diffusing on a neuronal cell membrane strewn with obstacles, in the quantification of the early steps of viral trafficking, in the regulation of diffusion between the mother and daughter cells during cell division, and many other cases. Brownian trajectories can represent the motion of a molecule, a protein, an ion in solution, a receptor in a cell or on its membrane, and many other biochemical processes. The small target can represent a binding site or an ionic channel, a hidden active site embedded in a complex protein structure, a receptor for a neurotransmitter on the membrane of a neuron, and so on. The mean time to attach to a receptor or activator determines diffusion fluxes that are key regulators of cell function. This review describes physical models of various subcellular microdomains, in which the NET coarse-grains the molecular scale to a higher cellular-level, thus clarifying the role of cell geometry in determining subcellular function.

  18. DiffuseModel: Modeling the diffuse ultraviolet background

    NASA Astrophysics Data System (ADS)

    Murthy, Jayant

    2015-12-01

    DiffuseModel calculates the scattered radiation from dust scattering in the Milky Way based on stars from the Hipparcos catalog. It uses Monte Carlo to implement multiple scattering and assumes a user-supplied grid for the dust distribution. The output is a FITS file with the diffuse light over the Galaxy. It is intended for use in the UV (900 - 3000 A) but may be modified for use in other wavelengths and galaxies.

  19. BEAM DIFFUSION MEASUREMENTS AT RHIC.

    SciTech Connect

    FLILLER,R.P.,IIIDREES,A.GASSNER,D.MCINTYRE,G.PEGGS,S.TRBOJEVIC,D.

    2003-05-12

    During a store, particles from the beam core continually diffuse outwards into the halo through a variety of mechanisms. Understanding the diffusion rate as a function of particle amplitude can help discover which processes are important to halo growth. A collimator can be used to measure the amplitude growth rate as a function of the particle amplitude. In this paper we present results of diffusion measurements performed at the Relativistic Heavy Ion Collider (RHIC) with fully stripped gold ions, deuterons, and protons. We compare these results with measurements from previous years, and simulations, and discuss any factors that relate to beam growth in RHIC.

  20. Phosphorus diffusion in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Losee, D. L.; Lavine, J. P.; Trabka, E. A.; Lee, S.-T.; Jarman, C. M.

    1984-02-01

    The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary-ion mass spectroscopy. A two-dimensional diffusion model is used to find effective grain (Dg) and grain-boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific-gravity measurements, which found a significantly lower ``mass defect'' for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.

  1. Configurational diffusion of coal macromolecules

    SciTech Connect

    Guin, J.A.; Curtis, C.W.; Tarrer, A.R.

    1990-01-01

    As shown in last quarter's report on the configurational diffusion of coal macromolecules, the hindered diffusion data for both TPP and coal macromolecules were significantly different from the theoretical correlations. In order to evaluate the factors which could lead to this difference an error analysis was conducted, and the detailed results reported herein. Generally, we did not find any errors which could account for the deviation from the theory, and thus we conclude that this deviation is real and can be ascribed to some factor not considered by the hindered diffusion theory, i.e., attractive or repulsive forces. 2 refs., 4 figs., 4 tabs.

  2. ALUMINUM IMPURITY DIFFUSION IN MAGNESIUM

    SciTech Connect

    Brennan, Sarah; Warren, Andrew; Coffey, Kevin; Kulkarni, Nagraj S; Todd, Peter J; Sohn, Yong Ho; Klimov, Mikhail

    2012-01-01

    The Al impurity diffusion in polycrystalline Mg (99.9%) via depth profiling with secondary ion mass spectrometry was studied in the temperature range of 673-573K, utilizing the thin film method and thin film solution to the diffusion equation. Multiple samples were utilized and multiple profiles were obtained to determine statistically confident coefficient with maximum standard deviation of 16%. Activation energy and pre-exponential factor of Al impurity diffusion in Mg was determined as 155 kJ/mole and 3.9 x 10-3 m2/sec.

  3. Chaotic diffusion in the Gliese-876 planetary system

    NASA Astrophysics Data System (ADS)

    Martí, J. G.; Cincotta, P. M.; Beaugé, C.

    2016-07-01

    Chaotic diffusion is supposed to be responsible for orbital instabilities in planetary systems after the dissipation of the protoplanetary disc, and a natural consequence of irregular motion. In this paper, we show that resonant multiplanetary systems, despite being highly chaotic, not necessarily exhibit significant diffusion in phase space, and may still survive virtually unchanged over time-scales comparable to their age. Using the GJ-876 system as an example, we analyse the chaotic diffusion of the outermost (and less massive) planet. We construct a set of stability maps in the surrounding regions of the Laplace resonance. We numerically integrate ensembles of close initial conditions, compute Poincaré maps and estimate the chaotic diffusion present in this system. Our results show that, the Laplace resonance contains two different regions: an inner domain characterized by low chaoticity and slow diffusion, and an outer one displaying larger values of dynamical indicators. In the outer resonant domain, the stochastic borders of the Laplace resonance seem to prevent the complete destruction of the system. We characterize the diffusion for small ensembles along the parameters of the outermost planet. Finally, we perform a stability analysis of the inherent chaotic, albeit stable Laplace resonance, by linking the behaviour of the resonant variables of the configurations to the different sub-structures inside the three-body resonance.

  4. Radial diffusion of radiation belt particles in nondipolar magnetic fields

    NASA Astrophysics Data System (ADS)

    Cunningham, Gregory S.

