Promote pressure ulcer healing in individuals with spinal cord injury using an individualized cyclic pressure-relief protocol.

PubMed

Makhsous, Mohsen; Lin, Fang; Knaus, Evan; Zeigler, Mary; Rowles, Diane M; Gittler, Michelle; Bankard, James; Chen, David

2009-11-01

To evaluate whether an individualized cyclic pressure-relief protocol accelerates wound healing in wheelchair users with established pressure ulcers (PrUs). Randomized controlled study. Spinal cord injury clinics. Forty-four subjects, aged 18-79 years, with a Stage II or Stage III PrU, were randomly assigned to the control (n = 22) or treatment (n = 22) groups. Subjects in the treatment group used wheelchairs equipped with an individually adjusted automated seat that provided cyclic pressure relief, and those in the control group used a standard wheelchair. All subjects sat in wheelchairs for a minimum of 4 hours per day for 30 days during their PrU treatment. Wound characteristics were assessed using the Pressure Ulcer Scale for Healing (PUSH) tool and wound dimensions recorded with digital photographs twice a week. Median healing time for a 30% healing relative to initial measurements, the percentage reduction in wound area, and the percentage improvement in PUSH score achieved at the end of the trial were compared between groups. At the end of 30 days, both groups demonstrated a general trend of healing. However, the treatment group was found to take significantly less time to achieve 30% healing for the wound measurement compared with the control group. The percentage improvement of the wound area and PUSH scores were greater in using cyclic seating (45.0 +/- 21.0, P < .003; 29.9 +/- 24. 6, P < .003) compared with standard seating (10.2 +/- 34.9, 5.8 +/- 9.2). The authors' findings show that cyclically relieving pressure in the area of a wound for seated individuals can greatly aid wound healing. The current study provides evidence that the individualized cyclic pressure-relief protocol helps promote pressure wound healing in a clinical setting. The authors concluded that the individualized cyclic pressure relief may have substantial benefits in accelerating the healing process in wheelchair users with existing PrUs, while maintaining the mobility of individuals with SCI during the PrU treatment.

SSME main combustion chamber life prediction

NASA Technical Reports Server (NTRS)

Cook, R. T.; Fryk, E. E.; Newell, J. F.

1983-01-01

Typically, low cycle fatigue life is a function of the cyclic strain range, the material properties, and the operating temperature. The reusable life is normally defined by the number of strain cycles that can be accrued before severe material degradation occurs. Reusable life is normally signified by the initiation or propagation of surface cracks. Hot-fire testing of channel wall combustors has shown significant mid-channel wall thinning or deformation during accrued cyclic testing. This phenomenon is termed cyclic-creep and appears to be significantly accelerated at elevated surface temperatures. This failure mode was analytically modelled. The cyclic life of the baseline SSME-MCC based on measured calorimeter heat transfer data, and the life sensitivity of local hot spots caused by injector effects were determined. Four life enhanced designs were assessed.

Contact fatigue of human enamel: Experiments, mechanisms and modeling.

PubMed

Gao, S S; An, B B; Yahyazadehfar, M; Zhang, D; Arola, D D

2016-07-01

Cyclic contact between natural tooth structure and engineered ceramics is increasingly common. Fatigue of the enamel due to cyclic contact is rarely considered. The objectives of this investigation were to evaluate the fatigue behavior of human enamel by cyclic contact, and to assess the extent of damage over clinically relevant conditions. Cyclic contact experiments were conducted using the crowns of caries-free molars obtained from young donors. The cuspal locations were polished flat and subjected to cyclic contact with a spherical indenter of alumina at 2Hz. The progression of damage was monitored through the evolution in contact displacement, changes in the contact hysteresis and characteristics of the fracture pattern. The contact fatigue life diagram exhibited a decrease in cycles to failure with increasing cyclic load magnitude. Two distinct trends were identified, which corresponded to the development and propagation of a combination of cylindrical and radial cracks. Under contact loads of less than 400N, enamel rod decussation resisted the growth of subsurface cracks. However, at greater loads the damage progressed rapidly and accelerated fatigue failure. Overall, cyclic contact between ceramic appliances and natural tooth structure causes fatigue of the enamel. The extent of damage is dependent on the magnitude of cyclic stress and the ability of the decussation to arrest the fatigue damage. Copyright © 2016 Elsevier Ltd. All rights reserved.

Levels of cyclic-2,3-diphosphoglycerate in Methanobacterium thermoautotrophicum during phosphate limitation.

PubMed Central

Seely, R J; Fahrney, D E

1984-01-01

Batch-grown Methanobacterium thermoautotrophicum cells grew nonexponentially in the absence of exogenous Pi until intracellular cyclic-2,3-diphosphoglycerate (cyclic DPG) had fallen below 2 mumol/g (dry weight), the limit of detection. Growth resumed immediately upon transfer to medium containing Pi Cyclic DPG levels were also below detection in Pi-limited chemostat cultures operating at a dilution rate of 0.173 h-1 (4-h doubling time), with reservoir Pi concentrations below 200 microM. At this dilution rate, the Pi concentration in the culture was 4 microM. An H2-limited steady state was achieved with 400 microM Pi in the inflowing medium (67 microM in the culture). The cyclic DPG content of these cells was 72 to 74 mumol/g, about one-third the amount in batch-grown cells. The specific growth rate accelerated immediately to 0.36 h-1 (1.9-h doubling time) under washout conditions at high dilution rate. The cellular content of cyclic DPG declined over a 2-h period, and then increased rapidly as the Pi level in the medium approached 200 microM. Expansion of the cyclic DPG pool coincided with a marked increase in Pi assimilation. These results indicated that M. thermoautotrophicum accumulated cyclic DPG only when Pi and H2 were readily available. PMID:6480564

Levels of cyclic-2,3-diphosphoglycerate in Methanobacterium thermoautotrophicum during phosphate limitation.

PubMed

Seely, R J; Fahrney, D E

1984-10-01

Batch-grown Methanobacterium thermoautotrophicum cells grew nonexponentially in the absence of exogenous Pi until intracellular cyclic-2,3-diphosphoglycerate (cyclic DPG) had fallen below 2 mumol/g (dry weight), the limit of detection. Growth resumed immediately upon transfer to medium containing Pi Cyclic DPG levels were also below detection in Pi-limited chemostat cultures operating at a dilution rate of 0.173 h-1 (4-h doubling time), with reservoir Pi concentrations below 200 microM. At this dilution rate, the Pi concentration in the culture was 4 microM. An H2-limited steady state was achieved with 400 microM Pi in the inflowing medium (67 microM in the culture). The cyclic DPG content of these cells was 72 to 74 mumol/g, about one-third the amount in batch-grown cells. The specific growth rate accelerated immediately to 0.36 h-1 (1.9-h doubling time) under washout conditions at high dilution rate. The cellular content of cyclic DPG declined over a 2-h period, and then increased rapidly as the Pi level in the medium approached 200 microM. Expansion of the cyclic DPG pool coincided with a marked increase in Pi assimilation. These results indicated that M. thermoautotrophicum accumulated cyclic DPG only when Pi and H2 were readily available.

Origins and health consequences of stress-induced ovarian dysfunction.

PubMed

Kaplan, Jay R

2008-01-01

Normal ovarian function is thought to protect women against coronary heart disease (CHD) and osteoporosis by delaying the pathobiological processes underlying these conditions. Supporting this proposition is the observation that, following menopause (i.e. the loss of cyclic ovarian function), these diseases accelerate and ultimately comprise a major portion of the health burden of older women. However, while all women eventually go through complete ovarian failure at menopause, many also experience episodes of cyclic ovarian disruption during their reproductive years (i.e. ages 18-40). These disruptions are relatively common and often are attributed to psychogenic factors (stress, anxiety, depression, or other emotional disturbance). This article hypothesizes that, to the extent that cyclic ovarian function affords protection against CHD and osteoporosis, ovulatory abnormalities associated with estrogen deficiency in young women - even if mild and subclinical - prematurely accelerate development of these two diseases of 'aging'. Consistent with this hypothesis are observations in group-housed, premenopausal monkeys confirming that reproductive deficits are commonly induced by psychosocial stress (social subordination), and, in the presence of a typical Western diet, accelerate the development of CHD and bone loss. Furthermore, in this model premenopausal disease extent predicts postmenopausal health outcomes irrespective of postmenopausal treatment, emphasizing the pathobiological importance of the premenopausal portion of the life cycle. Finally, data from both women and nonhuman primates suggest that reproductive deficits of the sort described here are adaptive when triggered appropriately, but detrimental when activated in an environment (e.g. sedentary lifestyle, high-fat diet) permissive to the development of chronic disease.

Betatron Application in Mobile and Relocatable Inspection Systems for Freight Transport Control

NASA Astrophysics Data System (ADS)

Chakhlov, S. V.; Kasyanov, S. V.; Kasyanov, V. A.; Osipov, S. P.; Stein, M. M.; Stein, A. M.; Xiaoming, Sun

2016-01-01

Accelerators with energy level up to 4 MeV having high level of penetration ability by steel equivalent are the popular to control oversize cargo transported by road, by railway and by river. Betatron's usage as cyclic induction accelerator has some advantages in comparison with linear accelerators and other sources. Tomsk Polytechnic University has developed many types of betatrons, most of them are being produced by separate affiliated company " Foton ". Article is shown the results of application of the betatrons in inspection custom systems.

A technique for accelerating the convergence of restarted GMRES

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

Baker, A H; Jessup, E R; Manteuffel, T

2004-03-09

We have observed that the residual vectors at the end of each restart cycle of restarted GMRES often alternate direction in a cyclic fashion, thereby slowing convergence. We present a new technique for accelerating the convergence of restarted GMRES by disrupting this alternating pattern. The new algorithm resembles a full conjugate gradient method with polynomial preconditioning, and its implementation requires minimal changes to the standard restarted GMRES algorithm.

Estimation of Stresses in a Dry Sand Layer Tested on Shaking Table

NASA Astrophysics Data System (ADS)

Sawicki, Andrzej; Kulczykowski, Marek; Jankowski, Robert

2012-12-01

Theoretical analysis of shaking table experiments, simulating earthquake response of a dry sand layer, is presented. The aim of such experiments is to study seismic-induced compaction of soil and resulting settlements. In order to determine the soil compaction, the cyclic stresses and strains should be calculated first. These stresses are caused by the cyclic horizontal acceleration at the base of soil layer, so it is important to determine the stress field as function of the base acceleration. It is particularly important for a proper interpretation of shaking table tests, where the base acceleration is controlled but the stresses are hard to measure, and they can only be deduced. Preliminary experiments have shown that small accelerations do not lead to essential settlements, whilst large accelerations cause some phenomena typical for limit states, including a visible appearance of slip lines. All these problems should be well understood for rational planning of experiments. The analysis of these problems is presented in this paper. First, some heuristic considerations about the dynamics of experimental system are presented. Then, the analysis of boundary conditions, expressed as resultants of respective stresses is shown. A particular form of boundary conditions has been chosen, which satisfies the macroscopic boundary conditions and the equilibrium equations. Then, some considerations are presented in order to obtain statically admissible stress field, which does not exceed the Coulomb-Mohr yield conditions. Such an approach leads to determination of the limit base accelerations, which do not cause the plastic state in soil. It was shown that larger accelerations lead to increase of the lateral stresses, and the respective method, which may replace complex plasticity analyses, is proposed. It is shown that it is the lateral stress coefficient K0 that controls the statically admissible stress field during the shaking table experiments.

MMS observations and hybrid simulations of rippled and reforming quasi-parallel shocks

NASA Astrophysics Data System (ADS)

Gingell, I.; Schwartz, S. J.; Burgess, D.; Johlander, A.; Russell, C. T.; Burch, J. L.; Ergun, R.; Fuselier, S. A.; Gershman, D. J.; Giles, B. L.; Goodrich, K.; Khotyaintsev, Y. V.; Lavraud, B.; Lindqvist, P. A.; Strangeway, R. J.; Trattner, K. J.; Torbert, R. B.; Wilder, F. D.

2017-12-01

Surface ripples, i.e. deviations in the nominal local shock orientation, are expected to propagate in the ramp and overshoot of collisionless shocks. These ripples have typically been associated with observations and simulations of quasi-perpendicular shocks. We present observations of a crossing of Earth's marginally quasi-parallel (θBn ˜ 45°) bow shock by the MMS spacecraft on 2015-11-27 06:01:44 UTC, for which we identify signatures consistent with a propagating surface ripple. In order to demonstrate the differences between ripples at quasi-perpendicular and quasi-parallel shocks, we also present two-dimensional hybrid simulations over a range of shock normal angles θBn under the observed solar wind conditions. We show that in the quasi-parallel cases surface ripples are transient phenomena modulated by the cyclic reformation of the shock front. These ripples develop faster than an ion gyroperiod and only during the period of the reformation cycle when a newly developed shock ramp is unaffected by turbulence in the foot. We conclude that the change of properties of the surface ripple observed by MMS while crossing Earth's quasi-parallel bow shock are consistent with the influence of cyclic reformation on shock structure. Given that both surface ripples and cyclic reformation are expected to affect the acceleration of electrons within the shock, the interaction of these phenomena and any other sources of shock non-stationary are important for models of particle acceleration. We therefore discuss signatures of electron heating and acceleration in several rippled shocks observed by MMS.

Accelerated Dynamic Corrosion Test Method Development

DTIC Science & Technology

test method has poor correlation to outdoor exposures, particularly for non-chromate primers. As a result, more realistic cyclic environmental...exposures have been developed to more closely resemble actual atmospheric corrosion damage. Several existing tests correlate well with the outdoor performance

Scale factor duality for conformal cyclic cosmologies

NASA Astrophysics Data System (ADS)

Camara da Silva, U.; Alves Lima, A. L.; Sotkov, G. M.

2016-11-01

The scale factor duality is a symmetry of dilaton gravity which is known to lead to pre-big-bang cosmologies. A conformal time version of the scale factor duality (SFD) was recently implemented as a UV/IR symmetry between decelerated and accelerated phases of the post-big-bang evolution within Einstein gravity coupled to a scalar field. The problem investigated in the present paper concerns the employment of the conformal time SFD methods to the construction of pre-big-bang and cyclic extensions of these models. We demonstrate that each big-bang model gives rise to two qualitatively different pre-big-bang evolutions: a contraction/expansion SFD model and Penrose's Conformal Cyclic Cosmology (CCC). A few examples of SFD symmetric cyclic universes involving certain gauged Kähler sigma models minimally coupled to Einstein gravity are studied. We also describe the specific SFD features of the thermodynamics and the conditions for validity of the generalized second law in the case of Gauss-Bonnet (GB) extension of these selected CCC models.

Design and Testing of a Small Inductive Pulsed Plasma Thruster

NASA Technical Reports Server (NTRS)

Martin, Adam K.; Dominguez, Alexandra; Eskridge, Richard H.; Polzin, Kurt A.; Riley, Daniel P.; Perdue, Kevin A.

2015-01-01

The design and testing of a small inductive pulsed plasma thruster (IPPT) is described. The device was built as a test-bed for the pulsed gas-valves and solid-state switches required for a thruster of this kind, and was designed to be modular to facilitate modification. The thruster in its present configuration consists of a multi-turn, spiral-wound acceleration coil (270 millimeters outer diameter, 100 millimeters inner diameter) driven by a 10 microfarad capacitor and switched with a high-voltage thyristor, a propellant delivery system including a fast pulsed gas-valve, and a glow-discharge pre-ionizer circuit. The acceleration coil circuit may be operated at voltages up to 4 kilovolts (the thyristor limit is 4.5 kilovolts) and the thruster operated at cyclic-rates up to 30 Herz. Initial testing of the thruster, both bench-top and in-vacuum, has been performed. Cyclic operation of the complete device was demonstrated (at 2 Herz), and a number of valuable insights pertaining to the design of these devices have been gained.

Virtual screening using combinatorial cyclic peptide libraries reveals protein interfaces readily targetable by cyclic peptides.

PubMed

Duffy, Fergal J; O'Donovan, Darragh; Devocelle, Marc; Moran, Niamh; O'Connell, David J; Shields, Denis C

2015-03-23

Protein-protein and protein-peptide interactions are responsible for the vast majority of biological functions in vivo, but targeting these interactions with small molecules has historically been difficult. What is required are efficient combined computational and experimental screening methods to choose among a number of potential protein interfaces worthy of targeting lead macrocyclic compounds for further investigation. To achieve this, we have generated combinatorial 3D virtual libraries of short disulfide-bonded peptides and compared them to pharmacophore models of important protein-protein and protein-peptide structures, including short linear motifs (SLiMs), protein-binding peptides, and turn structures at protein-protein interfaces, built from 3D models available in the Protein Data Bank. We prepared a total of 372 reference pharmacophores, which were matched against 108,659 multiconformer cyclic peptides. After normalization to exclude nonspecific cyclic peptides, the top hits notably are enriched for mimetics of turn structures, including a turn at the interaction surface of human α thrombin, and also feature several protein-binding peptides. The top cyclic peptide hits also cover the critical "hot spot" interaction sites predicted from the interaction crystal structure. We have validated our method by testing cyclic peptides predicted to inhibit thrombin, a key protein in the blood coagulation pathway of important therapeutic interest, identifying a cyclic peptide inhibitor with lead-like activity. We conclude that protein interfaces most readily targetable by cyclic peptides and related macrocyclic drugs may be identified computationally among a set of candidate interfaces, accelerating the choice of interfaces against which lead compounds may be screened.

Heaterless ignition of inert gas ion thruster hollow cathodes

NASA Technical Reports Server (NTRS)

Schatz, M. F.

1985-01-01

Heaterless inert gas ion thruster hollow cathodes were investigated with the aim of reducing ion thruster complexity and increasing ion thruster reliability. Cathodes heated by glow discharges are evaluated for power requirements, flowrate requirements, and life limiting mechanisms. An accelerated cyclic life test is presented.

Preliminary results of accelerated exposure testing of solar cell system components

NASA Technical Reports Server (NTRS)

Anagnostou, E.; Forestieri, A. F.

1977-01-01

Plastic samples and solar cell sub modules were exposed to an accelerated outdoor environment in Arizona and an accelerated simulated environment in a cyclic ultraviolet exposure tester which included humidity exposure. These tests were for preliminary screening of materials suitable for use in the manufacture of solar cell modules which are to have a 20-year lifetime. The samples were exposed for various times up to six months, equivalent to a real time exposure of four years. Suitable materials were found to be FEP-A, FEP-C, PFA, acrylic, silicone compounds and adhesives and possibly parylene. The method of packaging the sub modules was also found to be important to their performance.

The influence of dibutyryl adenosine cyclic monophosphate on cell proliferation in the epithelium of the jejunal crypts, the colonic crypts and in colonic carcinomata of rat.

PubMed

Tutton, P J; Barkla, D H

1980-01-01

1. Cell proliferation in the jejunal crypts, the colonic crypts and in dimethylhydrazine (DMH)-induced adenocarcinomata of rat colon was measured using a stathmokinetic technique. 2. Dibutryl cyclic adneosine monophosphate (dibutyryl cAMP) was found to inhibit cell proliferation in colonic crypts and in colonic adenocarcinomata. 3. Dibutryl cAMP at very high doses was found to inhibit jejunal crypt cell proliferation but at lower doses was found to accelerate jejunal crypt cell proliferation. 4. Neither bilateral adrenalectomy nor chemical sympathectomy was found to abolish the ability of dibutryl cAMP to stimulate jejunal crypt cell proliferation. 5. The present results are difficult to interpret in terms of known hormonal influences on cell proliferation in the tissues examined and of established actions, of these hormones on cyclic nucleotide metabolism in other tissues.

Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dong-Ming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

2003-01-01

In this paper, surface cracking and interface reactions of a BSAS coating and a multi-layer ZrO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions, which were largely enhanced by the coating surface cracking in the water vapor environment, were investigated in detail, and the reaction phases were identified for the coating system after the long-term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions.

Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

2003-01-01

In this paper, surface cracking and interface reactions of a BSAS coating and a multi-layer ZTO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions, which were largely enhanced by the coating surface cracking in the water vapor environment, were investigated in detail, and the reaction phases were identified for the coating system after the long- term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions.

America's Divided Recovery: College Haves and Have-Nots

ERIC Educational Resources Information Center

Carnevale, Anthony P.; Jayasundera, Tamara; Gulish, Artem

2016-01-01

The steady job growth and falling unemployment rate offer some reassurance that the economy is on the right track. Yet, the long-term structural changes accelerated by the cyclical impact of the Great Recession have resulted in a very unequal recovery. During the recession, the worst economic downturn since the Great Depression, workers without…

Failure mechanisms in wood joints bonded with urea-formaldehyde adhesives

Treesearch

B.H. River; R.O. Ebewele; G.E. Myers

1994-01-01

Wood joints bonded with urea-formaldehyde (UF) are weakened by cyclic swelling and shrinking. To study the failure mechanisms in UF-bonded joints, specimens were bonded with unmodified, modified (amine), or phenol formaldehyde adhesive and subjected to accelerated aging. Modification of the adhesive properties increased the cleavage fracture toughness and shear...

Pulsed electromagnetic fields dosing impacts postoperative pain in breast reduction patients.

PubMed

Taylor, Erin M; Hardy, Krista L; Alonso, Amanda; Pilla, Arthur A; Rohde, Christine H

2015-01-01

Pulsed electromagnetic fields (PEMF) reduce postoperative pain and narcotic requirements in breast augmentation, reduction, and reconstruction patients. PEMF enhances both calmodulin-dependent nitric oxide and/or cyclic guanosine monophosphate signaling and phosphodiesterase activity, which blocks cyclic guanosine monophosphate. The clinical effect of these competing responses on PEMF dosing is not known. Two prospective, nonrandomized, active cohorts of breast reduction patients, with 15 min PEMF per 2 h; "Q2 (active)", and 5 min PEMF per 20 min; "5/20 (active)", dosing regimens were added to a previously reported double-blind clinical study wherein 20 min PEMF per 4 h, "Q4 (active)", dosing significantly accelerated postoperative pain reduction compared with Q4 shams. Postoperative visual analog scale pain scores and narcotic use were compared with results from the previous study. Visual analog scale scores at 24 h were 43% and 35% of pain at 1 h in the Q4 (active) and Q2 (active) cohorts, respectively (P < 0.01). Pain at 24 h in the 5/20 (active) cohort was 87% of pain at 1 h, compared with 74% in the Q4 (sham) cohort (P = 0.451). Concomitantly, narcotic usage in the 5/20 (active) and Q4 (sham) cohorts was not different (P = 0.478), and 2-fold higher than the Q4 (active) and Q2 (active) cohorts (P < 0.02). This prospective study shows Q4/Q2, but not 5/20 PEMF dosing, accelerated postoperative pain reduction compared with historical shams. The 5/20 (active) regimen increases NO 4-fold faster than the Q4 (active) regimen, possibly accelerating phosphodiesterase inhibition of cyclic guanosine monophosphate sufficiently to block the PEMF effect. This study helps define the dosing limits of clinically useful PEMF signals. Copyright © 2015 Elsevier Inc. All rights reserved.

Innovative leasing engineering as tool for synchronization of innovative, leasing and buying cycles

NASA Astrophysics Data System (ADS)

Yaskova, Natalia; Alekseeva, Tatyana

2017-10-01

This article suggests a new principle of cyclic synchronization of innovative, leasing and buying cycles in construction “innovative leasing engineering” which facilitates the accelerated transition of the national economy to the innovative way of development. Cyclical nature of economic phenomena is not only their immanent property, but also the subject of economic analysis. Modern format of decision making management requires analysis of the many cycles which fill any kind of activity. Accounting and reconciliation of construction, design, investment, buying, reproduction, leasing and other cycles is important for investment and construction sphere from the point of view of necessity for synchronization and position of determining the nature of trends in sectoral development.

Elastic-Plastic Finite Element Analysis of Fatigue Crack Growth in Mode 1 and Mode 2 Conditions

NASA Technical Reports Server (NTRS)

Nakagaki, M.; Atluri, S. N.

1978-01-01

Presented is an alternate cost-efficient and accurate elastic-plastic finite element procedure to analyze fatigue crack closure and its effects under general spectrum loading. Both Modes 1 and 2 type cycling loadings are considered. Also presented are the results of an investigation, using the newly developed procedure, of various factors that cause crack growth acceleration or retardation and delay effects under high-to-low, low-to-high, single overload, and constant amplitude type cyclic loading in a Mode 1 situation. Further, the results of an investigation of a centercracked panel under external pure shear (Mode 2) cyclic loading, of constant amplitude, are reported.

Methods of geometrical integration in accelerator physics

NASA Astrophysics Data System (ADS)

Andrianov, S. N.

2016-12-01

In the paper we consider a method of geometric integration for a long evolution of the particle beam in cyclic accelerators, based on the matrix representation of the operator of particles evolution. This method allows us to calculate the corresponding beam evolution in terms of two-dimensional matrices including for nonlinear effects. The ideology of the geometric integration introduces in appropriate computational algorithms amendments which are necessary for preserving the qualitative properties of maps presented in the form of the truncated series generated by the operator of evolution. This formalism extends both on polarized and intense beams. Examples of practical applications are described.

Software package for modeling spin-orbit motion in storage rings

NASA Astrophysics Data System (ADS)

Zyuzin, D. V.

2015-12-01

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 106-109 particles in a beam during 109 turns in an accelerator (about 1012-1015 integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin-orbit dynamics.

Recording the synchrotron radiation by a picosecond streak camera for bunch diagnostics in cyclic accelerators

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

Vereshchagin, A K; Vorob'ev, N S; Gornostaev, P B

2016-02-28

A PS-1/S1 picosecond streak camera with a linear sweep is used to measure temporal characteristics of synchrotron radiation pulses on a damping ring (DR) at the Budker Institute of Nuclear Physics (BINP) of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). The data obtained allow a conclusion as to the formation processes of electron bunches and their 'quality' in the DR after injection from the linear accelerator. The expediency of employing the streak camera as a part of an optical diagnostic accelerator complex for adjusting the injection from a linear accelerator is shown. Discussed is the issue ofmore » designing a new-generation dissector with a time resolution up to a few picoseconds, which would allow implementation of a continuous bunch monitoring in the DR during mutual work with the electron-positron colliders at the BINP. (acoustooptics)« less

Fatigue Behavior of Glass Fiber-Reinforced Polymer Bars after Elevated Temperatures Exposure.

PubMed

Li, Guanghui; Zhao, Jun; Wang, Zike

2018-06-16

Fiber-reinforced polymer (FRP) bars have been widely applied in civil engineering. This paper presents the results of an experimental study to investigate the tensile fatigue mechanical properties of glass fiber-reinforced polymer (GFRP) bars after elevated temperatures exposure. For this purpose, a total of 105 GFRP bars were conducted for testing. The specimens were exposed to heating regimes of 100, 150, 200, 250, 300 and 350 °C for a period of 0, 1 or 2 h. The GFRP bars were tested with different times of cyclic load after elevated temperatures exposure. The results show that the tensile strength and elastic modulus of GFRP bars decrease with the increase of elevated temperature and holding time, and the tensile strength of GFRP bars decreases obviously by 19.5% when the temperature reaches 250 °C. Within the test temperature range, the tensile strength of GFRP bars decreases at most by 28.0%. The cyclic load accelerates the degradation of GFRP bars after elevated temperature exposure. The coupling of elevated temperature and holding time enhance the degradation effect of cyclic load on GFRP bars. The tensile strength of GFRP bars after elevated temperatures exposure at 350 °C under cyclic load is reduced by 50.5% compared with that at room temperature and by 36.3% compared with that after exposing at 350 °C without cyclic load. In addition, the elastic modulus of GFRP bars after elevated temperatures exposure at 350 °C under cyclic load is reduced by 17.6% compared with that at room temperature and by 6.0% compared with that after exposing at 350 °C without cyclic load.

Integration of auditory and kinesthetic information in motion: alterations in Parkinson's disease.

PubMed

Sabaté, Magdalena; Llanos, Catalina; Rodríguez, Manuel

2008-07-01

The main aim in this work was to study the interaction between auditory and kinesthetic stimuli and its influence on motion control. The study was performed on healthy subjects and patients with Parkinson's disease (PD). Thirty-five right-handed volunteers (young, PD, and age-matched healthy participants, and PD-patients) were studied with three different motor tasks (slow cyclic movements, fast cyclic movements, and slow continuous movements) and under the action of kinesthetic stimuli and sounds at different beat rates. The action of kinesthesia was evaluated by comparing real movements with virtual movements (movements imaged but not executed). The fast cyclic task was accelerated by kinesthetic but not by auditory stimuli. The slow cyclic task changed with the beat rate of sounds but not with kinesthetic stimuli. The slow continuous task showed an integrated response to both sensorial modalities. These data show that the influence of the multisensory integration on motion changes with the motor task and that some motor patterns are modulated by the simultaneous action of auditory and kinesthetic information, a cross-modal integration that was different in PD-patients. PsycINFO Database Record (c) 2008 APA, all rights reserved.

Cyclic Failure Mechanisms of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Lee, Kang N.; Miller, Robert A.

2002-01-01

Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally cyclic tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent cyclic fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure mechanisms of the coating systems are also discussed based on the cyclic test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.

Study on shear properties of coral sand under cyclic simple shear condition

NASA Astrophysics Data System (ADS)

Ji, Wendong; Zhang, Yuting; Jin, Yafei

2018-05-01

In recent years, the ocean development in our country urgently needs to be accelerated. The construction of artificial coral reefs has become an important development direction. In this paper, experimental studies of simple shear and cyclic simple shear of coral sand are carried out, and the shear properties and particle breakage of coral sand are analyzed. The results show that the coral sand samples show an overall shear failure in the simple shear test, which is more accurate and effective for studying the particle breakage. The shear displacement corresponding to the peak shear stress of the simple shear test is significantly larger than that corresponding to the peak shear stress of the direct shear test. The degree of particle breakage caused by the simple shear test is significantly related to the normal stress level. The particle breakage of coral sand after the cyclic simple shear test obviously increases compared with that of the simple shear test, and universal particle breakage occurs within the whole particle size range. The increasing of the cycle-index under cyclic simple shear test results in continuous compacting of the sample, so that the envelope curve of peak shearing force increases with the accumulated shear displacement.

Two-electron oxidation of deoxyguanosine by a Ru(III) complex without involving oxygen molecules through disproportionation.

PubMed

Choi, Sunhee; Ryu, DaWeon; DellaRocca, Joseph G; Wolf, Matthew W; Bogart, Justin A

2011-07-18

Among the many mechanisms for the oxidation of guanine derivatives (G) assisted by transition metals, Ru(III) and Pt(IV) metal ions share basically the same principle. Both Ru(III)- and Pt(IV)-bound G have highly positively polarized C8-H's that are susceptible to deprotonation by OH(-), and both undergo two-electron redox reactions. The main difference is that, unlike Pt(IV), Ru(III) is thought to require O(2) to undergo such a reaction. In this study, however, we report that [Ru(III)(NH(3))(5)(dGuo)] (dGuo = deoxyguanosine) yields cyclic-5'-O-C8-dGuo (a two-electron G oxidized product, cyclic-dGuo) without O(2). In the presence of O(2), 8-oxo-dGuo and cyclic-dGuo were observed. Both [Ru(II)(NH(3))(5)(dGuo)] and cyclic-dGuo were produced from [Ru(III)(NH(3))(5)(dGuo)] accelerated by [OH(-)]. We propose that [Ru(III)(NH(3))(5)(dGuo)] disproportionates to [Ru(II)(NH(3))(5)(dGuo)] and [Ru(IV)(NH(3))(4)(NH(2)(-))(dGuo)], followed by a 5'-OH attack on C8 in [Ru(IV)(NH(3))(4)(NH(2)(-))(dGuo)] to initiate an intramolecular two-electron transfer from dGuo to Ru(IV), generating cyclic-dGuo and Ru(II) without involving O(2).

Ribosomal synthesis and folding of peptide-helical aromatic foldamer hybrids

NASA Astrophysics Data System (ADS)

Rogers, Joseph M.; Kwon, Sunbum; Dawson, Simon J.; Mandal, Pradeep K.; Suga, Hiroaki; Huc, Ivan

2018-03-01

Translation, the mRNA-templated synthesis of peptides by the ribosome, can be manipulated to incorporate variants of the 20 cognate amino acids. Such approaches for expanding the range of chemical entities that can be produced by the ribosome may accelerate the discovery of molecules that can perform functions for which poorly folded, short peptidic sequences are ill suited. Here, we show that the ribosome tolerates some artificial helical aromatic oligomers, so-called foldamers. Using a flexible tRNA-acylation ribozyme—flexizyme—foldamers were attached to tRNA, and the resulting acylated tRNAs were delivered to the ribosome to initiate the synthesis of non-cyclic and cyclic foldamer-peptide hybrid molecules. Passing through the ribosome exit tunnel requires the foldamers to unfold. Yet foldamers encode sufficient folding information to influence the peptide structure once translation is completed. We also show that in cyclic hybrids, the foldamer portion can fold into a helix and force the peptide segment to adopt a constrained and stretched conformation.

The impact of posture and prolonged cyclic compressive loading on vertebral joint mechanics.

PubMed

Gooyers, Chad E; McMillan, Robert D; Howarth, Samuel J; Callaghan, Jack P

2012-08-01

An in vitro biomechanics investigation exposing porcine functional spinal units (FSUs) to submaximal cyclic or static compressive forces while in a flexed, neutral, or extended posture. To investigate the combined effect of cyclically applied compressive force (e.g., vibration) and postural deviation on intervertebral joint mechanics. Independently, prolonged vibration exposure and non-neutral postures are known risk factors for development of low back pain and injury. However, there is limited basic scientific evidence to explain how the risk of low back injury from vibration exposure is modified by other mechanical factors. This work examined the influence of static postural deviation on vertebral joint height loss and compressive stiffness under cyclically applied compressive force. Forty-eight FSUs, consisting of 2 adjacent vertebrae, ligaments, and the intervening intervertebral disc were included in the study. Each specimen was randomized to 1 of 3 experimental posture conditions (neutral, flexed, or extended) and assigned to 1 of 2 loading protocols, consisting of (1) cyclic (1500 ± 1200 N applied at 5 Hz using a sinusoidal waveform, resulting in 0.2 g rms acceleration) or (2) 1500 N of static compressive force. RESULTS.: As expected, FSU height loss followed a typical first-order response in both the static and cyclic loading protocols, with the majority (~50%) of the loss occurring in the first 20 minutes of testing. A significant interaction between posture and loading protocol (P < 0.001) was noted in the magnitude of FSU height loss. Subsequent analysis of simple effects revealed significant differences between cyclic and static loading protocols in both a neutral (P = 0.016) and a flexed posture (P < 0.0001). No significant differences (P = 0.320) were noted between pre/postmeasurements of FSU compressive stiffness. Posture is an important mechanical factor to consider when assessing the risk of injury from cyclic loading to the lumbar spine.

Tilt-rotor flutter control in cruise flight

NASA Technical Reports Server (NTRS)

Nasu, Ken-Ichi

1986-01-01

Tilt-rotor flutter control under cruising operation is analyzed. The rotor model consists of a straight fixed wing, a pylon attached to the wingtip, and a three-blade rotor. The wing is cantilevered to the fuselage and is allowed to bend forward and upward. It also has a torsional degree of freedom about the elastic axis. Each rotor blade has two bending degrees of freedom. Feedback of wingtip velocity and acceleration to cyclic pitch is investigated for flutter control, using strip theory and linearized equations of motion. To determine the feedback gain, an eigenvalue analysis is performed. A second, independent, timewise calculation is conducted to evaluate the control law while employing more sophisticated aerodynamics. The effectiveness of flutter control by cyclic pitch change was confirmed.

Accelerating axon growth to overcome limitations in functional recovery after peripheral nerve injury.

PubMed

Gordon, Tessa; Chan, K Ming; Sulaiman, Olawale A R; Udina, Esther; Amirjani, Nasim; Brushart, Thomas M

2009-10-01

Injured peripheral nerves regenerate at very slow rates. Therefore, proximal injury sites such as the brachial plexus still present major challenges, and the outcomes of conventional treatments remain poor. This is in part attributable to a progressive decline in the Schwann cells' ability to provide a supportive milieu for the growth cone to extend and to find the appropriate target. These challenges are compounded by the often considerable delay of regeneration across the site of nerve laceration. Recently, low-frequency electrical stimulation (as brief as an hour) has shown promise, as it significantly accelerated regeneration in animal models through speeding of axon growth across the injury site. To test whether this might be a useful clinical tool, we carried out a randomized controlled trial in patients who had experienced substantial axonal loss in the median nerve owing to severe compression in the carpal tunnel. To further elucidate the potential mechanisms, we applied rolipram, a cyclic adenosine monophosphate agonist, to rats after axotomy of the femoral nerve. We demonstrated that effects similar to those observed in animal studies could also be attained in humans. The mechanisms of action of electrical stimulation likely operate through up-regulation of neurotrophic factors and cyclic adenosine monophosphate. Indeed, the application of rolipram significantly accelerated nerve regeneration. With new mechanistic insights into the influencing factors of peripheral nerve regeneration, the novel treatments described above could form part of an armament of synergistic therapies that could make a meaningful difference to patients with peripheral nerve injuries.

Accelerate Genomic Aging in Congenital Neutropenia

DTIC Science & Technology

2017-10-01

syndrome (MDS) or acute myeloid leukemia (AML) in patients with congenital neutropenia. We hypothesize that replicative stress and/or changes in the...neutropenia; Shwachman Diamond syndrome ; Cyclic neutropenia; Hematopoietic stem cells; Granulocyte colony-stimulating factor; Acute myeloid leukemia... syndrome (MDS) or acute myeloid leukemia (AML). The cumulative incidence of MDS/AML in patients with SCN treated with G-CSF is 22%. Likewise, the

[The use of apparatus-supported physiotherapy for the accelerated recovery and enhancement of sports performance].

PubMed

Gigineĭshvili, G R; Dombrovskaia, I I; Belousov, A Iu; Kirova, E I; Orekhova, E M; Radzievskiĭ, S A; Liubimskaia, L I

1995-01-01

The effects of physiotherapeutic factors such as electric sleep, sinusoidal modulated currents. UV radiation, interference currents, decimeter waves, laser radiation were studied in 600 sportsmen active in cyclic and acyclic sports. Recommended are both single and course procedures because the above factors are found to diminish immunodeficiency and to increase muscular performance in sportsmen.

DNA transposon dynamics in populations of Daphnia pulex with and without sex.

PubMed

Schaack, Sarah; Pritham, Ellen J; Wolf, Abby; Lynch, Michael

2010-08-07

We investigate the role of recombination in transposable element (TE) proliferation in the cyclical parthenogen, Daphnia pulex. Recombination provides a mechanism by which the rate of both TE gain and loss can be accelerated, a duality that has long intrigued many biologists interested in the influence of sex on mutation accumulation. We compared TE loads among populations of D. pulex where sex occurs regularly (cyclical parthenogens or 'sexuals') with those in which the ability to reproduce sexually has been completely lost (obligate 'asexuals') for six different families of DNA transposons. Transposon display assays showed that sexuals have more TEs than asexuals, contrary to the expectations under Muller's ratchet but consistent with the idea that sex facilitates TE spread. Sexuals also exhibit higher insertion site polymorphism among lineages, as predicted because recombination accelerates rates of loss and gain. Asexuals, however, have proportionally more singletons (loci occupied in a single isolate), which differs from previous studies where selfing and outcrossing were used as a proxy for high and low recombination. Our multi-element survey reveals that the impact of sex on TE proliferation is consistent among different Class II TE families and we discuss the genomic consequences of different reproductive strategies over long time periods.

Cyclic AMP regulates formation of mammary epithelial acini in vitro

PubMed Central

Nedvetsky, Pavel I.; Kwon, Sang-Ho; Debnath, Jayanta; Mostov, Keith E.

2012-01-01

Epithelial cells form tubular and acinar structures notable for a hollow lumen. In three-dimensional culture utilizing MCF10A mammary epithelial cells, acini form due to integrin-dependent polarization and survival of cells contacting extracellular matrix (ECM), and the apoptosis of inner cells of acini lacking contact with the ECM. In this paper, we report that cyclic AMP (cAMP)-dependent protein kinase A (PKA) promotes acinus formation via two mechanisms. First, cAMP accelerates redistribution of α6-integrin to the periphery of the acinus and thus facilitates the polarization of outer acinar cells. Blocking of α6-integrin function by inhibitory antibody prevents cAMP-dependent polarization. Second, cAMP promotes the death of inner cells occupying the lumen. In the absence of cAMP, apoptosis is delayed, resulting in perturbed luminal clearance. cAMP-dependent apoptosis is accompanied by a posttranscriptional PKA-dependent increase in the proapoptotic protein Bcl-2 interacting mediator of cell death. These data demonstrate that cAMP regulates lumen formation in mammary epithelial cells in vitro, both through acceleration of polarization of outer cells and apoptosis of inner cells of the acinus. PMID:22675028

General Corrosion Resistance Assessments of AA7085, AA7129, and Other High-Performance Aluminum Alloys for Department of Defense (DOD) Systems UsingLaboratory Based Accelerated Corrosion Methods and Electrochemistry

DTIC Science & Technology

2013-09-01

laboratory should play a role in the final design decision process. Integration factors such as conversion coatings , primers, topcoats, and their...Cyclic Accelerated Corrosion Analysis of Nonchromate Conversion Coatings on Aluminum Alloys 2024, 2219, 5083, and 7075 Using DoD Paint Systems; ARL...Titanium 0.08 0.10 max 0.10 max 0.15 max 0.08 max 0.05 max Zirconium 0.05 – 0.15 0.05 – 0.15 - 0.10 – 0.25 0.05 – 0.15 - Vanadium - - - - - 0.05 max

Cyclic steps and superimposed antidune deposits: important elements of coarse-grained deepwater channel-levée complexes

NASA Astrophysics Data System (ADS)

Lang, Joerg; Brandes, Christian; Winsemann, Jutta

2017-04-01

The facies distribution and architecture of submarine fans can be strongly impacted by erosion and deposition by supercritical density flows. We present field examples from the Sandino Forearc Basin (southern Central America), where cyclic-step and antidune deposits represent important sedimentary facies of coarse-grained channel-levée complexes. These bedforms occur in all sub-environments of the depositional systems and relate to the different stages of avulsion, bypass, levée construction and channel backfilling. Large-scale scours (18 to 29 m deep, 18 to 25 m wide, 60 to >120 m long) with an amalgamated infill, comprising massive, normally coarse-tail graded or spaced subhorizontally stratified conglomerates and pebbly sandstones, are interpreted as deposits of the hydraulic-jump zone of cyclic steps. These cyclic steps probably formed during avulsion, when high-density flows were routed into the evolving channel. The large-scale scour fills can be distinguished from small-scale channel fills based on the preservation of a steep upper margin and a coarse-grained infill comprising mainly amalgamated hydraulic-jump deposits. Channel fills include repetitive successions deposited by cyclic steps with superimposed antidunes. The hydraulic-jump zone of cyclic-step deposits comprises regularly spaced scours (0.2 to 2.6 m deep, 0.8 to 23 m wide), which are infilled by intraclast-rich conglomerates or pebbly sandstones and display normal coarse-tail grading or backsets. Laterally and vertically these deposits are associated with subhorizontally stratified, low-angle cross-stratified or sinusoidal stratified pebbly sandstones and sandstones (wavelength 0.5 to 18 m), interpreted as representing antidune deposits formed on the stoss-side of the cyclic steps during flow re-acceleration. The field examples indicate that so-called crudely or spaced stratified deposits may commonly represent antidune deposits with varying stratification styles controlled by the aggradation rate, grain-size distribution and amalgamation. The deposits of small-scale cyclic steps with superimposed antidunes form fining upwards successions with decreasing antidune wavelengths. Such cyclic step-antidune successions are the characteristic basal infill of channels, probably related to supercritical high-density turbidity flows triggered by retrogressive slope failures.

Anti-knock quality of sugar derived levulinic esters and cyclic ethers

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

Tian, Miao; McCormick, Robert L.; Luecke, Jon

Here, the objective of this paper is to investigate the anti-knock quality of sugar-derived levulinic esters (methyl levulinate (ML) and ethyl levulinate (EL)) and cyclic ethers (furfuryl ethyl ether (FEE) and ethyl tetrahydrofurfuryl ether (ETE)). To this end, combustion experiments were carried out in both an engine and a constant volume autoignition device. The results from both apparati demonstrate that ML, EL and FEE have superior anti-knock quality than the reference Euro95 gasoline. ETE, conversely, performed markedly worse than the reference fuel on both setups and might therefore be a more appropriate fuel for compression ignition engines. The main reasonmore » of the distinctions in anti-knock quality can be found in the molecular structure of the neat biofuels. ML and EL are levulinic esters, with a ketone (C=O) functionality and an ester (C(=O)-O) group on the carbon chain. They can readily produce stable intermediates during the auto-ignition process, thereby slowing down the overall reaction rate. The unsaturated cyclic ether (FEE) has very strong ring C-H bonds. However, the saturated cyclic ether (ETE) has weak ring C-H bonds, which facilitate more readily ring opening reactions. Long side chains on the cyclic ethers further accelerate the reaction rate. Importantly for future research, our results suggest that IQT and engine experiments are interchangeable setups with respect to qualitative anti-knock quality evaluation of novel compounds.« less

Anti-knock quality of sugar derived levulinic esters and cyclic ethers

DOE PAGES

Tian, Miao; McCormick, Robert L.; Luecke, Jon; ...

2017-04-22

Here, the objective of this paper is to investigate the anti-knock quality of sugar-derived levulinic esters (methyl levulinate (ML) and ethyl levulinate (EL)) and cyclic ethers (furfuryl ethyl ether (FEE) and ethyl tetrahydrofurfuryl ether (ETE)). To this end, combustion experiments were carried out in both an engine and a constant volume autoignition device. The results from both apparati demonstrate that ML, EL and FEE have superior anti-knock quality than the reference Euro95 gasoline. ETE, conversely, performed markedly worse than the reference fuel on both setups and might therefore be a more appropriate fuel for compression ignition engines. The main reasonmore » of the distinctions in anti-knock quality can be found in the molecular structure of the neat biofuels. ML and EL are levulinic esters, with a ketone (C=O) functionality and an ester (C(=O)-O) group on the carbon chain. They can readily produce stable intermediates during the auto-ignition process, thereby slowing down the overall reaction rate. The unsaturated cyclic ether (FEE) has very strong ring C-H bonds. However, the saturated cyclic ether (ETE) has weak ring C-H bonds, which facilitate more readily ring opening reactions. Long side chains on the cyclic ethers further accelerate the reaction rate. Importantly for future research, our results suggest that IQT and engine experiments are interchangeable setups with respect to qualitative anti-knock quality evaluation of novel compounds.« less

Quantum Clique Gossiping.

PubMed

Li, Bo; Li, Shuang; Wu, Junfeng; Qi, Hongsheng

2018-02-09

This paper establishes a framework of quantum clique gossiping by introducing local clique operations to networks of interconnected qubits. Cliques are local structures in complex networks being complete subgraphs, which can be used to accelerate classical gossip algorithms. Based on cyclic permutations, clique gossiping leads to collective multi-party qubit interactions. We show that at reduced states, these cliques have the same acceleration effects as their roles in accelerating classical gossip algorithms. For randomized selection of cliques, such improved rate of convergence is precisely characterized. On the other hand, the rate of convergence at the coherent states of the overall quantum network is proven to be decided by the spectrum of a mean-square error evolution matrix. Remarkably, the use of larger quantum cliques does not necessarily increase the speed of the network density aggregation, suggesting quantum network dynamics is not entirely decided by its classical topology.

Software package for modeling spin–orbit motion in storage rings

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

Zyuzin, D. V., E-mail: d.zyuzin@fz-juelich.de

2015-12-15

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 10{sup 6}–10{sup 9} particles in a beam during 10{supmore » 9} turns in an accelerator (about 10{sup 12}–10{sup 15} integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin–orbit dynamics.« less

Development of an Accelerated Test Design for Predicting the Service Life of the Solar Array at Mead, Nebraska

NASA Technical Reports Server (NTRS)

Gaines, G. B.; Thomas, R. E.; Noel, G. T.; Shilliday, T. S.; Wood, V. E.; Carmichael, D. C.

1979-01-01

An accelerated life test is described which was developed to predict the life of the 25 kW photovoltaic array installed near Mead, Nebraska. A quantitative model for accelerating testing using multiple environmental stresses was used to develop the test design. The model accounts for the effects of thermal stress by a relation of the Arrhenius form. This relation was then corrected for the effects of nonthermal environmental stresses, such as relative humidity, atmospheric pollutants, and ultraviolet radiation. The correction factors for the nonthermal stresses included temperature-dependent exponents to account for the effects of interactions between thermal and nonthermal stresses on the rate of degradation of power output. The test conditions, measurements, and data analyses for the accelerated tests are presented. Constant-temperature, cyclic-temperature, and UV types of tests are specified, incorporating selected levels of relative humidity and chemical contamination and an imposed forward-bias current and static electric field.

Deciphering the function of the CNGB1b subunit in olfactory CNG channels.

PubMed

Nache, Vasilica; Wongsamitkul, Nisa; Kusch, Jana; Zimmer, Thomas; Schwede, Frank; Benndorf, Klaus

2016-07-11

Olfactory cyclic nucleotide-gated (CNG) ion channels are key players in the signal transduction cascade of olfactory sensory neurons. The second messengers cAMP and cGMP directly activate these channels, generating a depolarizing receptor potential. Olfactory CNG channels are composed of two CNGA2 subunits and two modulatory subunits, CNGA4, and CNGB1b. So far the exact role of the modulatory subunits for channel activation is not fully understood. By measuring ligand binding and channel activation simultaneously, we show that in functional heterotetrameric channels not only the CNGA2 subunits and the CNGA4 subunit but also the CNGB1b subunit binds cyclic nucleotides and, moreover, also alone translates this signal to open the pore. In addition, we show that the CNGB1b subunit is the most sensitive subunit in a heterotetrameric channel to cyclic nucleotides and that it accelerates deactivation to a similar extent as does the CNGA4 subunit. In conclusion, the CNGB1b subunit participates in ligand-gated activation of olfactory CNG channels and, particularly, contributes to rapid termination of odorant signal in an olfactory sensory neuron.

Fatigue and creep to leak tests of proton exchange membranes using pressure-loaded blisters

NASA Astrophysics Data System (ADS)

Li, Yongqiang; Dillard, David A.; Case, Scott W.; Ellis, Michael W.; Lai, Yeh-Hung; Gittleman, Craig S.; Miller, Daniel P.

In this study, three commercially available proton exchange membranes (PEMs) are biaxially tested using pressure-loaded blisters to characterize their resistance to gas leakage under either static (creep) or cyclic fatigue loading. The pressurizing medium, air, is directly used for leak detection. These tests are believed to be more relevant to fuel cell applications than quasi-static uniaxial tensile-to-rupture tests because of the use of biaxial cyclic and sustained loading and the use of gas leakage as the failure criterion. They also have advantages over relative humidity cycling test, in which a bare PEM or catalyst coated membrane is clamped with gas diffusion media and flow field plates and subjected to cyclic changes in relative humidity, because of the flexibility in allowing controlled mechanical loading and accelerated testing. Nafion ® NRE-211 membranes are tested at three different temperatures and the time-temperature superposition principle is used to construct stress-lifetime master curve. Tested at 90 °C, 2%RH extruded Ion Power ® N111-IP membranes have a longer lifetime than Gore™-Select ® 57 and Nafion ® NRE-211 membranes.