    2016-06-01

    The fact that charged particles trapped in Earth's magnetic field can be redistributed along their radial distance from Earth due to drift-resonant interactions with small-amplitude waves has been known since early in the space age. Early theoretical efforts assumed that a dipole background magnetic field was modified by a time-varying electromagnetic perturbation that changed the particle's distance from Earth while preserving the first two invariants of motion. The stochastic nature of the perturbation allowed the effect of the waves on the trapped particles to be represented by a Fokker-Planck equation, which updates the phase space density in time via radial diffusion with diffusion coefficients that depend on the wave characteristics. In this paper, we extend those early theoretical efforts to define radial diffusion coefficients in arbitrary static background fields and define a numerical scheme for their evaluation. The background fields we consider are allowed to have significant deviations from a dipole field. Radial diffusion coefficients are computed using the new scheme for one of the empirical magnetic field models (T89) developed by Tsyganenko and coauthors as the background on top of which the perturbations are added. The new diffusion coefficients are shown to be substantially larger than those computed with a dipole background field model, especially at large radial distances and during geomagnetically active times, and it is suggested that outward radial diffusion may be a more substantial loss process for trapped electrons in the outer radiation belt than previously believed.

  5. Chaotic Diffusion in the Gliese-876 Planetary System

    NASA Astrophysics Data System (ADS)

    Martí, J. G.; Cincotta, P. M.; Beaugé, C.

    2016-05-01

    Chaotic diffusion is supposed to be responsible for orbital instabilities in planetary systems after the dissipation of the protoplanetary disk, and a natural consequence of irregular motion. In this paper we show that resonant multi-planetary systems, despite being highly chaotic, not necessarily exhibit significant diffusion in phase space, and may still survive virtually unchanged over timescales comparable to their age.Using the GJ-876 system as an example, we analyze the chaotic diffusion of the outermost (and less massive) planet. We construct a set of stability maps in the surrounding regions of the Laplace resonance. We numerically integrate ensembles of close initial conditions, compute Poincaré maps and estimate the chaotic diffusion present in this system. Our results show that, the Laplace resonance contains two different regions: an inner domain characterized by low chaoticity and slow diffusion, and an outer one displaying larger values of dynamical indicators. In the outer resonant domain, the stochastic borders of the Laplace resonance seem to prevent the complete destruction of the system. We characterize the diffusion for small ensembles along the parameters of the outermost planet. Finally, we perform a stability analysis of the inherent chaotic, albeit stable Laplace resonance, by linking the behavior of the resonant variables of the configurations to the different sub-structures inside the three-body resonance.

  6. Diffusion and the Thermal Stability of Amorphous Copper-Zirconium

    NASA Astrophysics Data System (ADS)

    Stelter, Eric Carl

    Measurements have been made of diffusion and thermal relaxation in amorphous Cu(,50)Zr(,50). Samples were prepared by melt-spinning under vacuum. Diffusion measurements were made over the temperature range from 317 to 385 C, using Ag and Au as substitutional impurities, by means of Auger electron spectrometry (AES) and Rutherford backscattering spectrometry (RBS). Thermal measurements were made by differential scanning calorimetry (DSC) up to 550 C. The diffusion coefficients of Ag and Au in amorphous Cu(,50)Zr(,50) are found to be somewhat higher than, but very close in magnitude to the coefficient of self-diffusion in crystalline Cu at the same temperatures. The activation energies for diffusion in the amorphous alloy are 0.72 to 1.55 eV/atom, much closer to the activation energy for self-diffusion in liquid Cu, 0.42 eV/atom, than that for the crystalline solid, 2.19 eV/atom. The mechanism for diffusion in the amorphous metal is presumably quite different from the monovacancy mechanism dominant in the crystalline solid. The pre-exponential terms are found to be extremely small, on the order of 10('-10) to 10('-11) cm('2)/sec for Ag diffusion. This indicates that diffusion in amorphous Cu(,50)Zr(,50) may involve an extended defect of 10 or more atoms. Analysis of the data in terms of the free -volume model also lends strength to this conclusion and indicates that the glass is composed of liquid-like clusters of 15 to 20 atoms. The initial stage of relaxation in amorphous CuZr occurs with a spectrum of activation energies. The lowest activation energy involved, 0.78 eV/atom, is almost identical to the average activation energy of Ag diffusion in the glass, 0.77 eV/atom, indicating that relaxation occurs primarily through diffusion. The activation energy of crystallization, determined by Kissinger's method, is 3.10 eV/atom. The large difference, on the order of 2.3 eV/atom, between the activation energies of crystallization and diffusion is attributed to the energy

  7. Improved diffuser for augmenting a wind turbine

    DOEpatents

    Foreman, K.M.; Gilbert, B.L.

    A diffuser for augmenting a wind turbine having means for energizing the boundary layer at several locations along the diffuser walls is improved by the addition of a short collar extending radially outward from the outlet of the diffuser.

  8. Diffuser for augmenting a wind turbine

    DOEpatents

    Foreman, Kenneth M.; Gilbert, Barry L.

    1984-01-01

    A diffuser for augmenting a wind turbine having means for energizing the boundary layer at several locations along the diffuser walls is improved by the addition of a short collar extending radially outward from the outlet of the diffuser.

  9. Static and Dynamic Effects of Lateral Carrier Diffusion in Semiconductor Lasers

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Cheung, Samson H.; Ning, C. Z.; Biegel, Bryan A. (Technical Monitor)

    2002-01-01

    Electron and hole diffusions in the plane of semiconductor quantum wells play an important part in the static and dynamic operations of semiconductor lasers. It is well known that the value of diffusion coefficients affects the threshold pumping current of a semiconductor laser. At the same time, the strength of carrier diffusion process is expected to affect the modulation bandwidth of an AC-modulated laser. It is important not only to investigate the combined DC and AC effects due to carrier diffusion, but also to separate the AC effects from that of the combined effects in order to provide design insights for high speed modulation. In this presentation, we apply a hydrodynamic model developed by the present authors recently from the semiconductor Bloch equations. The model allows microscopic calculation of the lateral carrier diffusion coefficient, which is a nonlinear function of the carrier density and plasma temperature. We first studied combined AC and DC effects of lateral carrier diffusion by studying the bandwidth dependence on diffusion coefficient at a given DC current under small signal modulation. The results show an increase of modulation bandwidth with decrease in the diffusion coefficient. We simultaneously studied the effects of nonlinearity in the diffusion coefficient. To clearly identify how much of the bandwidth increase is a result of decrease in the threshold pumping current for smaller diffusion coefficient, thus an effective increase of DC pumping, we study the bandwidth dependence on diffusion coefficient at a given relative pumping. A detailed comparison of the two cases will be presented.

  10. Investigating axial diffusion in cylindrical pores using confocal single-particle fluorescence correlation spectroscopy.

    PubMed

    Chen, Fang; Neupane, Bhanu; Li, Peiyuan; Su, Wei; Wang, Gufeng

    2016-08-01

    We explored the feasibility of using confocal fluorescence correlation spectroscopy to study small nanoparticle diffusion in hundred-nanometer-sized cylindrical pores. By modeling single particle diffusion in tube-like confined three-dimensional space aligned parallel to the confocal optical axis, we showed that two diffusion dynamics can be observed in both original intensity traces and the autocorrelation functions (ACFs): the confined two-dimensional lateral diffusion and the unconfined one-dimensional (1D) axial diffusion. The separation of the axial and confined lateral diffusion dynamics provides an opportunity to study diffusions in different dimensions separately. We further experimentally studied 45 nm carboxylated polystyrene particles diffusing in 300 nm alumina pores. The experimental data showed consistency with the simulation. To extract the accurate axial diffusion coefficient, we found that a 1D diffusion model with a Lorentzian axial collection profile needs to be used to analyze the experimental ACFs. The diffusion of the 45 nm nanoparticles in polyethyleneglycol-passivated 300 nm pores slowed down by a factor of ∼2, which can be satisfactorily explained by hydrodynamic frictions. PMID:27196052

  11. Technology Diffusion and Productivity Growth in Health Care

    PubMed Central

    Skinner, Jonathan; Staiger, Douglas

    2015-01-01

    We draw on macroeconomic models of diffusion and productivity to explain empirical patterns of survival gains in heart attacks. Using Medicare data for 2.8 million patients during 1986–2004, we find that hospitals rapidly adopting cost-effective innovations such as beta blockers, aspirin, and reperfusion, had substantially better outcomes for their patients. Holding technology adoption constant, the marginal returns to spending were relatively modest. Hospitals increasing the pace of technology diffusion (“tigers”) experienced triple the survival gains compared to those with diminished rates (“tortoises”). In sum, small differences in the propensity to adopt effective technology lead to wide productivity differences across hospitals. PMID:26989267

  12. Optical tracking of anomalous diffusion kinetics in polymer microspheres.

    PubMed

    Foreman, Matthew R; Vollmer, Frank

    2015-03-20

    In this Letter we propose the use of whispering gallery mode resonance tracking as a label-free optical means to monitor diffusion kinetics in glassy polymer microspheres. Approximate solutions to the governing diffusion equations are derived for the case of slow relaxation and small Stefan number. Transduction of physical changes in the polymer, including formation of a rubbery layer, swelling, and dissolution, into detectable resonance shifts are described using a perturbative approach. Concrete examples of poly(methyl methacrylate) and polystyrene spheres in water are considered. PMID:25839311

  13. Optical Tracking of Anomalous Diffusion Kinetics in Polymer Microspheres

    NASA Astrophysics Data System (ADS)

    Foreman, Matthew R.; Vollmer, Frank

    2015-03-01

    In this Letter we propose the use of whispering gallery mode resonance tracking as a label-free optical means to monitor diffusion kinetics in glassy polymer microspheres. Approximate solutions to the governing diffusion equations are derived for the case of slow relaxation and small Stefan number. Transduction of physical changes in the polymer, including formation of a rubbery layer, swelling, and dissolution, into detectable resonance shifts are described using a perturbative approach. Concrete examples of poly(methyl methacrylate) and polystyrene spheres in water are considered.

  14. A microscale turbine driven by diffusive mass flux.

    PubMed

    Yang, Mingcheng; Liu, Rui; Ripoll, Marisol; Chen, Ke

    2015-10-01

    An external diffusive mass flux is shown to be able to generate a mechanical torque on a microscale object based on anisotropic diffusiophoresis. In light of this finding, we propose a theoretical prototype micro-turbine driven purely by diffusive mass flux, which is in strong contrast to conventional turbines driven by convective mass flows. The rotational velocity of the proposed turbine is determined by the external concentration gradient, the geometry and the diffusiophoretic properties of the turbine. This scenario is validated by performing computer simulations. Our finding thus provides a new type of chemo-mechanical response which could be used to exploit existing chemical energies at small scales. PMID:26288078

  15. Diffusion of hidden charm mesons in hadronic medium

    NASA Astrophysics Data System (ADS)

    Mitra, Sukanya; Ghosh, Sabyasachi; Das, Santosh K.; Sarkar, Sourav; Alam, Jan-e.

    2016-07-01

    The drag and diffusion coefficients of a hot hadronic medium have been evaluated by using hidden charm mesons as probes. The scattering amplitudes required for the evaluation of these coefficients are calculated using an effective theory and scattering lengths obtained from lattice QCD calculations. It is found that although the magnitude of the transport coefficients are small their temperature variation is strong. The insignificant momentum diffusion of J / ψ in the hadronic medium keeps their momentum distribution largely unaltered. Therefore, the task of characterization of quark gluon plasma by using the observed suppression of J / ψ at high momentum will be comparatively easier.