Five-centimeter diameter ion thruster development

NASA Technical Reports Server (NTRS)

Weigand, A. J.

1972-01-01

All system components were tested for endurance and steady state and cyclic operation. The following results were obtained: acceleration system (electrostatic type), 3100 hours continuous running; acceleration system (translation type), 2026 hours continuous running; cathode-isolator-vaporizer assembly, 5000 hours continuous operation and 190 restart cycles with 1750 hours operation; mercury expulsion system, 5000 hours continuous running; and neutralizer, 5100 hours continuous operation. The results of component optimization studies such as neutralizer position, neutralizer keeper hole, and screen grid geometry are included. Extensive mapping of the magnet field within and immediately outside the thruster are shown. A technique of electroplating the molybdenum accelerator grid with copper to study erosion patterns is described. Results of tests being conducted to more fully understand the operation of the hollow cathode are also given. This type of 5-cm thruster will be space tested on the Communication Technology Satellite in 1975.

Accelerated fatigue testing of dentin-composite bond with continuously increasing load.

PubMed

Li, Kai; Guo, Jiawen; Li, Yuping; Heo, Young Cheul; Chen, Jihua; Xin, Haitao; Fok, Alex

2017-06-01

The aim of this study was to evaluate an accelerated fatigue test method that used a continuously increasing load for testing the dentin-composite bond strength. Dentin-composite disks (ϕ5mm×2mm) made from bovine incisor roots were subjected to cyclic diametral compression with a continuously increasingly load amplitude. Two different load profiles, linear and nonlinear with respect to the number of cycles, were considered. The data were then analyzed by using a probabilistic failure model based on the Weakest-Link Theory and the classical stress-life function, before being transformed to simulate clinical data of direct restorations. All the experimental data could be well fitted with a 2-parameter Weibull function. However, a calibration was required for the effective stress amplitude to account for the difference between static and cyclic loading. Good agreement was then obtained between theory and experiments for both load profiles. The in vitro model also successfully simulated the clinical data. The method presented will allow tooth-composite interfacial fatigue parameters to be determined more efficiently. With suitable calibration, the in vitro model can also be used to assess composite systems in a more clinically relevant manner. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Beyond Inflation:. A Cyclic Universe Scenario

NASA Astrophysics Data System (ADS)

Turok, Neil; Steinhardt, Paul J.

2005-08-01

Inflation has been the leading early universe scenario for two decades, and has become an accepted element of the successful 'cosmic concordance' model. However, there are many puzzling features of the resulting theory. It requires both high energy and low energy inflation, with energy densities differing by a hundred orders of magnitude. The questions of why the universe started out undergoing high energy inflation, and why it will end up in low energy inflation, are unanswered. Rather than resort to anthropic arguments, we have developed an alternative cosmology, the cyclic universe [1], in which the universe exists in a very long-lived attractor state determined by the laws of physics. The model shares inflation's phenomenological successes without requiring an epoch of high energy inflation. Instead, the universe is made homogeneous and flat, and scale-invariant adiabatic perturbations are generated during an epoch of low energy acceleration like that seen today, but preceding the last big bang. Unlike inflation, the model requires low energy acceleration in order for a periodic attractor state to exist. The key challenge facing the scenario is that of passing through the cosmic singularity at t = 0. Substantial progress has been made at the level of linearised gravity, which is reviewed here. The challenge of extending this to nonlinear gravity and string theory remains.

Beyond Inflation: A Cyclic Universe Scenario

NASA Astrophysics Data System (ADS)

Turok, Neil; Steinhardt, Paul J.

2005-01-01

Inflation has been the leading early universe scenario for two decades, and has become an accepted element of the successful `cosmic concordance' model. However, there are many puzzling features of the resulting theory. It requires both high energy and low energy inflation, with energy densities differing by a hundred orders of magnitude. The questions of why the universe started out undergoing high energy inflation, and why it will end up in low energy inflation, are unanswered. Rather than resort to anthropic arguments, we have developed an alternative cosmology, the cyclic universe, in which the universe exists in a very long-lived attractor state determined by the laws of physics. The model shares inflation's phenomenological successes without requiring an epoch of high energy inflation. Instead, the universe is made homogeneous and flat, and scale-invariant adiabatic perturbations are generated during an epoch of low energy acceleration like that seen today, but preceding the last big bang. Unlike inflation, the model requires low energy acceleration in order for a periodic attractor state to exist. The key challenge facing the scenario is that of passing through the cosmic singularity at t = 0. Substantial progress has been made at the level of linearised gravity, which is reviewed here. The challenge of extending this to nonlinear gravity and string theory remains.

Effects of combined mechanical stimulation on the proliferation and differentiation of pre-osteoblasts

PubMed Central

Kang, Kyung Shin; Lee, Seung-Jae; Lee, Haksue; Moon, Wonkyu

2011-01-01

We observed how combined mechanical stimuli affect the proliferation and differentiation of pre-osteoblasts. For this research, a bioreactor system was developed that can simultaneously stimulate cells with cyclic strain and ultrasound, each of which is known to effectively stimulate bone tissue regeneration. MC3T3-E1 pre-osteoblasts were chosen for bone tissue engineering due to their osteoblast-like characteristics. 3-D scaffolds were fabricated with polycaprolactone and poly-L-lactic acid using the salt leaching method. The cells were stimulated by the bioreactor with cyclic strain and ultrasound. The bioreactor was set at a frequency of 1.0 Hz and 10% strain for cyclic strain and 1.0 MHz and 30 mW/cm2 for ultrasound. Three experimental groups (ultrasound, cyclic strain, and combined stimulation) and a control group were examined. Each group was stimulated for 20 min/day. Mechanical stimuli did not affect MC3T3-E1 cell proliferation significantly up to 10 days when measured with the cell counting kit-8. However, gene expression analysis of collagen type-I, osteocalcin, RUNX2, and osterix revealed that the combined mechanical stimulation accelerated the matrix maturation of MC3T3-E1 cells. These results indicate that the combined mechanical stimulation can enhance the differentiation of pre-osteoblasts more efficiently than simple stimuli, in spite of no effect on cell proliferation. PMID:21532314

Effect of Cyclic Precalcification of Nanotubular TiO2 Layer on the Bioactivity of Titanium Implant

PubMed Central

Park, Il Song; Yang, Eun Jin; Bae, Tae Sung

2013-01-01

The objective of this study is to investigate the effect of cyclic precalcification treatment to impart bioactive properties for titanium implants. Before precalcification, the titanium implants were subjected to blasting using hydroxyapatite (HAp), a resorbable blasting medium (RBM treated), and anodized using an electrolyte containing glycerol, H2O, and NH4F. Precalcification treatment was performed by two different methods, namely, continuous immersion treatment (CIT) and alternate immersion treatment (AIT). In CIT, the RBM treated and anodized titanium implants were immersed in 0.05 M NaH2PO4 solution at 80°C and saturated Ca(OH)2 solution at 100°C for 20 min, whereas during AIT, they were immersed alternatively in both solutions for 1 min for 20 cycles. Anodizing of the titanium implants enables the formation of self-organized TiO2 nanotubes. Cyclic precalcification treatment imparts a better bioactive property and enables an increase in activation level of the titanium implants. The removal torque values of the RBM treated, CIT treated, and AIT treated titanium implants are 10.8 ± 3.7 Ncm, 17.5 ± 3.5 Ncm, and 28.1 ± 2.4 Ncm, respectively. The findings of the study indicate the cyclic precalcification in an effective surface treatment method that would help accelerate osseointegration and impart bioactive property of titanium implants. PMID:24069596

Highly Efficient Catalytic Cyclic Carbonate Formation by Pyridyl Salicylimines.

PubMed

Subramanian, Saravanan; Park, Joonho; Byun, Jeehye; Jung, Yousung; Yavuz, Cafer T

2018-03-21

Cyclic carbonates as industrial commodities offer a viable nonredox carbon dioxide fixation, and suitable heterogeneous catalysts are vital for their widespread implementation. Here, we report a highly efficient heterogeneous catalyst for CO 2 addition to epoxides based on a newly identified active catalytic pocket consisting of pyridine, imine, and phenol moieties. The polymeric, metal-free catalyst derived from this active site converts less-reactive styrene oxide under atmospheric pressure in quantitative yield and selectivity to the corresponding carbonate. The catalyst does not need additives, solvents, metals, or co-catalysts, can be reused at least 10 cycles without the loss of activity, and scaled up easily to a kilogram scale. Density functional theory calculations reveal that the nucleophilicity of pyridine base gets stronger due to the conjugated imines and H-bonding from phenol accelerates the reaction forward by stabilizing the intermediate.

Analytical tools in accelerator physics

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

Litvinenko, V.N.

2010-09-01

This paper is a sub-set of my lectures presented in the Accelerator Physics course (USPAS, Santa Rosa, California, January 14-25, 2008). It is based on my notes I wrote during period from 1976 to 1979 in Novosibirsk. Only few copies (in Russian) were distributed to my colleagues in Novosibirsk Institute of Nuclear Physics. The goal of these notes is a complete description starting from the arbitrary reference orbit, explicit expressions for 4-potential and accelerator Hamiltonian and finishing with parameterization with action and angle variables. To a large degree follow logic developed in Theory of Cyclic Particle Accelerators by A.A.Kolmensky andmore » A.N.Lebedev [Kolomensky], but going beyond the book in a number of directions. One of unusual feature is these notes use of matrix function and Sylvester formula for calculating matrices of arbitrary elements. Teaching the USPAS course motivated me to translate significant part of my notes into the English. I also included some introductory materials following Classical Theory of Fields by L.D. Landau and E.M. Liftsitz [Landau]. A large number of short notes covering various techniques are placed in the Appendices.« less

Sources of the ultraheavy cosmic rays

NASA Technical Reports Server (NTRS)

Margolis, S. H.; Blake, J. B.

1985-01-01

The suggestions that the source abundances of cosmic ray nuclei heavier then Fe differ significantly from Solar System abundances are not well supported by the data without assuming preferential acceleration. The Solar System abundances of Pb and Bi are split into r-, standard s-, and cyclic 8-process components; the apprarent deficiency of Pb seen in the HEAO-3 Heavy Nuclei Experiment data might indicate an absence of Pb from the recycling 8-process.

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing

NASA Technical Reports Server (NTRS)

Montgomery, Eliza L.; Calle, Luz Marina; Curran, Jerone C.; Kolody, Mark R.

2011-01-01

Evaluation of metal-based structures has long relied on atmospheric exposure test sites to determine corrosion resistance in marine environments. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating salt spray and ultraviolet (UV) radiation, and exposing the metal to continuous or cyclic conditions of the corrosive environment. Their success for correlation to atmospheric exposure is often a concern when determining the timescale to which the accelerated tests can be related. Accelerated laboratory testing, which often focuses on the electrochemical reactions that occur during corrosion conditions, has yet to be universally accepted as a useful tool in predicting the long term service life of a metal despite its ability to rapidly induce corrosion. Although visual and mass loss methods of evaluating corrosion are the standard and their use is imperative, a method that correlates timescales from atmospheric exposure to accelerated testing would be very valuable. This work uses surface chemistry to interpret the chemical changes occurring on low carbon steel during atmospheric and accelerated corrosion conditions with the objective of finding a correlation between its accelerated and long-term corrosion performance. The current results of correlating data from marine atmospheric exposure conditions at the Kennedy Space Center beachside corrosion test site, alternating seawater spray, and immersion in typical electrochemical laboratory conditions, will be presented. Key words: atmospheric exposure, accelerated corrosion testing, alternating seawater spray, marine, correlation, seawater, carbon steel, long-term corrosion performance prediction, X-ray photoelectron spectroscopy.

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing - Part 2

NASA Technical Reports Server (NTRS)

Montgomery, Eliza L.; Calle, Luz Marina; Curran, Jerome C.; Kolody, Mark R.

2012-01-01

Evaluation of metals to predict service life of metal-based structures in corrosive environments has long relied on atmospheric exposure test sites. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating salt spray and ultraviolet (UV) radiation, and exposing the metal to continuous or cyclic conditions similar to those of the corrosive environment. Their reliability to correlate to atmospheric exposure test results is often a concern when determining the timescale to which the accelerated tests can be related. Accelerated corrosion testing has yet to be universally accepted as a useful tool in predicting the long-term service life of a metal, despite its ability to rapidly induce corrosion. Although visual and mass loss methods of evaluating corrosion are the standard, and their use is crucial, a method that correlates timescales from accelerated testing to atmospheric exposure would be very valuable. This paper presents work that began with the characterization of the atmospheric environment at the Kennedy Space Center (KSC) Beachside Corrosion Test Site. The chemical changes that occur on low carbon steel, during atmospheric and accelerated corrosion conditions, were investigated using surface chemistry analytical methods. The corrosion rates and behaviors of panels subjected to long-term and accelerated corrosion conditions, involving neutral salt fog and alternating seawater spray, were compared to identify possible timescale correlations between accelerated and long-term corrosion performance. The results, as well as preliminary findings on the correlation investigation, are presented.

Mechanistic Insight into Human ether-à-go-go-related Gene (hERG) K+ Channel Deactivation Gating from the Solution Structure of the EAG Domain

PubMed Central

Muskett, Frederick W.; Thouta, Samrat; Thomson, Steven J.; Bowen, Alexander; Stansfeld, Phillip J.; Mitcheson, John S.

2011-01-01

Human ether-à-go-go-related gene (hERG) K+ channels have a critical role in cardiac repolarization. hERG channels close (deactivate) very slowly, and this is vital for regulating the time course and amplitude of repolarizing current during the cardiac action potential. Accelerated deactivation is one mechanism by which inherited mutations cause long QT syndrome and potentially lethal arrhythmias. hERG deactivation is highly dependent upon an intact EAG domain (the first 135 amino acids of the N terminus). Importantly, deletion of residues 2–26 accelerates deactivation to a similar extent as removing the entire EAG domain. These and other experiments suggest the first 26 residues (NT1–26) contain structural elements required to slow deactivation by stabilizing the open conformation of the pore. Residues 26–135 form a Per-Arnt-Sim domain, but a structure for NT1–26 has not been forthcoming, and little is known about its site of interaction on the channel. In this study, we present an NMR structure for the entire EAG domain, which reveals that NT1–26 is structurally independent from the Per-Arnt-Sim domain and contains a stable amphipathic helix with one face being positively charged. Mutagenesis and electrophysiological studies indicate that neutralizing basic residues and breaking the amphipathic helix dramatically accelerate deactivation. Furthermore, scanning mutagenesis and molecular modeling studies of the cyclic nucleotide binding domain suggest that negatively charged patches on its cytoplasmic surface form an interface with the NT1–26 domain. We propose a model in which NT1–26 obstructs gating motions of the cyclic nucleotide binding domain to allosterically stabilize the open conformation of the pore. PMID:21135103

Lifetimes and reactivities of some 1,2-didehydroazepines commonly used in photoaffinity labeling experiments in aqueous solutions.

PubMed

Rizk, Mary S; Shi, Xiaofeng; Platz, Matthew S

2006-01-17

The reactive 1,2-didehydroazepine (cyclic ketenimine) intermediates produced upon photolysis of phenyl azide, 3-hydroxyphenyl azide, 3-methoxyphenyl azide, and 3-nitrophenyl azide in water and in HEPES buffer were studied by laser flash photolysis techniques with UV-vis detection of the transient intermediates. The lifetimes of the 1,2-didehydroazepines were obtained along with the absolute rate constants of their reactions with typical amino acids, nucleosides, and other simple reagents present in a biochemical milieu. The nitro substituent greatly accelerates the bimolecular reactions of the cyclic ketenimines, and the 3-methoxy group greatly decelerates the absolute reactivity of 1,2-didehydroazepines. The intermediate produced by photolysis of 3-hydroxyphenyl azide is much more reactive than the intermediate produced by photolysis of 3-methoxyphenyl azide. We propose that the hydroxyl-substituted 1,2-didehydoazepines rapidly (<10 micros) tautomerize in water to form azepinones and much more rapidly than the corresponding 3-methoxy-substituted cyclic ketenimines undergo hydrolysis. Azepinones react more rapidly with nucleophiles than do methoxy-substituted 1,2-didehydroazepines and are the active species present upon the photolysis of 3-hydroxyphenyl azide in aqueous solution.

Towards High-Frequency Shape Memory Alloy Actuators Incorporating Liquid Metal Energy Circuits

NASA Astrophysics Data System (ADS)

Hartl, Darren; Mingear, Jacob; Bielefeldt, Brent; Rohmer, John; Zamarripa, Jessica; Elwany, Alaa

2017-12-01

Large shape memory alloy (SMA) actuators are currently limited to applications with low cyclic actuation frequency requirements due to their generally poor heat transfer rates. This limitation can be overcome through the use of distributed body heating methods such as induction heating or by accelerated cooling methods such as forced convection in internal cooling channels. In this work, a monolithic SMA beam actuator containing liquid gallium-indium alloy-filled channels is fabricated through additive manufacturing. These liquid metal channels enable a novel multi-physical thermal control system, allowing for increased heating and cooling rates to facilitate an increased cyclic actuation frequency. Liquid metal flowing in the channels performs the dual tasks of inductively heating the surrounding SMA material and then actively cooling the SMA via forced internal fluid convection. A coupled thermoelectric model, implemented in COMSOL, predicts a possible fivefold increase in the cyclic actuation frequency due to these increased thermal transfer rates when compared to conventional SMA forms having external heating coils and being externally cooled via forced convection. The first ever experimental prototype SMA actuator of this type is described and, even at much lower flow rates, is shown to exhibit a decrease in cooling time of 40.9%.

Contributions of stress corrosion and cyclic fatigue to subcritical crack growth in a dental glass-ceramic.

PubMed

Joshi, Gaurav V; Duan, Yuanyuan; Della Bona, Alvaro; Hill, Thomas J; St John, Kenneth; Griggs, Jason A

2014-08-01

The objective of this study was to test the following hypotheses: (1) both cyclic degradation and stress-corrosion mechanisms result in subcritical crack growth (SCG) in a fluorapatite glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent) and (2) there is an interactive effect of stress corrosion and cyclic fatigue to accelerate subcritical crack growth. Rectangular beam specimens were fabricated using the lost-wax process. Two groups of specimens (N=30/group) with polished (15μm) or air-abraded surface were tested under rapid monotonic loading. Additional polished specimens were subjected to cyclic loading at two frequencies, 2Hz (N=44) and 10Hz (N=36), and at various stress amplitudes. All tests were performed using a fully articulated four-point flexure fixture in deionized water at 37°C. The SCG parameters were determined using the ratio of inert strength Weibull modulus to lifetime Weibull modulus. A general log-linear model was fit to the fatigue lifetime data including time to failure, frequency, peak stress, and the product of frequency and logarithm of stress in ALTA PRO software. SCG parameters determined were n=21.7 and A=4.99×10(-5) for 2Hz, and n=19.1 and A=7.39×10(-6) for 10Hz. After fitting the general log-linear model to cyclic fatigue data, the coefficients of the frequency term (α1), the stress term (α2), and the interaction term (α3) had estimates and 95% confidence intervals of α1=-3.16 (-15.1, 6.30), α2=-21.2 (-34.9, -9.73), and α3=0.820 (-1.59, 4.02). Only α2 was significantly different from zero. (1) Cyclic fatigue does not have a significant effect on SCG in the fluorapatite glass-ceramic evaluated and (2) there was no interactive effect between cyclic degradation and stress corrosion for this material. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Erosion and deposition by supercritical density flows during channel avulsion and backfilling: Field examples from coarse-grained deepwater channel-levée complexes (Sandino Forearc Basin, southern Central America)

NASA Astrophysics Data System (ADS)

Lang, Jörg; Brandes, Christian; Winsemann, Jutta

2017-03-01

Erosion and deposition by supercritical density flows can strongly impact the facies distribution and architecture of submarine fans. Field examples from coarse-grained channel-levée complexes from the Sandino Forearc Basin (southern Central America) show that cyclic-step and antidune deposits represent common sedimentary facies of these depositional systems and relate to the different stages of avulsion, bypass, levée construction and channel backfilling. During channel avulsion, large-scale scour-fill complexes (18 to 29 m deep, 18 to 25 m wide, 60 to > 120 m long) were incised by supercritical density flows. The multi-storey infill of the large-scale scour-fill complexes comprises amalgamated massive, normally coarse-tail graded or widely spaced subhorizontally stratified conglomerates and pebbly sandstones, interpreted as deposits of the hydraulic-jump zone of cyclic steps. The large-scale scour-fill complexes can be distinguished from small-scale channel fills based on the preservation of a steep upper margin and a coarse-grained infill comprising mainly amalgamated hydraulic-jump zone deposits. Channel fills include repeated successions deposited by cyclic steps with superimposed antidunes. The deposits of the hydraulic-jump zone of cyclic steps comprise regularly spaced scours (0.2 to 2.6 m deep, 0.8 to 23 m long) infilled by intraclast-rich conglomerates or pebbly sandstones, displaying normal coarse-tail grading or backsets. These deposits are laterally and vertically associated with subhorizontally stratified, low-angle cross-stratified or sinusoidally stratified sandstones and pebbly sandstones, which were deposited by antidunes on the stoss side of the cyclic steps during flow re-acceleration. The field examples indicate that so-called spaced stratified deposits may commonly represent antidune deposits with varying stratification styles controlled by the aggradation rate, grain-size distribution and amalgamation. The deposits of small-scale cyclic steps with superimposed antidunes form fining-upwards successions with decreasing antidune wavelengths, indicating waning flows. Such cyclic step-antidune successions form the characteristic basal infill of mid-fan channels, and are inferred to be related to successive supercritical high-density turbidity flows triggered by retrogressive slope failures.

Detecting dark energy in orbit: The cosmological chameleon

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

Brax, Philippe; Bruck, Carsten van de; Davis, Anne-Christine

2004-12-15

We show that the chameleon scalar field can drive the current phase of cosmic acceleration for a large class of scalar potentials that are also consistent with local tests of gravity. These provide explicit realizations of a quintessence model where the quintessence scalar field couples directly to baryons and dark matter with gravitational strength. We analyze the cosmological evolution of the chameleon field and show the existence of an attractor solution with the chameleon following the minimum of its effective potential. For a wide range of initial conditions, spanning many orders of magnitude in initial chameleon energy density, the attractormore » is reached before nucleosynthesis. Surprisingly, the range of allowed initial conditions leading to a successful cosmology is wider than in normal quintessence. We discuss applications to the cyclic model of the universe and show how the chameleon mechanism weakens some of the constraints on cyclic potentials.« less

Accelerated Thermal Depolymerization of Cyclic Polyphthalaldehyde with a Polymeric Thermoacid Generator.

PubMed

Lopez Hernandez, Hector; Lee, Olivia P; Possanza, Catherine; Kaitz, Joshua A; Park, Chan Woo; Plantz, Christopher L; Moore, Jeffrey S; White, Scott R

2018-04-30

Thermally triggerable polymer films that degrade at modest temperatures (≈85 °C) are created from a blend of cyclic polyphthalaldehyde (cPPA) and a polymeric thermoacid generator, poly(vinyl tert-butyl carbonate sulfone) (PVtBCS). PVtBCS depolymerizes when heated, generating acid which initiates the depolymerization of cPPA into volatile byproducts. The mass loss onset for 2 wt% PVtBCS/cPPA is 22 °C lower than the onset for neat cPPA alone in dynamic thermogravimetric analysis experiments. Increased concentrations of PVtBCS increase the rate of depolymerization of cPPA. Raman spectroscopy reveals that the monomer, o-phthalaldehyde, is the main depolymerization product of the acid-catalyzed depolymerization of cPPA. The PVtBCS/cPPA blend is a promising material for the design and manufacture of transient electronic packaging and polymers. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cyclic adenosine monophosphate levels and the function of skin microvascular endothelial cells.

PubMed

Tuder, R M; Karasek, M A; Bensch, K G

1990-02-01

The maintenance of the normal epithelioid morphology of human dermal microvascular endothelial cells (MEC) grown in vitro depends strongly on the presence of factors that increase intracellular levels of cyclic AMP. Complete removal of dibutyryl cAMP and isobutylmethylxanthine (IMX) from the growth medium results in a progressive transition from an epithelioid to a spindle-shaped cell line. This transition cannot be reversed by the readdition of dibutyryl cAMP and IMX to the growth medium or by addition of agonists that increase cAMP levels. Spindle-shaped MEC lose the ability to express Factor VIII rAG and DR antigens and to bind peripheral blood mononuclear leukocyte (PBML). Ultrastructural analyses of transitional cells and spindle-shaped cells show decreased numbers of Weibel-Palade bodies in transitional cells and their complete absence in spindle-shaped cells. Interferon-gamma alters several functional properties of both epithelioid and spindle-shaped cells. In the absence of dibutyryl cAMP it accelerates the transition from epithelial to spindle-shaped cells, whereas in the presence of cyclic AMP interferon-gamma increases the binding of PBMLs to both epithelioid and spindle-shaped MEC and the endocytic activity of the endothelial cells. These results suggest that cyclic AMP is an important second messenger in the maintenance of several key functions of microvascular endothelial cells. Factors that influence the levels of this messenger in vivo can be expected to influence the angiogenic and immunologic functions of the microvasculature.

Alleviation of whirl-flutter on a joined-wing tilt-rotor aircraft configuration using active controls

NASA Technical Reports Server (NTRS)

Vanaken, Johannes M.

1991-01-01

The feasibility of using active controls to delay the onset of whirl-flutter on a joined-wing tilt rotor aircraft was investigated. The CAMRAD/JA code was used to obtain a set of linear differential equations which describe the motion of the joined-wing tilt-rotor aircraft. The hub motions due to wing/body motion is a standard input to CAMRAD/JA and were obtained from a structural dynamics model of a representative joined-wing tilt-rotor aircraft. The CAMRAD/JA output, consisting of the open-loop system matrices, and the airframe free vibration motion were input to a separate program which performed the closed-loop, active control calculations. An eigenvalue analysis was performed to determine the flutter stability of both open- and closed-loop systems. Sensor models, based upon the feedback of pure state variables and based upon hub-mounted sensors, providing physically measurable accelerations, were evaluated. It was shown that the onset of tilt-rotor whirl-flutter could be delayed from 240 to above 270 knots by feeding back vertical and span-wise accelerations, measured at the rotor hub, to the longitudinal cyclic pitch. Time response calculations at a 270-knot cruise condition showed an active cyclic pitch control level of 0.009 deg, which equates to a very acceptable 9 pound active-control force applied at the rotor hub.

A modified PMMA cement (Sub-cement) for accelerated fatigue testing of cemented implant constructs using cadaveric bone.

PubMed

Race, Amos; Miller, Mark A; Mann, Kenneth A

2008-10-20

Pre-clinical screening of cemented implant systems could be improved by modeling the longer-term response of the implant/cement/bone construct to cyclic loading. We formulated bone cement with degraded fatigue fracture properties (Sub-cement) such that long-term fatigue could be simulated in short-term cadaver tests. Sub-cement was made by adding a chain-transfer agent to standard polymethylmethacrylate (PMMA) cement. This reduced the molecular weight of the inter-bead matrix without changing reaction-rate or handling characteristics. Static mechanical properties were approximately equivalent to normal cement. Over a physiologically reasonable range of stress-intensity factor, fatigue crack propagation rates for Sub-cement were higher by a factor of 25+/-19. When tested in a simplified 2 1/2-D physical model of a stem-cement-bone system, crack growth from the stem was accelerated by a factor of 100. Sub-cement accelerated both crack initiation and growth rate. Sub-cement is now being evaluated in full stem/cement/femur models.

Chloride-induced corrosion of steel in cracked concrete – Part I: Experimental studies under accelerated and natural marine environments

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

Otieno, M., E-mail: Mike.Otieno@wits.ac.za; Beushausen, H.; Alexander, M.

Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in a marine tidal zone. Experimental variables were crack width w{sub cr} (0, incipient crack, 0.4, 0.7 mm), cover c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). Results show that corrosion rate (i{sub corr}) was affected by the experimental variables in the following manner: i{sub corr} increased with increase in crack width, and decreased withmore » increase in concrete quality and cover depth. The results also show that the corrosion performance of concretes in the field under natural corrosion cannot be inferred from its performance in the laboratory under accelerated corrosion. Other factors such as corrosion process should be taken into account.« less

Effect of accelerated aging on the viscoelastic properties of a medical grade silicone.

PubMed

Mahomed, Aziza; Hukins, David W L; Kukureka, Stephen N

2015-01-01

The viscoelastic properties of cylinders (diameter 5 mm, height 2.2 ± 0.2 mm) of Nagor silicone elastomer of medium hardness, were investigated before and after the specimens had undergone accelerated aging in saline solution at 70°C for 38, 76 and 114 days (to simulate aging at 37°C, for 1, 2 and 3 years, respectively). All sets of specimens were immersed in physiological saline solution at 37°C during testing and the properties were measured using dynamic mechanical analysis (DMA). A sinusoidal cyclic compression of 40 N ± 5 N was applied over a frequency range, f, of 0.02-25 Hz. Values of the storage, E', and loss, E″, moduli were found to depend on f; the dependence of E' or E″ on the logarithm (base 10) of f was represented by a second-order polynomial. After accelerated aging, the E' and E″ values did not increase significantly (p<0.05). Furthermore, scanning electron microscopy (SEM) showed that accelerated aging did not affect the surface morphology of silicone. Attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR) showed that accelerated aging had a negligible effect on the surface chemical structures of the material. Differential scanning calorimetry (DSC) showed no changes to the bulk properties of silicone, following accelerated aging.

Partial characterization of the cross-reacting determinant, a carbohydrate epitope shared by decay accelerating factor and the variant surface glycoprotein of the African Trypanosoma brucei.

PubMed

Shak, S; Davitz, M A; Wolinsky, M L; Nussenzweig, V; Turner, M J; Gurnett, A

1988-03-15

The variant surface glycoprotein (VSG) of the African trypanosome is anchored in the cell membrane by a complex glycan attached to phosphatidylinositol. The carboxyl terminal portion of VSG contains a cryptic carbohydrate epitope, the cross-reacting determinant (CRD), that is revealed only after removal of the diacylglycerol by phosphatidylinositol-specific phospholipase C (PIPLC) or VSG lipase. Recently, we have shown that after hydrolysis by PIPLC, decay-accelerating factor (DAF)--a mammalian phosphatidylinositol-anchored protein--also contains the CRD epitope. Using a two site immunoradiometric assay in which the capturing antibody is a monoclonal antibody to DAF and the revealing antibody is anti-CRD, we now show that sugar phosphates significantly inhibited the binding of anti-CRD antibody to DAF released by PIPLC. DL-myo-inositol 1,2-cyclic phosphate was the most potent inhibitor of binding (IC50 less than 10(-8) M). Other sugar phosphates, such as alpha-D-glucose-1-phosphate, which also possess adjacent hydroxyl and phosphate moieties in cis also inhibited binding at low concentrations (IC50 = 10(-5) to 10(-4) M). In contrast, sugar phosphates which do not possess adjacent hydroxyl and phosphate moieties in cis and simple sugars weakly inhibited binding (IC50 greater than 10(-3) M). These results suggest that myo-inositol 1,2-cyclic phosphate contributes significantly to the epitope recognized by the anti-CRD antibody and is consistent with analysis of the carboxyl terminus of VSG, which also suggested the presence of the cyclic inositol phosphate. In light of the recent findings that human serum contains a glycan-phosphatidyl-inositol-specific phospholipase D, which converts DAF from a hydrophobic to a hydrophilic form lacking the CRD, the observation that the phosphate is crucial for expression of the epitope may be relevant in understanding the origin of CRD-negative DAF in urine and plasma.

Surgery accelerates the development of endometriosis in mice.

PubMed

Long, Qiqi; Liu, Xishi; Guo, Sun-Wei

2016-09-01

Surgery is currently the mainstay treatment for solid tumors and many benign diseases, including endometriosis, and women tend to receive substantially more surgeries than men mainly because of gynecological and cosmetic surgeries. Despite its cosmetic, therapeutic, or even life-saving benefits, surgery is reported to increase the cancer risk and promotes cancer metastasis. Surgery activates adrenergic signaling, which in turn suppresses cell-mediated immunity and promotes angiogenesis and metastasis. Because immunity, angiogenesis, and invasiveness are all involved in the pathophysiology of endometriosis, it is unclear whether surgery may accelerate the development of endometriosis. The objective of the study was to test the hypothesis that surgery activates adrenergic signaling, increases angiogenesis, and accelerates the growth of endometriotic lesions. This was a prospective, randomized experimentation. The first experiment used 42 female adult Balb/C mice, and the second used 90 female adult Balb/C mice. In experiment 1, 3 days after the induction of endometriosis, mice were randomly divided into 3 groups of approximately equal sizes, control, laparotomy, and mastectomy. In experiment 2, propranolol infusion via Alzet pumps was used to forestall the effect of sympathetic nervous system activation by surgery. In both experiments, mice were evaluated 2 weeks after surgery. Lesion size, hotplate latency, and immunohistochemistry analysis of vascular endothelial growth factor, CD31-positive microvessels, proliferating cell nuclear antigen, phosphorylated cyclic adenosine monophosphate-responsive element-binding protein, β2-adrenergic receptor (ADRB)-2, ADRB1, ADRB3, ADRA1, and ADRA2 in ectopic implants. Both mastectomy and laparotomy increased lesion weight and exacerbated hyperalgesia, increased microvessel density and elevated the immunoreactivity against ADRB2, phosphorylated cyclic adenosine monophosphate-responsive element-binding protein, vascular endothelial growth factor, and proliferating cell nuclear antigen but not ADRB1, ADRB3, ADRA1, and ADRA2, suggesting activated adrenergic signaling, increased angiogenesis, and accelerated growth of endometriotic lesions. β-Blockade completely abrogated the facilitory effect of surgery, further underscoring the critical role of β-adrenergic signaling in mediating the effect of surgery. Surgery activates adrenergic signaling, increases angiogenesis, and accelerates the growth of endometriotic lesions in the mouse, but such a facilitory effect of surgery can be completely abrogated by β-blockade. Whether surgery can promote the development of endometriosis in humans warrants further investigation. Copyright © 2016 Elsevier Inc. All rights reserved.

Comparison of pore space textural characteristics of natural stone exposed to real weathering environment and/or subjected to accelerated weathering tests: implications for durability assessment

NASA Astrophysics Data System (ADS)

Prikryl, Richard; Weishauptová, Zuzana

2017-04-01

One of the key questions in the debate on durability of natural stone is related to the relevance of accelerated weathering tests for durability assessments, specifically whether similar material responses can be achieved? In the recent study, specimens of opuka stone (extremely fine-grained clayey-calcareous silicite) was subjected to accelerated weathering tests in a climatic chamber (sulphur dioxide atmosphere, freezing/thawing). After completion of certain number of cycles, pore space textural characteristics by means of mercury porosimetry were studied. These data were compared with porosimetric data obtained from a piece of stone, sampled from a carved stone altar located in the interior of the St. Vitus Cathedral (Prague, Czech Republic) which was affected by 150-years lasting indoor decay processes (cyclic themohygric stresses due to variable indoor atmospheric conditions). Interestingly, the pore space textural characteristics of these two sets of specimens are closely related and show some distinct features different from fresh, non-weathered material. Our observation therefore supports relevance of some accelerated weathering simulations; however, conditions of these simulations must be based on parameters of real environment.

JPRS Report, Soviet Union, World Economy & International Relations, No. 12, December 1987

DTIC Science & Technology

1988-05-19

an anti-cyclic way by increasing investments in the years of crisis . The same must be said about the credit and financial system of the 80s and... crisis in the Persian Gulf zone it is largely due to US military activities. The author exposes the true motives of the American activity in the Persian...noting that three components are most visible: the arms race, fraught with global catastrophy, the accelerated ecological crisis caused by the

Liquefaction, ground oscillation, and soil deformation at the Wildlife Array, California

USGS Publications Warehouse

Holzer, T.L.; Youd, T.L.

2007-01-01

Excess pore-water pressure and liquefaction at the Wildlife Liquefaction Array in 1987 were caused by deformation associated with both high-frequency strong ground motion and 5.5-second-period Love waves. The Love waves produced large (???1.5%) cyclic shear strains well after the stronger high-frequency ground motion abated. These cyclic strains generated approximately from 13 to 35% of the excess pore-water pressure in the liquefied layer and caused excess pore-water pressures ultimately to reach effective overburden stress. The deformation associated with the Love waves explains the "postearthquake" increase of pore-water pressure that was recorded at the array. This explanation suggests that conventional methods for predicting liquefaction based on peak ground acceleration are incomplete and may need to consider cyclic strains associated with long-period surface waves. A post-earthquake survey of an inclinometer casing indicated permanent shear strain associated with lateral spreading primarily occurred in the upper part of the liquefied layer. Comparison of cone penetration test soundings conducted after the earthquake with pre-earthquake soundings suggests sleeve friction increased. Natural lateral variability of the liquefied layer obscured changes in tip resistance despite a ???1% reduction in volume. The large oscillatory motion associated with surface waves explains ground oscillation that has been reported at some liquefaction sites during earthquakes.

Reaction time in pilots during intervals of high sustained g.

PubMed

Truszczynski, Olaf; Lewkowicz, Rafal; Wojtkowiak, Mieczyslaw; Biernacki, Marcin P

2014-11-01

An important problem for pilots is visual disturbances occurring under +Gz acceleration. Assessment of the degree of intensification of these disturbances is generally accepted as the acceleration tolerance level (ATL) criterion determined in human centrifuges. The aim of this research was to evaluate the visual-motor responses of pilots during rapidly increasing acceleration contained in cyclic intervals of +6 Gz to the maximum ATL. The study involved 40 male pilots ages 32-41 yr. The task was a quick and faultless response to the light stimuli presented on a light bar during exposure to acceleration until reaching the ATL. Simple response time (SRT) measurements were performed using a visual-motor analysis system throughout the exposures which allowed assessment of a pilot's ATL. There were 29 pilots who tolerated the initial phase of interval acceleration and achieved +6 Gz, completing the test at ATL. Relative to the control measurements, the obtained results indicate a significant effect of the applied acceleration on response time. SRT during +6 Gz exposure was not significantly longer compared with the reaction time between each of the intervals. SRT and erroneous reactions indicated no statistically significant differences between the "lower" and "higher" ATL groups. SRT measurements over the +6-Gz exposure intervals did not vary between "lower" and "higher" ATL groups and, therefore, are not useful in predicting pilot performance. The gradual exposure to the maximum value of +6 Gz with exposure to the first three intervals on the +6-Gz plateau effectively differentiated pilots.

Centripetal Acceleration Reaction: An Effective and Robust Mechanism for Flapping Flight in Insects

PubMed Central

Zhang, Chao; Hedrick, Tyson L.; Mittal, Rajat

2015-01-01

Despite intense study by physicists and biologists, we do not fully understand the unsteady aerodynamics that relate insect wing morphology and kinematics to lift generation. Here, we formulate a force partitioning method (FPM) and implement it within a computational fluid dynamic model to provide an unambiguous and physically insightful division of aerodynamic force into components associated with wing kinematics, vorticity, and viscosity. Application of the FPM to hawkmoth and fruit fly flight shows that the leading-edge vortex is the dominant mechanism for lift generation for both these insects and contributes between 72–85% of the net lift. However, there is another, previously unidentified mechanism, the centripetal acceleration reaction, which generates up to 17% of the net lift. The centripetal acceleration reaction is similar to the classical inviscid added-mass in that it depends only on the kinematics (i.e. accelerations) of the body, but is different in that it requires the satisfaction of the no-slip condition, and a combination of tangential motion and rotation of the wing surface. Furthermore, the classical added-mass force is identically zero for cyclic motion but this is not true of the centripetal acceleration reaction. Furthermore, unlike the lift due to vorticity, centripetal acceleration reaction lift is insensitive to Reynolds number and to environmental flow perturbations, making it an important contributor to insect flight stability and miniaturization. This force mechanism also has broad implications for flow-induced deformation and vibration, underwater locomotion and flows involving bubbles and droplets. PMID:26252016

Centripetal Acceleration Reaction: An Effective and Robust Mechanism for Flapping Flight in Insects.

PubMed

Zhang, Chao; Hedrick, Tyson L; Mittal, Rajat

2015-01-01

Despite intense study by physicists and biologists, we do not fully understand the unsteady aerodynamics that relate insect wing morphology and kinematics to lift generation. Here, we formulate a force partitioning method (FPM) and implement it within a computational fluid dynamic model to provide an unambiguous and physically insightful division of aerodynamic force into components associated with wing kinematics, vorticity, and viscosity. Application of the FPM to hawkmoth and fruit fly flight shows that the leading-edge vortex is the dominant mechanism for lift generation for both these insects and contributes between 72-85% of the net lift. However, there is another, previously unidentified mechanism, the centripetal acceleration reaction, which generates up to 17% of the net lift. The centripetal acceleration reaction is similar to the classical inviscid added-mass in that it depends only on the kinematics (i.e. accelerations) of the body, but is different in that it requires the satisfaction of the no-slip condition, and a combination of tangential motion and rotation of the wing surface. Furthermore, the classical added-mass force is identically zero for cyclic motion but this is not true of the centripetal acceleration reaction. Furthermore, unlike the lift due to vorticity, centripetal acceleration reaction lift is insensitive to Reynolds number and to environmental flow perturbations, making it an important contributor to insect flight stability and miniaturization. This force mechanism also has broad implications for flow-induced deformation and vibration, underwater locomotion and flows involving bubbles and droplets.

Long-term cilostazol administration ameliorates memory decline in senescence-accelerated mouse prone 8 (SAMP8) through a dual effect on cAMP and blood-brain barrier.

PubMed

Yanai, Shuichi; Toyohara, Jun; Ishiwata, Kiichi; Ito, Hideki; Endo, Shogo

2017-04-01

Phosphodiesterases (PDEs), which hydrolyze and inactivate 3', 5'-cyclic adenosine monophosphate (cAMP) and 3', 5'-cyclic guanosine monophosphate (cGMP), play an important role in synaptic plasticity that underlies memory. Recently, several PDE inhibitors were assessed for their possible therapeutic efficacy in treating cognitive disorders. Here, we examined how cilostazol, a selective PDE3 inhibitor, affects brain functions in senescence-accelerated mouse prone 8 (SAMP8), an animal model of age-related cognitive impairment. Long-term administration of cilostazol restored the impaired context-dependent conditioned fear memory of SAMP8 to match that in normal aging control substrain SAMR1. Cilostazol also increased the number of cells containing phosphorylated cAMP-responsive element binding protein (CREB), a downstream component of the cAMP pathway. Finally, cilostazol improves blood-brain barrier (BBB) integrity, demonstrated by reduced extravasation of 2-deoxy-2- 18 F-fluoro-d-glucose and Evans Blue dye in the brains of SAMP8. This improvement in BBB integrity was associated with an increased amount of zona occludens protein 1 (ZO-1) and occludin proteins, components of tight junctions integral to the BBB. The results suggest that long-term administration of cilostazol exerts its beneficial effects on age-related cognitive impairment through a dual mechanism: by enhancing the cAMP system in the brain and by maintaining or improving BBB integrity. Copyright © 2016 Elsevier Ltd. All rights reserved.

C-field cosmological models: revisited

NASA Astrophysics Data System (ADS)

Yadav, Anil Kumar; Tawfiq Ali, Ahmad; Ray, Saibal; Rahaman, Farook; Hossain Sardar, Iftikar

2016-12-01

We investigate plane symmetric spacetime filled with perfect fluid in the C-field cosmology of Hoyle and Narlikar. A new class of exact solutions has been obtained by considering the creation field C as a function of time only. To get the deterministic solution, it has been assumed that the rate of creation of matter-energy density is proportional to the strength of the existing C-field energy density. Several physical aspects and geometrical properties of the models are discussed in detail, especially showing that some of our solutions of C-field cosmology are free from singularity in contrast to the Big Bang cosmology. A comparative study has been carried out between two models, one singular and the other nonsingular, by contrasting the behaviour of the physical parameters. We note that the model in a unique way represents both the features of the accelerating as well as decelerating universe depending on the parameters and thus seems to provide glimpses of the oscillating or cyclic model of the universe without invoking any other agent or theory in allowing cyclicity.

Mechanistic understanding of surface plasmon assisted catalysis on a single particle: cyclic redox of 4-aminothiophenol

DOE PAGES

Xu, Ping; Kang, Leilei; Mack, Nathan H.; ...

2013-10-21

We investigate surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,4'-dimercaptoazobenzene (DMAB) by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by energy transfer (plasmonic heating) from surface plasmon resonance to 4ATP, where O 2 (as an electron acceptor) is essential and H 2O (as a base) can accelerate the reaction. In contrast, hot electron (from surface plasmon decay) induction drives the reverse reaction of DMAB to 4ATP, where H 2O (or H 2) acts asmore » the hydrogen source. More interestingly, the cyclic redox between 4ATP and DMAB by SPAC approach has been demonstrated. Finally, this SPAC methodology presents a unique platform for studying chemical reactions that are not possible under standard synthetic conditions.« less

High-Heat-Flux Cyclic Durability of Thermal and Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Ghosn, Louis L.; Miller, Robert A.

2007-01-01

Advanced ceramic thermal and environmental barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to protect the engine components and further raise engine temperatures. For the supersonic vehicles currently envisioned in the NASA fundamental aeronautics program, advanced gas turbine engines will be used to provide high power density thrust during the extended supersonic flight of the aircraft, while meeting stringent low emission requirements. Advanced ceramic coating systems are critical to the performance, life and durability of the hot-section components of the engine systems. In this work, the laser and burner rig based high-heat-flux testing approaches were developed to investigate the coating cyclic response and failure mechanisms under simulated supersonic long-duration cruise mission. The accelerated coating cracking and delamination mechanism under the engine high-heat-flux, and extended supersonic cruise time conditions will be addressed. A coating life prediction framework may be realized by examining the crack initiation and propagation in conjunction with environmental degradation under high-heat-flux test conditions.

Study to eliminate ground resonance using active controls

NASA Technical Reports Server (NTRS)

Straub, F. K.

1984-01-01

The effectiveness of active control blade feathering in increasing rotor body damping and the possibility to eliminate ground resonance instabilities were investigated. An analytical model representing rotor flapping and lead-lag degrees of freedom and body pitch, roll, longitudinal and lateral motion is developed. Active control blade feathering is implemented as state variable feedback through a conventional swashplate. The influence of various feedback states, feedback gain, and weighting between the cyclic controls is studied through stability and response analyses. It is shown that blade cyclic inplane motion, roll rate and roll acceleration feedback can add considerable damping to the system and eliminate ground resonance instabilities, which the feedback phase is also a powerful parameter, if chosen properly, it maximizes augmentation of the inherent regressing lag mode damping. It is shown that rotor configuration parameters, like blade root hinge offset, flapping stiffness, and precone considerably influence the control effectiveness. It is found that active control is particularly powerful for hingeless and bearingless rotor systems.

Effect of moisture on the fatigue behavior of graphite/epoxy composite laminates

NASA Technical Reports Server (NTRS)

Ramani, S. V.; Nelson, H. G.

1979-01-01

The form of the moisture distribution in the specimen (gradient and flat profile) was considered to establish the influence of accelerated moisture conditioning on fatigue behavior. For the gradient specimens having an average moisture content of 1.4 percent, fatigue life was reduced by a factor of 8 at all stress levels investigated. Corresponding reduction in fatigue life for the flat moisture profile specimens at the same average moisture content was comparatively smaller, being about a factor of 5 from the value in dry specimens. X-ray radiographic analysis of damage accumulation in compression-compression fatigue revealed interlaminar cracking to be the dominant mode of failure responsible for the observed enhanced cyclic degradation of moisture-conditioned specimens. This finding was corroborated by the observed systematic reduction in interlaminar shear strength as a function of moisture content, which, in turn, increased the propensity for delamination under cyclic compressive loads. Residual strength measurements on cycled specimens indicated significant strength reductions at long lives, particularly in moisture conditioned specimens.

Analysis on weathering characteristics of volcanic rocks in Dokdo, Korea based on accelerated weatehring experiments

NASA Astrophysics Data System (ADS)

Woo, Ik; Song, Won-Kyong; Kim, Bok-Chul; Kang, Jinseok

2010-05-01

Dokdo consists of small volcanic islands located in the southern part of the East Sea. Accelerated weathering tests was performed to examine the physico-mechanical characteristics of volcanic rocks in Dokdo. Rock core specimens of trachyandesite, andesitic dyke and ash tuff were prepared, and double soxhlet extractors(DSE) and peristatic pumps were used for accelerating the weathering processes. The DSE was designed to perform cyclic leaching tests for rock core specimen using distilled water at seventy degrees centigrade. The core specimens which are classified according to pre-test weathering grades placed in the lower part of the DSE, and periodically exposed to hot distilled water at every ninety minutes. On the other hand the peristatic pumps were utilized to induce leaching by distilled or brine water at normal temperature. The physico-mechanical property changes including rock surface appearance, microscopic structure and rock strength were analyzed with the results obtained from both experiments performed for 120 days. The conducted research in this study have shown that the methodologies of artificial weathering experiments have strong capability to understand the weathering characteristics of the rocks effectively.

Cyclic-glycine-proline accelerates mammary involution by promoting apoptosis and inhibiting IGF-1 function.

PubMed

Singh-Mallah, Gagandeep; McMahon, Christopher D; Guan, Jian; Singh, Kuljeet

2017-12-01

In rodents, post-lactational involution of mammary glands is characterized by the loss of mammary epithelial cells via apoptosis, which is associated with a decline in the expression of insulin-like growth factor-1 (IGF-1). Overexpression of IGF-1 delays involution by inhibiting apoptosis of epithelial cells and preserving the remaining secretory alveoli. Cyclic-glycine-proline (cGP), a metabolite of IGF-1, normalizes IGF-1 function under pathological conditions by regulating the bioavailability of IGF-1. The present study investigated the effect of cGP on the physiological decline in IGF-1 function during post-lactational mammary involution. Rat dams were gavaged with either cGP (3 mg/kg) or saline once per day from post-natal d8-22. Before collecting tissue on post-natal d23, a pair of mammary glands were sealed on d20 (72 hr-engorgement, thus representative of late-involution) and d22 (24 hr-engorgement, thus representative of mid-involution), while the remaining glands were allowed to involute naturally (early-involution). During early-involution, cGP accelerated the loss of mammary cells through apoptosis, resulting in an earlier clearance of intact secretory alveoli compared with the control group. This coincided with an earlier up-regulation of the cell survival factors, Bcl-xl and IGF-1R, in the early-involution cGP glands compared with the control glands. During late-involution, cGP reduced the bioactivity of IGF-1, which was evident through decreased phosphorylation of IGF-1R in the regressed alveoli. Maternal administration of cGP did not alter milk production and composition during early-, peak-, or late-stage of lactation. These data show that cGP accelerates post-lactational involution by promoting apoptosis and the physiological decline in IGF-1 function. © 2017 Wiley Periodicals, Inc.

The Assessing of the Failure Behavior of Glass/Polyester Composites Subject to Quasi Static Stresses

NASA Astrophysics Data System (ADS)

Stanciu, M. D.; Savin, A.; Teodorescu-Drăghicescu, H.

2017-06-01

Using glass fabric reinforced composites for structure of wind turbine blades requires high mechanical strengths especially to cyclic stresses. Studies have shown that approximately 50% of composite material failure occurs because of fatigue. Composites behavior to cyclic stresses involves three stages regarding to stiffness variation: the first stage is characterized by the accelerated decline of stiffness with micro-cracks, the second stage - a slight decrease of stiffness characterized by the occurrence of delamination and third stage characterized by higher decreases of resistance and occurrence of fracture thereof. The aim of the paper is to analyzed the behavior of composites reinforced with glass fibers fabric type RT500 and polyester resin subjected to tensile cyclic loading with pulsating quasi-static regime with asymmetry coefficient R = 0. The samples were tested with the universal tensile machine LS100 Lloyd Instruments Plus, with a load capacity of 100 kN. The load was applied with different speeds of 1 mm/min, 10 mm/min and 20 mm/min. After tests, it was observed that the greatest permanent strains were recorded in the first load cycles when the total energy storage by material was lost due to internal friction. With increasing number of cycles, the glass/polyester composites ability to store energy of deformation decreases, the flow phenomenon characterized by large displacements to smaller loading forces appearing.

Cyclic oxidation behavior of some plasma-sprayed coatings in Na2SO4-60%V2O5 environment

NASA Astrophysics Data System (ADS)

Singh, Harpreet; Prakash, Satya; Puri, Devendra; Phase, D. M.

2006-12-01

Cyclic oxidation behavior of plasma-sprayed NiCrAlY, Ni-20Cr, Ni3Al, and Stellite-6 coatings was investigated in an aggressive environment of Na2SO4-60%V2O5 by thermogravimetric techniques for 50 cycles. These coatings were deposited on a Ni-base superalloy, namely Superni 600; 10Fe-15.5Cr-0.5Mn-0.2C-Bal Ni (wt.%). X-ray diffraction, scanning electron microscopy/energy dispersive x-ray (SEM/EDX), and electron probe microanalyzer (EPMA) techniques were used to analyze the oxidation products. The uncoated superalloy suffered accelerated oxidation in the form of intense spallation of its oxide scale. After deposition of the NiCrAlY coating, the superalloy showed a minimum mass gain, whereas after application of the Stellite-6 coating, a maximum mass gain was observed among the coatings studied. All of the coatings were found to be useful in reducing the spallation of the substrate superalloy. Moreover, the coatings were successful in maintaining continuous surface contact with the base superalloy during the cyclic oxidation. The phases revealed for the oxidized coatings were mainly the oxides of chromium and/or aluminum and the spinels containing nickel-chromium/cobalt-chromium/nickel-aluminum mixed oxides, which are reported to be protective against high-temperature oxidation/hot corrosion.

High-frequency ground motion amplification during the 2011 Tohoku earthquake explained by soil dilatancy

NASA Astrophysics Data System (ADS)

Roten, D.; Fäh, D.; Bonilla, L. F.

2013-05-01

Ground motions of the 2011 Tohoku earthquake recorded at Onahama port (Iwaki, Fukushima prefecture) rank among the highest accelerations ever observed, with the peak amplitude of the 3-D acceleration vector approaching 2g. The response of the site was distinctively non-linear, as indicated by the presence of horizontal acceleration spikes which have been linked to cyclic mobility during similar observations. Compared to records of weak ground motions, the response of the site during the Mw 9.1 earthquake was characterized by increased amplification at frequencies above 10 Hz and in peak ground acceleration. This behaviour contrasts with the more common non-linear response encountered at non-liquefiable sites, which results in deamplification at higher frequencies. We simulate propagation of SH waves through the dense sand deposit using a non-linear finite difference code that is capable of modelling the development of excess pore water pressure. Dynamic soil parameters are calibrated using a direct search method that minimizes the difference between observed and simulated acceleration envelopes and response spectra. The finite difference simulations yield surface acceleration time-series that are consistent with the observations in shape and amplitude, pointing towards soil dilatancy as a likely explanation for the high-frequency pulses recorded at Onahama port. The simulations also suggest that the occurrence of high-frequency spikes coincided with a rapid increase in pore water pressure in the upper part of the sand deposit between 145 and 170 s. This sudden increase is possibly linked to a burst of high-frequency energy from a large slip patch below the Iwaki region.

High-gradient low-β accelerating structure using the first negative spatial harmonic of the fundamental mode

NASA Astrophysics Data System (ADS)

Kutsaev, Sergey V.; Agustsson, Ronald; Boucher, Salime; Fischer, Richard; Murokh, Alex; Mustapha, Brahim; Nassiri, Alireza; Ostroumov, Peter N.; Plastun, Alexander; Savin, Evgeny; Smirnov, Alexander Yu.

2017-12-01

The development of high-gradient accelerating structures for low-β particles is the key for compact hadron linear accelerators. A particular example of such a machine is a hadron therapy linac, which is a promising alternative to cyclic machines, traditionally used for cancer treatment. Currently, the practical utilization of linear accelerators in radiation therapy is limited by the requirement to be under 50 m in length. A usable device for cancer therapy should produce 200-250 MeV protons and/or 400 - 450 MeV /u carbon ions, which sets the requirement of having 35 MV /m average "real-estate gradient" or gradient per unit of actual accelerator length, including different accelerating sections, focusing elements and beam transport lines, and at least 50 MV /m accelerating gradients in the high-energy section of the linac. Such high accelerating gradients for ion linacs have recently become feasible for operations at S-band frequencies. However, the reasonable application of traditional S-band structures is practically limited to β =v /c >0.4 . However, the simulations show that for lower phase velocities, these structures have either high surface fields (>200 MV /m ) or low shunt impedances (<35 M Ω /m ). At the same time, a significant (˜10 % ) reduction in the linac length can be achieved by using the 50 MV /m structures starting from β ˜0.3 . To address this issue, we have designed a novel radio frequency structure where the beam is synchronous with the higher spatial harmonic of the electromagnetic field. In this paper, we discuss the principles of this approach, the related beam dynamics and especially the electromagnetic and thermomechanical designs of this novel structure. Besides the application to ion therapy, the technology described in this paper can be applied to future high gradient normal conducting ion linacs and high energy physics machines, such as a compact hadron collider. This approach preserves linac compactness in settings with limited space availability.

Simulation of long-term fatigue damage in bioprosthetic heart valves: effects of leaflet and stent elastic properties

PubMed Central

Martin, Caitlin

2014-01-01

One of the major failure modes of bioprosthetic heart valves (BHVs) is noncalcific structural deterioration due to fatigue of the tissue leaflets; yet, the mechanisms of fatigue are not well understood. BHV durability is primarily assessed based on visual inspection of the leaflets following accelerated wear testing. In this study, we developed a computational framework to simulate BHV leaflet fatigue, which is both efficient and quantitative, making it an attractive alternative to traditional accelerated wear testing. We utilize a phenomenological soft tissue fatigue damage model developed previously to describe the stress softening and permanent set of the glutaraldehyde-treated bovine pericardium leaflets in BHVs subjected to cyclic loading. A parametric study was conducted to determine the effects of altered leaflet and stent elastic properties on the fatigue of the leaflets. The simulation results show that heterogeneity of the leaflet elastic properties, poor leaflet coaptation, and little stent-tip deflection may accelerate leaflet fatigue, which agrees with clinical findings. Therefore, the developed framework may be an invaluable tool for evaluating leaflet durability in new tissue valve designs, including traditional BHVs as well as new transcatheter valves. PMID:24092257

Influence of antimycin A and uncouplers on anaerobic photosynthesis in isolated chloroplasts

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

Slovacek, R.E.; Hind, G.

1977-10-01

Anaerobiosis depresses the light- and bicarbonate-saturated rates of O/sub 2/ evolution in intact spinach (Spinacia oleracea) chloroplasts by as much as 3-fold from those observed under aerobic conditions. These lower rates are accelerated 2-fold or more by the addition of 1 ..mu..m antimycin A or by low concentrations of the uncouplers 0.3 mM NH/sub 4/Cl or 0.25 ..mu..m carbonyl cyanide m-chlorophenylhydrazone. Oxaloacetate and glycerate 3-phosphate reduction rates are also increased by antimycin A or an uncoupler under anaerobic conditions. At intermediate light intensities, the rate accelerations by either antimycin A or uncoupler are inversely proportional to the adenosine 5'-triphosphate demandmore » of the reduction process for the acceptors HCO/sub 3//sup -/, glycerate 3-phosphate, and oxaloacetate. The acceleration of bicarbonate-supported O/sub 2/ evolution may also be produced by adding an adenosine 5'-triphosphate sink (ribose 5-phosphate) to anaerobic chloroplasts. The above results suggest that a proton gradient back pressure resulting from antimycin A-sensitive cyclic electron flow is responsible for the depression of light-saturated photosynthesis under anaerobiosis.« less

Grain boundary oxidation and fatigue crack growth at elevated temperatures

NASA Technical Reports Server (NTRS)

Liu, H. W.; Oshida, Y.

1986-01-01

Fatigue crack growth rate at elevated temperatures can be accelerated by grain boundary oxidation. Grain boundary oxidation kinetics and the statistical distribution of grain boundary oxide penetration depth were studied. At a constant delta K-level and at a constant test temperature, fatigue crack growth rate, da/dN, is a function of cyclic frequency, nu. A fatigue crack growth model of intermittent micro-ruptures of grain boundary oxide is constructed. The model is consistent with the experimental observations that, in the low frequency region, da/dN is inversely proportional to nu, and fatigue crack growth is intergranular.

Hierarchically porous carbon derived from banana peel for lithium sulfur battery with high areal and gravimetric sulfur loading

NASA Astrophysics Data System (ADS)

Li, Fanqun; Qin, Furong; Zhang, Kai; Fang, Jing; Lai, Yanqing; Li, Jie

2017-09-01

Facile and sustainable route is developed to convert biomass into hierarchically porous carbon matrix cooperating with highly conductive graphene. By tailoring the porosity of the carbon matrix to promote fast mass transfer and cooperating highly conductive interconnected graphene frameworks to accelerate the electron transport, the carbon sulfur cathodes simultaneously achieve high areal and gravimetric sulfur loading/content (6 mg cm-2/67 wt%) and deliver outstanding electrochemical performance. After 100 cyclic discharge-charge test at the current density of 0.2 C, the reversible capacity maintains at 707 mA h g-1.

Changes in the Earth's largest surge glacier system from satellite and airborne altimetry and imagery

NASA Astrophysics Data System (ADS)

Trantow, T.; Herzfeld, U. C.

2015-12-01

The Bering-Bagley Glacier System (BBGS), Alaska, one of the largest ice systems outside of Greenland and Antarctica, has recently surged (2011-2013), providing a rare opportunity to study the surge phenomenon in a large and complex system. Understanding fast-flowing glaciers and accelerations in ice flow, of which surging is one type, is critical to understanding changes in the cryosphere and ultimately changes in sea level. It is important to distinguish between types of accelerations and their consequences, especially between reversible or quasi-cyclic and irreversible forms of glacial acceleration, but current icesheet models treat all accelerating ice identically. Additionally, the surge provides an exceptional opportunity to study the influence of surface roughness and water content on return signals of altimeter systems. In this presentation, we analyze radar and laser altimeter data from CryoSat-2, NASA's Operation IceBridge (OIB), the ICESat Geoscience Laser Altimeter System (GLAS), ICESat-2's predecessor the Multiple Altimeter Beam Experimental Lidar (MABEL), and airborne laser altimeter and imagery campaigns by our research group. These measurements are used to study elevation, elevation change and crevassing throughout the glacier system. Analysis of the imagery from our airborne campaigns provides comprehensive characterizations of the BBGS surface over the course of the surge. Results from the data analysis are compared to numerical modeling experiments.

Creep-Fatigue Relationsihps in Electroactive Polymer Systems and Predicted Effects in an Actuator Design

NASA Technical Reports Server (NTRS)

Vinogradov, Aleksandra M.; Ihlefeld, Curtis M.; Henslee, Issac

2009-01-01

The paper concerns the time-dependent behavior of electroactive polymers (EAP) and their use in advanced intelligent structures for space exploration. Innovative actuator design for low weight and low power valves required in small plants planned for use on the moon for chemical analysis is discussed. It is shown that in-depth understanding of cyclic loading effects observed through accelerated creep rates due to creep-fatigue interaction in polymers is critical in terms of proper functioning of EAP based actuator devices. In the paper, an overview of experimental results concerning the creep properties and cyclic creep response of a thin film piezoelectric polymer polyvinylidene fluoride (PVDF) is presented. The development of a constitutive creep-fatigue interaction model to predict the durability and service life of electroactive polymers is discussed. A novel method is proposed to predict damage accumulation and fatigue life of polymers under oyclic loading conditions in the presence of creep. The study provides a basis for ongoing research initiatives at the NASA Kennedy Space Center in the pursuit of new technologies using EAP as active elements for lunar exploration systems.

Gum formation tendencies of olefinic structures in gasoline and synergistic effect of sulphur compounds

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

Nagpal, J.M.; Joshi, G.C.; Aswal, D.S.

1995-04-01

The high octane gasoline pool contains varying amounts of cracked naphthas as an important ingredient in formulating high octane lead free gasoline. The cracked naphthas are largely from Fluidized Catalytic Cracking (FCC) units and to lesser extend from thermal cracking units. While the role of olefinic unsaturation in gum formation during storage of gasoline has been extensively studied, there is little published work on contribution of individual olefin types in storage stability and gum formation tendency of gasoline containing these compound types. In the present work we report our results on storage stability and gum formation tendency of different olefinmore » types present in cracked naphthas through model compound matrix. It is found that cyclic olefins and cyclic diolefins are the most prolific gum formers. We have also studied the role of sulfur compounds present in the gasolines on gum formation tendency of olefins. While thiols enhance gum formation from all olefinic types, sulfides and disulfides interact depending on the structure of olefins. These can have either an accelerating, or inhibiting effect on gum formation.« less

Saliva and wound healing.

PubMed

Brand, Henk S; Ligtenberg, Antoon J M; Veerman, Enno C I

2014-01-01

Oral wounds heal faster and with less scar formation than skin wounds. One of the key factors involved is saliva, which promotes wound healing in several ways. Saliva creates a humid environment, thus improving the survival and functioning of inflammatory cells that are crucial for wound healing. In addition, saliva contains several proteins which play a role in the different stages of wound healing. Saliva contains substantial amounts of tissue factor, which dramatically accelerates blood clotting. Subsequently, epidermal growth factor in saliva promotes the proliferation of epithelial cells. Secretory leucocyte protease inhibitor inhibits the tissue-degrading activity of enzymes like elastase and trypsin. Absence of this protease inhibitor delays oral wound healing. Salivary histatins in vitro promote wound closure by enhancing cell spreading and cell migration, but do not stimulate cell proliferation. A synthetic cyclic variant of histatin exhibits a 1,000-fold higher activity than linear histatin, which makes this cyclic variant a promising agent for the development of a new wound healing medication. Conclusively, recognition of the many roles salivary proteins play in wound healing makes saliva a promising source for the development of new drugs involved in tissue regeneration.

Modeling of a viscoelastic damper and its application in structural control.

PubMed

Mehrabi, M H; Suhatril, Meldi; Ibrahim, Zainah; Ghodsi, S S; Khatibi, Hamed

2017-01-01

Conventional seismic rehabilitation methods may not be suitable for some buildings owing to their high cost and time-consuming foundation work. In recent years, viscoelastic dampers (VEDs) have been widely used in many mid- and high-rise buildings. This study introduces a viscoelastic passive control system called rotary rubber braced damper (RRBD). The RRBD is an economical, lightweight, and easy-to-assemble device. A finite element model considering nonlinearity, large deformation, and material damage is developed to conduct a parametric study on different damper sizes under pushover cyclic loading. The fundamental characteristics of this VED system are clarified by analyzing building structures under cyclic loading. The result show excellent energy absorption and stable hysteresis loops in all specimens. Additionally, by using a sinusoidal shaking table test, the effectiveness of the RRBD to manage the response displacement and acceleration of steel frames is considered. The RRBD functioned at early stages of lateral displacement, indicating that the system is effective for all levels of vibration. Moreover, the proposed damper shows significantly better performance in terms of the column compression force resulting from the brace action compared to chevron bracing (CB).

Successful completion of a cyclic ground test of a mercury ion auxiliary propulsion system

NASA Technical Reports Server (NTRS)

Francisco, David R.; Low, Charles A., Jr.; Power, John L.

1988-01-01

An engineering model Ion Auxiliary Propulsion System (IAPS) 8-cm thruster (S/N 905) has completed a life test at NASA Lewis Research Center. The mercury ion thruster successfully completed and exceeded the test goals of 2557 on/off cycles and 7057 hr of operation at full thrust. The final 1200 cycles and 3600 hr of the life test were conducted using an engineering model of the IAPS power electronics unit (PEU) and breadboard digital controller and interface unit (DCIU). This portion of the test is described in this paper with a charted history of thruster operating parameters and off-normal events. Performance and operating characteristics were constant throughout the test with only minor variations. The engineering model power electronics unit operated without malfunction; the flight software in the digital controller and interface unit was exercised and verified. Post-test inspection of the thruster revealed facility enhanced accelerator grid erosion but overall the thruster was in good condition. It was concluded that the thruster performance was not drastically degraded by time or cycles. Additional cyclic testing is currently under consideration.

Successful completion of a cyclic ground test of a mercury Ion Auxiliary Propulsion System

NASA Technical Reports Server (NTRS)

Francisco, David R.; Low, Charles A., Jr.; Power, John L.

1988-01-01

An engineering model Ion Auxiliary Propulsion System (IAPS) 8-cm thruster (S/N 905) has completed a life test at NASA Lewis Research Center. The mercury ion thruster successfully completed and exceeded the test goals of 2557 on/off cycles and 7057 hr of operation at full thrust. The final 1200 cycles and 3600 hr of the life test were conducted using an engineering model of the IAPS power electronics unit (PEU) and breadboard digital controller and interface unit (DCIU). This portion of the test is described in this paper with a charted history of thruster operating parameters and off-normal events. Performance and operating characteristics were constant throughout the test with only minor variations. The engineering model power electronics unit operated without malfunction; the flight software in the digital controller and interface unit was exercised and verified. Post-test inspection of the thruster revealed facility enhanced accelerator grid erosion but overall the thruster was in good condition. It was concluded that the thruster performance was not drastically degraded by time or cycles. Additional cyclic testing is currently under consideration.

Mechanical degradation of fuel cell membranes under fatigue fracture tests

NASA Astrophysics Data System (ADS)

Khorasany, Ramin M. H.; Sadeghi Alavijeh, Alireza; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

2015-01-01

The effects of cyclic stresses on the fatigue and mechanical stability of perfluorosulfonic acid (PFSA) membranes are experimentally investigated under standard fuel cell conditions. The experiments are conducted ex-situ by subjecting membrane specimens to cyclic uniaxial tension at controlled temperature and relative humidity. The fatigue lifetime is measured in terms of the number of cycles until ultimate fracture. The results indicate that the membrane fatigue lifetime is a strong function of the applied stress, temperature, and relative humidity. The fatigue life increases exponentially with reduced stresses in all cases. The effect of temperature is found to be more significant than that of humidity, with reduced fatigue life at high temperatures. The maximum membrane strain at fracture is determined to decrease exponentially with increasing membrane lifetime. At a given fatigue life, a membrane exposed to fuel cell conditions is shown to accommodate more plastic strain before fracture than one exposed to room conditions. Overall, the proposed ex-situ membrane fatigue experiment can be utilized to benchmark the fatigue lifetime of new materials in a fraction of the time and cost associated with conventional in-situ accelerated stress testing methods.

Accelerated crack growth, residual stress, and a cracked zinc coated pressure shell

NASA Technical Reports Server (NTRS)

Dittman, Daniel L.; Hampton, Roy W.; Nelson, Howard G.

1987-01-01

During a partial inspection of a 42 year old, operating, pressurized wind tunnel at NASA-Ames Research Center, a surface connected defect 114 in. long having an indicated depth of a 0.7 in. was detected. The pressure shell, constructed of a medium carbon steel, contains approximately 10 miles of welds and is cooled by flowing water over its zinc coated external surface. Metallurgical and fractographic analysis showed that the actual detect was 1.7 in. deep, and originated from an area of lack of weld penetration. Crack growth studies were performed on the shell material in the laboratory under various loading rates, hold times, and R-ratios with a simulated shell environment. The combination of zinc, water with electrolyte, and steel formed an electrolytic cell which resulted in an increase in cyclic crack growth rate by as much as 500 times over that observed in air. It was concluded that slow crack growth occurred in the pressure shell by a combination of stress corrosion cracking due to the welding residual stress and corrosion fatigue due to the cyclic operating stress.

Cyclic Game Dynamics Driven by Iterated Reasoning

PubMed Central

Frey, Seth; Goldstone, Robert L.

2013-01-01

Recent theories from complexity science argue that complex dynamics are ubiquitous in social and economic systems. These claims emerge from the analysis of individually simple agents whose collective behavior is surprisingly complicated. However, economists have argued that iterated reasoning–what you think I think you think–will suppress complex dynamics by stabilizing or accelerating convergence to Nash equilibrium. We report stable and efficient periodic behavior in human groups playing the Mod Game, a multi-player game similar to Rock-Paper-Scissors. The game rewards subjects for thinking exactly one step ahead of others in their group. Groups that play this game exhibit cycles that are inconsistent with any fixed-point solution concept. These cycles are driven by a “hopping” behavior that is consistent with other accounts of iterated reasoning: agents are constrained to about two steps of iterated reasoning and learn an additional one-half step with each session. If higher-order reasoning can be complicit in complex emergent dynamics, then cyclic and chaotic patterns may be endogenous features of real-world social and economic systems. PMID:23441191

Discrete Dislocation Modeling of Fatigue

NASA Astrophysics Data System (ADS)

Needleman, Alan

2004-03-01

In joint work with V.S. Deshpande of Cambridge University and E. Van der Giessen of the University of Groningen a framework has been developed for the analysis of crack growth under cyclic loading conditions where plastic flow arises from the motion of large numbers of discrete dislocations and the fracture properties are embedded in a cohesive surface constitutive relation. The material model is independent of the presence of a crack and the only distinction between an analysis of monotonic crack growth and fatigue crack growth is that in fatigue the remote loading is specified to be an oscillating function of time. Thus, a basic question is: within this framework, do cracks grow at a lower driving force under cyclic loading than under monotonic loading, and if so, what features of fatigue crack growth emerge? Fatigue does emerge from the calculations as a consequence of the evolution of internal stresses associated with the irreversibility of the dislocation motion. A fatigue threshold, Paris law behavior, striations and the accelerated growth of short cracks are outcomes of the simulations. Also, scaling predictions obtained for the fatigue threshold and the fatigue crack growth rate are discussed.

Size, History-Dependent, Activation and Three-Dimensional Effects on the Work and Power Produced During Cyclic Muscle Contractions.

PubMed

Ross, Stephanie A; Ryan, David S; Dominguez, Sebastian; Nigam, Nilima; Wakeling, James M

2018-05-03

Muscles undergo cycles of length change and force development during locomotion, and these contribute to their work and power production to drive body motion. Muscle fibres are typically considered to be linear actuators whose stress depends on their length, velocity, and activation state, and whose properties can be scaled up to explain the function of whole muscles. However, experimental and modelling studies have shown that a muscle's stress additionally depends on inactive and passive tissues within the muscle, the muscle's size, and its previous contraction history. These effects have not been tested under common sets of contraction conditions, especially the cyclic contractions that are typical of locomotion. Here we evaluate the relative effects of size, history-dependent, activation and three-dimensional effects on the work and power produced during cyclic contractions of muscle models. Simulations of muscle contraction were optimized to generate high power outputs: this resulted in the muscle models being largely active during shortening, and inactive during lengthening. As such, the history-dependent effects were dominated by force depression during simulated active shortening rather than force enhancement during active stretch. Internal work must be done to deform the muscle tissue, and to accelerate the internal muscle mass, resulting in reduced power and work that can be done on an external load. The effect of the muscle mass affects the scaling of muscle properties, with the inertial costs of contraction being relatively greater at larger sizes and lower activation levels.

Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling

NASA Astrophysics Data System (ADS)

Safaei, Farinaz; Castorena, Cassie; Kim, Y. Richard

2016-08-01

Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder's contribution to mixture fatigue and pavement fatigue cracking performance.

Engineering cellular fibers for musculoskeletal soft tissues using directed self-assembly.

PubMed

Schiele, Nathan R; Koppes, Ryan A; Chrisey, Douglas B; Corr, David T

2013-05-01

Engineering strategies guided by developmental biology may enhance and accelerate in vitro tissue formation for tissue engineering and regenerative medicine applications. In this study, we looked toward embryonic tendon development as a model system to guide our soft tissue engineering approach. To direct cellular self-assembly, we utilized laser micromachined, differentially adherent growth channels lined with fibronectin. The micromachined growth channels directed human dermal fibroblast cells to form single cellular fibers, without the need for a provisional three-dimensional extracellular matrix or scaffold to establish a fiber structure. Therefore, the resulting tissue structure and mechanical characteristics were determined solely by the cells. Due to the self-assembly nature of this approach, the growing fibers exhibit some key aspects of embryonic tendon development, such as high cellularity, the rapid formation (within 24 h) of a highly organized and aligned cellular structure, and the expression of cadherin-11 (indicating direct cell-to-cell adhesions). To provide a dynamic mechanical environment, we have also developed and characterized a method to apply precise cyclic tensile strain to the cellular fibers as they develop. After an initial period of cellular fiber formation (24 h postseeding), cyclic strain was applied for 48 h, in 8-h intervals, with tensile strain increasing from 0.7% to 1.0%, and at a frequency of 0.5 Hz. Dynamic loading dramatically increased cellular fiber mechanical properties with a nearly twofold increase in both the linear region stiffness and maximum load at failure, thereby demonstrating a mechanism for enhancing cellular fiber formation and mechanical properties. Tissue engineering strategies, designed to capture key aspects of embryonic development, may provide unique insight into accelerated maturation of engineered replacement tissue, and offer significant advances for regenerative medicine applications in tendon, ligament, and other fibrous soft tissues.

Endogenous Delta/Theta Sound-Brain Phase Entrainment Accelerates the Buildup of Auditory Streaming.

PubMed

Riecke, Lars; Sack, Alexander T; Schroeder, Charles E

2015-12-21

In many natural listening situations, meaningful sounds (e.g., speech) fluctuate in slow rhythms among other sounds. When a slow rhythmic auditory stream is selectively attended, endogenous delta (1‒4 Hz) oscillations in auditory cortex may shift their timing so that higher-excitability neuronal phases become aligned with salient events in that stream [1, 2]. As a consequence of this stream-brain phase entrainment [3], these events are processed and perceived more readily than temporally non-overlapping events [4-11], essentially enhancing the neural segregation between the attended stream and temporally noncoherent streams [12]. Stream-brain phase entrainment is robust to acoustic interference [13-20] provided that target stream-evoked rhythmic activity can be segregated from noncoherent activity evoked by other sounds [21], a process that usually builds up over time [22-27]. However, it has remained unclear whether stream-brain phase entrainment functionally contributes to this buildup of rhythmic streams or whether it is merely an epiphenomenon of it. Here, we addressed this issue directly by experimentally manipulating endogenous stream-brain phase entrainment in human auditory cortex with non-invasive transcranial alternating current stimulation (TACS) [28-30]. We assessed the consequences of these manipulations on the perceptual buildup of the target stream (the time required to recognize its presence in a noisy background), using behavioral measures in 20 healthy listeners performing a naturalistic listening task. Experimentally induced cyclic 4-Hz variations in stream-brain phase entrainment reliably caused a cyclic 4-Hz pattern in perceptual buildup time. Our findings demonstrate that strong endogenous delta/theta stream-brain phase entrainment accelerates the perceptual emergence of task-relevant rhythmic streams in noisy environments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Lorentz Force Detuning Analysis of the SNS Accelerating Cavities

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

R. Mitchell; K. Matsumoto; G. Ciovati

2001-09-01

The Spallation Neutron Source (SNS) project incorporates a superconducting radio-frequency (SRF) accelerator for the final section of the pulsed mode linac Cavities with geometrical {beta} values of {beta} = 0.61 and {beta} = 0.81 are utilized in the SRF section, and are constructed out of thin-walled niobium with stiffener rings welded between the cells near the iris. The welded titanium helium vessel and tuner assembly restrains the cavity beam tubes Cavities with {beta} values less than one have relatively steep and flat side-walls making the cavities susceptible to Ised RF induces cyclic Lorentz pressures that mechanically excite the cavities, producingmore » a dynamic Lorentz force detuning different from a continuous RF system. The amplitude of the dynamic detuning for a given cavity design is a function of the mechanical damping, stiffness of the tuner/helium vessel assembly, RF pulse profile, and the RF pulse rate. This paper presents analysis and testing results to date, and indicates areas where more investigation is required.« less

EFFECTS OF CYCLIC FLEXURAL FATIGUE ON PORCINE BIOPROSTHETIC HEART VALVE HETEROGRAFT BIOMATERIALS

PubMed Central

Mirnajafi, Ali; Zubiate, Brett; Sacks, Michael S.

2009-01-01

While bioprosthetic heart valves (BHV) remain the primary treatment modality for adult heart valve replacement, continued problems with durability remain. Several studies have implicated flexure as a major damage mode in porcine-derived heterograft biomaterials used in BHV fabrication. While conventional accelerated wear testing can provide valuable insights into BHV damage phenomena, the constituent tissues are subjected to complex, time-varying deformation modes (i.e. tension and flexure), that do not allow for the control of the amount, direction, and location of flexure. Thus, in the present study customized fatigue testing devices were developed to subject circumferentially oriented porcine BHV tissue strips to controlled cyclic flexural loading. By using this approach, we were able to study layer-specific structural damage induced by cyclic flexural tensile and compressive stresses alone. 10×106, 25×106 and 50×106 cycle levels were used, with resulting changes in flexural stiffness and collagen structure assessed. Results indicated that flexural rigidity was markedly reduced after only 10×106 cycles, and progressively decayed at a lower rate with cycle number thereafter. Moreover, the against-curvature fatigue direction induced the most damage, suggesting that the ventricularis and fibrosa layers have low resistance to cyclic flexural compressive and tensile loads, respectively. The histological analyses indicated progressive collagen fiber delamination as early as 10×106 cycles, but otherwise no change in gross collagen orientation. Our results underscore that porcine-derived heterograft biomaterials are very sensitive to flexural fatigue, with delamination of the tissue layers the primary underlying mechanism. This appears to be in contrast to pericardial BHV, wherein high tensile stresses are considered to be the major cause of structural failure. These findings point towards the need for the development of chemical fixation technologies that minimize flexure induced damage to extend porcine heterograft biomaterial durability. PMID:20166221

Shielding analysis of the Microtron MT-25 bunker using the MCNP-4C code and NCRP Report 51.

PubMed

Casanova, A O; López, N; Gelen, A; Guevara, M V Manso; Díaz, O; Cimino, L; D'Alessandro, K; Melo, J C

2004-01-01

A cyclic electron accelerator Microtron MT-25 will be installed in Havana, Cuba. Electrons, neutrons and gamma radiation up to 25 MeV can be produced in the MT-25. A detailed shielding analysis for the bunker is carried out using two ways: the NCRP-51 Report and the Monte Carlo Method (MCNP-4C Code). The walls and ceiling thicknesses are estimated with dose constraints of 0.5 and 20 mSv y(-1), respectively, and an area occupancy factor of 1/16. Both results are compared and a preliminary bunker design is shown. Copyright 2004 Oxford University Press

Non-Kinetic Losses Caused by Electrochemical Carbon Corrosion in PEM Fuel Cells

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

Park, Seh Kyu; Shao, Yuyan; Viswanathan, Vilayanur V.

2012-05-01

This paper presented non-kinetic losses in PEM fuel cells under an accelerated stress test of catalyst support. The cathode with carbon-supported Pt catalyst was prepared and characterized with potential hold at 1.2 V vs. SHE in PEM fuel cells. Irreversible losses caused by carbon corrosion were evaluated using a variety of electrochemical characterizations including cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, and polarization technique. Ohmic losses at the cathode with potential hold were determined using its capacitive responses. Concentration losses in PEM fuel cells were analyzed in terms of Tafel behavior and thin film/flooded-agglomerate dynamics.

The influence of thermal and cyclic stressing on the strength of rocks from Mount St. Helens, Washington

NASA Astrophysics Data System (ADS)

Kendrick, Jackie Evan; Smith, Rosanna; Sammonds, Peter; Meredith, Philip G.; Dainty, Matthew; Pallister, John S.

2013-07-01

Stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength. Here, we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks. Specifically, this laboratory study examines the properties of samples from Mount St. Helens; chosen because its strength and stability have played a key role in its history, influencing the character of the infamous 1980 eruption. We find that thermal stressing exerts different effects on the strengths of different volcanic units; increasing the heterogeneity of rocks in situ. Increasing the uniaxial compressive stress generates cracking, the timing and magnitude of which was monitored via acoustic emission (AE) output during our experiments. AEs accelerated in the approach to failure, sometimes following the pattern predicted by the failure forecast method (Kilburn 2003). Crack damage during the experiments was tracked using the evolving static Young's modulus and Poisson's ratio, which represent the quasi-static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models. Cyclic loading of these rocks resulted in a lower failure strength, confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice. Additionally, volcanic rocks in this study undergo significant elastic hysteresis; in some instances, a material may fail at a stress lower than the peak stress which has previously been endured. Thus, a volcanic dome repeatedly inflated and deflated may progressively weaken, possibly inducing failure without necessarily exceeding earlier conditions.

Spinor Field Nonlinearity and Space-Time Geometry

NASA Astrophysics Data System (ADS)

Saha, Bijan

2018-03-01

Within the scope of Bianchi type VI,VI0,V, III, I, LRSBI and FRW cosmological models we have studied the role of nonlinear spinor field on the evolution of the Universe and the spinor field itself. It was found that due to the presence of non-trivial non-diagonal components of the energy-momentum tensor of the spinor field in the anisotropic space-time, there occur some severe restrictions both on the metric functions and on the components of the spinor field. In this report we have considered a polynomial nonlinearity which is a function of invariants constructed from the bilinear spinor forms. It is found that in case of a Bianchi type-VI space-time, depending of the sign of self-coupling constants, the model allows either late time acceleration or oscillatory mode of evolution. In case of a Bianchi VI 0 type space-time due to the specific behavior of the spinor field we have two different scenarios. In one case the invariants constructed from bilinear spinor forms become trivial, thus giving rise to a massless and linear spinor field Lagrangian. This case is equivalent to the vacuum solution of the Bianchi VI 0 type space-time. The second case allows non-vanishing massive and nonlinear terms and depending on the sign of coupling constants gives rise to accelerating mode of expansion or the one that after obtaining some maximum value contracts and ends in big crunch, consequently generating space-time singularity. In case of a Bianchi type-V model there occur two possibilities. In one case we found that the metric functions are similar to each other. In this case the Universe expands with acceleration if the self-coupling constant is taken to be a positive one, whereas a negative coupling constant gives rise to a cyclic or periodic solution. In the second case the spinor mass and the spinor field nonlinearity vanish and the Universe expands linearly in time. In case of a Bianchi type-III model the space-time remains locally rotationally symmetric all the time, though the isotropy of space-time can be attained for a large proportionality constant. As far as evolution is concerned, depending on the sign of coupling constant the model allows both accelerated and oscillatory mode of expansion. A negative coupling constant leads to an oscillatory mode of expansion, whereas a positive coupling constant generates expanding Universe with late time acceleration. Both deceleration parameter and EoS parameter in this case vary with time and are in agreement with modern concept of space-time evolution. In case of a Bianchi type-I space-time the non-diagonal components lead to three different possibilities. In case of a full BI space-time we find that the spinor field nonlinearity and the massive term vanish, hence the spinor field Lagrangian becomes massless and linear. In two other cases the space-time evolves into either LRSBI or FRW Universe. If we consider a locally rotationally symmetric BI( LRSBI) model, neither the mass term nor the spinor field nonlinearity vanishes. In this case depending on the sign of coupling constant we have either late time accelerated mode of expansion or oscillatory mode of evolution. In this case for an expanding Universe we have asymptotical isotropization. Finally, in case of a FRW model neither the mass term nor the spinor field nonlinearity vanishes. Like in LRSBI case we have either late time acceleration or cyclic mode of evolution. These findings allow us to conclude that the spinor field is very sensitive to the gravitational one.

The effect of lunisolar tidal acceleration on stem elongation growth, nutations and leaf movements in peppermint (Mentha × piperita L.).

PubMed

Zajączkowska, U; Barlow, P W

2017-07-01

Orbital movement of the Moon generates a system of gravitational fields that periodically alter the gravitational force on Earth. This lunar tidal acceleration (Etide) is known to act as an external environmental factor affecting many growth and developmental phenomena in plants. Our study focused on the lunar tidal influence on stem elongation growth, nutations and leaf movements of peppermint. Plants were continuously recorded with time-lapse photography under constant illumination as well in constant illumination following 5 days of alternating dark-light cycles. Time courses of shoot movements were correlated with contemporaneous time courses of the Etide estimates. Optical microscopy and SEM were used in anatomical studies. All plant shoot movements were synchronised with changes in the lunisolar acceleration. Using a periodogram, wavelet analysis and local correlation index, a convergence was found between the rhythms of lunisolar acceleration and the rhythms of shoot growth. Also observed were cyclical changes in the direction of rotation of stem apices when gravitational dynamics were at their greatest. After contrasting dark-light cycle experiments, nutational rhythms converged to an identical phase relationship with the Etide and almost immediately their renewed movements commenced. Amplitudes of leaf movements decreased during leaf growth up to the stage when the leaf was fully developed; the periodicity of leaf movements correlated with the Etide rhythms. For the fist time, it was documented that lunisolar acceleration is an independent rhythmic environmental signal capable of influencing the dynamics of plant stem elongation. This phenomenon is synchronised with the known effects of Etide on nutations and leaf movements. © 2017 German Botanical Society and The Royal Botanical Society of the Netherlands.

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

Bartolac, S; Letourneau, D; University of Toronto, Toronto, Ontario

Purpose: Application of process control theory in quality assurance programs promises to allow earlier identification of problems and potentially better quality in delivery than traditional paradigms based primarily on tolerances and action levels. The purpose of this project was to characterize underlying seasonal variations in linear accelerator output that can be used to improve performance or trigger preemptive maintenance. Methods: Review of runtime plots of daily (6 MV) output data acquired using in house ion chamber based devices over three years and for fifteen linear accelerators of varying make and model were evaluated. Shifts in output due to known interventionsmore » with the machines were subtracted from the data to model an uncorrected scenario for each linear accelerator. Observable linear trends were also removed from the data prior to evaluation of periodic variations. Results: Runtime plots of output revealed sinusoidal, seasonal variations that were consistent across all units, irrespective of manufacturer, model or age of machine. The average amplitude of the variation was on the order of 1%. Peak and minimum variations were found to correspond to early April and September, respectively. Approximately 48% of output adjustments made over the period examined were potentially avoidable if baseline levels had corresponded to the mean output, rather than to points near a peak or valley. Linear trends were observed for three of the fifteen units, with annual increases in output ranging from 2–3%. Conclusion: Characterization of cyclical seasonal trends allows for better separation of potentially innate accelerator behaviour from other behaviours (e.g. linear trends) that may be better described as true out of control states (i.e. non-stochastic deviations from otherwise expected behavior) and could indicate service requirements. Results also pointed to an optimal setpoint for accelerators such that output of machines is maintained within set tolerances and interventions are required less frequently.« less

Does cyclic stress and accelerated ageing influence the wear behavior of highly crosslinked polyethylene?

PubMed

Affatato, Saverio; De Mattia, Jonathan Salvatore; Bracco, Pierangiola; Pavoni, Eleonora; Taddei, Paola

2016-06-01

First-generation (irradiated and remelted or annealed) and second-generation (irradiated and vitamin E blended or doped) highly crosslinked polyethylenes were introduced in the last decade to solve the problems of wear and osteolysis. In this study, the influence of the Vitamin-E addition on crosslinked polyethylene (XLPE_VE) was evaluated by comparing the in vitro wear behavior of crosslinked polyethylene (XLPE) versus Vitamin-E blended polyethylene XLPE and conventional ultra-high molecular weight polyethylene (STD_PE) acetabular cups, after accelerated ageing according to ASTM F2003-02 (70.0±0.1°C, pure oxygen at 5bar for 14 days). The test was performed using a hip joint simulator run for two millions cycles, under bovine calf serum as lubricant. Mass loss was found to decrease along the series XLPE_VE>STD_PE>XLPE, although no statistically significant differences were found between the mass losses of the three sets of cups. Micro-Raman spectroscopy was used to investigate at a molecular level the morphology changes induced by wear. The spectroscopic analyses showed that the accelerated ageing determined different wear mechanisms and molecular rearrangements during testing with regards to the changes in both the chain orientation and the distribution of the all-trans sequences within the orthorhombic, amorphous and third phases. The results of the present study showed that the addition of vitamin E was not effective to improve the gravimetric wear of PE after accelerated ageing. However, from a molecular point of view, the XLPE_VE acetabular cups tested after accelerated ageing appeared definitely less damaged than the STD_PE ones and comparable to XLPE samples. Copyright © 2016 Elsevier Ltd. All rights reserved.

Orthodontics at a Pivotal Point of Transformation

PubMed Central

Mao, Jeremy J.

2014-01-01

The profession of orthodontics is projected to face a multitude of challenges. Do cyclic forces accelerate the rate of tooth movement and hence the speed of orthodontic treatment? Would bioengineered cementum and dentine be a solution to root resorption? What would orthodontics be like when bioengineered periodontal ligament and alveolar bone become clinical practice, or one day, entire teeth are bioengineered? Would it be possible to selectively differentiate stem cells into osteoblasts or osteoclasts by either static or cyclic forces? What is the new demand on orthodontic expertise with increasingly automated appliances? What will be the impact of the next generation of dental implants or rapid prototyped crowns on orthodontics? A century ago, Edward Angle’s practice of fixed appliances, along with other seminal contributions, such as functional appliances, established the profession of orthodontics. Today, the biophysical principles of orthodontics remain largely unchanged from Angle’s era, despite incremental refinements of brackets and wires. The paucity of fundamental innovations in orthodontics for decades presents intrinsic risks for the profession. This review will identify challenges for contemporary orthodontics and delineate strategies for the profession to evolve in an era of unprecedented scientific and technological advances, and serve as a call to action for the orthodontic profession. PMID:25018618

Evaluation of the antibacterial activity of a cationic polymer in aqueous solution with a convenient electrochemical method.

PubMed

Wang, Yihong; Guo, Qing; Wang, Huafu; Qian, Kun; Tian, Liang; Yao, Chen; Song, Wei; Shu, Weixia; Chen, Ping; Qi, Jinxu

2017-02-01

Quaternized chitosan is a cationic biopolymer with good antibacterial activity, biocompatibility, and biodegradability, and it has been widely applied in many fields. We have developed a convenient method to evaluate the antibacterial activity of hydroxypropyltrimethylammonium chloride chitosan (HACC) with a nonionic surfactant poloxamer in aqueous solution by monitoring the change of the oxidation peak current in cyclic voltammetry. Increasing values of the oxidation peak current were positively correlated with the antibacterial activity of HACC-poloxamer solutions. Optical microscope images, the zeta potential, and fluorescence spectroscopy showed that the aggregation state of HACC-poloxamer was related to the ratio of the two polymers and also to the antibacterial activity and oxidation peak current. At an HACC-to-poloxamer ratio of 1:0.75, the maximum surface charge density and the smooth edge of HACC-poloxamer aggregates can accelerate diffusion in aqueous solution. It is expected that this convenient method can be applied for a quick evaluation of the antibacterial activity of cationic biopolymers in aqueous solution. Graphical Abstract The cyclic voltammograms of MB in HACC/poloxamer solution, and the antibacterial efficiency against S. aureus after incubated with HACC (a) and 1/0.75 of HACC/poloxamer (b).

Inhibition of intimal thickening after vascular injury with a cocktail of vascular endothelial growth factor and cyclic Arg-Gly-Asp peptide.

PubMed

Li, Yue; McRobb, Lucinda S; Khachigian, Levon M

2016-10-01

Percutaneous coronary intervention is widely used for the treatment of coronary artery disease; however, significant challenges such as restenosis remain. Key to solving these problems is to inhibit smooth muscle cell activation while enhancing re-endothelialization. Early growth response-1 (Egr-1) is a transcription factor that regulates vascular smooth muscle cell (SMC) proliferation and migration through its control of an array of downstream genes. A "cocktail" of vascular endothelial growth factor (VEGF)-A, VEGF-D and cyclic RGD was tested for its ability to inhibit neointima formation and accelerate re-endothelialization following balloon injury to carotid arteries of rats. In vitro, the cocktail stimulated endothelial cell growth yet inhibited smooth muscle cell growth. In vivo, cocktail-treated injured arteries exhibited reduced intimal thickening by >50% (P<0.05). It increased both re-endothelialization and endothelial nitric oxide synthase (NOS) expression. Cocktail reduced Egr-1 expression, an effect blocked by the NOS inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) that also prevented cocktail inhibition of neointima inhibition. This combination may potentially be useful for the treatment of restenosis with concomitant stimulation of revascularization. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

New Fusion Concept Using Coaxial Passing Through Each Other Self-focusing Colliding Beams (Invention)

NASA Astrophysics Data System (ADS)

Chikvashvili, Ioseb

2011-10-01

In proposed Concept it is offered to use two ion beams directed coaxially at the same direction but with different velocities (center-of-mass collision energy should be sufficient for fusion), to direct oppositely the relativistic electron beam for only partial compensation of positive space charge and for allowing the combined beam's pinch capability, to apply the longitudinal electric field for compensation of alignment of velocities of reacting particles and also for compensation of energy losses of electrons via Bremsstrahlung. On base of Concept different types of reactor designs can be realized: Linear and Cyclic designs. In the simplest embodiment the Cyclic Reactor (design) may include: betatron type device (circular store of externally injected particles - induction accelerator), pulse high-current relativistic electron injector, pulse high-current slower ion injector, pulse high-current faster ion injector and reaction products extractor. Using present day technologies and materials (or a reasonable extrapolation of those) it is possible to reach: for induction linear injectors (ions&electrons) - currents of thousands A, repeatability - up to 10Hz, the same for high-current betatrons (FFAG, Stellatron, etc.). And it is possible to build the fusion reactor using the proposed Method just today.

Modeling of a viscoelastic damper and its application in structural control

PubMed Central

Ibrahim, Zainah; Ghodsi, S. S.; Khatibi, Hamed

2017-01-01

Conventional seismic rehabilitation methods may not be suitable for some buildings owing to their high cost and time-consuming foundation work. In recent years, viscoelastic dampers (VEDs) have been widely used in many mid- and high-rise buildings. This study introduces a viscoelastic passive control system called rotary rubber braced damper (RRBD). The RRBD is an economical, lightweight, and easy-to-assemble device. A finite element model considering nonlinearity, large deformation, and material damage is developed to conduct a parametric study on different damper sizes under pushover cyclic loading. The fundamental characteristics of this VED system are clarified by analyzing building structures under cyclic loading. The result show excellent energy absorption and stable hysteresis loops in all specimens. Additionally, by using a sinusoidal shaking table test, the effectiveness of the RRBD to manage the response displacement and acceleration of steel frames is considered. The RRBD functioned at early stages of lateral displacement, indicating that the system is effective for all levels of vibration. Moreover, the proposed damper shows significantly better performance in terms of the column compression force resulting from the brace action compared to chevron bracing (CB). PMID:28570657

Fatigue Damage and Lifetime of SiC/SiC Ceramic-Matrix Composite under Cyclic Loading at Elevated Temperatures

PubMed Central

Li, Longbiao

2017-01-01

In this paper, the fatigue damage and lifetime of 2D SiC/SiC ceramic-matrix composites (CMCs) under cyclic fatigue loading at 750, 1000, 1100, 1200 and 1300 °C in air and in steam atmosphere have been investigated. The damage evolution versus applied cycles of 2D SiC/SiC composites were analyzed using fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain and interface shear stress. The presence of steam accelerated the damage development inside of SiC/SiC composites, which increased the increasing rate of the fatigue hysteresis dissipated energy and the fatigue peak strain, and the decreasing rate of the fatigue hysteresis modulus and the interface shear stress. The fatigue life stress-cycle (S-N) curves and fatigue limit stresses of 2D SiC/SiC composites at different temperatures in air and in steam condition have been predicted. The fatigue limit stresses approach 67%, 28%, 39% 17% and 28% tensile strength at 750, 1000, 1100, 1200 and 1300 °C in air, and 49%, 10%, 9% and 19% tensile strength at 750, 1000, 1200 and 1300 °C in steam conditions, respectively. PMID:28772736

Accelerated deflation promotes homogeneous airspace liquid distribution in the edematous lung.

PubMed

Wu, You; Nguyen, Tam L; Perlman, Carrie E

2017-04-01

Edematous lungs contain regions with heterogeneous alveolar flooding. Liquid is trapped in flooded alveoli by a pressure barrier-higher liquid pressure at the border than in the center of flooded alveoli-that is proportional to surface tension, T Stress is concentrated between aerated and flooded alveoli, to a degree proportional to T Mechanical ventilation, by cyclically increasing T , injuriously exacerbates stress concentrations. Overcoming the pressure barrier to redistribute liquid more homogeneously between alveoli should reduce stress concentration prevalence and ventilation injury. In isolated rat lungs, we test whether accelerated deflation can overcome the pressure barrier and catapult liquid out of flooded alveoli. We generate a local edema model with normal T by microinfusing liquid into surface alveoli. We generate a global edema model with high T by establishing hydrostatic edema, which does not alter T , and then gently ventilating the edematous lungs, which increases T at 15 cmH 2 O transpulmonary pressure by 52%. Thus ventilation of globally edematous lungs increases T , which should increase stress concentrations and, with positive feedback, cause escalating ventilation injury. In the local model, when the pressure barrier is moderate, accelerated deflation causes liquid to escape from flooded alveoli and redistribute more equitably. Flooding heterogeneity tends to decrease. In the global model, accelerated deflation causes liquid escape, but-because of elevated T -the liquid jumps to nearby, aerated alveoli. Flooding heterogeneity is unaltered. In pulmonary edema with normal T , early ventilation with accelerated deflation might reduce the positive feedback mechanism through which ventilation injury increases over time. NEW & NOTEWORTHY We introduce, in the isolated rat lung, a new model of pulmonary edema with elevated surface tension. We first generate hydrostatic edema and then ventilate gently to increase surface tension. We investigate the mechanical mechanisms through which 1 ) ventilation injures edematous lungs and 2 ) ventilation with accelerated deflation might lessen ventilation injury. Copyright © 2017 the American Physiological Society.