  16. Controlling Exciton Diffusion and Fullerene Distribution in Photovoltaic Blends by Side Chain Modification

    PubMed Central

    2015-01-01

    The influence of crystallinity on exciton diffusion and fullerene distribution was investigated by blending amorphous and semicrystalline copolymers. We measured exciton diffusion and fluorescence quenching in such blends by dispersing fullerene molecules into them. We find that the diffusion length is more than two times higher in the semicrystalline copolymer than in the amorphous copolymer. We also find that fullerene preferentially mixes into disordered regions of the polymer film. This shows that relatively small differences in molecular structure are important for exciton diffusion and fullerene distribution. PMID:26267202

  17. Diffusion and stochastic island generation in the magnetic field line random walk

    SciTech Connect

    Vlad, M.; Spineanu, F.

    2014-08-10

    The cross-field diffusion of field lines in stochastic magnetic fields described by the 2D+slab model is studied using a semi-analytic statistical approach, the decorrelation trajectory method. We show that field line trapping and the associated stochastic magnetic islands strongly influence the diffusion coefficients, leading to dependences on the parameters that are different from the quasilinear and Bohm regimes. A strong amplification of the diffusion is produced by a small slab field in the presence of trapping. The diffusion regimes are determined and the corresponding physical processes are identified.

  18. An effective phase shift diffusion equation method for analysis of PFG normal and fractional diffusions

    NASA Astrophysics Data System (ADS)

    Lin, Guoxing

    2015-10-01

    Pulsed field gradient (PFG) diffusion measurement has a lot of applications in NMR and MRI. Its analysis relies on the ability to obtain the signal attenuation expressions, which can be obtained by averaging over the accumulating phase shift distribution (APSD). However, current theoretical models are not robust or require approximations to get the APSD. Here, a new formalism, an effective phase shift diffusion (EPSD) equation method is presented to calculate the APSD directly. This is based on the idea that the gradient pulse effect on the change of the APSD can be viewed as a diffusion process in the virtual phase space (VPS). The EPSD has a diffusion coefficient, Kβ(t)D radβ/sα, where α is time derivative order and β is a space derivative order, respectively. The EPSD equations of VPS are built based on the diffusion equations of real space by replacing the diffusion coefficients and the coordinate system (from real space coordinate to virtual phase coordinate). Two different models, the fractal derivative model and the fractional derivative model from the literature were used to build the EPSD fractional diffusion equations. The APSD obtained from solving these EPSD equations were used to calculate the PFG signal attenuation. From the fractal derivative model the attenuation is exp(-γβgβδβDf1 tα), a stretched exponential function (SEF) attenuation, while from the fractional derivative model the attenuation is Eα,1(-γβgβδβDf2 tα), a Mittag-Leffler function (MLF) attenuation. The MLF attenuation can be reduced to SEF attenuation when α = 1, and can be approximated as a SEF attenuation when the attenuation is small. Additionally, the effect of finite gradient pulse widths (FGPW) is calculated. From the fractal derivative model, the signal attenuation including FGPW effect is exp[ -Df1 ∫0τ Kβ (t)dtα ] . The results obtained in this study are in good agreement with the results in literature. Several expressions that describe signal

  19. An effective phase shift diffusion equation method for analysis of PFG normal and fractional diffusions.

    PubMed

    Lin, Guoxing

    2015-10-01

    Pulsed field gradient (PFG) diffusion measurement has a lot of applications in NMR and MRI. Its analysis relies on the ability to obtain the signal attenuation expressions, which can be obtained by averaging over the accumulating phase shift distribution (APSD). However, current theoretical models are not robust or require approximations to get the APSD. Here, a new formalism, an effective phase shift diffusion (EPSD) equation method is presented to calculate the APSD directly. This is based on the idea that the gradient pulse effect on the change of the APSD can be viewed as a diffusion process in the virtual phase space (VPS). The EPSD has a diffusion coefficient, K(β)(t)D rad(β)/s(α), where α is time derivative order and β is a space derivative order, respectively. The EPSD equations of VPS are built based on the diffusion equations of real space by replacing the diffusion coefficients and the coordinate system (from real space coordinate to virtual phase coordinate). Two different models, the fractal derivative model and the fractional derivative model from the literature were used to build the EPSD fractional diffusion equations. The APSD obtained from solving these EPSD equations were used to calculate the PFG signal attenuation. From the fractal derivative model the attenuation is exp(-γ(β)g(β)δ(β)Df1t(α)), a stretched exponential function (SEF) attenuation, while from the fractional derivative model the attenuation is Eα,1(-γ(β)g(β)δ(β)Df2t(α)), a Mittag-Leffler function (MLF) attenuation. The MLF attenuation can be reduced to SEF attenuation when α=1, and can be approximated as a SEF attenuation when the attenuation is small. Additionally, the effect of finite gradient pulse widths (FGPW) is calculated. From the fractal derivative model, the signal attenuation including FGPW effect is exp[ -Df1∫0(τ) K(β)(t)dt(α)]. The results obtained in this study are in good agreement with the results in literature. Several expressions that

  20. Effective Diffusion Coefficient and Controlling Process of P Diffusion in Si Based on the Pair Diffusion Models of Vacancy and Interstitial Mechanisms

    NASA Astrophysics Data System (ADS)

    Yoshida, Masayuki; Morooka, Masami; Takahashi, Manabu; Tomokage, Hajime

    2000-05-01

    Based on the pair diffusion models of vacancy and interstitial (V and I) mechanisms, the V and I components of effective P diffusion coefficient, DP^+,Veff and DP^+,Ieff, and the controlling process of P diffusion in Si are obtained. Assuming that the I mechanism is dominant, not only the I- concentration, CI^-, but also its gradient, d CI^-/d λ , is effective on DP^+,Ieff at high CP^+. DP^+,Ieff is large at d CI^-/d λ <0 and small at d CI^-/d λ >0. P+ and I- are generated by the dissociation of P-I pair. When excess I- thus generated is removed, d CI^-/d λ <0 is obtained. d CI^-/d λ <0 is also obtained by the decrease in quasi self-interstitial formation energy. Several diffusion models simulate the P diffusion profile well under an inert atmosphere. Applying the controlling process to them, the reason why they simulate the P profile well is investigated. Because all of them simulate the P profile well, it is difficult to conclude which model is correct. It is suggested that it is possible to conclude which model is correct from the P profile under oxidation at CP^+s >1× 1020 cm-3 (s: surface).