Accelerated deflation promotes homogeneous airspace liquid distribution in the edematous lung

PubMed Central

Wu, You; Nguyen, Tam L.

2017-01-01

Edematous lungs contain regions with heterogeneous alveolar flooding. Liquid is trapped in flooded alveoli by a pressure barrier—higher liquid pressure at the border than in the center of flooded alveoli—that is proportional to surface tension, T. Stress is concentrated between aerated and flooded alveoli, to a degree proportional to T. Mechanical ventilation, by cyclically increasing T, injuriously exacerbates stress concentrations. Overcoming the pressure barrier to redistribute liquid more homogeneously between alveoli should reduce stress concentration prevalence and ventilation injury. In isolated rat lungs, we test whether accelerated deflation can overcome the pressure barrier and catapult liquid out of flooded alveoli. We generate a local edema model with normal T by microinfusing liquid into surface alveoli. We generate a global edema model with high T by establishing hydrostatic edema, which does not alter T, and then gently ventilating the edematous lungs, which increases T at 15 cmH2O transpulmonary pressure by 52%. Thus ventilation of globally edematous lungs increases T, which should increase stress concentrations and, with positive feedback, cause escalating ventilation injury. In the local model, when the pressure barrier is moderate, accelerated deflation causes liquid to escape from flooded alveoli and redistribute more equitably. Flooding heterogeneity tends to decrease. In the global model, accelerated deflation causes liquid escape, but—because of elevated T—the liquid jumps to nearby, aerated alveoli. Flooding heterogeneity is unaltered. In pulmonary edema with normal T, early ventilation with accelerated deflation might reduce the positive feedback mechanism through which ventilation injury increases over time. NEW & NOTEWORTHY We introduce, in the isolated rat lung, a new model of pulmonary edema with elevated surface tension. We first generate hydrostatic edema and then ventilate gently to increase surface tension. We investigate the mechanical mechanisms through which 1) ventilation injures edematous lungs and 2) ventilation with accelerated deflation might lessen ventilation injury. PMID:27979983

Our Universe from the cosmological constant

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

Barrau, Aurélien; Linsefors, Linda, E-mail: Aurelien.Barrau@cern.ch, E-mail: linda.linsefors@lpsc.in2p3.fr

The issue of the origin of the Universe and of its contents is addressed in the framework of bouncing cosmologies, as described for example by loop quantum gravity. If the current acceleration is due to a true cosmological constant, this constant is naturally conserved through the bounce and the Universe should also be in a (contracting) de Sitter phase in the remote past. We investigate here the possibility that the de Sitter temperature in the contracting branch fills the Universe with radiation that causes the bounce and the subsequent inflation and reheating. We also consider the possibility that this givesmore » rise to a cyclic model of the Universe and suggest some possible tests.« less

A Computational Fluid Dynamics Study of Swirling Flow Reduction by Using Anti-Vortex Baffle

NASA Technical Reports Server (NTRS)

Yang, H. Q.; West, Jeff; Peugeot, John W.

2017-01-01

OBJECTIVES: To evaluate proposed anti-vortex design in suppressing swirling flow during US burn. APPROACH: Include two major body forces in the analysis a)Vehicle acceleration (all three components); b)Vehicle maneuvers (roll, pitch, and yaw). Perform two drainage analyses of Ares I LOX tank using 6 DOF body forces predicted by GN&C analysis (Guidance Navigation and Control) during vehicle ascent: one with baffle, one without baffle. MODEL: Use Ares I defined geometry. O-Grid for easy fitting of baffle. In this preliminary analysis the holes are sealed. Use whole 360 deg. model with no assumption of symmetry or cyclic boundary conditions. Read in 6DOF data vs time from a file.

Waltz Mill testing of 345-kV PPP cable

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

Burghardt, R.R.

1991-09-01

A 345-kV PPP-insulated cable was subjected to a two-year accelerated life test program at the EPRI Waltz Mill Cable Test Facility. Testing started in November 1985 and was successfully completed in September 1988. The program included conductor temperatures ranging from 85{degrees}C to 105{degrees}C and line-to-line voltages from 362 kV to 474 kV. Cyclic testing was performed during 17 of the 24 months. Dissipation factor measurements were made throughout the program. The measurements indicated no deterioration of the cable or splices as a consequence of the high temperatures and voltages applied to them in this test program. 2 refs., 24 figs.

Waltz Mill testing of 765-kV paper-polypropylene-paper (PPP) cable. Final report

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

Burghardt, R.R.

1992-06-01

A 765-kV PPP-insulated cable was subjected to a 27-month accelerated life test program at the EPRI Waltz Mill Cable Test Facility. Testing started in August 1981 and was successfully completed in January 1985. The program included conductor temperatures ranging from 85{degree}C to 105{degree}C and line-to-line voltages from 800 kV to 1050 kV. Cyclic testing was performed during 20 of the 27 months. Dissipation factor measurements were made throughout the program. The measurements indicated no deterioration of the cable or splices as a consequence of the high temperatures and voltages applied to them in this test program.

Waltz Mill testing of 765-kV paper-polypropylene-paper (PPP) cable

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

Burghardt, R.R.

1992-06-01

A 765-kV PPP-insulated cable was subjected to a 27-month accelerated life test program at the EPRI Waltz Mill Cable Test Facility. Testing started in August 1981 and was successfully completed in January 1985. The program included conductor temperatures ranging from 85{degree}C to 105{degree}C and line-to-line voltages from 800 kV to 1050 kV. Cyclic testing was performed during 20 of the 27 months. Dissipation factor measurements were made throughout the program. The measurements indicated no deterioration of the cable or splices as a consequence of the high temperatures and voltages applied to them in this test program.

The failure of earthquake failure models

USGS Publications Warehouse

Gomberg, J.

2001-01-01

In this study I show that simple heuristic models and numerical calculations suggest that an entire class of commonly invoked models of earthquake failure processes cannot explain triggering of seismicity by transient or "dynamic" stress changes, such as stress changes associated with passing seismic waves. The models of this class have the common feature that the physical property characterizing failure increases at an accelerating rate when a fault is loaded (stressed) at a constant rate. Examples include models that invoke rate state friction or subcritical crack growth, in which the properties characterizing failure are slip or crack length, respectively. Failure occurs when the rate at which these grow accelerates to values exceeding some critical threshold. These accelerating failure models do not predict the finite durations of dynamically triggered earthquake sequences (e.g., at aftershock or remote distances). Some of the failure models belonging to this class have been used to explain static stress triggering of aftershocks. This may imply that the physical processes underlying dynamic triggering differs or that currently applied models of static triggering require modification. If the former is the case, we might appeal to physical mechanisms relying on oscillatory deformations such as compaction of saturated fault gouge leading to pore pressure increase, or cyclic fatigue. However, if dynamic and static triggering mechanisms differ, one still needs to ask why static triggering models that neglect these dynamic mechanisms appear to explain many observations. If the static and dynamic triggering mechanisms are the same, perhaps assumptions about accelerating failure and/or that triggering advances the failure times of a population of inevitable earthquakes are incorrect.

Lorentz force detuning analysis of the Spallation Neutron Source (SNS) accelerating cavities.

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

Mitchell, R.R.; Matsumoto, K. Y.; Ciovati, G.

2001-01-01

The Spallation Neutron Source (SNS) project incorporates a superconducting radio-frequency (SRF) accelerator for the final section of the pulsed mode linac. Cavities with geometrical {beta} values of {beta}=0.61 and {beta}=0.81 are utilized in the SRF section, and are constructed out of thin-walled niobium with stiffener rings welded between the cells near the iris. The welded titanium helium vessel and tuner assembly restrains the cavity beam tubes. Cavities with {beta} values less than one have relatively steep and flat side-walls making the cavities susceptible to Lorentz force detuning. In addition, the pulsed RF induces cyclic Lorentz pressures that mechanically excite themore » cavities, producing a dynamic Lorentz force detuning different from a continuous RF system. The amplitude of the dynamic detuning for a given cavity design is a function of the mechanical damping, stiffness of the tuner/helium vessel assembly, RF pulse profile, and the RF pulse rate. This paper presents analysis and testing results to date, and indicates areas where more investigation is required.« less

Accelerated azo dye degradation and concurrent hydrogen production in the single-chamber photocatalytic microbial electrolysis cell.

PubMed

Hou, Yanping; Zhang, Renduo; Yu, Zebin; Huang, Lirong; Liu, Yuxin; Zhou, Zili

2017-01-01

The single-chamber microbial electrolysis cell constructed with a TiO 2 -coated photocathode, termed photocatalytic microbial electrolysis cell (PMEC), was developed to accelerate methyl orange (MO) degradation and concurrent hydrogen (H 2 ) recovery under UV irradiation. Results showed that faster MO decolorization rates were achieved from the PMEC compared with those without UV irradiation or with open circuit. With increase of MO concentrations (acetate as co-substrate) from 50 to 300mg/L at an applied voltage of 0.8V, decolorization efficiencies decreased from 98% to 76% within 12h, and cyclic H 2 production declined from 113 to 68mL. As the possible mechanism of MO degradation, bioelectrochemical reduction, co-metabolism reduction, and photocatalysis were involved; and degradation intermediates (mainly sulfanilic acid and N,N-dimethylaniline) were further degraded by OH generated from photocatalysis. This makes MO mineralization be possible in the single-chamber PMEC. Hence, the PMEC is a promising system for dyeing wastewater treatment and simultaneous H 2 production. Copyright © 2016 Elsevier Ltd. All rights reserved.

Improving the transparency of a rehabilitation robot by exploiting the cyclic behaviour of walking.

PubMed

van Dijk, W; van der Kooij, H; Koopman, B; van Asseldonk, E H F; van der Kooij, H

2013-06-01

To promote active participation of neurological patients during robotic gait training, controllers, such as "assist as needed" or "cooperative control", are suggested. Apart from providing support, these controllers also require that the robot should be capable of resembling natural, unsupported, walking. This means that they should have a transparent mode, where the interaction forces between the human and the robot are minimal. Traditional feedback-control algorithms do not exploit the cyclic nature of walking to improve the transparency of the robot. The purpose of this study was to improve the transparent mode of robotic devices, by developing two controllers that use the rhythmic behavior of gait. Both controllers use adaptive frequency oscillators and kernel-based non-linear filters. Kernelbased non-linear filters can be used to estimate signals and their time derivatives, as a function of the gait phase. The first controller learns the motor angle, associated with a certain joint angle pattern, and acts as a feed-forward controller to improve the torque tracking (including the zero-torque mode). The second controller learns the state of the mechanical system and compensates for the dynamical effects (e.g. the acceleration of robot masses). Both controllers have been tested separately and in combination on a small subject population. Using the feedforward controller resulted in an improved torque tracking of at least 52 percent at the hip joint, and 61 percent at the knee joint. When both controllers were active simultaneously, the interaction power between the robot and the human leg was reduced by at least 40 percent at the thigh, and 43 percent at the shank. These results indicate that: if a robotic task is cyclic, the torque tracking and transparency can be improved by exploiting the predictions of adaptive frequency oscillator and kernel-based nonlinear filters.

Lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows: From cyclic steps to humpback dunes

NASA Astrophysics Data System (ADS)

Lang, Jörg; Winsemann, Jutta

2013-10-01

The preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record, although these bedforms are known from a variety of depositional environments. This field-based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps, chutes-and-pools, antidunes and humpback dunes from three-dimensional outcrops. The well exposed Middle Pleistocene successions from northern Germany comprise glacilacustrine ice-contact subaqueous fan and glacial lake-outburst flood deposits. The studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high-energy depositional environments such as fluvial settings, coarse-grained deltas or turbidite systems. Deposits of cyclic steps occur within the glacial lake-outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets. Cyclic steps formed due to acceleration and flow thinning when the glacial lake-outburst flood spilled over a push-moraine ridge. These bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes-and-pools and antidunes. The subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms, which are interpreted as deposits of aggrading stationary antidunes, which require quasi-steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation. Humpback dunes are characterised by downflow divergent cross-stratification, displaying differentiation into topsets, foresets and bottomsets, and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa. Gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common. The absence of planar-parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions. The large-scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows, which was strongly affected by the occurrence of hydraulic jumps. Small-scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge, bed topography and pulsating unstable flows.

Involvement of a cyclic adenosine monophosphate-dependent signal in the diet-induced canalicular trafficking of adenosine triphosphate-binding cassette transporter g5/g8.

PubMed

Yamazaki, Yasuhiro; Yasui, Kenta; Hashizume, Takahiro; Suto, Arisa; Mori, Ayaka; Murata, Yuzuki; Yamaguchi, Masahiko; Ikari, Akira; Sugatani, Junko

2015-10-01

The adenosine triphosphate-binding cassette (ABC) half-transporters Abcg5 and Abcg8 promote the secretion of neutral sterol into bile. Studies have demonstrated the diet-induced gene expression of these transporters, but the regulation of their trafficking when the nutritional status changes in the liver remains to be elucidated. Here, we generated a novel in vivo kinetic analysis that can monitor the intracellular trafficking of Abcg5/Abcg8 in living mouse liver by in vivo transfection of the genes of fluorescent protein-tagged transporters and investigated how hypernutrition affects the canalicular trafficking of these transporters. The kinetic analysis showed that lithogenic diet consumption accelerated the translocation of newly synthesized fluorescent-tagged transporters to intracellular pools in an endosomal compartment and enhanced the recruitment of these pooled gene products into the bile canalicular membrane in mouse liver. Because some ABC transporters are reported to be recruited from intracellular pools to the bile canaliculi by cyclic adenosine monophosphate (cAMP) signaling, we next evaluated the involvement of this machinery in a diet-induced event. Administration of a protein kinase A inhibitor, N-(2-{[3-(4-bromophenyl)-2-propenyl]amino}ethyl)-5-isoquinolinesulfonamide, decreased the canalicular expression of native Abcg5/Abcg8 in lithogenic diet-fed mice, and injection of a cAMP analog, dibutyryl cAMP, transiently increased their levels in standard diet-fed mice, indicating the involvement of cAMP signaling. Indeed, canalicular trafficking of the fluorescent-tagged Abcg5/Abcg8 was enhanced by dibutyryl cAMP administration. These observations suggest that diet-induced lipid loading into liver accelerates the trafficking of Abcg5/Abcg8 to the bile canalicular membrane through cAMP signaling machinery. © 2015 by the American Association for the Study of Liver Diseases.

Monitoring Tensile Fatigue of Superelastic NiTi Wire in Liquids by Electrochemical Potential

NASA Astrophysics Data System (ADS)

Racek, Jan; Stora, Marc; Šittner, Petr; Heller, Luděk; Kopeček, Jaromir; Petrenec, Martin

2015-06-01

Fatigue of superelastic NiTi wires was investigated by cyclic tension in simulated biofluid. The state of the surface of the fatigued NiTi wire was monitored by following the evolution of the electrochemical open circuit potential (OCP) together with macroscopic stresses and strains. The ceramic TiO2 oxide layer on the NiTi wire surface cannot withstand the large transformation strain and fractures in the first cycle. Based on the analysis of the results of in situ OCP experiments and SEM observation of cracks, it is claimed that the cycled wire surface develops mechanochemical reactions at the NiTi/liquid interface leading to cumulative generation of hydrogen, uptake of the hydrogen by the NiTi matrix, local loss of the matrix strength, crack transfer into the NiTi matrix, accelerated crack growth, and ultimately to the brittle fracture of the wire. Fatigue degradation is thus claimed to originate from the mechanochemical processes occurring at the excessively deforming surface not from the accumulation of defects due to energy dissipative bulk deformation processes. Ironically, combination of the two exciting properties of NiTi—superelasticity due to martensitic transformation and biocompatibility due to the protective TiO2 surface oxide layer—leads to excessive fatigue damage during cyclic mechanical loading in biofluids.

Evolutionary behaviour, trade-offs and cyclic and chaotic population dynamics.

PubMed

Hoyle, Andy; Bowers, Roger G; White, Andy

2011-05-01

Many studies of the evolution of life-history traits assume that the underlying population dynamical attractor is stable point equilibrium. However, evolutionary outcomes can change significantly in different circumstances. We present an analysis based on adaptive dynamics of a discrete-time demographic model involving a trade-off whose shape is also an important determinant of evolutionary behaviour. We derive an explicit expression for the fitness in the cyclic region and consequently present an adaptive dynamic analysis which is algebraic. We do this fully in the region of 2-cycles and (using a symbolic package) almost fully for 4-cycles. Simulations illustrate and verify our results. With equilibrium population dynamics, trade-offs with accelerating costs produce a continuously stable strategy (CSS) whereas trade-offs with decelerating costs produce a non-ES repellor. The transition to 2-cycles produces a discontinuous change: the appearance of an intermediate region in which branching points occur. The size of this region decreases as we move through the region of 2-cycles. There is a further discontinuous fall in the size of the branching region during the transition to 4-cycles. We extend our results numerically and with simulations to higher-period cycles and chaos. Simulations show that chaotic population dynamics can evolve from equilibrium and vice-versa.

Study on Dynamic Strain Aging and Low-Cycle Fatigue of Stainless Steel in Ultra-Supercritical Unit

NASA Astrophysics Data System (ADS)

Hongwei, Zhou; Yizhu, He; Jizu, Lv; Sixian, Rao

Dynamic strain aging (DSA) and low-cycle fatigue (LCF) behavior of TP347H stainless steel in ultra-supercritical unit were investigated at 550-650 °C. All the LCF tests were carried out under a fully-reversed, total axial strain control mode at the total strain amplitude from ±0.2% to ±1.0%. The effects of DSA in cyclic stress response, microstructure evolution and fatigue fracture surfaces and fatigue life were investigated in detail. The results show that DSA occurs during tensile, which is manifested as serrated flow in tensile stress-strain curves. The apparent activation energy for appearing of serrations in tensile stress-strain curves was 270 kJ/mol. Pipe diffusion of substitutional solutes such as Cr and Nb along the dislocation core, and strong interactions between segregated solutes and dislocations are considered as the mechanism of DSA. DSA partly restricts dislocation cross-slip, and dislocation cross-slip and planar-slip happen simultaneously during LCF. A lot of planar structures form, which is due to dislocation gliding on the special plane. This localized deformation structures result in many crack initiation sites. Meanwhile, DSA hardening increases cyclic stress response, accelerating crack propagation, which reduces high temperature strain fatigue life of steel.

Universal Responses of Cyclic-Oxidation Models Studied

NASA Technical Reports Server (NTRS)

Smialek, James L.

2003-01-01

Oxidation is an important degradation process for materials operating in the high-temperature air or oxygen environments typical of jet turbine or rocket engines. Reaction of the combustion gases with the component material forms surface layer scales during these oxidative exposures. Typically, the instantaneous rate of reaction is inversely proportional to the existing scale thickness, giving rise to parabolic kinetics. However, more realistic applications entail periodic startup and shutdown. Some scale spallation may occur upon cooling, resulting in loss of the protective diffusion barrier provided by a fully intact scale. Upon reheating, the component will experience accelerated oxidation due to this spallation. Cyclic-oxidation testing has, therefore, been a mainstay of characterization and performance ranking for high-temperature materials. Models simulate this process by calculating how a scale spalls upon cooling and regrows upon heating (refs. 1 to 3). Recently released NASA software (COSP for Windows) allows researchers to specify a uniform layer or discrete segments of spallation (ref. 4). Families of model curves exhibit consistent regularity and trends with input parameters, and characteristic features have been empirically described in terms of these parameters. Although much insight has been gained from experimental and model curves, no equation has been derived that can describe this behavior explicitly as functions of the key oxidation parameters.

A Comparative Study of Cyclic Oxidation and Sulfates-Induced Hot Corrosion Behavior of Arc-Sprayed Ni-Cr-Ti Coatings at Moderate Temperatures

NASA Astrophysics Data System (ADS)

Guo, Wenmin; Wu, Yuping; Zhang, Jianfeng; Hong, Sheng; Chen, Liyan; Qin, Yujiao

2015-06-01

The cyclic oxidation and sulfates-induced hot corrosion behaviors of a Ni-43Cr-0.3Ti arc-sprayed coating at 550-750 °C were characterized and compared in this study. In general, all the oxidation and hot corrosion kinetic curves of the coating followed a parabolic law, i.e., the weight of the specimens showed a rapid growth initially and then reached the gradual state. However, the initial stage of the hot corrosion process was approximately two times longer than that of the oxidation process, indicating a longer preparation time required for the formation of a protective scale in the former process. At 650 °C, the parabolic rate constant for the hot corrosion was 7.2 × 10-12 g2/(cm4·s), approximately 1.7 times higher than that for the oxidation at the same temperature. The lower parabolic rate constant for the oxidation was mainly attributed to the formation of a protective oxide scale on the surface of corroded specimens, which was composed of a mixture of NiO, Cr2O3, and NiCr2O4. However, as the liquid molten salts emerged during the hot corrosion, these protective oxides would be dissolved and the coating was corrupted acceleratedly.

Cyclic nucleotide content of tobacco BY-2 cells.

PubMed

Richards, Helen; Das, Swadipa; Smith, Christopher J; Pereira, Louisa; Geisbrecht, Alan; Devitt, Nicola J; Games, David E; van Geyschem, Jan; Gareth Brenton, A; Newton, Russell P

2002-11-01

The cyclic nucleotide content of cultured tobacco bright yellow-2 (BY-2) cells was determined, after freeze-killing, perchlorate extraction and sequential chromatography, by radioimmunoassay. The identities of the putative cyclic nucleotides, adenosine 3',5'-cyclic monophosphate (cyclic AMP), guanosine 3',5'-cyclic monophosphate (cyclic GMP) and cytidine 3',5'-cyclic monophosphate (cyclic CMP) were unambiguously confirmed by tandem mass spectrometry. The potential of BY-2 cell cultures as a model system for future investigations of cyclic nucleotide function in higher plants is discussed.

Interfacial Stresses and the Anomalous Character of Thermoelastic-Deformation Curves of a Cu-Al-Ni Shape-Memory Alloy

NASA Astrophysics Data System (ADS)

Malygin, G. A.; Nikolaev, V. I.; Pulnev, S. A.; Chikiryaka, A. V.

2017-12-01

Thermoelastic-deformation curves of a single-crystalline Cu-13.5 wt % Al-4.0 wt % Ni shapememory (SM) alloy have been studied. Cyclic temperature variation in a 300-450 K interval revealed an anomalous character of thermoelastic hysteresis loops with regions of accelerated straining at both heating and cooling stages. The observed phenomenon can be used for increasing the response speed of SM-alloy based drive and sensor devices. Analysis of this phenomenon in the framework of the theory of diffuse martensitic transformations showed that the anomalous character of thermoelastic hysteresis loops may be related to the influence of interfacial stresses on the dynamics of martensitic transformations in these SM alloys.

On improving the iterative convergence properties of an implicit approximate-factorization finite difference algorithm. [considering transonic flow

NASA Technical Reports Server (NTRS)

Desideri, J. A.; Steger, J. L.; Tannehill, J. C.

1978-01-01

The iterative convergence properties of an approximate-factorization implicit finite-difference algorithm are analyzed both theoretically and numerically. Modifications to the base algorithm were made to remove the inconsistency in the original implementation of artificial dissipation. In this way, the steady-state solution became independent of the time-step, and much larger time-steps can be used stably. To accelerate the iterative convergence, large time-steps and a cyclic sequence of time-steps were used. For a model transonic flow problem governed by the Euler equations, convergence was achieved with 10 times fewer time-steps using the modified differencing scheme. A particular form of instability due to variable coefficients is also analyzed.

Nonrelativistic Perpendicular Shocks Modeling Young Supernova Remnants: Nonstationary Dynamics and Particle Acceleration at Forward and Reverse Shocks

NASA Astrophysics Data System (ADS)

Wieland, Volkmar; Pohl, Martin; Niemiec, Jacek; Rafighi, Iman; Nishikawa, Ken-Ichi

2016-03-01

For parameters that are applicable to the conditions at young supernova remnants, we present results of two-dimensional, three-vector (2D3V) particle-in-cell simulations of a non-relativistic plasma shock with a large-scale perpendicular magnetic field inclined at a 45^\\circ angle to the simulation plane to approximate three-dimensional (3D) physics. We developed an improved clean setup that uses the collision of two plasma slabs with different densities and velocities, leading to the development of two distinctive shocks and a contact discontinuity. The shock formation is mediated by Weibel-type filamentation instabilities that generate magnetic turbulence. Cyclic reformation is observed in both shocks with similar period, for which we note global variations due to shock rippling and local variations arising from turbulent current filaments. The shock rippling occurs on spatial and temporal scales produced by the gyro-motions of shock-reflected ions. The drift motion of electrons and ions is not a gradient drift, but is commensurate with {\\boldsymbol{E}}× {\\boldsymbol{B}} drift. We observe a stable supra-thermal tail in the ion spectra, but no electron acceleration because the amplitude of the Buneman modes in the shock foot is insufficient for trapping relativistic electrons. We see no evidence of turbulent reconnection. A comparison with other two-dimensional (2D) simulation results suggests that the plasma beta and the ion-to-electron mass ratio are not decisive for efficient electron acceleration, but the pre-acceleration efficacy might be reduced with respect to the 2D results once 3D effects are fully accounted for. Other microphysical factors may also play a part in limiting the amplitude of the Buneman waves or preventing the return of electrons to the foot region.

Kinetic parameters and renal clearances of plasma adenosine 3′,5′-monophosphate and guanosine 3′,5′-monophosphate in man

PubMed Central

Broadus, Arthur E.; Kaminsky, Neil I.; Hardman, Joel G.; Sutherland, Earl W.; Liddle, Grant W.

1970-01-01

Kinetic parameters and the renal clearances of plasma adenosine 3′,5′-monophosphate (cyclic AMP) and guanosine 3′,5′-monophosphate (cyclic GMP) were evaluated in normal subjects using tritium-labeled cyclic nucleotides. Each tracer was administered both by single, rapid intravenous injection and by constant intravenous infusion, and the specific activities of the cyclic nucleotides in plasma and urine were determined. Both cyclic AMP and cyclic GMP were cleared from plasma by glomerular filtration. The kidney was found to add a variable quantity of endogenous cyclic AMP to the tubular urine, amounting to an average of approximately one-third of the total level of cyclic AMP excreted. Plasma was the source of virtually all of the cyclic GMP excreted. Plasma levels of the cyclic nucleotides appeared to be in dynamic steady state. The apparent volumes of distribution of both nucleotides exceeded extracellular fluid volume, averaging 27 and 38% of body weight for cyclic AMP and cyclic GMP, respectively. Plasma production rates ranged from 9 to 17 nmoles/min for cyclic AMP and from 7 to 13 nmoles/min for cyclic GMP. Plasma clearance rates averaged 668 ml/min for cyclic AMP and 855 ml/min for cyclic GMP. Approximately 85% of the elimination of the cyclic nucleotides from the circulation was due to extrarenal clearance. PMID:5480849

MMS Observations of Langmuir Collapse and Emission?

NASA Astrophysics Data System (ADS)

Boardsen, S. A.; Che, H.; Wilder, F. D.; Ergun, R.; Le Contel, O.; Gershman, D. J.; Giles, B. L.; Moore, T. E.; Paterson, W.

2017-12-01

Through the two stream instability, electron beams accelerated by solar flares and nanoflares are believed to be responsible for several types of solar radio bursts observed in the corona and interplanetary medium, including flare-associated coronal Type J, U, and Type III radio bursts, and nanoflare-associated weak coronal type III bursts. However the duration of these radio bursts is several orders of magnitude longer than the linear saturation time of the electron two-stream instability. This discrepancy has been a long-standing puzzle. Recently Che et al. [2017, doi: 10.1073/pnas.1614055114] proposed a mechanism in which the plasma coherent emission is maintained by the cyclic Langmuir collapse. Wave coupling between Langmuir waves and electrostatic whistler waves is the key process necessary to close the feedback loop. In the magnetosphere, electron beams are commonly produced by acceleration processes such as magnetic reconnection, during which both whistlers and Langmuir waves are observed and thus provide possible in-situ observations to test and study the emission process near the acceleration source region. The high spatial and time resolution MMS fields and particle data are used to test aspects of this mechanism. In this presentation, we will present some preliminary results from MMS observations of electron beams near a reconnection region. We investigate, in the regions where the electron beams are observed, the coupling between high frequency Langmuir waves and low frequency electrostatic whistler waves, and the associated electromagnetic emissions, along with other possible specific features predicted by this model.

Analysis of cerium-composite polymer-electrolyte membranes during and after accelerated oxidative-stability test

NASA Astrophysics Data System (ADS)

Shin, Dongwon; Han, Myungseong; Shul, Yong-Gun; Lee, Hyejin; Bae, Byungchan

2018-02-01

The oxidative stability of membranes constructed from a composite of pristine sulfonated poly(arylene ether sulfone) and cerium was investigated by conducting an accelerated oxidative-stability test at the open-circuit voltage (OCV). The membranes were analyzed in situ through OCV and impedance measurements, cyclic voltammetry, and linear-sweep voltammetry to monitor the electrochemical properties during the stability test. Although the high-frequency resistance of a composite membrane was slightly higher than that of a pristine membrane because of the exchange of protons from the sulfonic acid with cerium ions, the composite membrane maintained its potential for much longer than the pristine membrane. The effect of the cerium ions as radical scavengers was confirmed by analyzing the drain water and chemical structure after operation. These post-operation analyses confirmed that cerium ions improved the oxidative stability of the hydrocarbon-based polymer during fuel-cell operation. It is clear that the cerium-based radical scavengers prevented chemical degradation of the polymer membrane as well as the electrode in terms of hydrogen cross-over, polymer-chain scission, and the electrochemical surface area, while they rarely diffused outward from the membrane.

Structural diversity of marine cyclic peptides and their molecular mechanisms for anticancer, antibacterial, antifungal, and other clinical applications.

PubMed

Lee, Yeji; Phat, Chanvorleak; Hong, Soon-Cheol

2017-09-01

Many cyclic peptides and analogues derived from marine sources are known to possess biological properties, including anticancer, antitumor, antibacterial, antifungal, antiparasitic, anti-inflammation, anti-proliferative, anti-hypertensive, cytotoxic, and antibiotic properties. These compounds demonstrate different activities and modes of action according to their structure such as cyclic oligopeptide, cyclic lipopeptide, cyclic glycopeptide and cyclic depsipeptide. The recent advances in application of the above-mentioned cyclic peptides were reported in dolastatins, soblidotin, didemnin B, aplidine, salinosporamide A, kahalalide F and bryostatin 1 and they are currently in clinical trials. These cyclic peptides are possible novel drugs discovered and developed from marine origin. Literature data concerning the potential properties of marine cyclic peptides were reviewed here, and the structural diversity and biological activities of marine cyclic peptides are discussed in relation to the molecular mechanisms of these marine cyclic peptides. Copyright © 2017 Elsevier Inc. All rights reserved.

Visual search of cyclic spatio-temporal events

NASA Astrophysics Data System (ADS)

Gautier, Jacques; Davoine, Paule-Annick; Cunty, Claire

2018-05-01

The analysis of spatio-temporal events, and especially of relationships between their different dimensions (space-time-thematic attributes), can be done with geovisualization interfaces. But few geovisualization tools integrate the cyclic dimension of spatio-temporal event series (natural events or social events). Time Coil and Time Wave diagrams represent both the linear time and the cyclic time. By introducing a cyclic temporal scale, these diagrams may highlight the cyclic characteristics of spatio-temporal events. However, the settable cyclic temporal scales are limited to usual durations like days or months. Because of that, these diagrams cannot be used to visualize cyclic events, which reappear with an unusual period, and don't allow to make a visual search of cyclic events. Also, they don't give the possibility to identify the relationships between the cyclic behavior of the events and their spatial features, and more especially to identify localised cyclic events. The lack of possibilities to represent the cyclic time, outside of the temporal diagram of multi-view geovisualization interfaces, limits the analysis of relationships between the cyclic reappearance of events and their other dimensions. In this paper, we propose a method and a geovisualization tool, based on the extension of Time Coil and Time Wave, to provide a visual search of cyclic events, by allowing to set any possible duration to the diagram's cyclic temporal scale. We also propose a symbology approach to push the representation of the cyclic time into the map, in order to improve the analysis of relationships between space and the cyclic behavior of events.

Dynamic elastic-plastic response of a 2-DOF mass-spring system.

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

Corona, Edmundo

The objective of the work presented here arose from abnormal, drop scenarios and specifically the question of how the accelerations and accumulation of plastic strains of internal components could be a ected by the material properties of the external structure. In some scenarios, the impact loads can induce cyclic motion of the internal components. Therefore, a second objective was to explore di erences that could be expected when simulations are conducted using isotropic hardening vs. kinematic hardening plasticity models. The simplest model that can be used to investigate the objectives above is a two-degree-offreedom mass/spring model where the springs exhibitmore » elastic-plastic behavior. The purpose of this memo is to develop such model and present a few results that address the objectives.« less

Charging dynamics of supercapacitors with narrow cylindrical nanopores.

PubMed

Lee, Alpha A; Kondrat, Svyatoslav; Oshanin, Gleb; Kornyshev, Alexei A

2014-08-08

We present a coarse-grained, continuum kinetic theory for charging supercapacitors with narrow cylindrical nanopores. The theory reveals that the occupancy of a nonpolarized pore and the energy barrier for ion-ion interdiffusion are the key issues controlling the different regimes of dynamic response. For 'ionophobic' pores, where the pore is empty at no applied voltage, charge density advances into the pore via diffusion-like dynamics. The mechanism of charging an 'ionophilic' pore is starkly different: for moderate ionophilicities, co-ions are expelled from the pore in a front-like manner, with significant 'congestion' at the pore entrance predicted for strong ionophilicity. We thus show that pore ionophilicity is detrimental to the speed of charging/discharging cycles, whereas making pores more ionophobic can substantially accelerate charging and cyclic recharging.

Charging dynamics of supercapacitors with narrow cylindrical nanopores

NASA Astrophysics Data System (ADS)

Lee, Alpha A.; Kondrat, Svyatoslav; Oshanin, Gleb; Kornyshev, Alexei A.

2014-08-01

We present a coarse-grained, continuum kinetic theory for charging supercapacitors with narrow cylindrical nanopores. The theory reveals that the occupancy of a nonpolarized pore and the energy barrier for ion-ion interdiffusion are the key issues controlling the different regimes of dynamic response. For ‘ionophobic’ pores, where the pore is empty at no applied voltage, charge density advances into the pore via diffusion-like dynamics. The mechanism of charging an ‘ionophilic’ pore is starkly different: for moderate ionophilicities, co-ions are expelled from the pore in a front-like manner, with significant ‘congestion’ at the pore entrance predicted for strong ionophilicity. We thus show that pore ionophilicity is detrimental to the speed of charging/discharging cycles, whereas making pores more ionophobic can substantially accelerate charging and cyclic recharging.

Microporous layer based on SiC for high temperature proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Lobato, Justo; Zamora, Héctor; Cañizares, Pablo; Plaza, Jorge; Rodrigo, Manuel Andrés

2015-08-01

This work reports the evaluation of Silicon Carbide (SiC) for its application in microporous layers (MPL) of HT-PEMFC electrodes and compares results with those obtained using conventional MPL based on Vulcan XC72. Influence of the support load on the MPL prepared with SiC was evaluated, and the MPL were characterized by XRD, Hg porosimetry and cyclic voltammetries. In addition, a short lifetest was carried out to evaluate performance in accelerated stress conditions. Results demonstrate that SiC is a promising alternative to carbonaceous materials because of its higher electrochemical and thermal stability and the positive effect on mass transfer associated to its different pore size distribution. Ohmic resistance is the most significant challenge to be overcome in further studies.

Stress and the Hair Growth Cycle: Cortisol-Induced Hair Growth Disruption.

PubMed

Thom, Erling

2016-08-01

The stress hormone, cortisol, is known to affect the function and cyclic regulation of the hair follicle. When cortisol is present at high levels it has been demonstrated to reduce the synthesis and accelerate the degradation of important skin elements, namely hyaluronan and proteoglycans by approximately 40%. The following discussion outlines the relationship between stress, cortisol, and the effect on the normal function of the hair follicle. As a result of this connection, important correlations have been established in the literature to form a basis for novel, effective treatments of stress-related hair growth disorders.
Amongst various treatment methods and substances, oral supplementation with a specific bioavailable proteoglycan stands out as a promising new therapeutic treatment method.

J Drugs Dermatol. 2016;15(8):1001-1004.

Arsenic species in weathering mine tailings and biogenic solids at the Lava Cap Mine Superfund Site, Nevada City, CA

USGS Publications Warehouse

Foster, Andrea L.; Ashley, Roger P.; Rytuba, James J.

2011-01-01

Sub- to anoxic conditions minimize dissolution of arsenopyrite at the LCMS site, but may accelerate the dissolution of As-bearing secondary iron phases such as Fe3+-oxyhydroxides and arseniosiderite, if sufficient organic matter is present to spur anaerobic microbial activity. Oxidizing, dry conditions favor the stabilization of secondary phases, while promoting oxidative breakdown of the primary sulfides. The stability of both primary and secondary As phases is likely to be at a minimum under cyclic wet-dry conditions. Biogenic iron (hydr)oxide flocs can sequester significant amounts of arsenic; this property may be useful for treatment of perpetual sources of As such as mine adit water, but the fate of As associated with natural accumulations of floc material needs to be assessed.

Accelerated lamellar disintegration in eutectoid steel

NASA Astrophysics Data System (ADS)

Mishra, Shakti; Mishra, Alok; Show, Bijay Kumar; Maity, Joydeep

2017-04-01

The fastest kinetics of lamellar disintegration (predicted duration of 44 min) in AISI 1080 steel is obtained with a novel approach of incomplete austenitisation-based cyclic heat treatment involving forced air cooling with an air flow rate of 8.7 m3 h-1. A physical model for process kinetics is proposed that involves lamellar fragmentation, lamellar thickening, divorced eutectoid growth and generation of new lamellar faults in remaining cementite lamellae in each cycle. Lamellar fragmentation is accentuated with faster rate of cooling through generation of more intense lamellar faults; but divorced eutectoid growth is ceased. Accordingly, as compared to still air cooling, much faster kinetics of lamellar disintegration is obtained by forced air cooling together with the generation of much smaller submicroscopic cementite particles (containing more proportion of plate-shaped non-spheroids) in divorced eutectoid region.

Elevated Temperature Crack Growth Behavior in HSCT Structural Materials

NASA Technical Reports Server (NTRS)

Saxena, Ashok

1998-01-01

Structures in super-sonic aircraft are subjected to conditions of high temperature and cyclic and sustained loading for extended periods of time. The durability of structures fabricated from aluminum and certain titanium alloys in such demanding conditions is of primary concern to the designers and manufacturers of futuristic transport aircraft. Accordingly, the major goal of this project was to evaluate the performance and durability of high temperature aluminum and titanium alloys for use in high speed civil transport (HSCT) structures. Additional goals were to develop time-dependent fracture mechanics methodology and test methods for characterizing and predicting elevated temperature crack growth behavior in creep-brittle materials such as ones being considered for use in HSCT structures and to explore accelerated methods of simulating microstructural degradation during service and measuring degraded properties in these materials.

Cyclic Dipeptides from Bacillus vallismortis BS07 Require Key Components of Plant Immunity to Induce Disease Resistance in Arabidopsis against Pseudomonas Infection

PubMed Central

Noh, Seong Woo; Seo, Rira; Park, Jung-Kwon; Manir, Md. Maniruzzaman; Park, Kyungseok; Sang, Mee Kyung; Moon, Surk-Sik; Jung, Ho Won

2017-01-01

Cyclic dipeptides (CDPs) are one of the simplest compounds produced by living organisms. Plant-growth promoting rhizobacteria (PGPRs) also produce CDPs that can induce disease resistance. Bacillus vallismortis strain BS07 producing various CDPs has been evaluated as a potential biocontrol agent against multiple plant pathogens in chili pepper. However, plant signal pathway triggered by CDPs has not been fully elucidated yet. Here we introduce four CDPs, cyclo(Gly-L-Pro) previously identified from Aspergillus sp., and cyclo(L-Ala-L-Ile), cyclo(L-Ala-L-Leu), and cyclo(LLeu-L-Pro) identified from B. vallismortis BS07, which induce disease resistance in Arabidopsis against Pseudomonas syringae infection. The CDPs do not directly inhibit fungal and oomycete growth in vitro. These CDPs require PHYTOALEXIN DEFICIENT4, SALICYLIC ACID INDUCTION DEFICIENT2, and NONEXPRESSOR OF PATHOGENESIS-RELATED PROTEINS1 important for salicylic acid-dependent defense to induce resistance. On the other hand, regulators involved in jasmonate-dependent event, such as ETHYLENE RECEPTOR1, JASMONATE RESPONSE1, and JASMONATE INSENSITIVE1, are necessary to the CDP-induced resistance. Furthermore, treatment of these CDPs primes Arabidopsis plants to rapidly express PATHOGENESIS-RELATED PROTEIN4 at early infection phase. Taken together, we propose that these CDPs from PGPR strains accelerate activation of jasmonate-related signaling pathway during infection. PMID:28811757

Exposure to stallion accelerates the onset of mares' cyclicity.

PubMed

Wespi, B; Sieme, H; Wedekind, C; Burger, D

2014-07-15

Horses (Equus caballus) belong to the group of seasonally polyestrous mammals. Estrous cycles typically start with increasing daylight length after winter, but mares can differ greatly in the timing of onset of regular estrus cycles. Here, we test whether spatial proximity to a stallion also plays a role. Twenty-two anestrous mares were either exposed to one of two stallions (without direct physical contact) or not exposed (controls) under experimental conditions during two consecutive springs (February to April). Ovarian activity was monitored via transrectal ultrasound and stallion's direct contact time with each mare was determined three times per week for one hour each. We found that mares exposed to a stallion ovulated earlier and more often during the observational period than mares that were not exposed to stallions. Neither stallion identity nor direct contact time, mare age, body condition, size of her largest follicle at the onset of the experiment, or parasite burden significantly affected the onset of cyclicity. In conclusion, the timing of estrous cycles and cycle frequency, i.e., crucial aspects of female reproductive strategy, strongly depend on how the mares perceive their social environment. Exposing mares to the proximity of a stallion can therefore be an alternative to, for example, light programs or elaborated hormonal therapies to start the breeding season earlier and increase the number of estrous cycles in horses. Copyright © 2014 Elsevier Inc. All rights reserved.

Chemotaxis-mediated biodegradation of cyclic nitramine explosives RDX, HMX, and CL-20 by Clostridium sp. EDB2.

PubMed

Bhushan, Bharat; Halasz, Annamaria; Thiboutot, Sonia; Ampleman, Guy; Hawari, Jalal

2004-04-09

Cyclic nitramine explosives, RDX, HMX, and CL-20 are hydrophobic pollutants with very little aqueous solubility. In sediment and soil environments, they are often attached to solid surfaces and/or trapped in pores and distribute heterogeneously in aqueous environments. For efficient bioremediation of these explosives, the microorganism(s) must access them by chemotaxis ability. In the present study, we isolated an obligate anaerobic bacterium Clostridium sp. strain EDB2 from a marine sediment. Strain EDB2, motile with numerous peritrichous flagella, demonstrated chemotactic response towards RDX, HMX, CL-20, and NO(2)(-). The three explosives were biotransformed by strain EDB2 via N-denitration with concomitant release of NO(2)(-). Biotransformation rates of RDX, HMX, and CL-20 by the resting cells of strain EDB2 were 1.8+/-0.2, 1.1+/-0.1, and 2.6+/-0.2nmol h(-1)mgwet biomass(-1) (mean+/-SD; n=3), respectively. We found that commonly seen RDX metabolites such as TNX, methylenedinitramine, and 4-nitro-2,4-diazabutanal neither produced NO(2)(-) during reaction with strain EDB2 nor they elicited chemotaxis response in strain EDB2. The above data suggested that NO(2)(-) released from explosives during their biotransformation might have elicited chemotaxis response in the bacterium. Biodegradation and chemotactic ability of strain EDB2 renders it useful in accelerating the bioremediation of explosives under in situ conditions.

Role of nitric oxide and cyclic GMP signaling in melanocyte response to hypergravity

NASA Astrophysics Data System (ADS)

Ivanova, Krassimira; Lambers, Britta; Tsiockas, Wasiliki; Block, Ingrid; Gerzer, Rupert

Nitric oxide (NO) has a prominent role in many (patho)physiological processes in the skin including erythema, inflammation, and cancerogenesis. The soluble guanylyl cyclase (sGC), a key transducer in NO signaling, catalyzes the formation of the second messenger guanosine 3´,5´-cyclic monophosphate (cyclic cGMP or cGMP). For human melanocytes, which are responsible for skin pigmentation by synthesizing the pigment melanin, it has been reported that the NO/sGC/cGMP pathway is involved in UVB-induced melanogenesis. Melanin acts as a scavenger for free radicals that may arise during metabolic stress. It may also act as a photosensitizer that generates active oxygen species upon UV irradiation, which may initiate hypopigmentary disorders (e.g., vitiligo) as well as UV-induced oncogene cell transformation. In addition, melanoma, a deadly skin cancer, which arises from transformed melanocytes, is characterized by a resistance to chemotherapy. In our studies we have shown that NO can induce perturbation of melanocyte-extracellular matrix component interactions, which may contribute to loss of melanocytes or melanoma metastasis. Such NO effects appear to be modulated partly via cGMP. Moreover, we found that different guanylyl cyclase isoforms are responsible for cGMP synthesis in melanocytic cells. Normal human melanocytes and nonmetastatic melanoma cells predominantly express sGC, which appears to be associated with melanogenesis, whereas absence of NO-sensitive GC, but up-regulated activities of the natriuretic peptide-sensitive membrane guanylyl cyclase isoforms were found in highly metastatic phenotypes. Due to the growing interest in the regulation of signaling activities in normal and transformed cells under altered gravity conditions, we have further investigated whether the NO/cGMP signaling is involved in melanocyte response to gravitational stress. We found that normal human melanocytes and non-metastatic melanoma cell lines, but not highly metastatic cells, respond to hyper-g (up to 5xg for 24 h) with an increase in cGMP efflux and pigmentation in comparison to 1-g controls under conditions of reduced cGMP hydrolysis or accelerated cGMP synthesis (e.g., by NO but not natriuretic peptides). The elevated cGMP extrusion was related to a hyper-g-induced increase in the expression of the multidrug resistance proteins 4/5 as selective cGMP exporters as shown on mRNA and protein levels using real-time polymerase chain reaction and flow cytometric analysis. These results suggest that an environment modified by centrifugal acceleration represents a new factor for regulating cGMP levels in unstimulated and NO-stimulated human melanocytes that involves multidrug resistance proteins, which could be important for malignant transformation. Future studies on these aspects in real microgravity will be important for residents on the International Space Station and astronauts involved in long space flights.

SUMMARY OF THE SEVENTH MEETING OF THE REFRACTORY COMPOSITES WORKING GROUP

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

Gibeaut, W.A.; Ogden, H.R.

1963-05-30

Information on refractory composites for use above 2500 deg F is summarized. Reports are concerned with protective coatings, insulating ceramics, materials for rocket thrust chambers, dispersion strengthening of metals, joining of refractory materials, and testing techniques. The problem of accelerated failure of silicide coatings under conditions of very low air pressure at high temperatures is studied. Although the maximum temperature capability of most silicide coatings is reduced about 50 theta deg at low air pressures, several coatings can protect molybdenum for 1/2 hr at 2800 to 3000 deg F under these conditions. The tin-aluminum coating also is susceptible to earlymore » failure at reduced pressure. An evaluation of the mechanical properties of 6-mil foils of D- 36, B-68, and TZM coated with commercial coatings demonstrated that some coatings seriously degrade substrate mechanical properties. Research on thermal- protection systems for re-entry vehicles whose surface temperatures reach from 3300 to 5500 deg F has resulted in agreement upon oxide coatings and thick metal- reinforced oxide composites. Simple plasmaarc-sprayed oxide coatings have demonstrated adequate oxidation resistance, but their structural stability in cyclic thermal exposure is inferior to metal-reinforced oxide. Thin unreinforced oxide coatings tend to spall in tests involving cyclic heating. A metal- reinforced oxide composite (reinforcement welded to substrate) has survived cyclic tests such as five 3-minute exposures at 4500 deg F without failing. A new carbon material called glassy carbon has demonstrnted better oxidation resistance than pyrolytic graphite at very high temperatures. The erosion resistance of pyrolytic graphite coatings on regular graphite in rocket firing tests using solid propellants is encouraging. There is considerable interest in fabricating small radiation-cooled rocket thrust chambers by plasma arc spraying. The design concept of internal reinforcement of sprayed-metal rocket chambers with wrought ductile wife appears impractical because of poor bonding and porosity around the wire. (auth)« less

Cyclic steady state stress-strain behavior of UHMW polyethylene.

PubMed

Krzypow, D J; Rimnac, C M

2000-10-01

To increase the long-term performance of total joint replacements, finite element analyses of ultra high molecular weight polyethylene (UHMWPE) components have been conducted to predict the effect of load on the stress and strain distributions occurring on and within these components. Early models incorporated the monotonic behavior of UHMWPE without considering the unloading and cyclic loading behavior. However, UHMWPE components undergo cyclic loading during use and at least two wear damage modes (pitting and delamination) are thought to be associated with the fatigue fracture properties of UHMWPE. The objective of this study was to examine the fully reversed uniaxial tension/compression cyclic steady state stress-strain behavior of UHMWPE as a first step towards developing a cyclic constitutive relationship for UHMWPE. The hypothesis that cycling results in a permanent change in the stress-strain relationship, that is, that the cyclic steady state represents a new cyclically stabilized state, was examined. It was found that, like other ductile polymers, UHMWPE substantially cyclically softens under fully reversed uniaxial straining. More cyclic softening occurred in tension than in compression. Furthermore, cyclic steady state was attained, but not cyclic stability. It is suggested that it may be more appropriate to base a material constitutive relationship for UHMWPE for finite element analyses of components upon a cyclically modified stress-strain relationship.

Sequencing Cyclic Peptides by Multistage Mass Spectrometry

PubMed Central

Mohimani, Hosein; Yang, Yu-Liang; Liu, Wei-Ting; Hsieh, Pei-Wen; Dorrestein, Pieter C.; Pevzner, Pavel A.

2012-01-01

Some of the most effective antibiotics (e.g., Vancomycin and Daptomycin) are cyclic peptides produced by non-ribosomal biosynthetic pathways. While hundreds of biomedically important cyclic peptides have been sequenced, the computational techniques for sequencing cyclic peptides are still in their infancy. Previous methods for sequencing peptide antibiotics and other cyclic peptides are based on Nuclear Magnetic Resonance spectroscopy, and require large amount (miligrams) of purified materials that, for most compounds, are not possible to obtain. Recently, development of mass spectrometry based methods has provided some hope for accurate sequencing of cyclic peptides using picograms of materials. In this paper we develop a method for sequencing of cyclic peptides by multistage mass spectrometry, and show its advantages over single stage mass spectrometry. The method is tested on known and new cyclic peptides from Bacillus brevis, Dianthus superbus and Streptomyces griseus, as well as a new family of cyclic peptides produced by marine bacteria. PMID:21751357

Cyclic nucleotide binding proteins in the Arabidopsis thaliana and Oryza sativa genomes

PubMed Central

Bridges, Dave; Fraser, Marie E; Moorhead, Greg BG

2005-01-01

Background Cyclic nucleotides are ubiquitous intracellular messengers. Until recently, the roles of cyclic nucleotides in plant cells have proven difficult to uncover. With an understanding of the protein domains which can bind cyclic nucleotides (CNB and GAF domains) we scanned the completed genomes of the higher plants Arabidopsis thaliana (mustard weed) and Oryza sativa (rice) for the effectors of these signalling molecules. Results Our analysis found that several ion channels and a class of thioesterases constitute the possible cyclic nucleotide binding proteins in plants. Contrary to some reports, we found no biochemical or bioinformatic evidence for a plant cyclic nucleotide regulated protein kinase, suggesting that cyclic nucleotide functions in plants have evolved differently than in mammals. Conclusion This paper provides a molecular framework for the discussion of cyclic nucleotide function in plants, and resolves a longstanding debate about the presence of a cyclic nucleotide dependent kinase in plants. PMID:15644130

Desensitization of atriopeptin stimulated accumulation and extrusion of cyclic GMP from a kidney epithelial cell line (MDCK).

PubMed

Woods, M; Houslay, M D

1991-02-01

Atriopeptin caused dose- (EC50 ca. 2 x 10(-8) M) and time-dependent increases in the intracellular concentration of cyclic GMP in the MDCK kidney epithelial cell line; an effect potentiated by the phosphodiesterase inhibitor, IBMX. The atriopeptin-catalysed increase in cyclic GMP was transient and reached a maximum some 10-20 min after challenge of cells with atriopeptin. The basis for the transience of this increase was shown to be due to the desensitization of guanylate cyclase coupled with extrusion of cyclic GMP from the cells and the degradation of cyclic GMP by phosphodiesterase activity. Atriopeptin-catalysed extrusion of cyclic GMP was time- and dose-(EC50 ca. 1.5 x 10(-8) M) dependent and was inhibited by probenecid but not by high external cyclic GMP concentrations. The extrusion process underwent apparent desensitization as did guanylate cyclase with similar half lives (T1/2 of ca. 20 min). Desensitization was dose-dependent upon atriopeptin and did not appear to be mediated by elevated cyclic GMP concentrations as pre-incubation with 8-bromo cyclic GMP did not cause desensitization and the half-times for desensitization were similar whether or not IBMX was present. The majority of the cyclic nucleotide phosphodiesterase activity was found in the cytosol fraction of the cells and could be separated into two cyclic AMP specific forms and two cyclic GMP preferring forms.

Dielectric characterization of high-performance spaceflight materials

NASA Astrophysics Data System (ADS)

Kleppe, Nathan Alan

As commercial space travel increases, the need for reliable structural health monitoring to predict possible weaknesses or failures of structural materials also increases. Monitoring of polymer-based materials may be achieved through the use of dielectric spectroscopy by comparing permittivity or conductivity measurements performed on a sample in use to that of a pristine sample. Changes in these measured values or of the relaxation frequencies, if present, can indicate chemical or physical changes occurring within the material and the possible need for maintenance/replacement. In this work, we established indicative trends that occur in the dielectric spectra during accelerated aging of various high-performance polymeric materials (EVOH, PEEK, PPS, and UHMWPE). Uses for these materials range from electrical insulation and protective coatings to windows and air- or space-craft parts that may be subject to environmental damage over long-term operation. Accelerated thermal aging and ultraviolet/water-spray cyclic aging were performed in order to investigate the degradation of the aforementioned material. The Havriliak-Negami model was used in the analysis of the measured dielectric spectra in order to obtain the characteristic fit parameters from which aging-related trends were identified. With reference to the literature and from measured FTIR spectra, observations were connected to the underlying mechanisms causing the dielectric relaxations.

Accelerated fatigue durability of a high performance composite

NASA Technical Reports Server (NTRS)

Rotem, A.

1982-01-01

The fatigue behavior of multidirectional graphite-epoxy laminates was analyzed theoretically and experimentally in an effort to establish an accelerated testing methodology. Analysis of the failure mechanism in fatigue of the laminates led to the determination of the failure mode governing fracture. The nonlinear, cyclic-dependent shear modulus was used to calculate the changing stress field in the laminate during the fatigue loading. Fatigue tests were performed at three different temperatures: 25 C, 74 C, and 114 C. The prediction of the S-N curves was made based on the artificial static strength artificial static strength at a reference temperature and the fatigue functions associated with them. The prediction of an S-N curve at other temperatures was performed using shifting factors determined for the specific failure mode. For multidirectional laminates, different S-N curves at different temperatures could be predicted using these shifting factors. Different S-N curves at different temperatures occur only when the fatigue failure mode is matrix dominated. It was found that whenever the fatigue failure mode is fiber dominated, temperature, over the range investigated, had no influence on the fatigue life. These results permit the prediction of long-time, low temperature fatigue behavior from data obtained in short time, high temperature testing, for laminates governed by a matrix failure mode.

Predictive models of poly(ethylene-terephthalate) film degradation under multi-factor accelerated weathering exposures

PubMed Central

Ngendahimana, David K.; Fagerholm, Cara L.; Sun, Jiayang; Bruckman, Laura S.

2017-01-01

Accelerated weathering exposures were performed on poly(ethylene-terephthalate) (PET) films. Longitudinal multi-level predictive models as a function of PET grades and exposure types were developed for the change in yellowness index (YI) and haze (%). Exposures with similar change in YI were modeled using a linear fixed-effects modeling approach. Due to the complex nature of haze formation, measurement uncertainty, and the differences in the samples’ responses, the change in haze (%) depended on individual samples’ responses and a linear mixed-effects modeling approach was used. When compared to fixed-effects models, the addition of random effects in the haze formation models significantly increased the variance explained. For both modeling approaches, diagnostic plots confirmed independence and homogeneity with normally distributed residual errors. Predictive R2 values for true prediction error and predictive power of the models demonstrated that the models were not subject to over-fitting. These models enable prediction under pre-defined exposure conditions for a given exposure time (or photo-dosage in case of UV light exposure). PET degradation under cyclic exposures combining UV light and condensing humidity is caused by photolytic and hydrolytic mechanisms causing yellowing and haze formation. Quantitative knowledge of these degradation pathways enable cross-correlation of these lab-based exposures with real-world conditions for service life prediction. PMID:28498875

Ubiquinol-10 supplementation activates mitochondria functions to decelerate senescence in senescence-accelerated mice.

PubMed

Tian, Geng; Sawashita, Jinko; Kubo, Hiroshi; Nishio, Shin-ya; Hashimoto, Shigenari; Suzuki, Nobuyoshi; Yoshimura, Hidekane; Tsuruoka, Mineko; Wang, Yaoyong; Liu, Yingye; Luo, Hongming; Xu, Zhe; Mori, Masayuki; Kitano, Mitsuaki; Hosoe, Kazunori; Takeda, Toshio; Usami, Shin-ichi; Higuchi, Keiichi

2014-06-01

The present study was conducted to define the relationship between the anti-aging effect of ubiquinol-10 supplementation and mitochondrial activation in senescence-accelerated mouse prone 1 (SAMP1) mice. Here, we report that dietary supplementation with ubiquinol-10 prevents age-related decreases in the expression of sirtuin gene family members, which results in the activation of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a major factor that controls mitochondrial biogenesis and respiration, as well as superoxide dismutase 2 (SOD2) and isocitrate dehydrogenase 2 (IDH2), which are major mitochondrial antioxidant enzymes. Ubiquinol-10 supplementation can also increase mitochondrial complex I activity and decrease levels of oxidative stress markers, including protein carbonyls, apurinic/apyrimidinic sites, malondialdehydes, and increase the reduced glutathione/oxidized glutathione ratio. Furthermore, ubiquinol-10 may activate Sirt1 and PGC-1α by increasing cyclic adenosine monophosphate (cAMP) levels that, in turn, activate cAMP response element-binding protein (CREB) and AMP-activated protein kinase (AMPK). These results show that ubiquinol-10 may enhance mitochondrial activity by increasing levels of SIRT1, PGC-1α, and SIRT3 that slow the rate of age-related hearing loss and protect against the progression of aging and symptoms of age-related diseases.

Progress of Chiral Schiff Bases with C1 Symmetry in Metal-Catalyzed Asymmetric Reactions.

PubMed

Hayashi, Masahiko

2016-12-01

In this Personal Account, various chiral Schiff base-metal-catalyzed enantioselective organic reactions are reported; the Schiff bases used were O,N,O- as well as N,N,P-tridentate ligands and N,N-bidentate ligands having C 1 symmetry. In particular, the enantioselective addition of trimethylsilyl cyanide, dialkylzinc, and organozinc halides to aldehydes, enantioselective 1,4-addition of dialkylzinc to cyclic and acyclic enones, and asymmetric allylic oxidation are reported. Typically, ketimine-type Schiff base-metal complexes exhibited higher reactivity and enantioselectivity compared with the corresponding aldimine-type Schiff base-metal complexes. Notably, remarkable ligand acceleration was observed for all reactions. The obtained products can be used as key intermediates for optically active natural products and pharmaceuticals. © 2016 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the dynamical behaviour of low-frequency earthquake swarms prior to a dome collapse of Soufrière Hill volcano, Montserrat

NASA Astrophysics Data System (ADS)

Hammer, C.; Neuberg, J. W.

2009-03-01

A series of low-frequency earthquake swarms prior to a dome collapse on Soufrière Hills volcano, Montserrat, are investigated with the emphasis on event rate and amplitude behaviour. In a single swarm, the amplitudes of consecutive events tend to increase with time, while the rate of event occurrence accelerates initially and then decelerates toward the end of the swarm. However, when consecutive swarms are considered, the average event rates seem to follow the material failure law, and the time of the dome collapse can be successfully estimated using the inverse event rate. These patterns in amplitude and event rate are interpreted as fluctuations in magma ascent velocity, which result in both the generation of low-frequency events as well as cyclic ground deformation accompanying the swarm activity.

Electricity Market Liberalisation and Flexibility of Conventional Generation to Balance Intermittent Renewable Energy - Is It Possible to Stay Competitive?

NASA Astrophysics Data System (ADS)

Linkevics, O.; Ivanova, P.; Balodis, M.

2016-12-01

Intermittent generation (solar PV and wind energy) integration in power production portfolio as well as electricity price fluctuations have changed the running manner of conventional combined heat and power (CHP) plants: the shift from base load operation to running in cyclic modes. These cogeneration power plants are not adapted to new running conditions. The level of CHP plant flexibility should be improved to operate profitably and efficiently from both technical and fuel usage point of view. There are different ways to increase the flexibility of power plants. Before any improvements, the situation at power plants should be evaluated and the weakest points defined. In this publication, such measures are presented on Riga CHP-2 plant example: installation of heat storage tank; extension of operation rang; acceleration of start-ups.

A unified classification model for modeling of seismic liquefaction potential of soil based on CPT

PubMed Central

Samui, Pijush; Hariharan, R.

2014-01-01

The evaluation of liquefaction potential of soil due to an earthquake is an important step in geosciences. This article examines the capability of Minimax Probability Machine (MPM) for the prediction of seismic liquefaction potential of soil based on the Cone Penetration Test (CPT) data. The dataset has been taken from Chi–Chi earthquake. MPM is developed based on the use of hyperplanes. It has been adopted as a classification tool. This article uses two models (MODEL I and MODEL II). MODEL I employs Cone Resistance (qc) and Cyclic Stress Ratio (CSR) as input variables. qc and Peak Ground Acceleration (PGA) have been taken as inputs for MODEL II. The developed MPM gives 100% accuracy. The results show that the developed MPM can predict liquefaction potential of soil based on qc and PGA. PMID:26199749

A unified classification model for modeling of seismic liquefaction potential of soil based on CPT.

PubMed

Samui, Pijush; Hariharan, R

2015-07-01

The evaluation of liquefaction potential of soil due to an earthquake is an important step in geosciences. This article examines the capability of Minimax Probability Machine (MPM) for the prediction of seismic liquefaction potential of soil based on the Cone Penetration Test (CPT) data. The dataset has been taken from Chi-Chi earthquake. MPM is developed based on the use of hyperplanes. It has been adopted as a classification tool. This article uses two models (MODEL I and MODEL II). MODEL I employs Cone Resistance (q c) and Cyclic Stress Ratio (CSR) as input variables. q c and Peak Ground Acceleration (PGA) have been taken as inputs for MODEL II. The developed MPM gives 100% accuracy. The results show that the developed MPM can predict liquefaction potential of soil based on q c and PGA.

APPARATUS FOR MEASURING NEUTRON CROSS SECTIONS

DOEpatents

Cranberg, L.

1959-07-14

An apparatus is described for analyzing the nuclear reaction products resulting from impingement of nuclear particles against a selected target material and automatically recording the number of reaction prcducts in selected energy levels. The target is bombarded by ions from a particle accelerator and the target potential is cyclicly varied over a particular energy range by a modulator. A nuclear reaction detector is lccated adjacent the target to produce pulses for each reaction product. The output from the detector and the modulator are coupled to a function sampler, for generating a pulse in respcnse to each detected event having an amplitude proportional to the amplitude of the instantaneous target potential. The later pulses are coupled to a multichannel analyzer, whereby nuclear reactions are recorded in appropriate channels of the analyzer in correspcndence with the magnitude of the energy of the impinging ions.

Failure Mechanisms and Life Prediction of Thermal and Environmental Barrier Coatings under Thermal Gradients

NASA Technical Reports Server (NTRS)

Zju, Dongming; Ghosn, Louis J.; Miller, Robert A.

2008-01-01

Ceramic thermal and environmental barrier coatings (TEBCs) will play an increasingly important role in gas turbine engines because of their ability to further raise engine temperatures. However, the issue of coating durability is of major concern under high-heat-flux conditions. In particular, the accelerated coating delamination crack growth under the engine high heat-flux conditions is not well understood. In this paper, a laser heat flux technique is used to investigate the coating delamination crack propagation under realistic temperature-stress gradients and thermal cyclic conditions. The coating delamination mechanisms are investigated under various thermal loading conditions, and are correlated with coating dynamic fatigue, sintering and interfacial adhesion test results. A coating life prediction framework may be realized by examining the crack initiation and propagation driving forces for coating failure under high-heat-flux test conditions.

Genetics Home Reference: cyclic neutropenia

MedlinePlus

... Facebook Twitter Home Health Conditions Cyclic neutropenia Cyclic neutropenia Printable PDF Open All Close All Enable Javascript to view the expand/collapse boxes. Description Cyclic neutropenia is a disorder that causes frequent infections and ...

Regulation of Maltodextrin Phosphorylase Synthesis in Escherichia coli by Cyclic Adenosine 3′, 5′-Monophosphate and Glucose1

PubMed Central

Chao, Julie; Weathersbee, Carolyn J.

1974-01-01

Cyclic adenosine 3′, 5′-monophosphate (AMP) stimulates maltodextrin phosphorylase synthesis in Escherichia coli cells induced with maltose. A maximal effect occurs at 2 to 3 mM cyclic AMP. The action of cyclic AMP is specific, inasmuch as adenosine triphosphate, 3′-AMP, 5′-AMP, adenosine, and dibutyryl cyclic AMP are inactive. Glucose, α-methyl glucoside, 2-deoxyglucose, and pyridoxal 5′-phosphate repress maltodextrin phosphorylase synthesis. This repression is reversed by cyclic AMP. The action of cyclic AMP appears to be at the transcriptional level, since cyclic AMP fails to stimulate phosphorylase production in induced cells in which messenger ribonucleic acid synthesis has been arrested by rifampin or by inducer removal. The two other enzymes involved in the metabolism of maltose, amylomaltase and maltose permease, are also induced in this strain of E. coli and affected by glucose and cyclic AMP in a manner similar to phosphorylase. PMID:4358043

Selective phosphodiesterase 5 inhibition does not reduce propofol sedation requirements but affects speed of recovery and plasma cyclic guanosine 3',5'-monophosphate concentrations in healthy volunteers.

PubMed

Engelhardt, Thomas; MacDonald, Jamie; Galley, Helen F; Webster, Nigel R

2005-10-01

Cyclic guanosine 3',5'-monophosphate (cyclic GMP) has been implicated in modulating the effects of anesthesia. We hypothesized that limiting the breakdown of cyclic GMP through selective phosphodiesterase inhibition would influence propofol sedation requirements and plasma cyclic GMP concentrations. Ten volunteers received 100 mg of sildenafil or placebo orally in this placebo-controlled, double-blind, randomized crossover pilot study. Propofol sedation was achieved using a target-controlled infusion system until loss of verbal contact (LVC). Plasma cyclic GMP concentrations were determined at baseline, LVC, and 30 min after LVC. There was no difference in the amount of propofol used, predicted plasma concentration, or duration of sedation in volunteers after sildenafil compared with placebo treatment. Return of spontaneous verbal contact was faster after sildenafil (4 [3-8] min versus 6 [3-5] min, median [range], P = 0.019). Cyclic GMP concentrations were reduced during propofol sedation in the placebo group compared with baseline (P < 0.004). The plasma cyclic GMP concentrations were larger (P = 0.004) at LVC in the sildenafil group compared with placebo. We have shown that selective phosphodiesterase 5 inhibition decreases recovery time from propofol sedation without affecting propofol requirements. The decrease of plasma cyclic GMP concentrations during propofol sedation in the placebo group indicates a potential role of cyclic GMP in propofol anesthesia in humans. Plasma cyclic guanosine 3',5'-monophosphate (cyclic GMP) concentrations are reduced during propofol sedation. Selective phosphodiesterase 5 inhibition, however, does not reduce propofol sedation requirements or plasma cyclic GMP concentrations but affects speed of recovery in healthy volunteers.

cGMP and cyclic nucleotide-gated channels participate in mouse sperm capacitation.

PubMed

Cisneros-Mejorado, Abraham; Sánchez Herrera, Daniel P

2012-01-20

During capacitation of mammalian sperm intracellular [Ca(2+)] and cyclic nucleotides increase, suggesting that CNG channels play a role in the physiology of sperm. Here we study the effect of capacitation, 8Br-cAMP (8-bromoadenosine 3',5'-cyclic monophosphate) and 8Br-cGMP (8-bromoguanosine 3',5'-cyclic monophosphate) on the macroscopic ionic currents of mouse sperm, finding the existence of different populations of sperm, in terms of the recorded current and its response to cyclic nucleotides. Our results show that capacitation and cyclic nucleotides increase the ionic current, having a differential sensitivity to cGMP (cyclic guanosine monophosphate) and cAMP (cyclic adenosine monophosphate). Using a specific inhibitor we determine the contribution of CNG channels to macroscopic current and capacitation. Copyright © 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Growth promoting in vitro effect of synthetic cyclic RGD-peptides on human osteoblast-like cells attached to cancellous bone.

PubMed

Magdolen, Ursula; Auernheimer, Jörg; Dahmen, Claudia; Schauwecker, Johannes; Gollwitzer, Hans; Tübel, Jutta; Gradinger, Reiner; Kessler, Horst; Schmitt, Manfred; Diehl, Peter

2006-06-01

In tissue engineering, the application of biofunctional compounds on biomaterials such as integrin binding RGD-peptides has gained growing interest. Anchorage-dependent cells like osteoblasts bind to these peptides thus ameliorating the integration of a synthetic implant. In case sterilized bone grafts are used as substitutes for reconstruction of bone defects, the ingrowth of the implanted bone is often disturbed because of severe pretreatment such as irradiation or autoclaving, impairing the biological and mechanical properties of the bone. We report for the first time on the in vitro coating of the surface of freshly resected, cleaned bone discs with synthetic, cyclic RGD-peptides. For this approach, two different RGD-peptides were used, one containing two phosphonate anchors, the other peptide four of these binding moieties to allow efficient association of these reactive RGD-peptides to the inorganic bone matrix. Human osteoblast-like cells were cultured on RGD-coated bone discs and the adherence and growth of the cells were analyzed. Coating of bone discs with RGD-peptides did not improve the adhesion rate of osteoblast-like cells to the discs but significantly (up to 40%) accelerated growth of these cells within 8 days after attachment. This effect points to pretreatment of bone implants, especially at the critical interface area between the implanted bone and the non-resected residual bone structure, before re-implantation in order to stimulate and enhance osteointegration of a bone implant.

In Vivo Activation of cAMP Signaling Induces Growth Arrest and Differentiation in Acute Promyelocytic Leukemia

PubMed Central

Guillemin, Marie-Claude; Raffoux, Emmanuel; Vitoux, Dominique; Kogan, Scott; Soilihi, Hassane; Lallemand-Breitenbach, Valérie; Zhu, Jun; Janin, Anne; Daniel, Marie-Thérèse; Gourmel, Bernard; Degos, Laurent; Dombret, Hervé; Lanotte, Michel; de Thé, Hugues

2002-01-01

Differentiation therapy for acute myeloid leukemia uses transcriptional modulators to reprogram cancer cells. The most relevant clinical example is acute promyelocytic leukemia (APL), which responds dramatically to either retinoic acid (RA) or arsenic trioxide (As2O3). In many myeloid leukemia cell lines, cyclic adenosine monophosphate (cAMP) triggers growth arrest, cell death, or differentiation, often in synergy with RA. Nevertheless, the toxicity of cAMP derivatives and lack of suitable models has hampered trials designed to assess the in vivo relevance of theses observations. We show that, in an APL cell line, cAMP analogs blocked cell growth and unraveled As2O3-triggered differentiation. Similarly, in RA-sensitive or RA-resistant mouse models of APL, continuous infusions of 8-chloro-cyclic adenosine monophosphate (8-Cl-cAMP) triggered major growth arrest, greatly enhanced both spontaneous and RA- or As2O3-induced differentiation and accelerated the restoration of normal hematopoiesis. Theophylline, a well-tolerated phosphodiesterase inhibitor which stabilizes endogenous cAMP, also impaired APL growth and enhanced spontaneous or As2O3-triggered cell differentiation in vivo. Accordingly, in an APL patient resistant to combined RA–As2O3 therapy, theophylline induced blast clearance and restored normal hematopoiesis. Taken together, these results demonstrate that in vivo activation of cAMP signaling contributes to APL clearance, independently of its RA-sensitivity, thus raising hopes that other myeloid leukemias may benefit from this therapeutic approach. PMID:12438428

Removal of urea from dilute streams using RVC/nano-NiO x -modified electrode.

PubMed

Tammam, Reham H; Touny, Ahmed H; Saleh, Mahmoud M

2018-05-08

Reticulated vitreous carbon (RVC), a high surface area electrode (40 cm 2 /cm 3 ), has been modified with nickel oxide nanoparticles (nano-NiO x ) and used for electrochemical oxidation of urea from alkaline solution. For the cyclic voltammetry measurements, the used dimensions are 0.8 cm × 0.8 cm × 0.3 cm. The purpose was to offer high specific surface area using a porous open network structure to accelerate the electrochemical conversion. NiO x nanoparticles have been synthesized via an electrochemical route at some experimental conditions. The morphological, structural, and electrochemical properties of the RVC/nano-NiO x are characterized by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and potentiostatic measurements. The fabricated electrode, RVC/nano-NiO x , demonstrates high electrocatalytic activity towards urea oxidation in an alkaline electrolyte. The onset potential of the RVC/nano-NiO x compared to that of the planar GC/NiO x is shifted to more negative value with higher specific activity. The different loadings of the NiO x have a substantial influence on the conversion of urea which has been evaluated from concentration-time curves. The urea concentration decreases with time to a limit dependent on the loading extent. Maximum conversion is obtained at 0.86 mg of NiO x per cm 3 of the RVC matrix.

On cyclic yield strength in definition of limits for characterisation of fatigue and creep behaviour

NASA Astrophysics Data System (ADS)

Gorash, Yevgen; MacKenzie, Donald

2017-06-01

This study proposes cyclic yield strength as a potential characteristic of safe design for structures operating under fatigue and creep conditions. Cyclic yield strength is defined on a cyclic stress-strain curve, while monotonic yield strength is defined on a monotonic curve. Both values of strengths are identified using a two-step procedure of the experimental stress-strain curves fitting with application of Ramberg-Osgood and Chaboche material models. A typical S-N curve in stress-life approach for fatigue analysis has a distinctive minimum stress lower bound, the fatigue endurance limit. Comparison of cyclic strength and fatigue limit reveals that they are approximately equal. Thus, safe fatigue design is guaranteed in the purely elastic domain defined by the cyclic yielding. A typical long-term strength curve in time-to-failure approach for creep analysis has two inflections corresponding to the cyclic and monotonic strengths. These inflections separate three domains on the long-term strength curve, which are characterised by different creep fracture modes and creep deformation mechanisms. Therefore, safe creep design is guaranteed in the linear creep domain with brittle failure mode defined by the cyclic yielding. These assumptions are confirmed using three structural steels for normal and high-temperature applications. The advantage of using cyclic yield strength for characterisation of fatigue and creep strength is a relatively quick experimental identification. The total duration of cyclic tests for a cyclic stress-strain curve identification is much less than the typical durations of fatigue and creep rupture tests at the stress levels around the cyclic yield strength.

Advances in targeting cyclic nucleotide phosphodiesterases

PubMed Central

Maurice, Donald H.; Ke, Hengming; Ahmad, Faiyaz; Wang, Yousheng; Chung, Jay; Manganiello, Vincent C.

2014-01-01

Cyclic nucleotide phosphodiesterases (PDEs) catalyse the hydrolysis of cyclic AMP and cyclic GMP, thereby regulating the intracellular concentrations of these cyclic nucleotides, their signalling pathways and, consequently, myriad biological responses in health and disease. Currently, a small number of PDE inhibitors are used clinically for treating the pathophysiological dysregulation of cyclic nucleotide signalling in several disorders, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication and chronic obstructive pulmonary disease. However, pharmaceutical interest in PDEs has been reignited by the increasing understanding of the roles of individual PDEs in regulating the subcellular compartmentalization of specific cyclic nucleotide signalling pathways, by the structure-based design of novel specific inhibitors and by the development of more sophisticated strategies to target individual PDE variants. PMID:24687066

A cup product structure for cyclic cohomology

NASA Astrophysics Data System (ADS)

Espinosa Tintos, Jose Eduardo

In this work we construct a cup product structure for cyclic cohomology of a cyclic set X. introduced by Comics. We make use of a categorical construction of cyclic homology by Fiedorowicz and Loday to define our cup product structure by using a large resolution of the cyclic category. We also provide a way to construct a chain map from a smaller resolution where the action of the finite groups is clear. and in the process of constructing this map we learn the large complex can be viewed as all factorizations in the category DeltaC using the cyclic structure of X.

Cyclic Deformation of Ultra-Fine Grained Commercial Purity Aluminum Processed by Accumulative Roll-Bonding.

PubMed

Kwan, Charles C F; Wang, Zhirui

2013-08-13

Accumulative Roll-Bonding (ARB) is one of the more recently developed techniques capable of producing bulk ultra-fine grained (ufg) metals. There are still many aspects of the behavior of ufg metals that lacks an in-depth understanding, such as a generalized view of the factors that govern the cyclic deformation mechanism(s). This study aims to advance the understanding of the cyclic deformation behavior of ufg metals through the systematic investigation of ARB processed aluminum upon cyclic loading. It was found that the cyclic softening response often reported for ufg metals is largely influenced by the microstructure stability as the cyclic softening response is facilitated by grain coarsening which becomes inhibited with highly stable microstructure. On one hand, shear bands resembling braids of dislocations trespassing multiple grains have been observed to operate for the accommodation of the imposed cyclic strain in cases where grain coarsening is largely restricted. On the other hand, it was found that the microstructure stability can be overcome at higher applied cyclic plastic strain levels, leading to grain coarsening and thus a cyclic softening response. The findings in this study have further confirmed that the cyclic softening behavior found in many ufg metals, which may be detrimental in practical applications, can be inhibited by improvements in the microstructure stability.

Cyclic Deformation of Ultra-Fine Grained Commercial Purity Aluminum Processed by Accumulative Roll-Bonding

PubMed Central

Kwan, Charles C.F.; Wang, Zhirui

2013-01-01

Accumulative Roll-Bonding (ARB) is one of the more recently developed techniques capable of producing bulk ultra-fine grained (ufg) metals. There are still many aspects of the behavior of ufg metals that lacks an in-depth understanding, such as a generalized view of the factors that govern the cyclic deformation mechanism(s). This study aims to advance the understanding of the cyclic deformation behavior of ufg metals through the systematic investigation of ARB processed aluminum upon cyclic loading. It was found that the cyclic softening response often reported for ufg metals is largely influenced by the microstructure stability as the cyclic softening response is facilitated by grain coarsening which becomes inhibited with highly stable microstructure. On one hand, shear bands resembling braids of dislocations trespassing multiple grains have been observed to operate for the accommodation of the imposed cyclic strain in cases where grain coarsening is largely restricted. On the other hand, it was found that the microstructure stability can be overcome at higher applied cyclic plastic strain levels, leading to grain coarsening and thus a cyclic softening response. The findings in this study have further confirmed that the cyclic softening behavior found in many ufg metals, which may be detrimental in practical applications, can be inhibited by improvements in the microstructure stability. PMID:28811446

Ibudilast attenuates astrocyte apoptosis via cyclic GMP signalling pathway in an in vitro reperfusion model

PubMed Central

Takuma, K; Lee, E; Enomoto, R; Mori, K; Baba, A; Matsuda, T

2001-01-01

We examined the effect of 3-isobutyryl-2-isopropylpyrazolo[1,5-a]pyridine (ibudilast), which has been clinically used for bronchial asthma and cerebrovascular disorders, on cell viability induced in a model of reperfusion injury. Ibudilast at 10 – 100 μM significantly attenuated the H2O2-induced decrease in cell viability. Ibudilast inhibited the H2O2-induced cytochrome c release, caspase-3 activation, DNA ladder formation and nuclear condensation, suggesting its anti-apoptotic effect. Phosphodiesterase inhibitors such as theophylline, pentoxyfylline, vinpocetine, dipyridamole and zaprinast, which increased the guanosine-3′,5′-cyclic monophosphate (cyclic GMP) level, and dibutyryl cyclic GMP attenuated the H2O2-induced injury in astrocytes. Ibudilast increased the cyclic GMP level in astrocytes. The cyclic GMP-dependent protein kinase inhibitor KT5823 blocked the protective effects of ibudilast and dipyridamole on the H2O2-induced decrease in cell viability, while the cyclic AMP-dependent protein kinase inhibitor KT5720, the cyclic AMP antagonist Rp-cyclic AMPS, the mitogen-activated protein/extracellular signal-regulated kinase inhibitor PD98059 and the leukotriene D4 antagonist LY 171883 did not. KT5823 also blocked the effect of ibudilast on the H2O2-induced cytochrome c release and caspase-3-like protease activation. These findings suggest that ibudilast prevents the H2O2-induced delayed apoptosis of astrocytes via a cyclic GMP, but not cyclic AMP, signalling pathway. PMID:11454657

Method for separating isotopes

DOEpatents

Jepson, B.E.

1975-10-21

Isotopes are separated by contacting a feed solution containing the isotopes with a cyclic polyether wherein a complex of one isotope is formed with the cyclic polyether, the cyclic polyether complex is extracted from the feed solution, and the isotope is thereafter separated from the cyclic polyether.

Effects of protopine on blood platelet aggregation. II. Effect on metabolic system of adenosine 3',5'-cyclic monophosphate in platelets.

PubMed

Shiomoto, H; Matsuda, H; Kubo, M

1990-08-01

The mode of action of protopine on rabbit platelet aggregation was investigated in the metabolic system of adenosine 3',5'-cyclic monophosphate (cyclic AMP) in vitro experimental models. The inhibitory activity of protopine on adenosine 5'-diphosphate induced platelet aggregation was increased in the presence of prostaglandin I2 or papaverine in platelets. Protopine elevated content of the basal cyclic AMP accumulation in platelets and enhanced activity of crude adenylate cyclase prepared from platelets, but was ineffective on cyclic AMP phosphodiesterase. It is concluded that protopine has an inhibitory activity on platelet aggregation, activates adenylate cyclase and increases cyclic AMP content in platelets, in addition to other inhibitory actions in the metabolic system of cyclic AMP.

Metabolic control mechanisms in mammalian systems. Involvement of adenosine 3′:5′-cyclic monophosphate in androgen action

PubMed Central

Singhal, Radhey L.; Parulekar, M. R.; Vijayvargiya, R.; Robison, G. Alan

1971-01-01

1. The ability of exogenously administered cyclic AMP (adenosine 3′:5′-monophosphate) to exert andromimetic action on certain carbohydrate-metabolizing enzymes was investigated in the rat prostate gland and seminal vesicles. 2. Cyclic AMP, when injected concurrently with theophylline, produced marked increases in hexokinase, phosphofructokinase, glyceraldehyde phosphate dehydrogenase, pyruvate kinase, and two hexose monophosphate-shunt enzymes, as well as α-glycerophosphate dehydrogenase activity in accessory sexual tissues of castrated rats. The 6-N,2′-O-dibutyryl analogue of cyclic AMP caused increases of enzyme activity that were greater than those induced by the parent compound. 3. Time-course studies demonstrated that, whereas significant increases in the activities of most enzymes occurred within 4h after the injection of cyclic AMP, maximal increases were attained at 16–24h. 4. Increase in the activity of the various prostatic and vesicular enzymes was dependent on the dose of cyclic AMP; in most instances, 2.5mg of the cyclic nucleotide/rat was sufficient to elicit a statistically significant response. 5. Administration of cyclic AMP and theophylline also produced stimulation of enzyme activities in secondary sexual tissues of immature rats. 6. Cyclic AMP and theophylline did not affect significantly any of the enzymes studied in hepatic tissue. 7. Stimulation of various carbohydrate-metabolizing enzymes in the prostate gland and seminal vesicles by cyclic AMP was independent of adrenal function. 8. Concurrent treatment with actinomycin or cycloheximide prevented the cyclic AMP- and theophylline-induced increases in enzyme activities in both castrated and adrenalectomized–castrated animals. 9. Administration of a single dose of testosterone propionate (5.0mg/100g) to castrated rats caused a significant increase in cyclic AMP concentration in both accessory sexual tissues. 10. In addition, treatment with theophylline potentiated the effects of a submaximal dose of testosterone (1.0mg/100g) on all those prostatic and seminal-vesicular enzymes that are increased by exogenous cyclic AMP. 11. The evidence indicates that cyclic AMP may be involved in triggering the known metabolic actions of androgens on secondary sexual tissues of the rat. PMID:4110460

Motor control goes beyond physics: differential effects of gravity and inertia on finger forces during manipulation of hand-held objects.

PubMed

Zatsiorsky, Vladimir M; Gao, Fan; Latash, Mark L

2005-04-01

According to basic physics, the local effects induced by gravity and acceleration are identical and cannot be separated by any physical experiment. In contrast-as this study shows-people adjust the grip forces associated with gravitational and inertial forces differently. In the experiment, subjects oscillated a vertically-oriented handle loaded with five different weights (from 3.8 N to 13.8 N) at three different frequencies in the vertical plane: 1 Hz, 1.5 Hz and 2.0 Hz. Three contributions to the grip force-static, dynamic, and stato-dynamic fractions-were quantified. The static fraction reflects grip force related to holding a load statically. The stato-dynamic fraction reflects a steady change in the grip force when the same load is moved cyclically. The dynamic fraction is due to acceleration-related adjustments of the grip force during oscillation cycles. The slope of the relation between the grip force and the load force was steeper for the static fraction than for the dynamic fraction. The stato-dynamic fraction increased with the frequency and load. The slope of the dynamic grip force-load force relation decreased with frequency, and as a rule, increased with the load. Hence, when adjusting grip force to task requirements, the central controller takes into account not only the expected magnitude of the load force but also such factors as whether the force is gravitational or inertial and the contributions of the object mass and acceleration to the inertial force. As an auxiliary finding, a complex finger coordination pattern aimed at preserving the rotational equilibrium of the object during shaking movements was reported.

Effect of flood conditions on the deterioration of porous clay-based brick

NASA Astrophysics Data System (ADS)

Mol, L.; Tomor, A.

2017-12-01

Man-made materials represent an increasingly large proportion of geomaterials that are used to build up a rapidly expanding urbanised landscape. The deterioration of such materials is of increasing concern, in particular in light of the projected increase in storm and flood events and their associated high water levels. The effect of prolonged saturation in porous materials, man-made as well as natural, can lead to accelerated deterioration. This can be of particular concern for load-bearing structural materials, for example bridges. In this study, the effect of moisture movement has been investigated for brick masonry, as one of the most commonly used porous building materials. Saturation of brick masonry can be of particular concern for historical masonry, such as masonry arch bridges in conjunction with under increasing levels of long-term traffic loading. While flooding can lead to scour and sudden collapse of bridges, saturation can also lead to accelerated medium and long-term deterioration. A series of small-scale laboratory tests have been carried out on brick masonry to identify the effects of saturation on the material properties and changes in the rate of deterioration. Brick masonry prisms have been loaded to failure under quasi-static and long-term cyclic compression and monitored with the help of acoustic emission technique, accelerometers, linear variable differential transformers (LVDTs), permeametry and brick surface hardness measurements. Under quasi-static loading saturated samples showed significant reduction in the load capacity and increased fracture development. Under fatigue loading the number of cycles to failure reduced significantly for saturated specimens and characteristic changes in material parameters have been related to stages of fatigue deterioration. Test results indicated that increasing flood events can accelerate moisture-related deterioration in porous brick masonry.

Cyclic adenosine 3′,5′-monophosphate in human lymphocytes. Alterations after phytohemagglutinin stimulation

PubMed Central

Smith, Jay W.; Steiner, Alton L.; Newberry, W. Marcus; Parker, Charles W.

1971-01-01

We have studied cyclic adenosine 3′,5′-monophosphate (cyclic AMP) concentrations in human peripheral blood lymphocytes after stimulation with phytohemagglutinin (PHA), isoproterenol, prostaglandins, and aminophylline. Purified lymphocytes were obtained by nylon fiber chromatography, and low speed centrifugation to remove platelets. Cyclic AMP levels were determined by a highly sensitive radioimmunoassay. At concentrations of 0.1-1.0 mmoles/liter isoproterenol and aminophylline produced moderate increases in cyclic AMP concentrations, whereas prostaglandins produced marked elevations. High concentrations of PHA produced 25-300% increases in cyclic AMP levels, alterations being demonstrated within 1-2 min. The early changes in cyclic AMP concentration appear to precede previously reported metabolic changes in PHA-stimulated cells. After 6 hr cyclic AMP levels in PHA-stimulated cells had usually fallen to the levels of control cells. After 24 hr the level in PHA-stimulated cells was characteristically below that of the control cells. Adenyl cyclase, the enzyme which converts ATP to cyclic AMP, was measured in lymphocyte homogenates. Adenyl cyclase activity was rapidly stimulated by fluoride, isoproterenol, prostaglandins, and PHA. Since adenyl cyclase is characteristically localized in external cell membranes, our results are consistent with an initial action of PHA at this level. PMID:4395563

Cyclic strain increases protease-activated receptor-1 expression in vascular smooth muscle cells

NASA Technical Reports Server (NTRS)

Nguyen, K. T.; Frye, S. R.; Eskin, S. G.; Patterson, C.; Runge, M. S.; McIntire, L. V.

2001-01-01

Cyclic strain regulates many vascular smooth muscle cell (VSMC) functions through changing gene expression. This study investigated the effects of cyclic strain on protease-activated receptor-1 (PAR-1) expression in VSMCs and the possible signaling pathways involved, on the basis of the hypothesis that cyclic strain would enhance PAR-1 expression, reflecting increased thrombin activity. Uniaxial cyclic strain (1 Hz, 20%) of cells cultured on elastic membranes induced a 2-fold increase in both PAR-1 mRNA and protein levels. Functional activity of PAR-1, as assessed by cell proliferation in response to thrombin, was also increased by cyclic strain. In addition, treatment of cells with antioxidants or an NADPH oxidase inhibitor blocked strain-induced PAR-1 expression. Preincubation of cells with protein kinase inhibitors (staurosporine or Ro 31-8220) enhanced strain-increased PAR-1 expression, whereas inhibitors of NO synthase, tyrosine kinase, and mitogen-activated protein kinases had no effect. Cyclic strain in the presence of basic fibroblast growth factor induced PAR-1 mRNA levels beyond the effect of cyclic strain alone, whereas no additive effect was observed between cyclic strain and platelet-derived growth factor-AB. Our findings that cyclic strain upregulates PAR-1 mRNA expression but that shear stress downregulates this gene in VSMCs provide an opportunity to elucidate signaling differences by which VSMCs respond to different mechanical forces.

cCMP, cUMP, cTMP, cIMP and cXMP as possible second messengers: development of a hypothesis based on studies with soluble guanylyl cyclase α(1)β(1).

PubMed

Beste, Kerstin Y; Seifert, Roland

2013-02-01

Adenosine 3',5'-cyclic monophosphate and guanosine 3',5'-cyclic monophosphate are second messengers that regulate multiple physiological functions. The existence of additional cyclic nucleotides in mammalian cells was postulated many years ago, but technical problems hampered development of the field. Using highly specific and sensitive mass spectrometry methods, soluble guanylyl cyclase has recently been shown to catalyze the formation of several cyclic nucleotides in vitro. This minireview discusses the broad substrate-specificity of soluble guanylyl cyclase and the possible second messenger roles of cyclic nucleotides other than adenosine 3',5'-cyclic monophosphate and guanosine 3',5'-cyclic monophosphate. We hope that this article stimulates productive and critical research in an area that has been neglected for many years.

Oxidation of Alkyl-substituted Cyclic Hydrocarbons by a Nocardia during Growth on n-Alkanes

PubMed Central

Davis, J. B.; Raymond, R. L.

1961-01-01

Nocardia 107-332, a soil isolate, oxidizes short-chain alkyl-substituted cyclic hydrocarbons to cyclic acids while growing on n-alkanes. Cyclic acids are produced also from relatively long-chain alkyl-substituted cyclics such as n-nonylbenzene or n-dodecylbenzene which alone support growth in a mineral-salts medium. ω-Oxidation of the alkyl substituents is followed by β-oxidation. It is of particular interest that cyclic acids such as cyclohexaneacetic and phenylacetic with C2 residual carboxylic acid substituents are resistant to further oxidation by the nocardia but cyclic acids with C1 or C3 substituents are readily oxidized and utilized for growth. The specificity of microbial oxidations is demonstrated by the conversion of p-isopropyltoluene (p-cymene) to p-isopropylbenzoic acid in n-alkane, growth-supported nocardia cultures. PMID:13720182

cap alpha. /sub 2/-Adrenergic receptor-mediated sensitization of forskolin-stimulated cyclic AMP production

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

Jones, S.B.; Toews, M.L.; Turner, J.T.

1987-03-01

Preincubation of HT29 human colonic adenocarcinoma cells with ..cap alpha../sub 2/-adrenergic agonists resulted in a 10- to 20-fold increase in forskolin-stimulated cyclic AMP production as compared to cells preincubated without agonist. Similar results were obtained using either a (/sup 3/H)adenine prelabeling assay or a cyclic AMP radioimmunoassay to measure cyclic AMP levels. This phenomenon, which is termed sensitization, is ..cap alpha../sub 2/-adrenergic receptor-mediated and rapid in onset and reversal. Yohimbine, an ..cap alpha../sub 2/-adrenergic receptor-selective antagonist, blocked norepinephrine-induced sensitization, whereas prazosin (..cap alpha../sub 1/-adrenergic) and sotalol (..beta..-adrenergic) did not. The time for half-maximal sensitization was 5 min and the half-timemore » for reversal was 10 min. Only a 2-fold sensitization of cyclic AMP production stimulated by vasoactive intestinal peptide was observed, indicating that sensitization is relatively selective for forskolin. Sensitization reflects an increased production of cyclic AMP and not a decreased degradation of cyclic AMP, since incubation with a phosphodiesterase inhibitor and forskolin did not mimic sensitization. Increasing the levels of cyclic AMP during the preincubation had no effect on sensitization, indicating that sensitization is not caused by decreased cyclic AMP levels during the preincubation. This rapid and dramatic sensitization of forskolin-stimulated cyclic AMP production is a previously unreported effect that can be added to the growing list of ..cap alpha../sub 2/-adrenergic responses that are not mediated by a decrease in cyclic AMP.« less

History-independent cyclic response of nanotwinned metals

NASA Astrophysics Data System (ADS)

Pan, Qingsong; Zhou, Haofei; Lu, Qiuhong; Gao, Huajian; Lu, Lei

2017-11-01

Nearly 90 per cent of service failures of metallic components and structures are caused by fatigue at cyclic stress amplitudes much lower than the tensile strength of the materials involved. Metals typically suffer from large amounts of cumulative, irreversible damage to microstructure during cyclic deformation, leading to cyclic responses that are unstable (hardening or softening) and history-dependent. Existing rules for fatigue life prediction, such as the linear cumulative damage rule, cannot account for the effect of loading history, and engineering components are often loaded by complex cyclic stresses with variable amplitudes, mean values and frequencies, such as aircraft wings in turbulent air. It is therefore usually extremely challenging to predict cyclic behaviour and fatigue life under a realistic load spectrum. Here, through both atomistic simulations and variable-strain-amplitude cyclic loading experiments at stress amplitudes lower than the tensile strength of the metal, we report a history-independent and stable cyclic response in bulk copper samples that contain highly oriented nanoscale twins. We demonstrate that this unusual cyclic behaviour is governed by a type of correlated ‘necklace’ dislocation consisting of multiple short component dislocations in adjacent twins, connected like the links of a necklace. Such dislocations are formed in the highly oriented nanotwinned structure under cyclic loading and help to maintain the stability of twin boundaries and the reversible damage, provided that the nanotwins are tilted within about 15 degrees of the loading axis. This cyclic deformation mechanism is distinct from the conventional strain localizing mechanisms associated with irreversible microstructural damage in single-crystal, coarse-grained, ultrafine-grained and nanograined metals.

40 CFR 721.2120 - Cyclic amide.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Cyclic amide. 721.2120 Section 721... Cyclic amide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as a cyclic amide (PMN P-92-131) is subject to reporting under this section for the...

On 3D inelastic analysis methods for hot section components

NASA Technical Reports Server (NTRS)

Mcknight, R. L.; Chen, P. C.; Dame, L. T.; Holt, R. V.; Huang, H.; Hartle, M.; Gellin, S.; Allen, D. H.; Haisler, W. E.

1986-01-01

Accomplishments are described for the 2-year program, to develop advanced 3-D inelastic structural stress analysis methods and solution strategies for more accurate and cost effective analysis of combustors, turbine blades and vanes. The approach was to develop a matrix of formulation elements and constitutive models. Three constitutive models were developed in conjunction with optimized iterating techniques, accelerators, and convergence criteria within a framework of dynamic time incrementing. Three formulations models were developed; an eight-noded mid-surface shell element, a nine-noded mid-surface shell element and a twenty-noded isoparametric solid element. A separate computer program was developed for each combination of constitutive model-formulation model. Each program provides a functional stand alone capability for performing cyclic nonlinear structural analysis. In addition, the analysis capabilities incorporated into each program can be abstracted in subroutine form for incorporation into other codes or to form new combinations.

Machine learning modelling for predicting soil liquefaction susceptibility

NASA Astrophysics Data System (ADS)

Samui, P.; Sitharam, T. G.

2011-01-01

This study describes two machine learning techniques applied to predict liquefaction susceptibility of soil based on the standard penetration test (SPT) data from the 1999 Chi-Chi, Taiwan earthquake. The first machine learning technique which uses Artificial Neural Network (ANN) based on multi-layer perceptions (MLP) that are trained with Levenberg-Marquardt backpropagation algorithm. The second machine learning technique uses the Support Vector machine (SVM) that is firmly based on the theory of statistical learning theory, uses classification technique. ANN and SVM have been developed to predict liquefaction susceptibility using corrected SPT [(N1)60] and cyclic stress ratio (CSR). Further, an attempt has been made to simplify the models, requiring only the two parameters [(N1)60 and peck ground acceleration (amax/g)], for the prediction of liquefaction susceptibility. The developed ANN and SVM models have also been applied to different case histories available globally. The paper also highlights the capability of the SVM over the ANN models.

The 3D inelastic analysis methods for hot section components

NASA Technical Reports Server (NTRS)

Mcknight, R. L.; Maffeo, R. J.; Tipton, M. T.; Weber, G.

1992-01-01

A two-year program to develop advanced 3D inelastic structural stress analysis methods and solution strategies for more accurate and cost effective analysis of combustors, turbine blades, and vanes is described. The approach was to develop a matrix of formulation elements and constitutive models. Three constitutive models were developed in conjunction with optimized iterating techniques, accelerators, and convergence criteria within a framework of dynamic time incrementing. Three formulation models were developed: an eight-noded midsurface shell element; a nine-noded midsurface shell element; and a twenty-noded isoparametric solid element. A separate computer program has been developed for each combination of constitutive model-formulation model. Each program provides a functional stand alone capability for performing cyclic nonlinear structural analysis. In addition, the analysis capabilities incorporated into each program can be abstracted in subroutine form for incorporation into other codes or to form new combinations.

Simulation of plasma double-layer structures

NASA Technical Reports Server (NTRS)

Borovsky, J. E.; Joyce, G.

1982-01-01

Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2 dimensional particle in cell method. The investigation of planar double layers indicates that these one dimensional potential structures are susceptible to periodic disruption by instabilities in the low potential plasmas. Only a slight increase in the double layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double layer electric field alignment of accelerated particles and strong magnetization results in their magnetic field alignment. The numerical simulations of spatially periodic two dimensional double layers also exhibit cyclical instability. A morphological invariance in two dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron beam excited electrostatic electron cyclotron waves and (ion beam driven) solitary waves are present in the plasmas adjacent to the double layers.

Site-specific labeling of RNA at internal ribose hydroxyl groups: terbium-assisted deoxyribozymes at work.

PubMed

Büttner, Lea; Javadi-Zarnaghi, Fatemeh; Höbartner, Claudia

2014-06-04

A general and efficient single-step method was established for site-specific post-transcriptional labeling of RNA. Using Tb(3+) as accelerating cofactor for deoxyribozymes, various labeled guanosines were site-specifically attached to 2'-OH groups of internal adenosines in in vitro transcribed RNA. The DNA-catalyzed 2',5'-phosphodiester bond formation proceeded efficiently with fluorescent, spin-labeled, biotinylated, or cross-linker-modified guanosine triphosphates. The sequence context of the labeling site was systematically analyzed by mutating the nucleotides flanking the targeted adenosine. Labeling of adenosines in a purine-rich environment showed the fastest reactions and highest yields. Overall, practically useful yields >70% were obtained for 13 out of 16 possible nucleotide (nt) combinations. Using this approach, we demonstrate preparative labeling under mild conditions for up to ~160-nt-long RNAs, including spliceosomal U6 small nuclear RNA and a cyclic-di-AMP binding riboswitch RNA.

Vehicle test report: South Coast technology electric conversion of a Volkswagen Rabbit

NASA Technical Reports Server (NTRS)

Price, T. W.; Shain, T. W.; Bryant, J. A.