  1. Brownian simulations and unidirectional flux in diffusion.

    PubMed

    Singer, A; Schuss, Z

    2005-02-01

    The prediction of ionic currents in protein channels of biological membranes is one of the central problems of computational molecular biophysics. Existing continuum descriptions of ionic permeation fail to capture the rich phenomenology of the permeation process, so it is therefore necessary to resort to particle simulations. Brownian dynamics (BD) simulations require the connection of a small discrete simulation volume to large baths that are maintained at fixed concentrations and voltages. The continuum baths are connected to the simulation through interfaces, located in the baths sufficiently far from the channel. Average boundary concentrations have to be maintained at their values in the baths by injecting and removing particles at the interfaces. The particles injected into the simulation volume represent a unidirectional diffusion flux, while the outgoing particles represent the unidirectional flux in the opposite direction. The classical diffusion equation defines net diffusion flux, but not unidirectional fluxes. The stochastic formulation of classical diffusion in terms of the Wiener process leads to a Wiener path integral, which can split the net flux into unidirectional fluxes. These unidirectional fluxes are infinite, though the net flux is finite and agrees with classical theory. We find that the infinite unidirectional flux is an artifact caused by replacing the Langevin dynamics with its Smoluchowski approximation, which is classical diffusion. The Smoluchowski approximation fails on time scales shorter than the relaxation time 1/gamma of the Langevin equation. We find that the probability of Brownian trajectories that cross an interface in one direction in unit time Deltat equals that of the probability of the corresponding Langevin trajectories if gammaDeltat=2 . That is, we find the unidirectional flux (source strength) needed to maintain average boundary concentrations in a manner consistent with the physics of Brownian particles. This

  2. Phenomenology and energetics of diffusion across cell phase states.

    PubMed

    Ashrafuzzaman, Md

    2015-11-01

    Cell based transport properties have been mathematically addressed. Cell contained cross boundary diffusion of materials has been explained using valid formalisms and related analytical expressions have been developed. Various distinguishable physical structures and their properties raise different general structure specific diffusion mechanisms and controlled transport related parameters. Some of these parameters play phenomenological roles and some cause regulatory effects. The cell based compartments may be divided into three major physical phase states namely liquid, plasma and solid phase states. Transport of ions, nutrients, small molecules like proteins, etc. across inter phase states and intraphase states follows general transport related formalisms. Creation of some localized permanent and/or temporary structures e.g., ion channels, clustering of constituents, etc. and the transitions between such structures appear as regulators of the transport mechanisms. In this article, I have developed mainly a theoretical analysis of the commonly observed cell transport phenomena. I have attempted to develop formalisms on general cell based diffusion followed by a few numerical computations to address the analytical expression phenomenologically. I have then extended the analysis to adopting with the local structure originated energetics. Independent or correlated molecular transport naturally relies on some general parameters that define the nature of local cell environment as well as on some occasionally raised or transiently active stochastic resonance due to localized interactions. Short and long range interaction energies play crucial roles in this regard. Physical classification of cellular compartments has led us developing analytical expressions on both biologically observed diffusion mechanisms and the diffusions's occasional stochasticity causing energetics. These analytical expressions help us address the diffusion phenomena generally considering the

  3. Fluid diffusion in porous silica

    NASA Astrophysics Data System (ADS)

    McCann, Lowell I.

    Fluid motion in porous media has received a great deal of theoretical and experimental attention due to its importance in systems as diverse as ground water aquifers, catalytic processes, and size separation schemes. Often, the motion of interest is the random thermal motion of molecules in a fluid undergoing no net flow. This diffusive motion is particularly important when the size of the pores is nearly the same as the size of the molecules. In this study, fluid diffusion is measured in several varieties of porous silica whose pore structure is determined by the process by which it is made. The samples in this study have porosities (φ, the ratio of the pore volume to the total sample volume) that vary from 0.3 to 0.75 and average pore radii that range from approximately 15 to 120 A. Determining the effect of the pore structure on the diffusion of a liquid in a porous material is complicated by the chemical interactions between the diffusing molecules and the pore surface. In this study, ions in a hydrophilic fluid are used to block the adsorption of the diffusing dye molecules to the hydroxyl groups covering the silica surface. This technique is unlike typical surface treatments of silica in that it does not permanently alter the pore geometry. In this work, fluid diffusion is measured with a transient holographic grating technique where interfering laser beams create a periodic refractive index modulation in the fluid. The diffraction of a third laser off this grating is monitored to determine how quickly the grating relaxes, thereby determining the diffusion coefficient of the molecules in the fluid. Varying the grating periodicity controls the length scale of the diffusion measurement from 1.2 to 100 μm which is much larger than the average pore sizes of the samples. Therefore, over these large scales, we measure 'normal' diffusion, where the mean squared displacement of a diffusing particle varies linearly with time. In one particular type of porous silica