1981-01-01

The South Coast Technology Volkswagen Rabbit, was tested at the Jet Propulsion Laboratory's (JPL) dynamometer facility and at JPL's Edwards Test Station (ETS). The tests were performed to characterize certain parameters of the South Coast Rabbit and to provide baseline data that will be used for the comparison of near term batteries that are to be incorporated into the vehicle. The vehicle tests were concentrated on the electrical drive system; i.e., the batteries, controller, and motor. The tests included coastdowns to characterize the road load, maximum effort acceleration, and range evaluation for both cyclic and constant speed conditions. A qualitative evaluation of the vehicle was made by comparing its constant speed range performance with those vehicles described in the document 'state of the Art assessment of Electric and Hybrid Vehicles'. The Rabbit performance was near to the best of the 1977 vehicles.

Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

DOE PAGES

Song, Na; Concepcion, Javier J.; Binstead, Robert A.; ...

2015-04-06

In aqueous solution above pH 2.4 with 4% (vol/vol) CH 3CN, the complex [Ru II(bda)(isoq) 2] (bda is 2,2'-bipyridine-6,6'-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [Ru II(CO 2-bpy-CO 2 $-$)(isoq) 2(NCCH 3)], as shown by 1H and 13C-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0 M PO 4 3–, the calculated half-time for water oxidation is ~7 μs. In conclusion, the key to the rate accelerations with added bases is direct involvement of the buffer basemore » in either atom–proton transfer (APT) or concerted electron–proton transfer (EPT) pathways.« less

Freeze-drying synthesis of three-dimensional porous LiFePO4 modified with well-dispersed nitrogen-doped carbon nanotubes for high-performance lithium-ion batteries

NASA Astrophysics Data System (ADS)

Tu, Xiaofeng; Zhou, Yingke; Song, Yijie

2017-04-01

The three-dimensional porous LiFePO4 modified with uniformly dispersed nitrogen-doped carbon nanotubes has been successfully prepared by a freeze-drying method. The morphology and structure of the porous composites are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and the electrochemical performances are evaluated using the constant current charge/discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. The nitrogen-doped carbon nanotubes are uniformly dispersed inside the porous LiFePO4 to construct a superior three-dimensional conductive network, which remarkably increases the electronic conductivity and accelerates the diffusion of lithium ion. The porous composite displays high specific capacity, good rate capability and excellent cycling stability, rendering it a promising positive electrode material for high-performance lithium-ion batteries.

Experimental observations of Lagrangian sand grain kinematics under bedload transport: statistical description of the step and rest regimes

NASA Astrophysics Data System (ADS)

Guala, M.; Liu, M.

2017-12-01

The kinematics of sediment particles is investigated by non-intrusive imaging methods to provide a statistical description of bedload transport in conditions near the threshold of motion. In particular, we focus on the cyclic transition between motion and rest regimes to quantify the waiting time statistics inferred to be responsible for anomalous diffusion, and so far elusive. Despite obvious limitations in the spatio-temporal domain of the observations, we are able to identify the probability distributions of the particle step time and length, velocity, acceleration, waiting time, and thus distinguish which quantities exhibit well converged mean values, based on the thickness of their respective tails. The experimental results shown here for four different transport conditions highlight the importance of the waiting time distribution and represent a benchmark dataset for the stochastic modeling of bedload transport.

Gravitational attraction until relativistic equipartition of internal and translational kinetic energies

NASA Astrophysics Data System (ADS)

Bulyzhenkov, I. E.

2018-02-01

Translational ordering of the internal kinematic chaos provides the Special Relativity referents for the geodesic motion of warm thermodynamical bodies. Taking identical mathematics, relativistic physics of the low speed transport of time-varying heat-energies differs from Newton's physics of steady masses without internal degrees of freedom. General Relativity predicts geodesic changes of the internal heat-energy variable under the free gravitational fall and the geodesic turn in the radial field center. Internal heat variations enable cyclic dynamics of decelerated falls and accelerated takeoffs of inertial matter and its structural self-organization. The coordinate speed of the ordered spatial motion takes maximum under the equipartition of relativistic internal and translational kinetic energies. Observable predictions are discussed for verification/falsification of the principle of equipartition as a new basic for the ordered motion and self-organization in external fields, including gravitational, electromagnetic, and thermal ones.

Combining Orthogonal Chain-End Deprotections and Thiol-Maleimide Michael Coupling: Engineering Discrete Oligomers by an Iterative Growth Strategy.

PubMed

Huang, Zhihao; Zhao, Junfei; Wang, Zimu; Meng, Fanying; Ding, Kunshan; Pan, Xiangqiang; Zhou, Nianchen; Li, Xiaopeng; Zhang, Zhengbiao; Zhu, Xiulin

2017-10-23

Orthogonal maleimide and thiol deprotections were combined with thiol-maleimide coupling to synthesize discrete oligomers/macromolecules on a gram scale with molecular weights up to 27.4 kDa (128mer, 7.9 g) using an iterative exponential growth strategy with a degree of polymerization (DP) of 2 n -1. Using the same chemistry, a "readable" sequence-defined oligomer and a discrete cyclic topology were also created. Furthermore, uniform dendrons were fabricated using sequential growth (DP=2 n -1) or double exponential dendrimer growth approaches (DP=22n -1) with significantly accelerated growth rates. A versatile, efficient, and metal-free method for construction of discrete oligomers with tailored structures and a high growth rate would greatly facilitate research into the structure-property relationships of sophisticated polymeric materials. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Durability test with fuel starvation using a Pt/CNF catalyst in PEMFC.

PubMed

Jung, Juhae; Park, Byungil; Kim, Junbom

2012-01-05

In this study, a catalyst was synthesized on carbon nanofibers [CNFs] with a herringbone-type morphology. The Pt/CNF catalyst exhibited low hydrophilicity, low surface area, high dispersion, and high graphitic behavior on physical analysis. Electrodes (5 cm2) were prepared by a spray method, and the durability of the Pt/CNF was evaluated by fuel starvation. The performance was compared with a commercial catalyst before and after accelerated tests. The fuel starvation caused carbon corrosion with a reverse voltage drop. The polarization curve, EIS, and cyclic voltammetry were analyzed in order to characterize the electrochemical properties of the Pt/CNF. The performance of a membrane electrode assembly fabricated from the Pt/CNF was maintained, and the electrochemical surface area and cell resistance showed the same trend. Therefore, CNFs are expected to be a good support in polymer electrolyte membrane fuel cells.

Durability test with fuel starvation using a Pt/CNF catalyst in PEMFC

PubMed Central

2012-01-01

In this study, a catalyst was synthesized on carbon nanofibers [CNFs] with a herringbone-type morphology. The Pt/CNF catalyst exhibited low hydrophilicity, low surface area, high dispersion, and high graphitic behavior on physical analysis. Electrodes (5 cm2) were prepared by a spray method, and the durability of the Pt/CNF was evaluated by fuel starvation. The performance was compared with a commercial catalyst before and after accelerated tests. The fuel starvation caused carbon corrosion with a reverse voltage drop. The polarization curve, EIS, and cyclic voltammetry were analyzed in order to characterize the electrochemical properties of the Pt/CNF. The performance of a membrane electrode assembly fabricated from the Pt/CNF was maintained, and the electrochemical surface area and cell resistance showed the same trend. Therefore, CNFs are expected to be a good support in polymer electrolyte membrane fuel cells. PMID:22221426

Preparation and Characterization of Silanes Films to Protect Electrogalvanized Steel

NASA Astrophysics Data System (ADS)

Seré, Pablo R.; Egli, Walter; Di Sarli, Alejandro R.; Deyá, Cecilia

2018-03-01

Silanes are an interesting alternative to chromate-based surface treatments for temporary protection of electrogalvanized steel. In this work, the protective behavior of 3-mercaptopropyltrimethoxysilane (MTMO), 3-aminopropyltriethoxysilane (AMEO), or 3-glycidoxypropyltrimethoxysilane (GLYMO) films applied on electrogalvanized automotive quality steel sheets has been studied. The silane coating morphology, composition, and porosity were characterized by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), x-ray fluorescence, immersion in copper sulfate, and cyclic voltammetry. The corrosion protection was evaluated by polarization curves, electrochemical noise measurements, electrochemical impedance spectrometry, and accelerated humidity chamber tests. The results showed that the silanes protect temporarily electrogalvanized steel from corrosion. MTMO forms a relatively thick and cracked film. AMEO and GLYMO films were so thin that they could not be observed by SEM but silicon was detected by EDS. MTMO provided good temporary protection, being an alternative to replace Cr(VI) as protector of electrogalvanized steel.

Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

PubMed Central

Song, Na; Concepcion, Javier J.; Binstead, Robert A.; Rudd, Jennifer A.; Vannucci, Aaron K.; Dares, Christopher J.; Coggins, Michael K.; Meyer, Thomas J.

2015-01-01

In aqueous solution above pH 2.4 with 4% (vol/vol) CH3CN, the complex [RuII(bda)(isoq)2] (bda is 2,2′-bipyridine-6,6′-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [RuII(CO2-bpy-CO2−)(isoq)2(NCCH3)], as shown by 1H and 13C-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0 M PO43–, the calculated half-time for water oxidation is ∼7 μs. The key to the rate accelerations with added bases is direct involvement of the buffer base in either atom–proton transfer (APT) or concerted electron–proton transfer (EPT) pathways. PMID:25848035

High-pressure endurable flexible tactile actuator based on microstructured dielectric elastomer

NASA Astrophysics Data System (ADS)

Pyo, Dongbum; Ryu, Semin; Kyung, Ki-Uk; Yun, Sungryul; Kwon, Dong-Soo

2018-02-01

We demonstrate a robust flexible tactile actuator that is capable of working under high external pressures. The tactile actuator is based on a pyramidal microstructured dielectric elastomer layer inducing variation in both mechanical and dielectric properties. The vibrational performance of the actuator can be modulated by changing the geometric parameter of the microstructures. We evaluated the performance of the actuator under high-pressure loads up to 25 kPa, which is over the typical range of pressure applied when humans touch or manipulate objects. Due to the benefit of nonlinearity of the pyramidal structure, the actuator could maintain high mechanical output under various external pressures in the frequency range of 100-200 Hz, which is the most sensitive to vibration acceleration for human finger pads. The responses are not only fast, reversible, and highly durable under consecutive cyclic operations, but also large enough to impart perceivable vibrations for haptic feedback on practical wearable device applications.

A review of carbide fuel corrosion for nuclear thermal propulsion applications

NASA Astrophysics Data System (ADS)

Pelaccio, Dennis G.; El-Genk, Mohamed S.; Butt, Darryl P.

1993-10-01

At the operation conditions of interest in nuclear thermal propulsion reactors, carbide materials have been known to exhibit a number of life limiting phenomena. These include the formation of liquid, loss by vaporization, creep and corresponding gas flow restrictions, and local corrosion and fuel structure degradation due to excessive mechanical and/or thermal loading. In addition, the radiation environment in the reactor core can produce a substantial change in its local physical properties, which can produce high thermal stresses and corresponding stress fractures (cracking). Time-temperature history and cyclic operation of the nuclear reactor can also accelerate some of these processes. The University of New Mexico's Institute for Space Nuclear Power Studies, under NASA sponsorship has recently initiated a study to model the complicated hydrogen corrosion process. In support of this effort, an extensive review of the open literature was performed, and a technical expert workshop was conducted. This paper summarizes the results of this review.

A Review of Carbide Fuel Corrosion for Nuclear Thermal Propulsion Applications

NASA Astrophysics Data System (ADS)

Pelaccio, Dennis G.; El-Genk, Mohamed S.; Butt, Darryl P.

1994-07-01

At the operation conditions of interest in nuclear thermal propulsion reactors, carbide materials have been known to exhibit a number of life limiting phenomena. These include the formation of liquid, loss by vaporization, creep and corresponding gas flow restrictions, and local corrosion and fuel structure degradation due to excessive mechanical and/or thermal loading. In addition, the radiation environment in the reactor core can produce a substantial change in its local physical properties, which can produce high thermal stresses and corresponding stress fractures (cracking). Time-temperature history and cyclic operation of the nuclear reactor can also accelerate some of these processes. The University of New Mexico's Institute for Space Nuclear Power Studies, under NASA sponsorship has recently initiated a study to model the complicated hydrogen corrosion process. In support of this effort, an extensive review of the open literature was performed, and a technical expert workshop was conducted. This paper summarizes the results of this review.

Study of changes in properties of solar sail materials from radiation exposure

NASA Technical Reports Server (NTRS)

Smith, T.

1977-01-01

Techniques for monitoring changes in preparation of solar sail materials resulting from space radiation simulation, stressing (e.g., thermal, mechanical) and exposure to terrestrial environments are developed. The properties of interest are: metallic coating deterioration, polymeric film deterioration, interfacial debonding and possible metallic coating diffusion into the polymeric film. Four accelerated tests were devised to simulate the possible degradation processes mentioned above. These four tests are: a thermal shock test to simulate the wide variation of temperature expected in space (260 C to -100 C), a cyclic temperature test to stimulate the 6 minute temperature cycle anticipated in space, a mechanical vibration test to simulate mechanical bonding, folding and handling, and a humidity test to simulate terrestrial environment effects. The techniques for monitoring property changes are: visual and microscopic examination, ellipsometry, surface potential difference (SPD), photoelectron emission (PEE), and water contact angles.

An AgI@g-C3N4 hybrid core@shell structure: Stable and enhanced photocatalytic degradation

NASA Astrophysics Data System (ADS)

Liu, Li; Qi, Yuehong; Yang, Jinyi; Cui, Wenquan; Li, Xingang; Zhang, Zisheng

2015-12-01

A novel visible-light-active material AgI@g-C3N4 was prepared by ultrasonication/chemisorption method. The core@shell structure AgI@g-C3N4 catalyst showed high efficiency for the degradation of MB under visible light irradiation (λ > 420 nm). Nearly 96.5% of MB was degraded after 120 min of irradiation in the presence of the AgI@g-C3N4 photocatalyst. Superior stability was also observed in the cyclic runs indicating that the as prepared hybrid composite is highly desirable for the remediation of organic contaminated wastewaters. The improved photocatalytic performance is due to synergistic effects at the interface of AgI and g-C3N4 which can effectively accelerate the charge separation and reinforce the photostability of hybrid composite. The possible mechanism for the photocatalytic activity of AgI@g-C3N4 was tentatively proposed.

Modal forced vibration analysis of aerodynamically excited turbosystems

NASA Technical Reports Server (NTRS)

Elchuri, V.

1985-01-01

Theoretical aspects of a new capability to determine the vibratory response of turbosystems subjected to aerodynamic excitation are presented. Turbosystems such as advanced turbopropellers with highly swept blades, and axial-flow compressors and turbines can be analyzed using this capability. The capability has been developed and implemented in the April 1984 release of the general purpose finite element program NASTRAN. The dynamic response problem is addressed in terms of the normal modal coordinates of these tuned rotating cyclic structures. Both rigid and flexible hubs/disks are considered. Coriolis and centripetal accelerations, as well as differential stiffness effects are included. Generally non-uniform steady inflow fields and uniform flow fields arbitrarily inclined at small angles with respect to the axis of rotation of the turbosystem are considered sources of aerodynamic excitation. The spatial non-uniformities are considered to be small deviations from a principally uniform inflow. Subsonic and supersonic relative inflows are addressed, with provision for linearly interpolating transonic airloads.

Electric vehicle test report Cutler-Hammer Corvette

NASA Technical Reports Server (NTRS)

1981-01-01

Vehicles were characterized for the state of the art assessment of electric vehicles. The vehicle evaluated was a Chevrolet Corvette converted to electric operation. The original internal combustion engine was replaced by an electric traction motor. Eighteen batteries supplied the electrical energy. A controller, an onboard battery charger, and several dashboard instruments completed the conversion. The emphasis was on the electrical portion of the drive train, although some analysis and discussion of the mechanical elements are included. Tests were conducted both on the road (actually a mile long runway) and in a chassis dynamometer equipped laboratory. The majority of the tests performed were according to SAE Procedure J227a and included maximum effort accelerations, constant speed range, and cyclic range. Some tests that are not a part of the SAE Procedure J227a are described and the analysis of the data from all tests is discussed.

Binder-free NiFe2O4/C nanofibers as air cathodes for Li-O2 batteries

NASA Astrophysics Data System (ADS)

Zhang, Xin; Wang, Chengyi; Chen, Ya-Nan; Wang, Xin-Gai; Xie, Zhaojun; Zhou, Zhen

2018-02-01

Rechargeable Li-O2 batteries have aroused much attention for their high energy density. However, the poor rechargeability and low efficiency hinder their practical applications. To solve these issues, free-standing carbon films combined with high-activity NiFe2O4 catalysts are prepared by electrospinning method, and directly used as air cathodes for Li-O2 batteries. The obtained films have 3D networks formed by stacking and interlacing massive nanofibers with uniformly dispersed NiFe2O4 nanoparticles on them. The Li-O2 batteries with such binder-free air cathodes show low charging overpotential even comparable to precious metal cathodes, and can sustain excellent discharge/charge cyclic stability. The unique structure and binder-free superiority greatly facilitates the Li+ and O2 diffusion, accelerates the decomposition of Li2O2, and avoid the disturbance of polymer binders.

Neutron and Gamma-ray Detection in Reversed-Field Pinch Deuterium Plasmas in the RFX-mod Device

NASA Astrophysics Data System (ADS)

Zuin, Matteo; Stevanato, Luca; Martines, Emilio; Gonzalez, Winder; Cavazzana, Roberto; Cester, Davide; Nebbia, G.; Sajo-Bohus, Laszlo; Viesti, Giuseppe

2014-10-01

An experimental analysis of neutron and gamma-ray fluxes exiting purely ohmically heated plasmas in reversed-field pinch (RFP) configuration is presented. The diagnostic system, installed in the RFX-mod, is made of 2 scintillators (EJ-301 liquid and NaI(Tl)) coupled to flat-panel photomultipliers, which can be operated under magnetic fields. The production of neutrons and gamma rays in Deuterium plasmas is found to be strongly dependent on the Ohmic input power, with a threshold value of about 1.2 MA in terms of plasma current level, below which low levels of gamma rays and almost no neutrons are detected. Neutron and gamma production is characterized by a bursty behavior, correlated to the spontaneous magnetic reconnection events, occurring almost cyclically in the RFP plasmas. The role of ion heating and particle acceleration during such events is discussed.

Global Precipitation Measurement (GPM) Spacecraft Lithium Ion Battery Micro-Cycling Investigation

NASA Technical Reports Server (NTRS)

Dakermanji, George; Lee, Leonine; Spitzer, Thomas

2016-01-01

The Global Precipitation Measurement (GPM) spacecraft was jointly developed by NASA and JAXA. It is a Low Earth Orbit (LEO) spacecraft launched on February 27, 2014. The power system is a Direct Energy Transfer (DET) system designed to support 1950 watts orbit average power. The batteries use SONY 18650HC cells and consist of three 8s by 84p batteries operated in parallel as a single battery. During instrument integration with the spacecraft, large current transients were observed in the battery. Investigation into the matter traced the cause to the Dual-Frequency Precipitation Radar (DPR) phased array radar which generates cyclical high rate current transients on the spacecraft power bus. The power system electronics interaction with these transients resulted in the current transients in the battery. An accelerated test program was developed to bound the effect, and to assess the impact to the mission.

Mechanistic insights into lithium ion battery electrolyte degradation - a quantitative NMR study.

PubMed

Wiemers-Meyer, S; Winter, M; Nowak, S

2016-09-29

The changes in electrolyte composition on the molecular level and the reaction mechanisms of electrolyte degradation upon thermal aging are monitored by quantitative NMR spectroscopy, revealing similar rates of degradation for pristine and already aged electrolytes. The data analysis is not in favor of an autocatalytic reaction mechanism based on OPF 3 but rather indicates that the degradation of LiPF 6 in carbonate based solvents proceeds via a complex sequence of "linear" reactions rather than a cyclic reaction pattern which is determined by the amount of water present in the samples. All investigated electrolytes are reasonably stable at temperatures of up to 60 °C in the presence of minor amounts or absence of water hence indicating that chemical instability of electrolyte components against water is decisive for degradation and an increase in temperature ("thermal aging") just accelerates the degradation impact of water.

Comparative Effects of Angiotensin and ACTH on Cyclic AMP and Steroidogenesis in Isolated Bovine Adrenal Cells

PubMed Central

Peytremann, Andre; Nicholson, Wendell E.; Brown, Ronald D.; Liddle, Grant W.; Hardman, Joel G.

1973-01-01

The comparative effects of angiotensin II and adrenocorticotropic hormone (ACTH) on cyclic AMP and steroidogenesis were investigated employing isolated bovine adrenal cells from the zona fasciculata. Like ACTH, angiotensin produced a prompt increase in cyclic AMP which preceded the increase in corticosteroid production. Although this increase in cyclic AMP was small when compared to that induced by ACTH, it correlated with the amount of steroidogenesis. This observation is consistent with the view that cyclic AMP is the intracellular mediator of the steroidogenic action of angiotensin. Angiotensin acted synergistically with ACTH on cyclic AMP levels. This synergism was not explained by inhibition of phosphodiesterase activity. Unlike ACTH, angiotensin failed to stimulate adenylate cyclase in broken cell preparations. The observations suggest that more than one mechanism may be involved in effects of ACTH and angiotensin on cyclic AMP levels. PMID:4348344

The role of peel stresses in cyclic debonding

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.

1982-01-01

When an adhesively bonded joint is undergoing cyclic loading, one of the possible damage modes that occurs is called cyclic debonding - progressive separation of the adherends by failure of the adhesive bond under cyclic loading. In most practical structures, both peel and shear stresses exist in the adhesive bonding during cyclic loading. The results of an experimental and analytical study to determine the role of peel stresses on cyclic debonding in a mixed mode specimen are presented. Experimentally, this was done by controlling the forces that create the peel stresses by applying a clamping force to oppose the peel stresses. Cracked lap shear joints were chosen for this study. A finite element analysis was developed to assess the effect of the clamping force on the strain energy release rates due to shear and peel stresses. The results imply that the peel stress is the principal stress causing cyclic debonding.

Elevational gradient in the cyclicity of a forest-defoliating insect

Treesearch

Kyle J. Haynes; Andrew M. Liebhold; Derek M. Johnson

2012-01-01

Observed changes in the cyclicity of herbivore populations along latitudinal gradients and the hypothesis that shifts in the importance of generalist versus specialist predators explain such gradients has long been a matter of intense interest. In contrast, elevational gradients in population cyclicity are largely unexplored. We quantified the cyclicity of gypsy moth...

Brucella β 1,2 Cyclic Glucan Is an Activator of Human and Mouse Dendritic Cells

PubMed Central

Martirosyan, Anna; Pérez-Gutierrez, Camino; Banchereau, Romain; Dutartre, Hélène; Lecine, Patrick; Dullaers, Melissa; Mello, Marielle; Pinto Salcedo, Suzana; Muller, Alexandre; Leserman, Lee; Levy, Yves; Zurawski, Gerard; Zurawski, Sandy; Moreno, Edgardo; Moriyón, Ignacio; Klechevsky, Eynav; Banchereau, Jacques; Oh, SangKon; Gorvel, Jean-Pierre

2012-01-01

Bacterial cyclic glucans are glucose polymers that concentrate within the periplasm of alpha-proteobacteria. These molecules are necessary to maintain the homeostasis of the cell envelope by contributing to the osmolarity of Gram negative bacteria. Here, we demonstrate that Brucella β 1,2 cyclic glucans are potent activators of human and mouse dendritic cells. Dendritic cells activation by Brucella β 1,2 cyclic glucans requires TLR4, MyD88 and TRIF, but not CD14. The Brucella cyclic glucans showed neither toxicity nor immunogenicity compared to LPS and triggered antigen-specific CD8+ T cell responses in vivo. These cyclic glucans also enhanced antigen-specific CD4+ and CD8+ T cell responses including cross-presentation by different human DC subsets. Brucella β 1,2 cyclic glucans increased the memory CD4+ T cell responses of blood mononuclear cells exposed to recombinant fusion proteins composed of anti-CD40 antibody and antigens from both hepatitis C virus and Mycobacterium tuberculosis. Thus cyclic glucans represent a new class of adjuvants, which might contribute to the development of effective antimicrobial therapies. PMID:23166489

Novel biodegradable aliphatic poly(butylene succinate-co-cyclic carbonate)s bearing functionalizable carbonate building blocks: II. Enzymatic biodegradation and in vitro biocompatibility assay.

PubMed

Yang, Jing; Tian, Weisheng; Li, Qiaobo; Li, Yang; Cao, Amin

2004-01-01

In a previous study, we have reported chemical synthesis of novel aliphatic poly(butylene succinate-co-cyclic carbonate) P(BS-co-CC)s bearing various functionalizable carbonate building blocks, and this work will continue to present our new studies on their enzymatic degradation and in vitro cell biocompatibility assay. First, enzymatic degradation of the novel P(BS-co-CC) film samples was investigated with two enzymes of lipase B Candida Antartic (Novozyme 435) and lipase Porcine Pancreas PPL, and it was revealed that copolymerizing linear poly(butylene succinate) PBS with a functionalizable carbonate building block could remarkably accelerate the enzymatic degradation of a synthesized product P(BS-co-CC), and its biodegradation behavior was found to strongly depend on the overall impacts of several important factors as the cyclic carbonate (CC) comonomer structure and molar content, molar mass, thermal characteristics, morphology, the enzyme-substrate specificity, and so forth. Further, the biodegraded residual film samples and water-soluble enzymatic degradation products were allowed to be analyzed by means of proton nuclear magnetic resonance (1H NMR), gel permeation chromatograph (GPC), differential scanning calorimeter (DSC), attenuated total reflection FTIR (ATR-FTIR), scanning electron microscope (SEM), and liquid chromatograph-mass spectrometry (LC-MS). On the experimental evidences, an exo-type mechanism of enzymatic chain hydrolysis preferentially occurring in the noncrystalline domains was suggested for the synthesized new P(BS-co-CC) film samples. With regard to their cell biocompatibilities, an assay with NIH 3T3 mouse fibroblast cell was conducted using the novel synthesized P(BS-co-CC) films as substrates with respect to the cell adhesion and proliferation, and these new biodegradable P(BS-co-CC) samples were found to exhibit as low cell toxicity as the PLLA control, particularly the two samples of poly(butylene succinate-co-18.7 mol % dimethyl trimethylene carbonate) P(BS-co-18.7 mol % DMTMC) and poly(butylene succinate-co-21.9 mol % 5-benzyloxy trimethylene carbonate) P(BS-co-21.9 mol % BTMC) were interestingly found to show much better cell biocompatibilities than the PLLA reference.

Cyclic density functional theory: A route to the first principles simulation of bending in nanostructures

NASA Astrophysics Data System (ADS)

Banerjee, Amartya S.; Suryanarayana, Phanish

2016-11-01

We formulate and implement Cyclic Density Functional Theory (Cyclic DFT) - a self-consistent first principles simulation method for nanostructures with cyclic symmetries. Using arguments based on Group Representation Theory, we rigorously demonstrate that the Kohn-Sham eigenvalue problem for such systems can be reduced to a fundamental domain (or cyclic unit cell) augmented with cyclic-Bloch boundary conditions. Analogously, the equations of electrostatics appearing in Kohn-Sham theory can be reduced to the fundamental domain augmented with cyclic boundary conditions. By making use of this symmetry cell reduction, we show that the electronic ground-state energy and the Hellmann-Feynman forces on the atoms can be calculated using quantities defined over the fundamental domain. We develop a symmetry-adapted finite-difference discretization scheme to obtain a fully functional numerical realization of the proposed approach. We verify that our formulation and implementation of Cyclic DFT is both accurate and efficient through selected examples. The connection of cyclic symmetries with uniform bending deformations provides an elegant route to the ab-initio study of bending in nanostructures using Cyclic DFT. As a demonstration of this capability, we simulate the uniform bending of a silicene nanoribbon and obtain its energy-curvature relationship from first principles. A self-consistent ab-initio simulation of this nature is unprecedented and well outside the scope of any other systematic first principles method in existence. Our simulations reveal that the bending stiffness of the silicene nanoribbon is intermediate between that of graphene and molybdenum disulphide - a trend which can be ascribed to the variation in effective thickness of these materials. We describe several future avenues and applications of Cyclic DFT, including its extension to the study of non-uniform bending deformations and its possible use in the study of the nanoscale flexoelectric effect.

Properties of Tangential and Cyclic Polygons: An Application of Circulant Matrices

ERIC Educational Resources Information Center

Leung, Allen; Lopez-Real, Francis

2003-01-01

In this paper, the properties of tangential and cyclic polygons proposed by Lopez-Real are proved rigorously using the theory of circulant matrices. In particular, the concepts of slippable tangential polygons and conformable cyclic polygons are defined. It is shown that an n-sided tangential (or cyclic) polygon P[subscript n] with n even is…

Cyclic completion of the anamorphic universe

NASA Astrophysics Data System (ADS)

Ijjas, Anna

2018-04-01

Cyclic models of the universe have the advantage of avoiding initial conditions problems related to postulating any sort of beginning in time. To date, the best known viable examples of cyclic models have been ekpyrotic. In this paper, we show that the recently proposed anamorphic scenario can also be made cyclic. The key to the cyclic completion is a classically stable, non-singular bounce. Remarkably, even though the bounce construction was originally developed to connect a period of contraction with a period of expansion both described by Einstein gravity, we show here that it can naturally be modified to connect an ordinary contracting phase described by Einstein gravity with a phase of anamorphic smoothing. The paper will present the basic principles and steps in constructing cyclic anamorphic models.

Approximate stresses in 2-D flat elastic contact fretting problems

NASA Astrophysics Data System (ADS)

Urban, Michael Rene

Fatigue results from the cyclic loading of a solid body. If the body subject to fatigue is in contact with another body and relative sliding motion occurs between these two bodies, then rubbing surface damage can accelerate fatigue failure. The acceleration of fatigue failure is especially important if the relative motion between the two bodies results in surface damage without excessive surface removal via wear. The situation just described is referred to as fretting fatigue. Understanding of fretting fatigue is greatly enhanced if the stress state associated with fretting can be characterized. For Hertzian contact, this can readily be done. Unfortunately, simple stress formulae are not available for flat body contact. The primary result of the present research is the development of a new, reasonably accurate, approximate closed form expression for 2-dimensional contact stresses which has been verified using finite element modeling. This expression is also combined with fracture mechanics to provide a simple method of determining when a crack is long enough to no longer be affected by the contact stress field. Lower bounds on fatigue life can then easily be calculated using fracture mechanics. This closed form expression can also be used to calculate crack propagation within the contact stress field. The problem of determining the cycles required to generate an initial crack and what to choose as an initial crack size is unresolved as it is in non-fretting fatigue.

Ubiquinol-10 Supplementation Activates Mitochondria Functions to Decelerate Senescence in Senescence-Accelerated Mice

PubMed Central

Tian, Geng; Sawashita, Jinko; Kubo, Hiroshi; Nishio, Shin-ya; Hashimoto, Shigenari; Suzuki, Nobuyoshi; Yoshimura, Hidekane; Tsuruoka, Mineko; Wang, Yaoyong; Liu, Yingye; Luo, Hongming; Xu, Zhe; Mori, Masayuki; Kitano, Mitsuaki; Hosoe, Kazunori; Takeda, Toshio; Usami, Shin-ichi

2014-01-01

Abstract Aim: The present study was conducted to define the relationship between the anti-aging effect of ubiquinol-10 supplementation and mitochondrial activation in senescence-accelerated mouse prone 1 (SAMP1) mice. Results: Here, we report that dietary supplementation with ubiquinol-10 prevents age-related decreases in the expression of sirtuin gene family members, which results in the activation of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a major factor that controls mitochondrial biogenesis and respiration, as well as superoxide dismutase 2 (SOD2) and isocitrate dehydrogenase 2 (IDH2), which are major mitochondrial antioxidant enzymes. Ubiquinol-10 supplementation can also increase mitochondrial complex I activity and decrease levels of oxidative stress markers, including protein carbonyls, apurinic/apyrimidinic sites, malondialdehydes, and increase the reduced glutathione/oxidized glutathione ratio. Furthermore, ubiquinol-10 may activate Sirt1 and PGC-1α by increasing cyclic adenosine monophosphate (cAMP) levels that, in turn, activate cAMP response element-binding protein (CREB) and AMP-activated protein kinase (AMPK). Innovation and Conclusion: These results show that ubiquinol-10 may enhance mitochondrial activity by increasing levels of SIRT1, PGC-1α, and SIRT3 that slow the rate of age-related hearing loss and protect against the progression of aging and symptoms of age-related diseases. Antioxid. Redox Signal. 20, 2606–2620 PMID:24124769

Murine remote preconditioning increases glucose uptake and suppresses gluconeogenesis in hepatocytes via a brain-liver neurocircuit, leading to counteracting glucose intolerance.

PubMed

Kurabayashi, Atsushi; Tanaka, Chiharu; Matsumoto, Waka; Naganuma, Seiji; Furihata, Mutsuo; Inoue, Keiji; Kakinuma, Yoshihiko

2018-05-01

Our previous study revealed that cyclic hindlimb ischaemia-reperfusion (IR) activates cardiac acetylcholine (ACh) synthesis through the cholinergic nervous system and cell-derived ACh accelerates glucose uptake. However, the mechanisms regulating glucose metabolism in vivo remain unknown. We investigated the effects and mechanisms of IR in mice under pathophysiological conditions. Using IR-subjected male C57BL/6J mice, the effects of IR on blood sugar (BS), glucose uptake, central parasympathetic nervous system (PNS) activity, hepatic gluconeogenic enzyme expression and those of ACh on hepatocellular glucose uptake were assessed. IR decreased BS levels by 20% and increased c-fos immunoreactivity in the center of the PNS (the solitary tract and the dorsal motor vagal nucleus). IR specifically downregulated hepatic gluconeogenic enzyme expression and activities (glucose-6-phosphatase and phosphoenolpyruvate carboxykinase) and accelerated hepatic glucose uptake. Transection of a hepatic vagus nerve branch decreased this uptake and reversed BS decrease. Suppressed gluconeogenic enzyme expression was reversed by intra-cerebroventricular administration of a choline acetyltransferase inhibitor. Moreover, IR significantly attenuated hyperglycaemia in murine model of type I and II diabetes mellitus. IR provides another insight into a therapeutic modality for diabetes mellitus due to regulating gluconeogenesis and glucose-uptake and advocates an adjunctive mode rectifying disturbed glucose metabolism. Copyright © 2018 Elsevier B.V. All rights reserved.

Material Characterization and Computer Model Simulation of Low Density Polyurethane Foam Used in a Rodent Traumatic Brain Injury Model

PubMed Central

Zhang, Liying; Gurao, Manish; Yang, King H.; King, Albert I.

2011-01-01

Computer models of the head can be used to simulate the events associated with traumatic brain injury (TBI) and quantify biomechanical response within the brain. Marmarou’s impact acceleration rodent model is a widely used experimental model of TBI mirroring axonal pathology in humans. The mechanical properties of the low density polyurethane (PU) foam, an essential piece of energy management used in Marmarou’s impact device, has not been fully characterized. The foam used in Marmarou’s device was tested at seven strain rates ranging from quasi-static to dynamic (0.014 ~ 42.86 s−1) to quantify the stress-strain relationships in compression. Recovery rate of the foam after cyclic compression was also determined through the periods of recovery up to three weeks. The experimentally determined stress-strain curves were incorporated into a material model in an explicit Finite Element (FE) solver to validate the strain rate dependency of the FE foam model. Compression test results have shown that the foam used in the rodent impact acceleration model is strain rate dependent. The foam has been found to be reusable for multiple impacts. However the stress resistance of used foam is reduced to 70% of the new foam. The FU_CHANG_FOAM material model in an FE solver has been found to be adequate to simulate this rate sensitive foam. PMID:21459114

Material characterization and computer model simulation of low density polyurethane foam used in a rodent traumatic brain injury model.

PubMed

Zhang, Liying; Gurao, Manish; Yang, King H; King, Albert I

2011-05-15

Computer models of the head can be used to simulate the events associated with traumatic brain injury (TBI) and quantify biomechanical response within the brain. Marmarou's impact acceleration rodent model is a widely used experimental model of TBI mirroring axonal pathology in humans. The mechanical properties of the low density polyurethane (PU) foam, an essential piece of energy management used in Marmarou's impact device, has not been fully characterized. The foam used in Marmarou's device was tested at seven strain rates ranging from quasi-static to dynamic (0.014-42.86 s⁻¹) to quantify the stress-strain relationships in compression. Recovery rate of the foam after cyclic compression was also determined through the periods of recovery up to three weeks. The experimentally determined stress-strain curves were incorporated into a material model in an explicit Finite Element (FE) solver to validate the strain rate dependency of the FE foam model. Compression test results have shown that the foam used in the rodent impact acceleration model is strain rate dependent. The foam has been found to be reusable for multiple impacts. However the stress resistance of used foam is reduced to 70% of the new foam. The FU_CHANG_FOAM material model in an FE solver has been found to be adequate to simulate this rate sensitive foam. Copyright © 2011 Elsevier B.V. All rights reserved.

Switching Cyclic Nucleotide-Selective Activation of Cyclic Adenosine Monophosphate-Dependent Protein Kinase Holoenzyme Reveals Distinct Roles of Tandem Cyclic Nucleotide-Binding Domains.

PubMed

He, Daniel; Lorenz, Robin; Kim, Choel; Herberg, Friedrich W; Lim, Chinten James

2017-12-15

The cyclic adenosine monophosphate (cAMP)- and cyclic guanosine monophosphate (cGMP)-dependent protein kinases (PKA and PKG) are key effectors of cyclic nucleotide signaling. Both share structural features that include tandem cyclic nucleotide-binding (CNB) domains, CNB-A and CNB-B, yet their functions are separated through preferential activation by either cAMP or cGMP. Based on structural studies and modeling, key CNB contact residues have been identified for both kinases. In this study, we explored the requirements for conversion of PKA activation from cAMP-dependent to cGMP-dependent. The consequences of the residue substitutions T192R/A212T within CNB-A or G316R/A336T within CNB-B of PKA-RIα on cyclic nucleotide binding and holoenzyme activation were assessed in vitro using purified recombinant proteins, and ex vivo using RIα-deficient mouse embryonic fibroblasts genetically reconstituted with wild-type or mutant PKA-RIα. In vitro, a loss of binding and activation selectivity was observed when residues in either one of the CNB domains were mutated, while mutations in both CNB domains resulted in a complete switch of selectivity from cAMP to cGMP. The switch in selectivity was also recapitulated ex vivo, confirming their functional roles in cells. Our results highlight the importance of key cyclic nucleotide contacts within each CNB domain and suggest that these domains may have evolved from an ancestral gene product to yield two distinct cyclic nucleotide-dependent protein kinases.

Gαs regulates Glucagon-Like Peptide 1 Receptor-mediated cyclic AMP generation at Rab5 endosomal compartment.

PubMed

Girada, Shravan Babu; Kuna, Ramya S; Bele, Shilpak; Zhu, Zhimeng; Chakravarthi, N R; DiMarchi, Richard D; Mitra, Prasenjit

2017-10-01

Upon activation, G protein coupled receptors (GPCRs) associate with heterotrimeric G proteins at the plasma membrane to initiate second messenger signaling. Subsequently, the activated receptor experiences desensitization, internalization, and recycling back to the plasma membrane, or it undergoes lysosomal degradation. Recent reports highlight specific cases of persistent cyclic AMP generation by internalized GPCRs, although the functional significance and mechanistic details remain to be defined. Cyclic AMP generation from internalized Glucagon-Like Peptide-1 Receptor (GLP-1R) has previously been reported from our laboratory. This study aimed at deciphering the molecular mechanism by which internalized GLP-R supports sustained cyclic AMP generation upon receptor activation in pancreatic beta cells. We studied the time course of cyclic AMP generation following GLP-1R activation with particular emphasis on defining the location where cyclic AMP is generated. Detection involved a novel GLP-1 conjugate coupled with immunofluorescence using specific endosomal markers. Finally, we employed co-immunoprecipitation as well as immunofluorescence to assess the protein-protein interactions that regulate GLP-1R mediated cyclic AMP generation at endosomes. Our data reveal that prolonged association of G protein α subunit Gαs with activated GLP-1R contributed to sustained cyclic AMP generation at Rab 5 endosomal compartment. The findings provide the mechanism of endosomal cyclic AMP generation following GLP-1R activation. We identified the specific compartment that serves as an organizing center to generate endosomal cyclic AMP by internalized activated receptor complex. Copyright © 2017 The Authors. Published by Elsevier GmbH.. All rights reserved.

A comparison of the use of urinary cortisol to creatinine ratios and nocturnal salivary cortisol in the evaluation of cyclicity in patients with Cushing's syndrome.

PubMed

Graham, U M; Hunter, S J; McDonnell, M; Mullan, K R; Atkinson, A B

2013-01-01

Cyclical Cushing's syndrome is detected in our center by collecting sequential early morning urine (EMU) samples for cortisol to creatinine ratio over 28 d. The Endocrine Society suggests that nocturnal salivary cortisol (NSC) may be used to assess patients for cyclical Cushing's. However, there is only very limited evidence that it correlates with EMU testing or that it demonstrates cycling over 28 d. We sought to correlate NSC with EMU results collected the following morning and to determine whether NSC could be used to detect cyclical Cushing's. An observation study of 28-d collections for NSC and EMU was performed in a tertiary referral center over 1 yr. A 28-d collection of NSC and EMU was performed in 10 patients with confirmed or suspected Cushing's syndrome. The main outcome of the study was the correlation of salivary and urinary cortisol with graphical assessment of results for cycling. Eleven collections were performed. One patient with cyclical Cushing's completed the collection before and after cabergoline therapy. Two hundred seventy matched salivary and urinary results were correlated (r = 0.79; P < 0.001). In two patients with cyclical Cushing's, EMU and NSC followed a similar cyclical pattern. In one patient with recurrent cyclical Cushing's, cortisol was elevated in both saliva and urine but with more prominent cycles in saliva. NSC correlated well with EMU. NSC detected all cases of cyclical Cushing's. Therefore, NSC may prove to be an additional option or replacement for EMU in detecting cyclical Cushing's syndrome.

On Fitts's and Hooke's laws: simple harmonic movement in upper-limb cyclical aiming.

PubMed

Guiard, Y

1993-03-01

Can discrete, single-shot movements and continuous, cyclical movements be reduced to a single concept? In the classical, computational approach to human motor behaviour, cyclical aimed movement has generally been considered to derive from discrete primitives through a concatenation mechanism. Much importance, accordingly, has been attached to discrete-movement paradigms and to techniques allowing the segmentation of continuous data. An alternative approach, suggested by the nonlinear dynamical systems theory, views discreteness as a limiting case of cyclicity. Although attempts have been made recently to account for discrete movements in dynamical terms, cyclical paradigms have been favoured. The concatenation interpretation of cyclical aimed movement is criticized on the ground that it implies a complete waste of mechanical energy once in every half-cycle. Some kinematic data from a one-dimensional reciprocal (i.e., cyclical) aiming experiment are reported, suggesting that human subjects do save muscular efforts from one movement to the next in upper-limb cyclical aiming. The experiment demonstrated convergence on simple harmonic motion as aiming tolerance was increased, an outcome interpreted with reference to Hooke's law, in terms of the muscles' capability of storing potential, elastic energy across movement reversals. Not only is the concatenation concept problematic for understanding cyclical aimed movements, but the very reality of discrete movements is questionable too. It is pointed out that discrete motor acts of real life are composed of complete cycles, rather than half-cycles.

ON THE MECHANISM OF ACTION OF ADRENOCORTICOTROPIC HORMONE: THE BINDING OF CYCLIC-3′,5′-ADENOSINE MONOPHOSPHATE TO AN ADRENAL CORTICAL PROTEIN*

PubMed Central

Gill, Gordon N.; Garren, Leonard D.

1969-01-01

The binding of cyclic 3′,5′-adenosine monophosphate (cyclic AMP) within the adrenal cortical cell was studied. Cyclic AMP binds specifically to a protein which is associated predominantly with the microsomal fraction of the cell. The binding protein was purified approximately 100-fold. PMID:4308274

Probing the Reactivity of Cyclic "N,O"-Acetals versus Cyclic "O,O"-Acetals with NaBH[subscript 4] and CH[subscript 3]MgI

ERIC Educational Resources Information Center

Ciaccio, James A.; Saba, Shahrokh; Bruno, Samantha M.; Bruppacher, John H.; McKnight, Alexa G.

2018-01-01

An operationally straightforward, project-like laboratory experiment has been developed in which students directly compare the reactivity of two heterocycles, a cyclic "O,O"-acetal (standard C-O protecting group) and a cyclic "N,O"-acetal (oxazolidine), toward sodium borohydride and methylmagnesium iodide. Students synthesize a…

The Contribution of Compressional Magnetic Pumping to the Energization of the Earth's Outer Electron Radiation Belt During High-Speed Stream-Driven Storms

NASA Astrophysics Data System (ADS)

Borovsky, Joseph E.; Horne, Richard B.; Meredith, Nigel P.

2017-12-01

Compressional magnetic pumping is an interaction between cyclic magnetic compressions and pitch angle scattering with the scattering acting as a catalyst to allow the cyclic compressions to energize particles. Compressional magnetic pumping of the outer electron radiation belt at geosynchronous orbit in the dayside magnetosphere is analyzed by means of computer simulations, wherein solar wind compressions of the dayside magnetosphere energize electrons with electron pitch angle scattering by chorus waves and by electromagnetic ion cyclotron (EMIC) waves. The magnetic pumping is found to produce a weak bulk heating of the electron radiation belt, and it also produces an energetic tail on the electron energy distribution. The amount of energization depends on the robustness of the solar wind compressions and on the amplitude of the chorus and/or EMIC waves. Chorus-catalyzed pumping is better at energizing medium-energy (50-200 keV) electrons than it is at energizing higher-energy electrons; at high energies (500 keV-2 MeV) EMIC-catalyzed pumping is a stronger energizer. The magnetic pumping simulation results are compared with energy diffusion calculations for chorus waves in the dayside magnetosphere; in general, compressional magnetic pumping is found to be weaker at accelerating electrons than is chorus-driven energy diffusion. In circumstances when solar wind compressions are robust and when EMIC waves are present in the dayside magnetosphere without the presence of chorus, EMIC-catalyzed magnetic pumping could be the dominant energization mechanism in the dayside magnetosphere, but at such times loss cone losses will be strong.

ANF-RGC gene motif 669WTAPELL675 is vital for blood pressure regulation: Biochemical mechanism

PubMed Central

Duda, Teresa; Pertzev, Alexandre; Sharma, Rameshwar K.

2013-01-01

ANF-RGC is the prototype membrane guanylate cyclase, both the receptor and the signal transducer of the hormones ANF and BNP. After binding them at the extracellular domain it, at its intracellular domain, signals activation of the C-terminal catalytic module and accelerates production of the second messenger, cyclic GMP. This, in turn, controls the physiological processes of blood pressure, cardiovascular function, and fluid secretion, and others: metabolic syndrome, obesity and apoptosis. What is the biochemical mechanism by which this single molecule controls these diverse processes, explicitly of the blood pressure regulation is the subject of the present study. In line with the concept that the structural modules of ANF-RGC are designed to respond to more than one, yet distinctive signals, the study demonstrates the construction of a novel ANF-RGC-In-gene-669WTAPELL675 mouse model. Through this model, the study establishes that 669WTAPELL675 is a vital ANF signal transducer motif of the guanylate cyclase. Its striking physiological features linked with their biochemistry are that (1) it controls the hormonally-dependent cyclic GMP production in the kidney and the adrenal gland; (3) its deletion causes hypertension, and (3) cardiac hypertrophy; and (4) these mice show higher levels of the plasma aldosterone. For the first time, a mere 7-amino acid encoded motif of the mouse gene has been directly linked with the physiological control of the blood pressure regulation, a detailed biochemistry of this linkage has been established and a model for this linkage has been offered. PMID:23464624

The effect of matrix microstructure on cyclic response and fatigue behavior of particle-reinforced 2219 aluminum: Part II. Behavior at 150 °C

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; van Aken, D. C.; Allison, J. E.

1995-12-01

The 150 °C cyclic response of peak-aged and overaged 2219/TiC/15p and 2219 Al was examined using fully reversed plastic strain-controlled testing. The cyclic response of peak-aged and overaged particle-reinforced materials showed extensive cyclic softening. This softening began at the commencement of cycling and continued until failure. At a plastic strain below 5 × 103, the unreinforced materials did not show evidence of cyclic softening until approximately 30 pct of the life was consumed. In addition, the degree of cyclic softening (†σ) was significantly lower in the unreinforced microstructures. The cyclic softening in both reinforced and unreinforced materials was attributed to the decomposition of the θ' strengthening precipitates. The extent of the precipitate decomposition was much greater in the composite materials due to the increased levels of local plastic strain in the matrix caused by constrained deformation near the TiC particles.

Arrangement of Proteinogenic α-Amino Acids on a Cyclic Peptide Comprising Alternate Biphenyl-Cored ζ-Amino Acids.

PubMed

Tashiro, Shohei; Chiba, Masayuki; Shionoya, Mitsuhiko

2017-05-18

Aiming at precisely arranging several proteinogenic α-amino acids on a folded scaffold, we have developed a cyclic hexapeptide comprising an alternate sequence of biphenyl-cored ζ-amino acids and proteinogenic α-amino acids such as l-leucine. The amino acids were connected by typical peptide synthesis, and the resultant linear hexapeptide was intramolecularly cyclized to form a target cyclic peptide. Theoretical analyses and NMR spectroscopy suggested that the cyclic peptide was folded into an unsymmetrical conformation, and the structure was likely to be flexible in CHCl 3 . The optical properties including UV/Vis absorption, fluorescence, and circular dichroism (CD) were also evaluated. Furthermore, the cyclic peptide became soluble in water by introducing three carboxylate groups at the periphery of the cyclic skeleton. This α/ζ-alternating cyclic peptide is therefore expected to serve as a unique scaffold for arranging several functionalities. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

TSH-induced cyclic AMP production in an ovine thyroid cell line: OVNIS 5H.

PubMed

Fayet, G; Aouani, A; Hovsépian, S

1986-01-06

The TSH-induced cyclic AMP response was studied using a 3-year-old ovine thyroid cell line TSH-independent for growth: OVNIS 5H. The kinetics of cyclic AMP production was followed both in cell layers and in cell culture media, with or without phosphodiesterase inhibitor. It is noteworthy that following the first wave in cyclic AMP obtained within minutes, we observed later a sustained exponential increase in cyclic AMP during the 5 days following TSH stimulation. A bioassay of TSH was derived allowing measurement of 1 microU/ml TSH from a crude bTSH preparation.

Cyclic stress effect on stress corrosion cracking of duplex stainless steel in chloride and caustic solutions

NASA Astrophysics Data System (ADS)

Yang, Di

Duplex stainless steel (DSS) is a dual-phase material with approximately equal volume amount of austenite and ferrite. It has both great mechanical properties (good ductility and high tensile/fatigue strength) and excellent corrosion resistance due to the mixture of the two phases. Cyclic loadings with high stress level and low frequency are experienced by many structures. However, the existing study on corrosion fatigue (CF) study of various metallic materials has mainly concentrated on relatively high frequency range. No systematic study has been done to understand the ultra-low frequency (˜10-5 Hz) cyclic loading effect on stress corrosion cracking (SCC) of DSSs. In this study, the ultra-low frequency cyclic loading effect on SCC of DSS 2205 was studied in acidified sodium chloride and caustic white liquor (WL) solutions. The research work focused on the environmental effect on SCC of DSS 2205, the cyclic stress effect on strain accumulation behavior of DSS 2205, and the combined environmental and cyclic stress effect on the stress corrosion crack initiation of DSS 2205 in the above environments. Potentiodynamic polarization tests were performed to investigate the electrochemical behavior of DSS 2205 in acidic NaCl solution. Series of slow strain rate tests (SSRTs) at different applied potential values were conducted to reveal the optimum applied potential value for SCC to happen. Room temperature static and cyclic creep tests were performed in air to illustrate the strain accumulation effect of cyclic stresses. Test results showed that cyclic loading could enhance strain accumulation in DSS 2205 compared to static loading. Moreover, the strain accumulation behavior of DSS 2205 was found to be controlled by the two phases of DSS 2205 with different crystal structures. The B.C.C. ferrite phase enhanced strain accumulation due to extensive cross-slips of the dislocations, whereas the F.C.C. austenite phase resisted strain accumulation due to cyclic strain hardening. Cyclic SSRTs were performed under the conditions that SCC occurs in sodium chloride and WL solutions. Test results show that cyclic stress facilitated crack initiations in DSS 2205. Stress corrosion cracks initiated from the intermetallic precipitates in acidic chloride environment, and the cracks initiated from austenite phase in WL environment. Cold-working has been found to retard the crack initiations induced by cyclic stresses.

[Cyclic Cushing's Syndrome - rare or rarely recognized].

PubMed

Kiałka, Marta; Doroszewska, Katarzyna; Mrozińska, Sandra; Milewicz, Tomasz; Stochmal, Ewa

2015-01-01

Cyclic Cushing's syndrome is a type of Cushing's disease which is characterized by alternating periods of increasing and decreasing levels of cortisol in the blood. The diagnostic criteria for cyclic Cushing's syndrome are at least three periods of hypercortisolism alternating with at least two episodes of normal levels of serum cortisol concentration. The epidemiology, signs, symptoms, pathogenesis and treatment of cyclic Cushing's syndrome have been discussed.

A theoretical study of the hydrogen bonding between the vic-, cis- and trans-C 2H 2F 2 isomers and hydrogen fluoride

NASA Astrophysics Data System (ADS)

Rusu, Victor H.; da Silva, João Bosco P.; Ramos, Mozart N.

2009-04-01

MP2/6-31++G(d,p) and B3LYP/6-31++G(d,p) theoretical calculations have been employed to investigate the hydrogen bonding formation involving the vic-, cis- and trans-C 2H 2F 2 isomers and hydrogen fluoride. Our calculations have revealed for each isomer the preferential existence of two possible hydrogen-bonded complexes: a non-cyclic complex and a cyclic complex. For all the three isomers the binding energies for the non-cyclic and cyclic hydrogen complexes are essentially equal using both the MP2 and B3LYP calculations, being that the cyclic structure is slightly more stable. For instance, the binding energies including BSSE and ZPE corrections for the non-cyclic and cyclic structures of cis-C 2H 2F···HF are 8.7 and 9.0 kJ mol -1, respectively, using B3LYP calculations. The cyclic complex formation reduces the polarity, in contrast to what occurs with the non-cyclic complex. This result is more accentuated in vic-C 2H 2F 2···HF. In this latter, Δ μ(cyclic) is -3.07 D, whereas Δ μ(non-cyclic) is +1.92 D using B3LYP calculations. Their corresponding MP2 values are +0.44 D and -1.89 D, respectively. As expected, the complexation produces an H sbnd F stretching frequency downward shift, whereas its IR intensity is enhanced. On the other hand, the vibrational modes of the vic-, cis- and trans-C 2H 2F 2 isomers are little affected by complexation. The new vibrational modes due to hydrogen bonding formation show several interesting features, in particular the HF bending modes which are pure rotations in the free molecule.

Physiological cyclic strain promotes endothelial cell survival via the induction of heme oxygenase-1

PubMed Central

Liu, Xiao-ming; Peyton, Kelly J.

2013-01-01

Endothelial cells (ECs) are constantly subjected to cyclic strain that arises from periodic change in vessel wall diameter as a result of pulsatile blood flow. Application of physiological levels of cyclic strain inhibits EC apoptosis; however, the underlying mechanism is not known. Since heme oxygenase-1 (HO-1) is a potent inhibitor of apoptosis, the present study investigated whether HO-1 contributes to the antiapoptotic action of cyclic strain. Administration of physiological cyclic strain (6% at 1 Hz) to human aortic ECs stimulated an increase in HO-1 activity, protein, and mRNA expression. The induction of HO-1 was preceded by a rise in reactive oxygen species (ROS) and Nrf2 protein expression. Cyclic strain also stimulated an increase in HO-1 promoter activity that was prevented by mutating the antioxidant responsive element in the promoter or by overexpressing dominant-negative Nrf2. In addition, the strain-mediated induction of HO-1 and activation of Nrf2 was abolished by the antioxidant N-acetyl-l-cysteine. Finally, application of cyclic strain blocked inflammatory cytokine-mediated EC death and apoptosis. However, the protective action of cyclic strain was reversed by the HO inhibitor tin protoporphyrin-IX and was absent in ECs isolated from HO-1-deficient mice. In conclusion, the present study demonstrates that a hemodynamically relevant level of cyclic strain stimulates HO-1 gene expression in ECs via the ROS-Nrf2 signaling pathway to inhibit EC death. The ability of cyclic strain to induce HO-1 expression may provide an important mechanism by which hemodynamic forces promote EC survival and vascular homeostasis. PMID:23604711

Diguanylate cyclase activity of the Mycobacterium leprae T cell antigen ML1419c

PubMed Central

Rotcheewaphan, Suwatchareeporn; Belisle, John T.; Webb, Kristofor J.; Kim, Hee-Jin; Spencer, John S.

2016-01-01

The second messenger, bis-(3′,5′)-cyclic dimeric guanosine monophosphate (cyclic di-GMP), is involved in the control of multiple bacterial phenotypes, including those that impact host–pathogen interactions. Bioinformatics analyses predicted that Mycobacterium leprae, an obligate intracellular bacterium and the causative agent of leprosy, encodes three active diguanylate cyclases. In contrast, the related pathogen Mycobacterium tuberculosis encodes only a single diguanylate cyclase. One of the M. leprae unique diguanylate cyclases (ML1419c) was previously shown to be produced early during the course of leprosy. Thus, functional analysis of ML1419c was performed. The gene encoding ML1419c was cloned and expressed in Pseudomonas aeruginosa PAO1 to allow for assessment of cyclic di-GMP production and cyclic di-GMP-mediated phenotypes. Phenotypic studies revealed that ml1419c expression altered colony morphology, motility and biofilm formation of P. aeruginosa PAO1 in a manner consistent with increased cyclic di-GMP production. Direct measurement of cyclic di-GMP levels by liquid chromatography–mass spectrometry confirmed that ml1419c expression increased cyclic di-GMP production in P. aeruginosa PAO1 cultures in comparison to the vector control. The observed phenotypes and increased levels of cyclic di-GMP detected in P. aeruginosa expressing ml1419c could be abrogated by mutation of the active site in ML1419c. These studies demonstrated that ML1419c of M. leprae functions as diguanylate cyclase to synthesize cyclic di-GMP. Thus, this protein was renamed DgcA (Diguanylate cyclase A). These results also demonstrated the ability to use P. aeruginosa as a heterologous host for characterizing the function of proteins involved in the cyclic di-GMP pathway of a pathogen refractory to in vitro growth, M. leprae. PMID:27450520

Diguanylate cyclase activity of the Mycobacterium leprae T cell antigen ML1419c.

PubMed

Rotcheewaphan, Suwatchareeporn; Belisle, John T; Webb, Kristofor J; Kim, Hee-Jin; Spencer, John S; Borlee, Bradley R

2016-09-01

The second messenger, bis-(3',5')-cyclic dimeric guanosine monophosphate (cyclic di-GMP), is involved in the control of multiple bacterial phenotypes, including those that impact host-pathogen interactions. Bioinformatics analyses predicted that Mycobacterium leprae, an obligate intracellular bacterium and the causative agent of leprosy, encodes three active diguanylate cyclases. In contrast, the related pathogen Mycobacterium tuberculosis encodes only a single diguanylate cyclase. One of the M. leprae unique diguanylate cyclases (ML1419c) was previously shown to be produced early during the course of leprosy. Thus, functional analysis of ML1419c was performed. The gene encoding ML1419c was cloned and expressed in Pseudomonas aeruginosa PAO1 to allow for assessment of cyclic di-GMP production and cyclic di-GMP-mediated phenotypes. Phenotypic studies revealed that ml1419c expression altered colony morphology, motility and biofilm formation of P. aeruginosa PAO1 in a manner consistent with increased cyclic di-GMP production. Direct measurement of cyclic di-GMP levels by liquid chromatography-mass spectrometry confirmed that ml1419c expression increased cyclic di-GMP production in P. aeruginosa PAO1 cultures in comparison to the vector control. The observed phenotypes and increased levels of cyclic di-GMP detected in P. aeruginosa expressing ml1419c could be abrogated by mutation of the active site in ML1419c. These studies demonstrated that ML1419c of M. leprae functions as diguanylate cyclase to synthesize cyclic di-GMP. Thus, this protein was renamed DgcA (Diguanylate cyclase A). These results also demonstrated the ability to use P. aeruginosa as a heterologous host for characterizing the function of proteins involved in the cyclic di-GMP pathway of a pathogen refractory to in vitro growth, M. leprae.

Removal torque evaluation of three different abutment screws for single implant restorations after mechanical cyclic loading.

PubMed

Paepoemsin, T; Reichart, P A; Chaijareenont, P; Strietzel, F P; Khongkhunthian, P

2016-01-01

The aim of this study was to evaluate the removal torque of three different abutment screws and pull out strength of implant-abutment connection for single implant restorations after mechanical cyclic loading. The study was performed in accordance with ISO 14801:2007. Three implant groups (n=15) were used: group A, PW Plus® with flat head screw; group B, PW Plus® with tapered screw; and group C, Conelog® with flat head screw. All groups had the same implant-abutment connection feature: cone with mandatory index. All screws were tightened with manufacturer's recommended torque. Ten specimens in each group underwent cyclic loading (1×106 cycles, 10 Hz, and 250 N). Then, all specimens were un-tightened, measured for the removal torque, and underwent a tensile test. The force that dislodged abutment from implant fixture was recorded. The data were analysed using independent sample t-test, ANOVA and Tukey HSD test. Before cyclic loading, removal torque in groups A, B and C were significantly different (B> A> C, P<.05). After cyclic loading, removal torque in all groups decreased significantly (P<.05). Group C revealed significantly less removal torque than groups A and B (P<.005). Tensile force in all groups significantly increased after cyclic loading (P<.05), group A had significantly less tensile force than groups B and C (P<.005). Removal torque reduced significantly after cyclic loading. Before cyclic loading, tapered screws maintained more preload than did flat head screws. After cyclic loading, tapered and flat head screws maintained even amounts of preload. The tensile force that dislodged abutment from implant fixture increased immensely after cyclic loading.

Removal torque evaluation of three different abutment screws for single implant restorations after mechanical cyclic loading

PubMed Central

PAEPOEMSIN, T.; REICHART, P. A.; CHAIJAREENONT, P.; STRIETZEL, F. P.; KHONGKHUNTHIAN, P.

2016-01-01

SUMMARY Purpose The aim of this study was to evaluate the removal torque of three different abutment screws and pull out strength of implant-abutment connection for single implant restorations after mechanical cyclic loading. Methods The study was performed in accordance with ISO 14801:2007. Three implant groups (n=15) were used: group A, PW Plus® with flat head screw; group B, PW Plus® with tapered screw; and group C, Conelog® with flat head screw. All groups had the same implant-abutment connection feature: cone with mandatory index. All screws were tightened with manufacturer’s recommended torque. Ten specimens in each group underwent cyclic loading (1×106 cycles, 10 Hz, and 250 N). Then, all specimens were un-tightened, measured for the removal torque, and underwent a tensile test. The force that dislodged abutment from implant fixture was recorded. The data were analysed using independent sample t-test, ANOVA and Tukey HSD test. Results Before cyclic loading, removal torque in groups A, B and C were significantly different (B> A> C, P<.05). After cyclic loading, removal torque in all groups decreased significantly (P<.05). Group C revealed significantly less removal torque than groups A and B (P<.005). Tensile force in all groups significantly increased after cyclic loading (P<.05), group A had significantly less tensile force than groups B and C (P<.005). Conclusions Removal torque reduced significantly after cyclic loading. Before cyclic loading, tapered screws maintained more preload than did flat head screws. After cyclic loading, tapered and flat head screws maintained even amounts of preload. The tensile force that dislodged abutment from implant fixture increased immensely after cyclic loading. PMID:28042450

Design, synthesis and biological evaluation of (S)-valine thiazole-derived cyclic and non-cyclic peptidomimetic oligomers as modulators of human P-glycoprotein (ABCB1)

PubMed Central

Singh, Satyakam; Prasad, Nagarajan Rajendra; Kapoor, Khyati; Chufan, Eduardo E.; Patel, Bhargav A.; Ambudkar, Suresh V.; Talele, Tanaji T.

2014-01-01

Multidrug resistance (MDR) caused by ATP-binding cassette (ABC) transporter P-glycoprotein (P-gp) through extrusion of anticancer drugs from the cells is a major cause of failure to cancer chemotherapy. Previously, selenazole containing cyclic peptides were reported as P-gp inhibitors and these were also used for co-crystallization with mouse P-gp, which has 87% homology to human P-gp. It has been reported that human P-gp, can simultaneously accommodate 2-3 moderate size molecules at the drug binding pocket. Our in-silico analysis based on the homology model of human P-gp spurred our efforts to investigate the optimal size of (S)-valine-derived thiazole units that can be accommodated at drug-binding pocket. Towards this goal, we synthesized varying lengths of linear and cyclic derivatives of (S)-valine-derived thiazole units to investigate the optimal size, lipophilicity and the structural form (linear and cyclic) of valine-derived thiazole peptides that can accommodate well in the P-gp binding pocket and affects its activity, previously an unexplored concept. Among these oligomers, lipophilic linear- (13) and cyclic-trimer (17) derivatives of QZ59S-SSS were found to be the most and equally potent inhibitors of human P-gp (IC50 = 1.5 μM). Cyclic trimer and linear trimer being equipotent, future studies can be focused on non-cyclic counterparts of cyclic peptides maintaining linear trimer length. Binding model of the linear trimer (13) within the drug-binding site on the homology model of human P-gp represents an opportunity for future optimization, specifically replacing valine and thiazole groups in the non-cyclic form. PMID:24288265

Lanthanum inhibition of Vibrio cholerae and Escherichia coli enterotoxin-induced enterosorption and its effects on intestinal mucosa cyclic adenosine 3',5'-monophosphate and cyclic guanosine 3',5'-monophosphate levels.

PubMed Central

Leitch, G J; Amer, M S

1975-01-01

Several trivalent cations, including lanthanum (La3+), inhibited the secretion (enterosorption) induced by the enterotoxins of Vibrio cholerae and Escherichia coli in the rabbit ileum in vivo. High concentrations (greater than 10 mM) of La3+ were required to inhibit cholera enterotoxin (CE)-induced enterosorption, probably because of the adsorption of the La3+ often potentiated the CE-induced enterosorption. If luminal La3+ exposure followed CE exposure, some recovery of the enterosorptive response was observed. The longer the lag between the CE exposure and the La3+ exposure, the greater was the recovery of the enterosorptive response. Lanthanum inhibited HCO3- secretion more than Cl- secretion. By altering the luminal fluid pH at the time of La3+ exposure, it was found that La3+ was adsorbed to negatively charged luminal sites, having an apparent pK between 2.5 and 3.0. Although La3+ antagonized the enterosorptive response to CE, it mimicked rather than antagonized the cyclic adenosine 3',5'-monophosphate elevation and cyclic guanosine 3',5'-monophosphate depression induced by the toxin. It is therefore concluded that the La3+ inhibition of the CE-induced enterosorption must have occurred at a site following the generation of the cyclic nucleotides. Cholera enterotoxin caused complex time-dependent changes in the mucosal cyclic adenosine 3',5'-monophosphate and cyclic guanosine 3',5'-monophosphate levels, as revealed by studying tissue cyclic adenosine 3',5'-monophosphate/cyclic guanosine 3',5'-monophosphate ratios. The possible roles these two cyclic nucleotides may play in the pathogenesis of the cholera diarrhea are discussed. PMID:164410

Cyclic hardening behavior of extruded ZK60 magnesium alloy with different grain sizes

NASA Astrophysics Data System (ADS)

Zhang, Lixin; Zhang, Wencong; Chen, Wenzhen; Wang, Wenke

2018-04-01

Montonic and fully reversed strain-controlled cyclic deformation experiments were conducted on extruded ZK60 magnesium alloy with two different grain sizes in ambient air. Results revealed that the hardening rates of the ZK60 magnesium alloy rods with fine grain and coarse grain in the monotonic deformation and the fully reversed strain-controlled cyclic deformation were opposite along the extrusion direction. Electron Backscatter Diffration analysis revealed that fine grains were more easily rotated than coarse grains under the cyclic deformation. Under the twinning and detwinning process of the cyclic deformation at a large strain amplitude, the coarse grained ZK60 magnesium alloys were more prone to tension twinning {10-12}<10-11> and more residual twins were observed. Texture hardening of coarse grained magnesium alloy was more obvious in cyclic defromation than fine-grained magnesium alloy.

Cyclic polyalcohols: fingerprints to identify the botanical origin of natural woods used in wine aging.

PubMed

Alañón, M Elena; Díaz-Maroto, M Consuelo; Díaz-Maroto, Ignacio J; Vila-Lameiro, Pablo; Pérez-Coello, M Soledad

2011-02-23

Cyclic polyalcohol composition of 80 natural wood samples from different botanical species, with the majority of them used in the oenology industry for aging purposes, has been studied by gas chromatography-mass spectrometry (GC-MS) after its conversion into their trimethylsilyloxime derivatives. Each botanical species showed a different and specific cyclic polyalcohol profile. Oak wood samples were characterized by the richness in deoxyinositols, especially proto-quercitol. Meanwhile, other botanical species showed a very low content of cyclic polyalcohols. The qualitative and quantitative study of cyclic polyalcohols was a useful tool to characterize and differentiate woods of different botanical origin to guarantee the authenticity of chips used in the wine-aging process. Monosaccharide composition was also analyzed, showing some quantitative differences among species, but cyclic polyalcohols were the compounds that revealed the main differentiation power.

Effects of fenspiride on human bronchial cyclic nucleotide phosphodiesterase isoenzymes: functional and biochemical study.

PubMed

Cortijo, J; Naline, E; Ortiz, J L; Berto, L; Girard, V; Malbezin, M; Advenier, C; Morcillo, E J

1998-01-02

We have investigated the role of human bronchial cyclic nucleotide phosphodiesterases in the effects of fenspiride, a drug endowed with bronchodilator and anti-inflammatory properties. Functional studies on human isolated bronchi showed that fenspiride (10(-6)-3 x 10(-3) M, 30 min) induced a shift to the left of the concentration-response curves for isoprenaline and sodium nitroprusside with -logEC50 values of 4.1+/-0.1 (n = 7) and 3.5+/-0.2 (n = 8), respectively. Biochemical studies were carried out on three human bronchi in which separation of cyclic nucleotide phosphodiesterase isoenzymes was performed by ion exchange chromatography followed by determination of phosphodiesterase activity with a radioisotopic method. Phosphodiesterase 4 (cyclic AMP-specific) and phosphodiesterase 5 (cyclic GMP-specific) were the major phosphodiesterase isoforms present in the human bronchial tissue. The presence of phosphodiesterase 1 (Ca2+/calmodulin-stimulated), phosphodiesterase 2 (cyclic GMP-stimulated) and, in two cases, phosphodiesterase 3 (cyclic GMP-inhibited) was also identified. Fenspiride inhibited phosphodiesterase 4 and phosphodiesterase 3 activities with -logIC50 values of 4.16+/-0.09 and 3.44+/-0.12, respectively. Phosphodiesterase 5 activity was also inhibited with a -logIC50 value of approximately 3.8. Fenspiride (< or = 10(-3) M) produced less than 25% inhibition of phosphodiesterase 1 and phosphodiesterase 2 activities. In conclusion, fenspiride is an effective inhibitor of both cyclic AMP and cyclic GMP hydrolytic activity in human bronchial tissues and this action may contribute to its airway effects.

Fourier-based integration of quasi-periodic gait accelerations for drift-free displacement estimation using inertial sensors.

PubMed

Sabatini, Angelo Maria; Ligorio, Gabriele; Mannini, Andrea

2015-11-23

In biomechanical studies Optical Motion Capture Systems (OMCS) are considered the gold standard for determining the orientation and the position (pose) of an object in a global reference frame. However, the use of OMCS can be difficult, which has prompted research on alternative sensing technologies, such as body-worn inertial sensors. We developed a drift-free method to estimate the three-dimensional (3D) displacement of a body part during cyclical motions using body-worn inertial sensors. We performed the Fourier analysis of the stride-by-stride estimates of the linear acceleration, which were obtained by transposing the specific forces measured by the tri-axial accelerometer into the global frame using a quaternion-based orientation estimation algorithm and detecting when each stride began using a gait-segmentation algorithm. The time integration was performed analytically using the Fourier series coefficients; the inverse Fourier series was then taken for reconstructing the displacement over each single stride. The displacement traces were concatenated and spline-interpolated to obtain the entire trace. The method was applied to estimate the motion of the lower trunk of healthy subjects that walked on a treadmill and it was validated using OMCS reference 3D displacement data; different approaches were tested for transposing the measured specific force into the global frame, segmenting the gait and performing time integration (numerically and analytically). The width of the limits of agreements were computed between each tested method and the OMCS reference method for each anatomical direction: Medio-Lateral (ML), VerTical (VT) and Antero-Posterior (AP); using the proposed method, it was observed that the vertical component of displacement (VT) was within ±4 mm (±1.96 standard deviation) of OMCS data and each component of horizontal displacement (ML and AP) was within ±9 mm of OMCS data. Fourier harmonic analysis was applied to model stride-by-stride linear accelerations during walking and to perform their analytical integration. Our results showed that analytical integration based on Fourier series coefficients was a useful approach to accurately estimate 3D displacement from noisy acceleration data.

Biosynthesis of cyclic 2,3-diphosphoglycerate. Isolation and characterization of 2-phosphoglycerate kinase and cyclic 2,3-diphosphoglycerate synthetase from Methanothermus fervidus.

PubMed

Lehmacher, A; Vogt, A B; Hensel, R

1990-10-15

Starting from 2-phosphoglycerate the biosynthesis of cDPG comprises two steps: (i) the phosphorylation of 2-phosphoglycerate to 2,3-diphosphoglycerate and (ii) the intramolecular cyclization to cyclic 2,3-diphosphoglycerate. The involved enzymes, 2-phosphoglycerate kinase and cyclic 2,3-diphosphoglycerate synthetase, were purified form Methanothermus fervidus. Their molecular and catalytic properties were characterized.

Cyclical vomiting syndrome secondary to a Chiari I malformation-a case report.

PubMed

White, William L; Bagga, Veejay; Campbell, David I; Hart, Anthony R; Ushewokunze, Shungu

2017-12-01

Cyclical vomiting syndrome is a disorder characterised by recurrent episodes of profuse vomiting. There are no cases in the literature on the management of children with presenting with cyclical vomiting syndrome and a Chiari malformation type I. We report the case of a 12-year-old child diagnosed with cyclical vomiting syndrome and a Chiari malformation type I. The patient received symptomatic relief following a craniocervical decompression.

The diastolic function to cyclic variation of myocardial ultrasonic backscatter relation: the influence of parameterized diastolic filling (PDF) formalism determined chamber properties.

PubMed

Lloyd, Christopher W; Shmuylovich, Leonid; Holland, Mark R; Miller, James G; Kovács, Sándor J

2011-08-01

Myocardial tissue characterization represents an extension of currently available echocardiographic imaging. The systematic variation of backscattered energy during the cardiac cycle (the "cyclic variation" of backscatter) has been employed to characterize cardiac function in a wide range of investigations. However, the mechanisms responsible for observed cyclic variation remain incompletely understood. As a step toward determining the features of cardiac structure and function that are responsible for the observed cyclic variation, the present study makes use of a kinematic approach of diastolic function quantitation to identify diastolic function determinants that influence the magnitude and timing of cyclic variation. Echocardiographic measurements of 32 subjects provided data for determination of the cyclic variation of backscatter to diastolic function relation characterized in terms of E-wave determined, kinematic model-based parameters of chamber stiffness, viscosity/relaxation and load. The normalized time delay of cyclic variation appears to be related to the relative viscoelasticity of the chamber and predictive of the kinematic filling dynamics as determined using the parameterized diastolic filling formalism (with r-values ranging from .44 to .59). The magnitude of cyclic variation does not appear to be strongly related to the kinematic parameters. Copyright © 2011 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Compressed sensing with cyclic-S Hadamard matrix for terahertz imaging applications

NASA Astrophysics Data System (ADS)

Ermeydan, Esra Şengün; ćankaya, Ilyas

2018-01-01

Compressed Sensing (CS) with Cyclic-S Hadamard matrix is proposed for single pixel imaging applications in this study. In single pixel imaging scheme, N = r . c samples should be taken for r×c pixel image where . denotes multiplication. CS is a popular technique claiming that the sparse signals can be reconstructed with samples under Nyquist rate. Therefore to solve the slow data acquisition problem in Terahertz (THz) single pixel imaging, CS is a good candidate. However, changing mask for each measurement is a challenging problem since there is no commercial Spatial Light Modulators (SLM) for THz band yet, therefore circular masks are suggested so that for each measurement one or two column shifting will be enough to change the mask. The CS masks are designed using cyclic-S matrices based on Hadamard transform for 9 × 7 and 15 × 17 pixel images within the framework of this study. The %50 compressed images are reconstructed using total variation based TVAL3 algorithm. Matlab simulations demonstrates that cyclic-S matrices can be used for single pixel imaging based on CS. The circular masks have the advantage to reduce the mechanical SLMs to a single sliding strip, whereas the CS helps to reduce acquisition time and energy since it allows to reconstruct the image from fewer samples.

[Erythromycin in therapy of cyclic vomiting syndrome].

PubMed

Pavlović, Momcilo; Radlović, Nedeljko; Leković, Zoran; Berenji, Karolina

2007-01-01

Cyclic vomiting syndrome is an insufficiently understood disorder which manifests itself in stereotypical episodes of vomiting with no detectable organic cause. Considering its unknown aetiology, drugs borrowed from various medication classes are applied in the therapy of this disorder, with variable success. Among other medicaments, erythromycin is also used in treatment of cyclic vomiting syndrome. This is a case study in which the application of erythromycin led to the prevention of attacks of cyclic vomiting syndrome. Our case report presents how periodical erythromycin therapy in two-week intervals at expected attack periods in a girl led to disappearance of cyclic vomiting. Adverse effects of erythromycin did not show up.

Rhodium-Catalyzed Dehydrogenative Borylation of Cyclic Alkenes

PubMed Central

Kondoh, Azusa; Jamison, Timothy F.

2010-01-01

A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki-Miyaura cross-coupling applications are also presented. PMID:20107646

Cyclic Polymers: From Scientific Curiosity to Advanced Materials for Gene Delivery and Surface Modification.

PubMed

Verbraeken, Bart; Hoogenboom, Richard

2017-06-12

Cyclic versus linear: The superiority of cyclic polymers over their linear counterparts is highlighted. Cyclic poly(2-oxazoline)s have been shown to provide excellent shielding properties when grafted to TiO 2 surfaces and Fe 3 O 4 nanoparticles owing to their ultrahigh grafting densities leading to low friction surfaces, superior antifouling properties, and extreme nanoparticle stabilization. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cadmium Coating Alternatives for High- Strength Steel JTP - Phase 2

DTIC Science & Technology

2009-09-03

Substrate 4130 Washer 17 - 4PH Washer CuBe Washer AlNiBr Washer Salt Spray Cyclic Salt Spray Cyclic Salt Spray Cyclic Salt Spray Cyclic No coating...2009, Westminster, CO. Sponsored by SERDP/ESTCP. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17 . LIMITATION OF ABSTRACT Same...Passed Appearance Testing U.S. AIR FORCE Primary Coating Bend Adhesion Test Results Coating Bend Adhesion Results 4130 steel substrate 17 -4 PH stainless

Toward structure prediction of cyclic peptides.

PubMed

Yu, Hongtao; Lin, Yu-Shan

2015-02-14

Cyclic peptides are a promising class of molecules that can be used to target specific protein-protein interactions. A computational method to accurately predict their structures would substantially advance the development of cyclic peptides as modulators of protein-protein interactions. Here, we develop a computational method that integrates bias-exchange metadynamics simulations, a Boltzmann reweighting scheme, dihedral principal component analysis and a modified density peak-based cluster analysis to provide a converged structural description for cyclic peptides. Using this method, we evaluate the performance of a number of popular protein force fields on a model cyclic peptide. All the tested force fields seem to over-stabilize the α-helix and PPII/β regions in the Ramachandran plot, commonly populated by linear peptides and proteins. Our findings suggest that re-parameterization of a force field that well describes the full Ramachandran plot is necessary to accurately model cyclic peptides.

Synthesis and screening of one-bead-one-compound cyclic peptide libraries.

PubMed

Qian, Ziqing; Upadhyaya, Punit; Pei, Dehua

2015-01-01

Cyclic peptides have been a rich source of biologically active molecules. Herein we present a method for the combinatorial synthesis and screening of large one-bead-one-compound (OBOC) libraries of cyclic peptides against biological targets such as proteins. Up to ten million different cyclic peptides are rapidly synthesized on TentaGel microbeads by the split-and-pool synthesis method and subjected to a multistage screening protocol which includes magnetic sorting, on-bead enzyme-linked and fluorescence-based assays, and in-solution binding analysis of cyclic peptides selectively released from single beads by fluorescence anisotropy. Finally, the most active hit(s) is identified by the partial Edman degradation-mass spectrometry (PED-MS) method. This method allows a single researcher to synthesize and screen up to ten million cyclic peptides and identify the most active ligand(s) in ~1 month, without the time-consuming and expensive hit resynthesis or the use of any special equipment.

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

PubMed Central

Borisov, Dmitry A; Vil’, Vera A; Dembitsky, Valery M

2014-01-01

Summary The present review describes the current status of synthetic five and six-membered cyclic peroxides such as 1,2-dioxolanes, 1,2,4-trioxolanes (ozonides), 1,2-dioxanes, 1,2-dioxenes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes. The literature from 2000 onwards is surveyed to provide an update on synthesis of cyclic peroxides. The indicated period of time is, on the whole, characterized by the development of new efficient and scale-up methods for the preparation of these cyclic compounds. It was shown that cyclic peroxides remain unchanged throughout the course of a wide range of fundamental organic reactions. Due to these properties, the molecular structures can be greatly modified to give peroxide ring-retaining products. The chemistry of cyclic peroxides has attracted considerable attention, because these compounds are used in medicine for the design of antimalarial, antihelminthic, and antitumor agents. PMID:24454562

Prediction of elemental creep. [steady state and cyclic data from regression analysis

NASA Technical Reports Server (NTRS)

Davis, J. W.; Rummler, D. R.

1975-01-01

Cyclic and steady-state creep tests were performed to provide data which were used to develop predictive equations. These equations, describing creep as a function of stress, temperature, and time, were developed through the use of a least squares regression analyses computer program for both the steady-state and cyclic data sets. Comparison of the data from the two types of tests, revealed that there was no significant difference between the cyclic and steady-state creep strains for the L-605 sheet under the experimental conditions investigated (for the same total time at load). Attempts to develop a single linear equation describing the combined steady-state and cyclic creep data resulted in standard errors of estimates higher than obtained for the individual data sets. A proposed approach to predict elemental creep in metals uses the cyclic creep equation and a computer program which applies strain and time hardening theories of creep accumulation.

[Cyclic fatigue of Vita mark II machinable ceramics under Hertzian's contact].

PubMed

Liu, Wei-Cai; Zhang, Zhi-Shen; Huang, Cheng-Min; Chao, Yong-Lie; Wan, Qian-Bing

2006-08-01

To investigate the cyclic fatigue modes of Vita mark II machinable ceramics under Hertzian's contact. Hertzian's contact technique (WC spheres r = 3.18 mm) was used to investigate the cyclic fatigue of Vita mark II machinable ceramic. All specimens were fatigued by cyclic loading in moist environment, furthermore, surviving strength was examined by three point test and morphology damage observation. In homogeneous Vita mark II machinable ceramics, two fatigue damage modes existed after cyclic loading with spheres under moist environment, including conventional tensile-driven cone cracking (brittle mode) and shear-driven microdamage accumulation (quasi-plastic mode). The latter generated radial cracks and deeply penetrating secondary cone crack. Initial strength degradation were caused by the cone cracks, subsequent and much more deleterious loss was caused by radial cracks. Cyclic fatigue modes of Vita mark II machinable ceramics includes brittle and quasi-plastic mode.

Biomechanical contributions of the trunk and upper extremity in discrete versus cyclic reaching in survivors of stroke.

PubMed

Massie, Crystal L; Malcolm, Matthew P; Greene, David P; Browning, Raymond C

2014-01-01

Stroke rehabilitation interventions and assessments incorporate discrete and/or cyclic reaching tasks, yet no biomechanical comparison exists between these 2 movements in survivors of stroke. To characterize the differences between discrete (movements bounded by stationary periods) and cyclic (continuous repetitive movements) reaching in survivors of stroke. Seventeen survivors of stroke underwent kinematic motion analysis of discrete and cyclic reaching movements. Outcomes collected for each side included shoulder, elbow, and trunk range of motion (ROM); peak velocity; movement time; and spatial variability at target contact. Participants used significantly less shoulder and elbow ROM and significantly more trunk flexion ROM when reaching with the stroke-affected side compared with the less-affected side (P < .001). Participants used significantly more trunk rotation during cyclic reaching than discrete reaching with the stroke-affected side (P = .01). No post hoc differences were observed between tasks within the stroke-affected side for elbow, shoulder, and trunk flexion ROM. Peak velocity, movement time, and spatial variability were not different between discrete and cyclic reaching in the stroke-affected side. Survivors of stroke reached with altered kinematics when the stroke-affected side was compared with the less-affected side, yet there were few differences between discrete and cyclic reaching within the stroke-affected side. The greater trunk rotation during cyclic reaching represents a unique segmental strategy when using the stroke-affected side without consequences to end-point kinematics. These findings suggest that clinicians should consider the type of reaching required in therapeutic activities because of the continuous movement demands required with cyclic reaching.

The effects of cyclical axial motion on rotary endodontic instrument fatigue.

PubMed

Dederich, D N; Zakariasen, K L

1986-02-01

A potential problem with the use of rotary engine-driven files to flare canals is metal fatigue and subsequent breakage. This study analyzes the effects of cyclical axial motion on instrument failure by fatigue testing of endodontic files with and without cyclical axial motion. Eighteen new instruments, sizes 15 to 45, were mounted in a lathe and turned at 1650 rpm in the lubricated lumen of a curved Pyrex capillary tube until failure occurred. Nine instruments of each size were turned with cyclical axial motion and nine were turned without it. The results indicated that cyclical axial motion can significantly extend the life span of rotary engine files. Torsional forces were not considered in this study.

Regulation of theta-antigen expression by agents altering cyclic AMP level and by thymic factor.

PubMed

Bach, M A; Fournier, C; Bach, J F

1975-02-28

Thymic factor, cyclic AMP, and products increasing its cellular level, such as Prostaglandin E1, induce the appearance of the theta-antigen on T-cell precursors whether assessed by a rossette-inhibition assay or a cytotoxic assay after cell fractionation on BSA discontinuous gradiet. Synergism has been demonstrated between cyclic AMPT and TF for that effect. Conversely, decrease of theta expression has been obtained by altering cyclic AMP level in theta-positive cells either increasing it by dibutyryl cAMP treatment or decreasing it by indomethacin treatment. Finally, these data suggest the involvement of cyclic AMP in the regulation of theta expression under thymic hormone control.

Safety Discrete Event Models for Holonic Cyclic Manufacturing Systems

NASA Astrophysics Data System (ADS)

Ciufudean, Calin; Filote, Constantin

In this paper the expression “holonic cyclic manufacturing systems” refers to complex assembly/disassembly systems or fork/join systems, kanban systems, and in general, to any discrete event system that transforms raw material and/or components into products. Such a system is said to be cyclic if it provides the same sequence of products indefinitely. This paper considers the scheduling of holonic cyclic manufacturing systems and describes a new approach using Petri nets formalism. We propose an approach to frame the optimum schedule of holonic cyclic manufacturing systems in order to maximize the throughput while minimize the work in process. We also propose an algorithm to verify the optimum schedule.

Transplantation of allogenic bone marrow in canine cyclic neutropenia

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

Dale, D.C.; Graw, R.G. Jr.

Transplantation of normal bone marrow cells to a gray collie dog with cyclic neutropenia resulted in normal granulocytopoiesis. The finding suggests that cyclic neutropenia occurs because the hematopoietic stem cells are defective. Because of the similarity of human and canine cyclic neutropenia, it also suggests that the human disease may be curable by marrow transplantation. One day before transplantation, the recipient received 1000 rads gamma irradiation from opposing /sup 60/Co sources at 9 rad/min. (CH)

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2011-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2010-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Effect of Cyclic Thermo-Mechanical Loads on Fatigue Reliability in Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Shah, A. R.; Murthy, P. L. N.; Chamis, C. C.

1996-01-01

A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multi-factor interaction relationship developed at NASA Lewis Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability- based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)(sub s) graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

A Critical Assessment of Cyclic Softening and Hardening Behavior in a Near- α Titanium Alloy During Thermomechanical Fatigue

NASA Astrophysics Data System (ADS)

Prasad, Kartik; Sarkar, Rajdeep; Rao, K. Bhanu Sankara; Sundararaman, M.

2016-10-01

Thermomechanical fatigue behavior of Ti-alloy Timetal 834 has been studied at two temperature intervals viz. 573 K to 723 K (300 °C to 450 °C) and 723 K to 873 K (450 °C to 600 °C) under mechanical strain-controlled cycling. Among the temperatures studied, the alloy exhibited initial cyclic softening followed by cyclic hardening at 723 K (450 °C) in the temperature interval of 573 K to 723 K (300 °C to 450 °C). However, continuous cyclic hardening was observed at 723 K (450 °C) in 723 K to 873 K (450 °C to 600 °C). At 573 K (300 °C) and 873 K (600 °C), cyclic softening was observed in the cyclic stress response curves in both the temperature intervals. The dislocation substructure was observed to be planar in both the modes of TMF loading. Based on TEM microstructures and few unconventional fatigue tests, the observed cyclic hardening is attributed to dynamic strain aging. The reduced fatigue life at 723 K to 873 K (450 °C to 600 °C) under OP-TMF loading was attributed to the combined effect of cyclic hardening (leading to early strain localization and crack initiation), oxidation, and development of tensile mean stresses.

Role of selective cyclic GMP phosphodiesterase inhibition in the myorelaxant actions of M&B 22,948, MY-5445, vinpocetine and 1-methyl-3-isobutyl-8-(methylamino)xanthine.

PubMed Central

Souness, J. E.; Brazdil, R.; Diocee, B. K.; Jordan, R.

1989-01-01

1. The mechanism by which M&B 22,948, MY-5445, vinpocetine and 1-methyl-3-isobutyl-8-(methylamino)xanthine (MIMAX), which have been described as selective cyclic GMP phosphodiesterase (PDE) inhibitors, relax rat aorta was investigated. 2. Three cyclic nucleotide PDEs were identified in the soluble fraction of rat aorta; a Ca2+-insensitive form exhibiting substrate selectivity for cyclic GMP (cGMP PDE), a Ca2+/calmodulin-stimulated form which also preferentially hydrolyzed cyclic GMP (Ca2+ PDE), and a form demonstrating substrate selectivity for cyclic AMP (cAMP PDE). 3. M&B 22,948 and MIMAX inhibited cGMP PDE (Ki = 0.16 microM and 0.43 microM, respectively) and Ca2+ PDE (Ki = 9.9 microM and 0.55 microM, respectively), but exhibited weak activity against cAMP PDE (Ki = 249 microM and 42 microM, respectively). MY-5445 selectivity inhibited cGMP PDE (Ki = 1.3 microM) and vinpocetine selectively inhibited Ca2+ PDE (Ki = 14 microM). 4. M&B 22,948 and MIMAX induced dose-dependent increases in the accumulation of cyclic GMP, but not cyclic AMP, in rat aorta pieces. These effects were greatly reduced by endothelial denudation and by methylene blue (5 microM) which blocks the actions of endothelium-derived relaxant factor. MY-5445 and vinpocetine had no effect on rat aorta cyclic GMP or cyclic AMP accumulation. 5. All four compounds caused dose-related relaxation of 5-hydroxytryptamine (10 microM) contracted, endothelium-intact rat aorta, the effects of M&B 22,948 and MIMAX being greatly reduced by methylene blue (5 microM). Methylene blue also caused 10 fold and 100 fold rightward shifts in the dose-response curves of MY-5445 and vinpocetine, respectively. 6. The results are consistent with the smooth muscle relaxant actions of M&B 22,948 and MIMAX, but not vinpocetine and MY-5445, being mediated through a mechanism involving inhibition of cyclic GMP hydrolysis. PMID:2480168

Cyclicity of Suicides May Be Modulated by Internal or External - 11-Year Cycles: An Example of Suicide Rates in Finland

NASA Astrophysics Data System (ADS)

Dimitrov, B. D.; Atanassova, P. A.; Rachkova, M. I.

2009-12-01

Multicomponent cyclicity in monthly suicides (periods T = 18, 46 and 198 months) was found and close similarity with heliogeophysical activity (HGA) suggested by Dimitrov in 1999. The current report aimed at scrutinizing the results on suicide annual cyclicity (seasonality) in Slovenia as reported by Oravecz et al in 2007 as well as at analyzing suicide data from Finland in this regard. We postulated that: (i) trans-year (12-24 months) or far-trans-year long-term cycles of suicides might interfere with their seasonality; and (ii) associations to environmental factors with alike cyclicity (e.g. HGA, temperature) could exist. Annual suicide incidence from Oulu, Finland over years 1987-1999 was analyzed. Annual data on solar activity (sunspot index Rz or Wolf number), planetary geomagnetic activity (aa-index) and local daily mean temperatures were used. The exploration of underlying chronomes (time structures) was done by periodogram regression analysis with trigonometric approximation. We analyzed temporal dynamics, revealed cyclicity, decomposed and reconstructed significant cycles and correlated the time series data. Suicide seasonality in Slovenia during the years 1971-2002 (n=384 months, peak May-June) was considered and, although some discrepancies and methodological weaknesses were suspected, we further hypothesized about trans-year and/or longer (far-transyear) cyclic components. Suicide incidence data from Finland indicated that the 12.5-year cyclic component (or trend) was almost parallel (coherent) to the cyclic heliogeophysical parameters and similar to local decreasing temperature dynamics. Also, 8-year and 24.5-year cycles were revealed. A correlation between the 12.5-year suicide cycle and 11-year solar cycle was found (R=0.919, p=0.000009). Above findings on cyclicity and temporal correlations of suicides with cyclic environmental factors, even being still preliminary, might not only allow for further more specific analyses. They might also corroborate to improved forecasting and prevention and confer a better understanding of suicide dynamics and aetiology.

Cyclic Bis-porphyrin-Based Flexible Molecular Containers: Controlling Guest Arrangements and Supramolecular Catalysis by Tuning Cavity Size.

PubMed

Mondal, Pritam; Sarkar, Sabyasachi; Rath, Sankar Prasad

2017-05-23

Three cyclic zinc(II) bis-porphyrins (CB) with highly flexible linkers are employed as artificial molecular containers that efficiently encapsulate/coordinate various aromatic aldehydes within their cavities. Interestingly, the arrangements of guests and their reactivity inside the molecular clefts are significantly influenced by the cavity size of the cyclic containers. In the presence of polycyclic aromatic aldehydes, such as 3-formylperylene, as a guest, the cyclic bis-porphyrin host with a smaller cavity (CB1) forms a 1:1 sandwich complex. Upon slightly increasing the spacer length and thereby the cavity size, the cyclic host (CB2) encapsulates two molecules of 3-formylperylene that are also stacked together due to strong π-π interactions between them and CH-π interactions with the porphyrin rings. However, in the cyclic host (CB3) with an even larger cavity, two metal centers of the bis-porphyrin axially coordinate two molecules of 3-formylperylene within its cavity. Different arrangements of guest inside the cyclic bis-porphyrin hosts are investigated by using UV/Vis, ESI-MS, and 1 H NMR spectroscopy, along with X-ray structure determination of the host-guest complexes. Moreover, strong binding of guests within the cyclic bis-porphyrin hosts support the robust nature of the host-guest assemblies in solution. Such preferential binding of the bis-porphyrinic cavity towards aromatic aldehydes through encapsulation/coordination has been employed successfully to catalyze the Knoevenagel condensation of a series of polycyclic aldehydes with active methylene compounds (such as Meldrum's acid and 1, 3-dimethylbarbituric acid) under ambient conditions. Interestingly, the yields of the condensed products significantly increase upon increasing spacer lengths of the cyclic bis-porphyrins because more substrates can then be encapsulated within the cavity. Such controllable cavity size of the cyclic containers has profound implications for constructing highly functional and modular enzyme mimics. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation into the Cyclic Strength of the Bodies of Steam Shutoff Valves from 10Kh9MFB-Sh Steel

NASA Astrophysics Data System (ADS)

Skorobogatykh, V. N.; Kunavin, S. A.; Prudnikov, D. A.; Shchenkova, I. A.; Bazhenov, A. M.; Zadoinyi, V. A.; Starkovskii, G. L.

2018-02-01

Steam shutoff valves are operated under complex loading conditions at thermal and nuclear power stations. In addition to exposure to high temperature and stresses resulting in fatigue, these valves are subjected to cyclic loads in heating-up-cooling down, opening-closing, etc. cycles. The number of these cycles to be specified in designing the valves should not exceed the maximum allowable value. Hence, the problem of cyclic failure rate of steam shutoff valve bodies is critical. This paper continues the previous publications about properties of the construction material for steam shutoff valve bodies (grade 10Kh9MFB-Sh steel) produced by electroslag melting and gives the results of investigation into the cyclic strength of this material. Fatigue curves for the steal used for manufacturing steam shutoff valve bodies are presented. The experimental data are compared with the calculated fatigue curves plotted using the procedures outlined in PNAE G-002-986 and RD 10-249-98. It is confirmed that these procedures may be used in designing valve bodies from 10Kh9MFB-Sh steel. The effect of the cyclic damage after preliminary cyclic loading of the specimens according to the prescribed load conditions on the high-temperature strength of the steel is examined. The influence of cyclic failure rate on the long-term strength was investigated using cylindrical specimens with a smooth working section in the as-made conditions and after two regimes of preliminary cyclic loading (training) at a working temperature of 570°C and the number of load cycles exceeding the design value, which was 2 × 103 cycles. The experiments corroborated that the material (10Kh9MFB-Sh steel) of the body manufactured by the method of electroslag melting had high resistance to cyclic failure rate. No effect of cyclic damages in the metal of the investigated specimens on the high-temperature strength has been found.

Characterization of the homologous and heterologous desensitization of rat Leydig-tumour-cell adenylate cyclase.

PubMed

Dix, C J; Habberfield, A D; Cooke, B A

1984-06-15

The homologous and heterologous desensitization of rat Leydig-tumour-cell adenylate cyclase induced by lutropin (LH) was characterized with the aid of forskolin and cholera toxin. Forskolin stimulated cyclic AMP production in a dose-dependent manner, with linear kinetics up to 2h. Forskolin also potentiated the action of LH on cyclic AMP production, but was only additive with cholera toxin. Preincubation of rat Leydig tumour cells with LH (1.0 micrograms/ml) for 1 h produced a desensitization of the subsequent LH (1.0 micrograms/ml)-stimulated cyclic AMP production, whereas the responses to cholera toxin (5.0 micrograms/ml), forskolin (100 microM), LH plus forskolin or cholera toxin plus forskolin were unaltered. In contrast, preincubation with LH for 20h produced a desensitization to all the stimuli tested. When rat Leydig tumour cells were preincubated for 1h with forskolin or dibutyryl cyclic AMP, the only subsequent response that was significantly altered was that to LH plus forskolin after preincubation with forskolin. However, preincubation for 20h with forskolin or dibutyryl cyclic AMP induced a desensitization to all stimuli subsequently tested. LH produced a rapid (0-1h) homologous desensitization, which was followed by a slower (2-8h)-onset heterologous desensitization. Forskolin and dibutyryl cyclic AMP were only able to induce heterologous desensitization. The rate of desensitization induced by either forskolin or dibutyryl cyclic AMP was similar to the rate of heterologous desensitization induced by LH. These results demonstrate that in purified rat Leydig tumour cells LH produces an initial homologous desensitization of adenylate cyclase that involves a cyclic AMP-independent lesion at or proximal to the guanine nucleotide regulatory protein (G-protein). This is followed by heterologous desensitization, which can also be induced by forskolin or dibutyryl cyclic AMP, thus indicating that LH-induced heterologous desensitization of rat Leydig-tumour-cell adenylate cyclase involves a cyclic AMP-dependent lesion that is after the G-protein.

Phosphodiesterase Inhibitors as a Therapeutic Approach to Neuroprotection and Repair

PubMed Central

Knott, Eric P.; Assi, Mazen; Rao, Sudheendra N. R.; Ghosh, Mousumi; Pearse, Damien D.

2017-01-01

A wide diversity of perturbations of the central nervous system (CNS) result in structural damage to the neuroarchitecture and cellular defects, which in turn are accompanied by neurological dysfunction and abortive endogenous neurorepair. Altering intracellular signaling pathways involved in inflammation and immune regulation, neural cell death, axon plasticity and remyelination has shown therapeutic benefit in experimental models of neurological disease and trauma. The second messengers, cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP), are two such intracellular signaling targets, the elevation of which has produced beneficial cellular effects within a range of CNS pathologies. The only known negative regulators of cyclic nucleotides are a family of enzymes called phosphodiesterases (PDEs) that hydrolyze cyclic nucleotides into adenosine monophosphate (AMP) or guanylate monophosphate (GMP). Herein, we discuss the structure and physiological function as well as the roles PDEs play in pathological processes of the diseased or injured CNS. Further we review the approaches that have been employed therapeutically in experimental paradigms to block PDE expression or activity and in turn elevate cyclic nucleotide levels to mediate neuroprotection or neurorepair as well as discuss both the translational pathway and current limitations in moving new PDE-targeted therapies to the clinic. PMID:28338622

Cyclic Peptides Arising by Evolutionary Parallelism via Asparaginyl-Endopeptidase–Mediated Biosynthesis[C][W

PubMed Central

Mylne, Joshua S.; Chan, Lai Yue; Chanson, Aurelie H.; Daly, Norelle L.; Schaefer, Hanno; Bailey, Timothy L.; Nguyencong, Philip; Cascales, Laura; Craik, David J.