  4. Geometric diffusion of quantum trajectories

    PubMed Central

    Yang, Fan; Liu, Ren-Bao

    2015-01-01

    A quantum object can acquire a geometric phase (such as Berry phases and Aharonov–Bohm phases) when evolving along a path in a parameter space with non-trivial gauge structures. Inherent to quantum evolutions of wavepackets, quantum diffusion occurs along quantum trajectories. Here we show that quantum diffusion can also be geometric as characterized by the imaginary part of a geometric phase. The geometric quantum diffusion results from interference between different instantaneous eigenstate pathways which have different geometric phases during the adiabatic evolution. As a specific example, we study the quantum trajectories of optically excited electron-hole pairs in time-reversal symmetric insulators, driven by an elliptically polarized terahertz field. The imaginary geometric phase manifests itself as elliptical polarization in the terahertz sideband generation. The geometric quantum diffusion adds a new dimension to geometric phases and may have applications in many fields of physics, e.g., transport in topological insulators and novel electro-optical effects. PMID:26178745

  5. Geometric diffusion of quantum trajectories.

    PubMed

    Yang, Fan; Liu, Ren-Bao

    2015-01-01

    A quantum object can acquire a geometric phase (such as Berry phases and Aharonov-Bohm phases) when evolving along a path in a parameter space with non-trivial gauge structures. Inherent to quantum evolutions of wavepackets, quantum diffusion occurs along quantum trajectories. Here we show that quantum diffusion can also be geometric as characterized by the imaginary part of a geometric phase. The geometric quantum diffusion results from interference between different instantaneous eigenstate pathways which have different geometric phases during the adiabatic evolution. As a specific example, we study the quantum trajectories of optically excited electron-hole pairs in time-reversal symmetric insulators, driven by an elliptically polarized terahertz field. The imaginary geometric phase manifests itself as elliptical polarization in the terahertz sideband generation. The geometric quantum diffusion adds a new dimension to geometric phases and may have applications in many fields of physics, e.g., transport in topological insulators and novel electro-optical effects. PMID:26178745

  6. Flow development through interturbine diffusers

    SciTech Connect

    Dominy, R.G.; Kirkham, D.A.; Smith, A.D.

    1998-04-01

    Interturbine diffusers offer the potential advantage of reducing the flow coefficient in the following stages, leading to increased efficiency. The flows associated with these ducts differ from those in simple annular diffusers both as a consequence of their high-curvature S-shaped geometry and of the presence of wakes created by the upstream turbine. Experimental data and numerical simulations clearly reveal the generation of significant secondary flows as the flow develops through the diffuser in the presence of cross-passage pressure gradients. The further influence of inlet swirl is also demonstrated. Data from experimental measurements with and without an upstream turbine are discussed and computational simulations are shown not only to give a good prediction of the flow development within the diffuser but also to demonstrate the importance of modeling the fully three-dimensional nature of the flow.

  7. ANALYSIS OF DIFFUSION FIELD EXPERIMENTS

    EPA Science Inventory

    The report describes general theoretical frameworks for the ordering of diffusion field data in terms of meteorological measurements. The three methods described are surface-layer (Monin-Obukhov) similarity, convective scaling, and statistical theory using wind fluctuations. Earl...

  8. Fractional-calculus diffusion equation

    PubMed Central

    2010-01-01

    Background Sequel to the work on the quantization of nonconservative systems using fractional calculus and quantization of a system with Brownian motion, which aims to consider the dissipation effects in quantum-mechanical description of microscale systems. Results The canonical quantization of a system represented classically by one-dimensional Fick's law, and the diffusion equation is carried out according to the Dirac method. A suitable Lagrangian, and Hamiltonian, describing the diffusive system, are constructed and the Hamiltonian is transformed to Schrodinger's equation which is solved. An application regarding implementation of the developed mathematical method to the analysis of diffusion, osmosis, which is a biological application of the diffusion process, is carried out. Schrödinger's equation is solved. Conclusions The plot of the probability function represents clearly the dissipative and drift forces and hence the osmosis, which agrees totally with the macro-scale view, or the classical-version osmosis. PMID:20492677

  9. Energy Transfer and Joint Diffusion

    NASA Astrophysics Data System (ADS)

    Pajor-Gyulai, Zs.; Szász, D.

    2012-03-01

    A paradigm model is suggested for describing the diffusive limit of trajectories of two Lorentz disks moving in a finite horizon periodic configuration of smooth, strictly convex scatterers and interacting with each other via elastic collisions. For this model the diffusive limit of the two trajectories is a mixture of joint Gaussian laws (analogous behavior is expected for the mechanical model of two Lorentz disks).

  10. Visualization of Diffusion within Nanoarrays.

    PubMed

    Liu, Yang; Holzinger, Angelika; Knittel, Peter; Poltorak, Lukasz; Gamero-Quijano, Alonso; Rickard, William D A; Walcarius, Alain; Herzog, Grégoire; Kranz, Christine; Arrigan, Damien W M

    2016-07-01

    The direct experimental characterization of diffusion processes at nanoscale remains a challenge that could help elucidate processes in biology, medicine and technology. In this report, two experimental approaches were employed to visualize ion diffusion profiles at the orifices of nanopores (radius (ra) of 86 ± 6 nm) in array format: (1) electrochemically assisted formation of silica deposits based on surfactant ion transfer across nanointerfaces between two immiscible electrolyte solutions (nanoITIES); (2) combined atomic force - scanning electrochemical microscopy (AFM-SECM) imaging of topography and redox species diffusion through the nanopores. The nature of the diffusion zones formed around the pores is directly related to the interpore distance within the array. Nanopore arrays with different ratios of pore center-to-center separation (rc) to pore radius (ra) were fabricated by focused ion beam (FIB) milling of silicon nitride (SiN) membranes, with 100 pores in a hexagonal arrangement. The ion diffusion profiles determined by the two visualization methods indicated the formation of overlapped or independent diffusion profiles at nanopore arrays with rc/ra ratios of 21 ± 2 and 91 ± 7, respectively. In particular, the silica deposition method resulted in formation of a single deposit encompassing the complete array with closer nanopore arrangement, whereas individual silica deposits were formed around each nanopore within the more widely spaced array. The methods reveal direct experimental evidence of diffusion zones at nanopore arrays and provide practical illustration that the pore-pore separation within such arrays has a significant impact on diffusional transport as the pore size is reduced to the nanoscale. These approaches to nanoscale diffusion zone visualization open up possibilities for better understanding of molecular transport processes within miniaturized systems. PMID:27264360

  11. Uphill diffusion in multicomponent mixtures.

    PubMed

    Krishna, Rajamani

    2015-05-21

    Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations. PMID:25761383

  12. Boron diffusion in silicon devices

    DOEpatents

    Rohatgi, Ajeet; Kim, Dong Seop; Nakayashiki, Kenta; Rounsaville, Brian

    2010-09-07

    Disclosed are various embodiments that include a process, an arrangement, and an apparatus for boron diffusion in a wafer. In one representative embodiment, a process is provided in which a boric oxide solution is applied to a surface of the wafer. Thereafter, the wafer is subjected to a fast heat ramp-up associated with a first heating cycle that results in a release of an amount of boron for diffusion into the wafer.

  13. Suppression of Acid Diffusion in Chemical Amplification Resists by Molecular Control of Base Matrix Polymers

    NASA Astrophysics Data System (ADS)

    Yoshimura, Toshiyuki; Shiraishi, Hiroshi; Okazaki, Shinji

    1995-12-01

    Suppression of acid diffusion during post-exposure baking (PEB) of chemical amplification resists is investigated from the standpoint of molecular control of base matrix polymers. Negative-type chemical amplification resists composed of cresol novolak-based matrix polymers, acid-catalyzed crosslinkers of melamine resins, and acid generators of onium salts are prepared. The molecular weight distributions of the base matrix polymers are controlled by means of a precipitation method. The resists are exposed with electron beams in isolated lines to evaluate the acid diffusion characteristics. Dependence of pattern sizes on the PEB time clearly shows that acid diffusion determines the resist pattern sizes based on Fick's law. The diffusion coefficients of resists with base matrix polymers with small polydispersities are smaller than those of resists with base matrix polymers with large polydispersities. Acid diffusion can still be suppressed by applying base matrix polymers with small weight-average molecular weights and small polydispersities. Diffusion coefficients can be further decreased by using base matrix polymers with more p-cresol components. A diffusion mechanism is proposed based on acid diffusion channels composed of active OH-groups and vacancies in the base matrix polymers.

  14. Gibbs Ringing in Diffusion MRI

    PubMed Central

    Veraart, Jelle; Fieremans, Els; Jelescu, Ileana O.; Knoll, Florian; Novikov, Dmitry S.

    2016-01-01

    Purpose To study and reduce the effect of Gibbs ringing artifact on computed diffusion parameters. Methods We reduce the ringing by extrapolating the k-space of each diffusion weighted image beyond the measured part by selecting an adequate regularization term. We evaluate several regularization terms and tune the regularization parameter to find the best compromise between anatomical accuracy of the reconstructed image and suppression of the Gibbs artifact. Results We demonstrate empirically and analytically that the Gibbs artifact, which is typically observed near sharp edges in magnetic resonance images, has a significant impact on the quantification of diffusion model parameters, even for infinitesimal diffusion weighting. We find the second order total generalized variation to be a good choice for the penalty term to regularize the extrapolation of the k-space, as it provides a parsimonious representation of images, a practically full suppression of Gibbs ringing, and the absence of staircasing artifacts typical for total variation methods. Conclusions Regularized extrapolation of the k-space data significantly reduces truncation artifacts without compromising spatial resolution in comparison to the default option of window filtering. In particular, accuracy of estimating diffusion tensor imaging and diffusion kurtosis imaging parameters improves so much that unconstrained fits become possible. PMID:26257388

  15. Osmosis and Diffusion Conceptual Assessment

    PubMed Central

    Fisher, Kathleen M.; Williams, Kathy S.; Lineback, Jennifer Evarts

    2011-01-01

    Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large public university, we developed and validated an 18-item Osmosis and Diffusion Conceptual Assessment (ODCA). This assessment includes two-tiered items, some adopted or modified from the previously published Diffusion and Osmosis Diagnostic Test (DODT) and some newly developed items. The ODCA, a validated instrument containing fewer items than the DODT and emphasizing different content areas within the realm of osmosis and diffusion, better aligns with our curriculum. Creation of the ODCA involved removal of six DODT item pairs, modification of another six DODT item pairs, and development of three new item pairs addressing basic osmosis and diffusion concepts. Responses to ODCA items testing the same concepts as the DODT were remarkably similar to responses to the DODT collected from students 15 yr earlier, suggesting that student mastery regarding the mechanisms of diffusion and osmosis remains elusive. PMID:22135375

  16. An Introduction to Fractional Diffusion

    NASA Astrophysics Data System (ADS)

    Henry, B. I.; Langlands, T. A. M.; Straka, P.

    The mathematical description of diffusion has a long history with many different formulations including phenomenological models based on conservation of mass and constitutive laws; probabilistic models based on random walks and central limit theorems; microscopic stochastic models based on Brownian motion and Langevin equations; and mesoscopic stochastic models based on master equations and Fokker-Planck equations. A fundamental result common to the different approaches is that the mean square displacement of a diffusing particle scales linearly with time. However there have been numerous experimental measurements in which the mean square displacement of diffusing particles scales as a fractional order power law in time. In recent years a great deal of progress has been made in extending the different models for diffusion to incorporate this fractional diffusion. The tools of fractional calculus have proven very useful in these developments, linking together fractional constitutive laws, continuous time random walks, fractional Langevin equations and fractional Brownian motions. These notes provide a tutorial style overview of standard and fractional diffusion processes.

  17. Water diffusion in phonolite melts

    NASA Astrophysics Data System (ADS)

    Schmidt, Burkhard C.; Blum-Oeste, Nils; Flagmeier, Jens

    2013-04-01

    We report an experimental study of total water diffusion (irrespective of water speciation) in two different phonolite melts, which are representative of Montaña Blanca, Tenerife, Spain (MBP) and Laacher See, East Eifel, Germany (LSP-II). Both phonolites have Na-rich compositions, but differ in their alumina saturation index, with MBP being peralkaline and LSP-II being slightly peraluminous. Diffusion couple experiments for MBP were performed at 200-250 MPa in the temperature range of 800-1050 °C and water contents between 1 and 6.5 wt.%. Due to higher liquidus temperatures of LSP-II, the accessible temperature and water concentration range was reduced to 875-1050 °C and 3-6.5 wt.% water. All experiments were performed in rapid quench cold-seal pressure vessels, which enabled rapid heating and quenching of the samples within seconds. Compared to the run durations of 30-90 min, these short heating and cooling periods can be neglected and no corrections needed to be applied for the calculation of the diffusion coefficients. Water diffusion profiles were determined by FT-IR micro-spectroscopy on doubly polished glass sections and the diffusion coefficients were determined by Boltzmann-Matano analysis. Water diffusion increases with increasing water content and temperature and follows the empirical relations:

  18. Relevance of Pore Structure and Diffusion-Accessible Porosity for Calcium-Bromide Diffusion in Na-Montmorillonite

    NASA Astrophysics Data System (ADS)

    Tinnacher, R. M.; Davis, J. A.

    2013-12-01

    Bentonite is an important hydraulic barrier material in many geotechnical applications, such as geosynthetic clay liners at solid waste landfills, or as proposed backfill material in engineered barrier systems at nuclear waste repositories. The limited permeability of bentonite is at least partially the result of its low porosity and the swelling of Na-montmorillonite, its major mineralogical component, in water. Due to these characteristics, the transport of contaminants through bentonite layers is expected to be limited and dominated by diffusion processes. In bentonite, the majority of the connected porosity is associated with montmorillonite particles, which consist of stacks of negatively-charged smectite layers. As a result, compacted smectite has two types of porosities: (1) large pores between clay particles, where diffusion is less affected by electric-double-layer forces, and (2) very thin interlayer spaces within individual clay particles, where diffusion is strongly impacted by surface charge and ionic strength. As diffusion is expected to take place differently in these two volumes, this essentially creates two 'small-scale diffusion pathways', where each may become dominant under different system conditions. Furthermore, for surface-reactive solutes, these two porous regimes differ with regards to surface complexation reactions. Electrostatic and hydration forces only are thought to govern interlayer binding, whereas chemical bonding with surface ligands is dominant for reactions at edge sites of layered clay particles and for iron oxide nanoparticles on outer basal planes. In this presentation, we will demonstrate the relevance of clay pore structure and diffusion-accessible porosity for solute diffusion rates, and hence, contaminant mobility in bentonites. First, we will discuss the effects of chemical solution conditions on montmorillonite properties, such as clay surface charge, diffusion-accessible porosity, clay tortuosity and constrictivity

  19. Small Device for Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Dr. Daniel Carter (center), president of New Century Pharmaceuticals, and Dr. Joseph Ho (right), vice president, examine a diffusion Controlled Apparatus for Microgravity (DCAM). At left, Dr. John Ruble, a senior scientist, examines some specimens. The plastic DCAM has two chambers joined by a porous plug through which fluids can diffuse at a controlled rate. This allows researchers to mix protein solutions on Earth and load them aboard the Space Shuttle shortly before launch. The diffusion and crystallization processes are already under way, but at such a slow pace that crystals do not start growing before the DCAM is in orbit aboard the Shuttle or a space station. Dozens of DCAM units can be flown in a small volume and require virtually no crew attention. Specimens are returned to Earth for analysis. Photo credit: NASA/Marshall Space Flight Center

  20. Photoinduced diffusion molecular transport

    NASA Astrophysics Data System (ADS)

    Rozenbaum, Viktor M.; Dekhtyar, Marina L.; Lin, Sheng Hsien; Trakhtenberg, Leonid I.

    2016-08-01

    We consider a Brownian photomotor, namely, the directed motion of a nanoparticle in an asymmetric periodic potential under the action of periodic rectangular resonant laser pulses which cause charge redistribution in the particle. Based on the kinetics for the photoinduced electron redistribution between two or three energy levels of the particle, the time dependence of its potential energy is derived and the average directed velocity is calculated in the high-temperature approximation (when the spatial amplitude of potential energy fluctuations is small relative to the thermal energy). The thus developed theory of photoinduced molecular transport appears applicable not only to conventional dichotomous Brownian motors (with only two possible potential profiles) but also to a much wider variety of molecular nanomachines. The distinction between the realistic time dependence of the potential energy and that for a dichotomous process (a step function) is represented in terms of relaxation times (they can differ on the time intervals of the dichotomous process). As shown, a Brownian photomotor has the maximum average directed velocity at (i) large laser pulse intensities (resulting in short relaxation times on laser-on intervals) and (ii) excited state lifetimes long enough to permit efficient photoexcitation but still much shorter than laser-off intervals. A Brownian photomotor with optimized parameters is exemplified by a cylindrically shaped semiconductor nanocluster which moves directly along a polar substrate due to periodically photoinduced dipole moment (caused by the repetitive excited electron transitions to a non-resonant level of the nanocylinder surface impurity).