2012-01-01

The cyclic miniprotein Momordica cochinchinensis Trypsin Inhibitor II (MCoTI-II) (34 amino acids) is a potent trypsin inhibitor (TI) and a favored scaffold for drug design. We have cloned the corresponding genes and determined that each precursor protein contains a tandem series of cyclic TIs terminating with the more commonly known, and potentially ancestral, acyclic TI. Expression of the precursor protein in Arabidopsis thaliana showed that production of the cyclic TIs, but not the terminal acyclic TI, depends on asparaginyl endopeptidase (AEP) for maturation. The nature of their repetitive sequences and the almost identical structures of emerging TIs suggest these cyclic peptides evolved by internal gene amplification associated with recruitment of AEP for processing between domain repeats. This is the third example of similar AEP-mediated processing of a class of cyclic peptides from unrelated precursor proteins in phylogenetically distant plant families. This suggests that production of cyclic peptides in angiosperms has evolved in parallel using AEP as a constraining evolutionary channel. We believe this is evolutionary evidence that, in addition to its known roles in proteolysis, AEP is especially suited to performing protein cyclization. PMID:22822203

The effect of matrix microstructure on cyclic response and fatigue behavior of particle- reinforced 2219 aluminum: Part I. room temperature behavior

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; Allison, J. E.; van Aken, D. C.

1995-12-01

The low-cycle and high-cycle fatigue behavior and cyclic response of naturally aged and overaged 2219/TiC/15p and unreinforced 2219 Al were investigated using plastic strain-controlled and stress-controlled testing. In addition, the influence of grain size on the particle-reinforced materials was examined. In both reinforced and unreinforced materials, the naturally aged conditions were cyclically unstable, exhibiting an initial hardening behavior followed by an extended region of cyclic stability and ultimately a softening region. The overaged reinforced material was cyclically stable for the plastic strains examined, while the overaged unreinforced material exhibited cyclic hardening at plastic strains greater than 2.5 × 10-4. Decreasing grain size of particle-reinforced materials modestly increased the cyclic flow stress of both naturally aged and overaged materials. Reinforced and unreinforced materials exhibited similar fatigue life behaviors; however, the reinforced and unreinforced naturally aged materials had superior fatigue lives in comparison to the overaged materials. Grain size had no effect on the fatigue life behavior of the particle-reinforced materials. The fatigue lives were strongly influenced by the presence of clusters of TiC particles and exogenous Al3Ti intermetallics.

Concept of improved rigidity: how to make enantioselective hydrophosphonylation of cyclic imines catalyzed by chiral heterobimetallic lanthanoid complexes almost perfect

PubMed

Schlemminger; Saida; Groger; Maison; Durot; Sasai; Shibasaki; Martens

2000-08-11

The catalytic and enantioselective hydrophosphonylation of cyclic imines using cyclic phosphites is described for the first time. In contrast to the application of acyclic phosphites, significant improvements are presented arising from the concept of improved rigidity by utilization of cyclic phosphites in the lanthanoid BINOL complex catalyzed hydrophosphonylation of 3-thiazolines. Cyclic phosphites are shown to provide certain improvements within the catalytic cycle. Influence of parameters such as concentration of the catalyst and the phosphite on the catalysis is examined as well as the effects of the substituents on the starting material. The pharmacologically interesting thiazolidinyl phosphonates are synthesized in excellent optical purities of up to 99% ee and high chemical yields of up to 99%. The required amount of catalyst is reduced to 2.5 mol %. The highest efficiency of the reaction involving cyclic phosphites is achieved using the catalytic system "2.5 mol % (S)-YbPB/2.5 equiv phosphite/50 degrees C/48 h/THF-toluene (1:7)". On the basis of the results a refinement of the proposed catalytic cycle has been provided. For comparison cyclic phosphites were used in hydrophosphonylation with a chiral titanium catalyst.

Multiplex De Novo Sequencing of Peptide Antibiotics

NASA Astrophysics Data System (ADS)

Mohimani, Hosein; Liu, Wei-Ting; Yang, Yu-Liang; Gaudêncio, Susana P.; Fenical, William; Dorrestein, Pieter C.; Pevzner, Pavel A.

Proliferation of drug-resistant diseases raises the challenge of searching for new, more efficient antibiotics. Currently, some of the most effective antibiotics (i.e., Vancomycin and Daptomycin) are cyclic peptides produced by non-ribosomal biosynthetic pathways. The isolation and sequencing of cyclic peptide antibiotics, unlike the same activity with linear peptides, is time-consuming and error-prone. The dominant technique for sequencing cyclic peptides is NMR-based and requires large amounts (milligrams) of purified materials that, for most compounds, are not possible to obtain. Given these facts, there is a need for new tools to sequence cyclic NRPs using picograms of material. Since nearly all cyclic NRPs are produced along with related analogs, we develop a mass spectrometry approach for sequencing all related peptides at once (in contrast to the existing approach that analyzes individual peptides). Our results suggest that instead of attempting to isolate and NMR-sequence the most abundant compound, one should acquire spectra of many related compounds and sequence all of them simultaneously using tandem mass spectrometry. We illustrate applications of this approach by sequencing new variants of cyclic peptide antibiotics from Bacillus brevis, as well as sequencing a previously unknown familiy of cyclic NRPs produced by marine bacteria.

Affordable Cyclic Voltammetry

ERIC Educational Resources Information Center

Stewart, Greg; Kuntzleman, Thomas S.; Amend, John R.; Collins, Michael J.

2009-01-01

Cyclic voltammetry is an important component of the undergraduate chemical curriculum. Unfortunately, undergraduate students rarely have the opportunity to conduct experiments in cyclic voltammetry owing to the high cost of potentiostats, which are required to control these experiments. By using MicroLab data acquisition interfaces in conjunction…

Fatigue and fracture: Overview

NASA Technical Reports Server (NTRS)

Halford, G. R.

1984-01-01

A brief overview of the status of the fatigue and fracture programs is given. The programs involve the development of appropriate analytic material behavior models for cyclic stress-strain-temperature-time/cyclic crack initiation, and cyclic crack propagation. The underlying thrust of these programs is the development and verification of workable engineering methods for the calculation, in advance of service, of the local cyclic stress-strain response at the critical life governing location in hot section compounds, and the resultant crack initiation and crack growth lifetimes.

Sweet taste transduction in hamster: sweeteners and cyclic nucleotides depolarize taste cells by reducing a K+ current.

PubMed

Cummings, T A; Daniels, C; Kinnamon, S C

1996-03-01

1. The gigaseal voltage-clamp technique was used to record responses of hamster taste receptor cells to synthetic sweeteners and cyclic nucleotides. Voltage-dependent currents and steady-state currents were monitored during bath exchanges of saccharin, two high-potency sweeteners, 8-chlorophenylthio-adenosine 3',5'-cyclic monophosphate (8cpt-cAMP), and dibutyryl-guanosine 3',5'-cyclic monophosphate (db-cGMP). 2. Of the 237 fungiform taste cells studied, only one in eight was sweet responsive. Outward currents, both voltage-dependent and resting, were reduced by all of the sweeteners tested in sweet-responsive taste cells, whereas these currents were unaffected by sweeteners in sweet-unresponsive taste cells. 3. In every sweet-responsive cell tested, 8cpt-cAMP and db-cGMP mimicked the response to the sweeteners, but neither nucleotide elicited responses in sweet-unresponsive cells. Thus there was a one-to-one correlation between sweet responsivity and cyclic nucleotide responsivity. 4. Sweet responses showed cross adaptation with cyclic nucleotide responses. This indicates that the same ion channel is modulated by sweeteners and cyclic nucleotides. 5. The sweetener- and cyclic nucleotide-blocked current had an apparent reversal potential of -50 mV, which was close to the potassium reversal potential in these experiments. In addition, there was no effect of sweeteners and cyclic nucleotides in the presence of the K+ channel blocker tetraethylammonium bromide (TEA). These data suggest that block of a resting, TEA-sensitive K+ current is the final common step leading to taste cell depolarization during sweet transduction. 6. These data, together with data from a previous study (Cummings et al. 1993), suggest that both synthetic sweeteners and sucrose utilize second-messenger pathways that block a resting K+ conductance to depolarize the taste cell membrane.

Cyclic fatigue resistance of D-RaCe, ProTaper, and Mtwo nickel-titanium retreatment instruments after immersion in sodium hypochlorite.

PubMed

Topçuoğlu, Hüseyin Sinan; Pala, Kanşad; Aktı, Ahmet; Düzgün, Salih; Topçuoğlu, Gamze

2016-07-01

The aim of this study was to investigate the effect of immersion in sodium hypochlorite (NaOCl) on cyclic fatigue resistance of three different rotary nickel-titanium (NiTi) retreatment files. A total of 90 new ProTaper, D-RaCe, and Mtwo retreatment files were tested. Thirty files of the same brand were randomly assigned to two groups (n = 15). Group 1 was no immersion (control group) and 16 mm of group 2 instruments were immersed in 5 % NaOCl at 37 °C for 5 min. All instruments were then tested for cyclic fatigue. Resistance to cyclic fatigue was determined by counting the numbers of cycles to failure in a 60° curve with a 5-mm radius, recording the time in seconds to fracture. Data were analyzed by two-way analysis of variance. Resistance to cyclic fatigue decreased significantly for D-RaCe retreatment files after immersion in NaOCl. ProTaper and Mtwo retreatment files were not affected from immersion to NaOCl. D-RaCe retreatment instruments showed better cyclic fatigue resistance than ProTaper and Mtwo retreatment instruments, and the difference was statistically significant (p < 0.05). There was no significant difference between ProTaper and Mtwo retreatment instrument groups (p > 0.05). D-RaCe retreatment instruments had the highest cyclic fatigue resistance among retreatment files tested in this study, but immersion to NaOCl decreased the cyclic fatigue resistance of D-RaCe retreatment instrument. It should be considered that cyclic fatigue resistance of D-RaCe can decrease in contact with NaOCl during the removal of canal filling material.

Roles of PDE1 in Pathological Cardiac Remodeling and Dysfunction.

PubMed

Chen, Si; Knight, Walter E; Yan, Chen

2018-04-23

Pathological cardiac hypertrophy and dysfunction is a response to various stress stimuli and can result in reduced cardiac output and heart failure. Cyclic nucleotide signaling regulates several cardiac functions including contractility, remodeling, and fibrosis. Cyclic nucleotide phosphodiesterases (PDEs), by catalyzing the hydrolysis of cyclic nucleotides, are critical in the homeostasis of intracellular cyclic nucleotide signaling and hold great therapeutic potential as drug targets. Recent studies have revealed that the inhibition of the PDE family member PDE1 plays a protective role in pathological cardiac remodeling and dysfunction by the modulation of distinct cyclic nucleotide signaling pathways. This review summarizes recent key findings regarding the roles of PDE1 in the cardiac system that can lead to a better understanding of its therapeutic potential.

Effect of nitrogen starvation on the level of adenosine 3',5'-monophosphate in Anabaena variabilis.

PubMed

Hood, E E; Armour, S; Ownby, J D; Handa, A K; Bressan, R A

1979-12-03

Low levels of adenosine 3',5'-monophosphate (cyclic AMP) were detected in the cyanobacterium Anabaena variabilis using a protein binding assay and two radioisotopic labelling methods. The basal concentration of intracellular cyclic AMP ranged from 0.27 pmol/mg protein in A. variabilis Kutz grown under heterotrophic conditions to 1.0--2.7 pmol/mg protein in A. variabilis strain 377 grown autotrophically. Extracellular cyclic AMP was found to comprise as much as 90% of the total cyclic AMP in rapidly growing cultures. When A. variabilis strain 377 was starved of nitrogen, a 3--4-fold increase in intracellular cyclic AMP was observed during the 24 h period coincident with early heterocyst development.

Aggregation of luteinizing hormone receptors in granulosa cells: a possible mechanism of desensitization to the hormone.

PubMed Central

Amsterdam, A; Berkowitz, A; Nimrod, A; Kohen, F

1980-01-01

The temporal relationship between redistribution of receptors to lutropin (luteinizing hormone)/human chorionic gonadotropin in cultured rat ovarian granulosa cells and the cellular response to hormonal challenge were studied. Visualization of receptor-bound human chorionic gonadotropin by indirect immunofluorescence, with hormone-specific antibodies after fixation with 2% formaldehyde, revealed the existence of small clusters around the entire cell circumference 5--20 min after exposure to the hormone at 37 degrees C. Such small receptor aggregates were also evident if hormone incubation was at 4 degrees C or if cells were fixed with 2% formaldehyde before incubation. Larger clusters were evident after prolonged incubation with the hormone (2--4 hr) at 37 degrees C. The later change coincided with diminished cyclic AMP accumulation in respose to challenge with fresh hormone. When the fixation step was omitted and antibodies to human chorionic gonadotropin were applied after hormonal binding, acceleration of both receptor clustering and the desensitization process was observed. This maneuver also induced capping of the hormone receptors. In contrast, monovalent Fab' fragments of the antibodies were without effect. Internalization of the bound hormone in lysosomes, and subsequent degradation, was evident 8 hr after hormonal application and was not accelerated by the antibodies. It is suggested that clustering of the luteinizing hormone receptors may play a role in cellular responsiveness to the hormone. Massive aggregation of the receptors may desensitize the cell by interferring with coupling to adenylate cyclase. Images PMID:6251459

MICROWAVE-ASSISTED PREPARATION OF CYCLIC UREAS FROM DIAMINES

EPA Science Inventory

Rajender S. Varma* and Yong-Jin Kim
Cyclic ureas are useful intermediates for a variety of pharmaceuticals and pesticides. One of the attractive approaches for the synthesis of cyclic ureas uses condensation of diamines with urea as a carbonyl source under dynamic evacuation. ...

An improved Armstrong-Frederick-Type Plasticity Model for Stable Cyclic Stress-Strain Responses Considering Nonproportional Hardening

NASA Astrophysics Data System (ADS)

Li, Jing; Zhang, Zhong-ping; Li, Chun-wang

2018-03-01

This paper modified an Armstrong-Frederick-type plasticity model for investigating the stable cyclic deformation behavior of metallic materials with different sensitivity to nonproportional loadings. In the modified model, the nonproportionality factor and nonproportional cyclic hardening coefficient coupled with the Jiang-Sehitoglu incremental plasticity model were used to estimate the stable stress-strain responses of the two materials (1045HR steel and 304 stainless steel) under various tension-torsion strain paths. A new equation was proposed to calculate the nonproportionality factor on the basis of the minimum normal strain range. Procedures to determine the minimum normal strain range were presented for general multiaxial loadings. Then, the modified model requires only the cyclic strain hardening exponent and cyclic strength coefficient to determine the material constants. It is convenient for predicting the stable stress-strain responses of materials in engineering application. Comparisons showed that the modified model can reflect the effect of nonproportional cyclic hardening well.

Theory of chromatography of partially cyclic polymers: Tadpole-type and manacle-type macromolecules.

PubMed

Vakhrushev, Andrey V; Gorbunov, Alexei A

2016-02-12

A theory of chromatography is developed for partially cyclic polymers of tadpole- and manacle-shaped topological structures. We present exact equations for the distribution coefficient K at different adsorption interactions; simpler approximate formulae are also derived, relevant to the conditions of size-exclusion, adsorption, and critical chromatography. Theoretical chromatograms of heterogeneous partially cyclic polymers are simulated, and conditions for good separation by topology are predicted. According to the theory, an effective SEC-radius of tadpoles and manacles is mostly determined by the molar mass M, and by the linear-cyclic composition. In the interactive chromatography, the effect of molecular topology on the retention becomes significant. At the critical interaction point, partial dependences K(Mlin) and K(Mring) are qualitatively different: while being almost independent of Mlin, K increases with Mring. This behavior could be realized in critical chromatography-for separation of partially cyclic polymers by the number and molar mass of cyclic elements. Copyright © 2015 Elsevier B.V. All rights reserved.

CNG and HCN channels: two peas, one pod.

PubMed

Craven, Kimberley B; Zagotta, William N

2006-01-01

Cyclic nucleotide-activated ion channels play a fundamental role in a variety of physiological processes. By opening in response to intracellular cyclic nucleotides, they translate changes in concentrations of signaling molecules to changes in membrane potential. These channels belong to two families: the cyclic nucleotide-gated (CNG) channels and the hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels. The two families exhibit high sequence similarity and belong to the superfamily of voltage-gated potassium channels. Whereas HCN channels are activated by voltage and CNG channels are virtually voltage independent, both channels are activated by cyclic nucleotide binding. Furthermore, the channels are thought to have similar channel structures, leading to similar mechanisms of activation by cyclic nucleotides. However, although these channels are structurally and behaviorally similar, they have evolved to perform distinct physiological functions. This review describes the physiological roles and biophysical behavior of CNG and HCN channels. We focus on how similarities in structure and activation mechanisms result in common biophysical models, allowing CNG and HCN channels to be viewed as a single genre.

Structure of a eukaryotic cyclic nucleotide-gated channel

PubMed Central

Li, Minghui; Zhou, Xiaoyuan; Wang, Shu; Michailidis, Ioannis; Gong, Ye; Su, Deyuan; Li, Huan; Li, Xueming; Yang, Jian

2018-01-01

Summary Cyclic nucleotide-gated (CNG) channels are essential for vision and olfaction. They belong to the voltage-gated ion channel superfamily but their activities are controlled by intracellular cyclic nucleotides instead of transmembrane voltage. Here we report a 3.5 Å-resolution single-particle electron cryomicroscopy structure of a CNG channel from C. elegans in the cGMP-bound open state. The channel has an unusual voltage-sensor-like domain (VSLD), accounting for its deficient voltage dependence. A C-terminal linker connecting S6 and the cyclic nucleotide-binding domain interacts directly with both the VSLD and pore domain, forming a gating ring that couples conformational changes triggered by cyclic nucleotide binding to the gate. The selectivity filter is lined by the carboxylate side chains of a functionally important glutamate and three rings of backbone carbonyls. This structure provides a new framework for understanding mechanisms of ion permeation, gating and channelopathy of CNG channels and cyclic nucleotide modulation of related channels. PMID:28099415

Rapid bonding enhancement by auxiliary ultrasonic actuation for the fabrication of cyclic olefin copolymer (COC) microfluidic devices

NASA Astrophysics Data System (ADS)

Yu, H.; Tor, S. B.; Loh, N. H.

2014-11-01

Thermal compression bonding is a straightforward, inexpensive and widely used method for enclosing open microchannels in thermoplastic microfluidic devices. It is advantageous over adhesive, solvent and grafting bonding methods in retaining material homogeneity. However, the trade-off between high bond strength and low microchannel deformation is always a crucial consideration in thermal compression bonding. In this study, an effective method for improving bond strength while retaining the microchannel integrity with negligible distortion is proposed and analyzed. Longitudinal ultrasonic actuation was applied to the preheated cyclic olefin copolymer (COC) substrates to achieve accelerated and enhanced bonding with an ultrasonic welding system. Intimate contact between the bonding surfaces before the ultrasonic actuation was found to be an important prior condition. With improper contact, several bonding defects would occur, such as voids, localized spot melting and edge melting. Under auxiliary ultrasonic vibration, within 10 s, the bond strength developed at the bonding interface could be dramatically improved compared with those achieved without ultrasonic actuation. The enhanced bond strength obtained at a preheating temperature of 20 °C lower than its Tg could be comparable to the strength for pure thermal compression at 5 °C higher than its Tg. It is believed that the ultrasonic energy introduced could elevate the interfacial temperature and facilitate the interdiffusion of molecular chain segments at the interface, consequently resulting in rapidly enhanced bonding. Also, the microchannel distortion after ultrasonic actuation was found to be satisfactory—another important requirement. From dynamic mechanical analysis, the glass transition temperature of COC was found to increase with increasing frequency, and the temperature of the bulk polymer under ultrasonic actuation was still well under Tg; therefore the deformation is minor under ultrasonic actuation.

Cyclic phosphatidic acid inhibits the secretion of vascular endothelial growth factor from diabetic human coronary artery endothelial cells through peroxisome proliferator-activated receptor gamma.

PubMed

Tsukahara, Tamotsu; Tsukahara, Ryoko; Haniu, Hisao; Matsuda, Yoshikazu; Murakami-Murofushi, Kimiko

2015-09-05

Atherosclerosis is a disease characterized by building up plaques formation and leads to a potentially serious condition in which arteries are clogged by fatty substances such as cholesterol. Increasing evidence suggests that atherosclerosis is accelerated in type 2 diabetes. Recent study reported that high level of alkyl glycerophosphate (AGP) was accumulated in atherosclerotic lesions. The presence of this phospholipid in mildly oxidized low-density lipoprotein (LDL) is likely to be involved in atherogenesis. It has been reported that the activation of peroxisome proliferator-activated receptor gamma plays a key role in developing atherosclerosis. Our previous result indicates that cyclic phosphatidic acid (cPA), one of bioactive lipids, potently suppresses neointima formation by inhibiting the activation of peroxisome proliferator-activated receptor gamma (PPARγ). However, the detailed mechanism is still unclear. In this study, to elucidate the mechanism of the cPA-PPARγ axis in the coronary artery endothelium, especially in patients with type 2 diabetes, we investigated the proliferation, migration, and secretion of VEGF in human coronary artery endothelial cells from diabetes patients (D-HCAECs). AGP induced cell growth and migration; however, cPA suppressed the AGP-elicited growth and migration in D-HCAECs. Moreover, AGP increased VEGF secretion from D-HCAECs, and this event was attenuated by cPA. Taken together, these results suggest that cPA suppresses VEGF-stimulated growth and migration in D-HCAECs. These findings could be important for regulatory roles of PPARγ and VEGF in the vascular processes associated with diabetes and atherosclerosis. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Oceanographic variability on the West Antarctic Peninsula during the Holocene and the influence of upper circumpolar deep water

NASA Astrophysics Data System (ADS)

Peck, Victoria L.; Allen, Claire S.; Kender, Sev; McClymont, Erin L.; Hodgson, Dominic A.

2015-07-01

Recent intensification of wind-driven upwelling of warm upper circumpolar deep water (UCDW) has been linked to accelerated melting of West Antarctic ice shelves and glaciers. To better assess the long term relationship between UCDW upwelling and the stability of the West Antarctic Ice Sheet, we present a multi-proxy reconstruction of surface and bottom water conditions in Marguerite Bay, West Antarctic Peninsula (WAP), through the Holocene. A combination of sedimentological, diatom and foraminiferal records are, for the first time, presented together to infer a decline in UCDW influence within Marguerite Bay through the early to mid Holocene and the dominance of cyclic forcing in the late Holocene. Extensive glacial melt, limited sea ice and enhanced primary productivity between 9.7 and 7.0 ka BP is considered to be most consistent with persistent incursions of UCDW through Marguerite Trough. From 7.0 ka BP sea ice seasons increased and productivity decreased, suggesting that UCDW influence within Marguerite Bay waned, coincident with the equatorward migration of the Southern Hemisphere Westerly Winds (SWW). UCDW influence continued through the mid Holocene, and by 4.2 ka BP lengthy sea ice seasons persisted within Marguerite Bay. Intermittent melting and reforming of this sea ice within the late Holocene may be indicative of episodic incursions of UCDW into Marguerite Bay during this period. The cyclical changes in the oceanography within Marguerite Bay during the late Holocene is consistent with enhanced sensitively to ENSO forcing as opposed to the SWW-forcing that appears to have dominated the early to mid Holocene. Current measurements of the oceanography of the WAP continental shelf suggest that the system has now returned to the early Holocene-like oceanographic configuration reported here, which in both cases has been associated with rapid deglaciation.

Modulation of the pharmacological actions of nitrovasodilators by methylene blue and pyocyanin.

PubMed Central

Gryglewski, R. J.; Zembowicz, A.; Salvemini, D.; Taylor, G. W.; Vane, J. R.

1992-01-01

1. In superfused precontracted strips of rabbit aorta, methylene blue (MeB) or pyocyanin (Pyo, 1-hydroxy-5-methyl phenazinum betaine) at concentrations of 1-10 microM inhibited relaxations induced by endothelium-derived relaxing factor (EDRF), glyceryl trinitrate (GTN), S-nitroso-N-acetyl-penicillamine (SNAP) or 3-morpholino-sydnonimine (SIN-1). However, the vasorelaxant actions of sodium nitroprusside (NaNP) or sodium nitrite (NaNO2) were enhanced by MeB or Pyo. Oxyhaemoglobin (HbO2, 1 microM) inhibited the activities of EDRF and all of the nitrovasodilators studied. Vascular preparations were not relaxed by Pyo unless pretreated with NaNP (0.05-10 microM). 2. In bathed, precontracted rings of rabbit aorta, Pyo (10 microM) produced a shift to the left of the cumulative concentration-response curve for NaNP (0.01-10 microM). The rise in guanosine-3':5'-cyclic monophosphate (cyclic GMP) content of aortic tissue was also enhanced. 3. The vasorelaxant potency of NaNP (30 microM) at pH 5-8 and at 37 degrees C remained unchanged over 2.5 h while a solution of SNAP (30 microM) progressively lost its biological activity over 60 min. The in vitro degradation of the biological activity of SNAP was accelerated by MeB (150 microM) or Pyo (150 microM), whereas the vasorelaxant potency NaNP (30 microM) was doubled when incubated with MeB or Pyo. 4. In human platelet-rich plasma, MeB or Pyo (0.3-3.0 microM) uncovered an anti-aggregatory action of subthreshold concentrations of NaNP (4-8 microM). This was abrogated by HbO2 (10 microM).(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1327388

Free energy landscape remodeling of the cardiac pacemaker channel explains the molecular basis of familial sinus bradycardia

PubMed Central

Boulton, Stephen; Akimoto, Madoka; Akbarizadeh, Sam; Melacini, Giuseppe

2017-01-01

The hyperpolarization-activated and cyclic nucleotide-modulated ion channel (HCN) drives the pacemaker activity in the heart, and its malfunction can result in heart disorders. One such disorder, familial sinus bradycardia, is caused by the S672R mutation in HCN, whose electrophysiological phenotypes include a negative shift in the channel activation voltage and an accelerated HCN deactivation. The outcomes of these changes are abnormally low resting heart rates. However, the molecular mechanism underlying these electrophysiological changes is currently not fully understood. Crystallographic investigations indicate that the S672R mutation causes limited changes in the structure of the HCN intracellular gating tetramer, but its effects on protein dynamics are unknown. Here, we utilize comparative S672R versus WT NMR analyses to show that the S672R mutation results in extensive perturbations of the dynamics in both apo- and holo-forms of the HCN4 isoform, reflecting how S672R remodels the free energy landscape for the modulation of HCN4 by cAMP, i.e. the primary cyclic nucleotide modulator of HCN channels. We show that the S672R mutation results in a constitutive shift of the dynamic auto-inhibitory equilibrium toward inactive states of HCN4 and broadens the free-energy well of the apo-form, enhancing the millisecond to microsecond dynamics of the holo-form at sites critical for gating cAMP binding. These S672R-induced variations in dynamics provide a molecular basis for the electrophysiological phenotypes of this mutation and demonstrate that the pathogenic effects of the S672R mutation can be rationalized primarily in terms of modulations of protein dynamics. PMID:28174302

Pigment Translocation in Caridean Shrimp Chromatophores: Receptor Type, Signal Transduction, Second Messengers, and Cross Talk Among Multiple Signaling Cascades.

PubMed

Milograna, Sarah Ribeiro; Ribeiro, Márcia Regina; Bell, Fernanda Tinti; McNamara, John Campbell

2016-11-01

Pigment aggregation in shrimp chromatophores is triggered by red pigment concentrating hormone (RPCH), a neurosecretory peptide whose plasma membrane receptor may be a G-protein coupled receptor (GPCR). While RPCH binding activates the Ca 2+ /cGMP signaling cascades, a role for cyclic AMP (cAMP) in pigment aggregation is obscure, as are the steps governing Ca 2+ release from the smooth endoplasmic reticulum (SER). A role for the antagonistic neuropeptide, pigment dispersing homone (α-PDH) is also unclear. In red, ovarian chromatophores from the freshwater shrimp Macrobrachium olfersi, we show that a G-protein antagonist (AntPG) strongly inhibits RPCH-triggered pigment aggregation, suggesting that RPCH binds to a GPCR, activating an inhibitory G-protein. Decreasing cAMP levels may cue pigment aggregation, since cytosolic cAMP titers, when augmented by cholera toxin, forskolin or vinpocentine, completely or partially impair pigment aggregation. Triggering opposing Ca 2+ /cGMP and cAMP cascades by simultaneous perfusion with lipid-soluble cyclic nucleotide analogs induces a "tug-of-war" response, pigments aggregating in some chromatosomes with unpredictable, oscillatory movements in others. Inhibition of cAMP-dependent protein kinase accelerates aggregation and reduces dispersion velocities, suggesting a role in phosphorylation events, possibly regulating SER Ca 2+ release and pigment aggregation. The second messengers IP 3 and cADPR do not stimulate SER Ca 2+ release. α-PDH does not sustain pigment dispersion, suggesting that pigment translocation in caridean chromatophores may be regulated solely by RPCH, since PDH is not required. We propose a working hypothesis to further unravel key steps in the mechanisms of pigment translocation within crustacean chromatophores that have remained obscure for nearly a century. © 2016 Wiley Periodicals, Inc.

Influence of traditional agricultural practices on mobilization of arsenic from sediments to groundwater in Bengal delta.

PubMed

Farooq, S H; Chandrasekharam, D; Berner, Z; Norra, S; Stüben, D

2010-11-01

In the wake of the idea that surface derived dissolved organic carbon (DOC) plays an important role in the mobilization of arsenic (As) from sediments to groundwater and may provide a vital tool in understanding the mechanism of As contamination (mobilization/fixation) in Bengal delta; a study has been carried out. Agricultural fields that mainly cultivate rice (paddy fields) leave significantly large quantities of organic matter/organic carbon on the surface of Bengal delta which during monsoon starts decomposing and produces DOC. The DOC thus produced percolates down with rain water and mobilizes As from the sediments. Investigations on sediment samples collected from a paddy field clearly indicate that As coming on to the surface along with the irrigation water accumulates itself in the top few meters of sediment profile. The column experiments carried out on a 9 m deep sediment profile demonstrates that DOC has a strong potential to mobilize As from the paddy fields and the water recharging the aquifer through such agricultural fields contain As well above the WHO limit thus contaminating the shallow groundwater. Experiment also demonstrates that decay of organic matter induces reducing condition in the sediments. Progressively increasing reducing conditions not only prevent the adsorption of As on mineral surfaces but also cause mobilization of previously sorbed arsenic. There seems to be a cyclic pattern where As from deeper levels comes to the surface with irrigational water, accumulates itself in the sediments, and ultimately moves down to the shallow groundwater. The extensive and continual exploitation of intermediate/deep groundwater accelerates this cyclic process and helps in the movement of shallow contaminated groundwater to the deeper levels. Copyright © 2010 Elsevier Ltd. All rights reserved.

Flight Dynamics Aspects of a Large Civil Tiltrotor Simulation Using Translational Rate Command

NASA Technical Reports Server (NTRS)

Lawrence, Ben; Malpica, Carlos A.; Theodore, Colin R.; Decker, William A.; Lindsey, James E.

2011-01-01

An in-depth analysis of a Large Civil Tiltrotor simulation with a Translational Rate Command control law that uses automatic nacelle deflections for longitudinal velocity control and lateral cyclic for lateral velocity control is presented. Results from piloted real-time simulation experiments and offline time and frequency domain analyses are used to investigate the fundamental flight dynamic and control mechanisms of the control law. The baseline Translational Rate Command conferred handling qualities improvements over an attitude command attitude hold control law but in some scenarios there was a tendency to enter PIO. Nacelle actuator rate limiting strongly influenced the PIO tendency and reducing the rate limits degraded the handling qualities further. Counterintuitively, increasing rate limits also led to a worsening of the handling qualities ratings. This led to the identification of a nacelle rate to rotor longitudinal flapping coupling effect that induced undesired pitching motions proportional to the allowable amount of nacelle rate. A modification that applied a counteracting amount of longitudinal cyclic proportional to the nacelle rate significantly improved the handling qualities. The lateral axis of the Translational Rate Command conferred Level 1 handling qualities in a Lateral Reposition maneuver. Analysis of the influence of the modeling fidelity on the lateral flapping angles is presented. It is showed that the linear modeling approximation is likely to have under-predicted the side-force and therefore under-predicted the lateral flapping at velocities above 15 ft/s. However, at lower velocities, and therefore more weakly influenced by the side force modeling, the accelerations that the control law commands also significantly influenced the peak levels of lateral flapping achieved.

Cafestol Inhibits Cyclic-Strain-Induced Interleukin-8, Intercellular Adhesion Molecule-1, and Monocyte Chemoattractant Protein-1 Production in Vascular Endothelial Cells

PubMed Central

Hao, Wen-Rui; Sung, Li-Chin; Chen, Chun-Chao; Chen, Jin-Jer

2018-01-01

Moderate coffee consumption is inversely associated with cardiovascular disease mortality; however, mechanisms underlying this causal effect remain unclear. Cafestol, a diterpene found in coffee, has various properties, including an anti-inflammatory property. This study investigated the effect of cafestol on cyclic-strain-induced inflammatory molecule secretion in vascular endothelial cells. Cells were cultured under static or cyclic strain conditions, and the secretion of inflammatory molecules was determined using enzyme-linked immunosorbent assay. The effects of cafestol on mitogen-activated protein kinases (MAPK), heme oxygenase-1 (HO-1), and sirtuin 1 (Sirt1) signaling pathways were examined using Western blotting and specific inhibitors. Cafestol attenuated cyclic-strain-stimulated intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein- (MCP-) 1, and interleukin- (IL-) 8 secretion. Cafestol inhibited the cyclic-strain-induced phosphorylation of extracellular signal-regulated kinase and p38 MAPK. By contrast, cafestol upregulated cyclic-strain-induced HO-1 and Sirt1 expression. The addition of zinc protoporphyrin IX, sirtinol, or Sirt1 silencing (transfected with Sirt1 siRNA) significantly attenuated cafestol-mediated modulatory effects on cyclic-strain-stimulated ICAM-1, MCP-1, and IL-8 secretion. This is the first study to report that cafestol inhibited cyclic-strain-induced inflammatory molecule secretion, possibly through the activation of HO-1 and Sirt1 in endothelial cells. The results provide valuable insights into molecular pathways that may contribute to the effects of cafestol. PMID:29854096

Cyclic Strain Resistance, Stress Response, Fatigue Life, and Fracture Behavior of High Strength Low Alloy Steel 300 M

NASA Astrophysics Data System (ADS)

Manigandan, K.; Srivatsan, T. S.; Tammana, Deepthi; Poorgangi, Behrang; Vasudevan, Vijay K.

2014-05-01

The focus of this technical manuscript is a record of the specific role of microstructure and test specimen orientation on cyclic stress response, cyclic strain resistance, and cyclic stress versus strain response, deformation and fracture behavior of alloy steel 300 M. The cyclic strain amplitude-controlled fatigue properties of this ultra-high strength alloy steel revealed a linear trend for the variation of log elastic strain amplitude with log reversals-to-failure, and log plastic strain amplitude with log reversals-to-failure for both longitudinal and transverse orientations. Test specimens of the longitudinal orientation showed only a marginal improvement over the transverse orientation at equivalent values of plastic strain amplitude. Cyclic stress response revealed a combination of initial hardening for the first few cycles followed by gradual softening for a large portion of fatigue life before culminating in rapid softening prior to catastrophic failure by fracture. Fracture characteristics of test specimens of this alloy steel were different at both the macroscopic and fine microscopic levels over the entire range of cyclic strain amplitudes examined. Both macroscopic and fine microscopic observations revealed fracture to be a combination of both brittle and ductile mechanisms. The underlying mechanisms governing stress response, deformation characteristics, fatigue life, and final fracture behavior are presented and discussed in light of the competing and mutually interactive influences of test specimen orientation, intrinsic microstructural effects, deformation characteristics of the microstructural constituents, cyclic strain amplitude, and response stress.

New perspectives in cyclic nucleotide-mediated functions in the CNS: the emerging role of cyclic nucleotide-gated (CNG) channels.

PubMed

Podda, Maria Vittoria; Grassi, Claudio

2014-07-01

Cyclic nucleotides play fundamental roles in the central nervous system (CNS) under both physiological and pathological conditions. The impact of cAMP and cGMP signaling on neuronal and glial cell functions has been thoroughly characterized. Most of their effects have been related to cyclic nucleotide-dependent protein kinase activity. However, cyclic nucleotide-gated (CNG) channels, first described as key mediators of sensory transduction in retinal and olfactory receptors, have been receiving increasing attention as possible targets of cyclic nucleotides in the CNS. In the last 15 years, consistent evidence has emerged for their expression in neurons and astrocytes of the rodent brain. Far less is known, however, about the functional role of CNG channels in these cells, although several of their features, such as Ca(2+) permeability and prolonged activation in the presence of cyclic nucleotides, make them ideal candidates for mediators of physiological functions in the CNS. Here, we review literature suggesting the involvement of CNG channels in a number of CNS cellular functions (e.g., regulation of membrane potential, neuronal excitability, and neurotransmitter release) as well as in more complex phenomena, like brain plasticity, adult neurogenesis, and pain sensitivity. The emerging picture is that functional and dysfunctional cyclic nucleotide signaling in the CNS has to be reconsidered including CNG channels among possible targets. However, concerted efforts and multidisciplinary approaches are still needed to get more in-depth knowledge in this field.

Optimal resolution in maximum entropy image reconstruction from projections with multigrid acceleration

NASA Technical Reports Server (NTRS)

Limber, Mark A.; Manteuffel, Thomas A.; Mccormick, Stephen F.; Sholl, David S.

1993-01-01

We consider the problem of image reconstruction from a finite number of projections over the space L(sup 1)(Omega), where Omega is a compact subset of the set of Real numbers (exp 2). We prove that, given a discretization of the projection space, the function that generates the correct projection data and maximizes the Boltzmann-Shannon entropy is piecewise constant on a certain discretization of Omega, which we call the 'optimal grid'. It is on this grid that one obtains the maximum resolution given the problem setup. The size of this grid grows very quickly as the number of projections and number of cells per projection grow, indicating fast computational methods are essential to make its use feasible. We use a Fenchel duality formulation of the problem to keep the number of variables small while still using the optimal discretization, and propose a multilevel scheme to improve convergence of a simple cyclic maximization scheme applied to the dual problem.

Programmable Payload Release from Transient Polymer Microcapsules Triggered by a Specific Ion Coactivation Effect.

PubMed

Tang, Shijia; Tang, Liuyan; Lu, Xiaocun; Liu, Huiying; Moore, Jeffrey S

2018-01-10

Stimuli-responsive materials activated by a pair of molecular or ionic species are of interest in the design of chemical logic gates and signal amplification schemes. There are relatively few materials whose coactivated response has been well-characterized. Here, we demonstrate a specific ion coactivation (SICA) effect at the interfaces of transient polymer solids and liquid solutions. We found that depolymerization of the transient polymer, cyclic poly(phthalaldehyde) (cPPA), exhibited a SICA effect when the cPPA core-shell microcapsules were suspended in ion-containing acidic methanol solutions. Significant acceleration in cPPA depolymerization rate is triggered by the combination of acid and ion coactivators. Intriguingly, the SICA effect is related to the Hofmeister behavior. The SICA effect is primarily determined by anions, and cations exhibit a secondary effect that modulates the coactivation strength. Based on these observations, we developed cPPA programmable microcapsules whose payload release rates depend on the composition and concentration of the salt/acidic-methanol solutions.

NASTRAN supplemental documentation for modal forced vibration analysis of aerodynamically excited turbosystems

NASA Technical Reports Server (NTRS)

Elchuri, V.; Pamidi, P. R.

1985-01-01

This report is a supplemental NASTRAN document for a new capability to determine the vibratory response of turbosystems subjected to aerodynamic excitation. Supplements of NASTRAN Theoretical, User's, Programmer's, and Demonstration Manuals are included. Turbosystems such as advanced turbopropellers with highly swept blades, and axial-flow compressors and turbines can be analyzed using this capability, which has been developed and implemented in the April 1984 release of the general purpose finite element program NASTRAN. The dynamic response problem is addressed in terms of the normal modal coordinates of these tuned rotating cyclic structures. Both rigid and flexible hubs/disks are considered. Coriolis and centripetal accelerations, as well as differential stiffness effects are included. Generally nonuniform steady inflow fields and uniform flow fields arbitrarily inclined at small angles with respect to the axis of rotation of the turbosystem are considered as the sources of aerodynamic excitation. The spatial nonuniformities are considered to be small deviations from a principally uniform inflow. Subsonic relative inflows are addressed, with provision for linearly interpolating transonic airloads.

An effective method to screen sodium-based layered materials for sodium ion batteries

NASA Astrophysics Data System (ADS)

Zhang, Xu; Zhang, Zihe; Yao, Sai; Chen, An; Zhao, Xudong; Zhou, Zhen

2018-03-01

Due to the high cost and insufficient resource of lithium, sodium-ion batteries are widely investigated for large-scale applications. Typically, insertion-type materials possess better cyclic stability than alloy-type and conversion-type ones. Therefore, in this work, we proposed a facile and effective method to screen sodium-based layered materials based on Materials Project database as potential candidate insertion-type materials for sodium ion batteries. The obtained Na-based layered materials contains 38 kinds of space group, which reveals that the credibility of our screening approach would not be affected by the space group. Then, some important indexes of the representative materials, including the average voltage, volume change and sodium ion mobility, were further studied by means of density functional theory computations. Some materials with extremely low volume changes and Na diffusion barriers are promising candidates for sodium ion batteries. We believe that our classification algorithm could also be used to search for other alkali and multivalent ion-based layered materials, to accelerate the development of battery materials.

Accelerating the discovery of space-time patterns of infectious diseases using parallel computing.

PubMed

Hohl, Alexander; Delmelle, Eric; Tang, Wenwu; Casas, Irene

2016-11-01

Infectious diseases have complex transmission cycles, and effective public health responses require the ability to monitor outbreaks in a timely manner. Space-time statistics facilitate the discovery of disease dynamics including rate of spread and seasonal cyclic patterns, but are computationally demanding, especially for datasets of increasing size, diversity and availability. High-performance computing reduces the effort required to identify these patterns, however heterogeneity in the data must be accounted for. We develop an adaptive space-time domain decomposition approach for parallel computation of the space-time kernel density. We apply our methodology to individual reported dengue cases from 2010 to 2011 in the city of Cali, Colombia. The parallel implementation reaches significant speedup compared to sequential counterparts. Density values are visualized in an interactive 3D environment, which facilitates the identification and communication of uneven space-time distribution of disease events. Our framework has the potential to enhance the timely monitoring of infectious diseases. Copyright © 2016 Elsevier Ltd. All rights reserved.

Development of an Accelerated Test Method for the Determination of Susceptibility to Atmospheric Corrosion

NASA Technical Reports Server (NTRS)

Ambrose, John R.

1991-01-01

The theoretical rationale is presented for use of a repetitive cyclic current reversal voltammetric technique for characterization of localized corrosion processes, including atmospheric corrosion. Applicability of this proposed experimental protocol is applied to characterization of susceptibility to crevice and pitting corrosion, atmospheric corrosion and stress corrosion cracking. Criteria upon which relative susceptibility is based were determined and tested using two iron based alloys commonly in use at NASA-Kennedy; A36 (a low carbon steel) and 4130 (a low alloy steel). Practicality of the procedure was demonstrated by measuring changes in anodic polarization behavior during high frequency current reversal cycles of 25 cycles per second with 1 mA/sq cm current density amplitude in solutions containing Cl anions. The results demonstrated that, due to excessive polarization which affects conductivity of barrier corrosion product layers, A36 was less resistant to atmospheric corrosion than its 4130 counterpart; behavior which was also demonstrated during exposure tests.

Peptidic Macrocycles - Conformational Sampling and Thermodynamic Characterization

PubMed Central

2018-01-01

Macrocycles are of considerable interest as highly specific drug candidates, yet they challenge standard conformer generators with their large number of rotatable bonds and conformational restrictions. Here, we present a molecular dynamics-based routine that bypasses current limitations in conformational sampling and extensively profiles the free energy landscape of peptidic macrocycles in solution. We perform accelerated molecular dynamics simulations to capture a diverse conformational ensemble. By applying an energetic cutoff, followed by geometric clustering, we demonstrate the striking robustness and efficiency of the approach in identifying highly populated conformational states of cyclic peptides. The resulting structural and thermodynamic information is benchmarked against interproton distances from NMR experiments and conformational states identified by X-ray crystallography. Using three different model systems of varying size and flexibility, we show that the method reliably reproduces experimentally determined structural ensembles and is capable of identifying key conformational states that include the bioactive conformation. Thus, the described approach is a robust method to generate conformations of peptidic macrocycles and holds promise for structure-based drug design. PMID:29652495

Novel targets for Huntington’s disease in an mTOR-independent autophagy pathway

PubMed Central

Williams, Andrea; Sarkar, Sovan; Cuddon, Paul; Ttofi, Evangelia K.; Saiki, Shinji; Siddiqi, Farah H.; Jahreiss, Luca; Fleming, Angeleen; Pask, Dean; Goldsmith, Paul; O’Kane, Cahir J.; Floto, R. Andres; Rubinsztein, David C.

2009-01-01

Autophagy is a major clearance route for intracellular aggregate-prone proteins causing diseases like Huntington’s disease. Autophagy induction with the mTOR inhibitor, rapamycin, accelerates clearance of these toxic substrates. As rapamycin has non-trivial side effects, we screened FDA-approved drugs to identify novel autophagy-inducing pathways. We found that L-type Ca2+ channel antagonists, the K+ATP channel opener minoxidil, and the Gi signaling activator clonidine, induce autophagy. These drugs revealed a cyclical mTOR-independent pathway regulating autophagy, where cAMP regulates IP3 levels, influencing calpain activity, which completes the cycle by cleaving and activating Gsα, which regulates cAMP levels. This pathway has numerous potential points where autophagy can be induced and we provide proof-of-principle for therapeutic relevance in Huntington’s disease using mammalian cell, fly and zebrafish models. Our data also suggest that insults that elevate intracytosolic Ca2+, like excitotoxicity, will inhibit autophagy, thus retarding clearance of aggregate-prone proteins. PMID:18391949

Application of system identification to analytic rotor modeling from simulated and wind tunnel dynamic test data, part 2

NASA Technical Reports Server (NTRS)

Hohenemser, K. H.; Banerjee, D.

1977-01-01

An introduction to aircraft state and parameter identification methods is presented. A simplified form of the maximum likelihood method is selected to extract analytical aeroelastic rotor models from simulated and dynamic wind tunnel test results for accelerated cyclic pitch stirring excitation. The dynamic inflow characteristics for forward flight conditions from the blade flapping responses without direct inflow measurements were examined. The rotor blades are essentially rigid for inplane bending and for torsion within the frequency range of study, but flexible in out-of-plane bending. Reverse flow effects are considered for high rotor advance ratios. Two inflow models are studied; the first is based on an equivalent blade Lock number, the second is based on a time delayed momentum inflow. In addition to the inflow parameters, basic rotor parameters like the blade natural frequency and the actual blade Lock number are identified together with measurement bias values. The effect of the theoretical dynamic inflow on the rotor eigenvalues is evaluated.

Pulsating Flows in a Tube with Expandable Wall

NASA Astrophysics Data System (ADS)

Raguso, Frank; Goushcha, Oleg

2017-11-01

A mean axial fluid flow inside a cardiovascular system has a periodic behavior driven by a heart. In one period, the flow through aorta is accelerated to a Reynolds number associated with turbulent flow and decelerated to nearly stagnant condition. The cyclic pressure in the aorta also exerts time-dependent forces on the walls of the cardiovascular system. Since walls are not rigid, they can expand under fluidic pressure. It is of interest to examine the effect of expandable walls on the flow regime transition. To achieve this, an experimental apparatus has been set up. The periodic mean axial flow inside the tubes is driven by a motor-controlled piston programmed to induce a periodic flow. A time-resolved particle image velocimetry method has been used to calculate the flow velocity field in two tubes: (1) a rigid tube and (2) a flexible tube with expandable walls. The velocity fields from two tubes were comparted to identify any differences in flow transition mechanisms.

Modeling of gun barrel surface erosion: Historic perspective

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

Buckingham, A.C.

1996-08-01

Results and interpretations of numerical simulations of some dominant processes influencing gun barrel propellant combustion and flow-induced erosion are presented. Results include modeled influences of erosion reduction techniques such as solid additives, vapor phase chemical modifications, and alteration of surface solid composition through use of thin coatings. Precedents and historical perspective are provided with predictions from traditional interior ballistics compared to computer simulations. Accelerating reactive combustion flow, multiphase and multicomponent transport, flow-to-surface thermal/momentum/phase change/gas-surface chemical exchanges, surface and micro-depth subsurface heating/stress/composition evolution and their roles in inducing surface cracking, spall, ablation, melting, and vaporization are considered. Recognition is given tomore » cyclic effects of previous firing history on material preconditioning. Current perspective and outlook for future are based on results of a US Army-LLNL erosion research program covering 7 y in late 1970s. This is supplemented by more recent research on hypervelocity electromagnetic projectile launchers.« less

Environmentally Friendly Corrosion Preventative Compounds for Ground Support Structures

NASA Technical Reports Server (NTRS)

Montgomery Eliza L.; Calle, Luz, Marina; Curran, Jerome P.; Kolody, Mark R.

2013-01-01

The need to use environmentally friendly technologies throughout future space-related launch programs prompted a study aimed at replacing current petroleum and solvent-based Corrosion Preventive Compounds (CPCs) with environmentally friendly alternatives. The work in this paper focused on the identification and evaluation of environmentally friendly CPCs for use in protecting flight hardware and ground support equipment from atmospheric corrosion. CPCs are used as temporary protective coatings and must survive in the aggressive coastal marine environment that exists throughout the Kennedy Space Center, Florida. The different protection behaviors of fifteen different oily film CPCs, both common petroleum-based and newer environmentally friendly types, were evaluated on various steel and aluminum substrates. CPC and substrate systems were subjected to atmospheric testing at the Kennedy Space Center's Beachside Atmospheric Corrosion Test Site, as well as cyclic accelerated corrosion testing. Each CPC also underwent physical characterization and launch-related compatibility testing. The results for the fifteen CPC systems are presented in this paper.

Peptidic Macrocycles - Conformational Sampling and Thermodynamic Characterization.

PubMed

Kamenik, Anna S; Lessel, Uta; Fuchs, Julian E; Fox, Thomas; Liedl, Klaus R

2018-05-29

Macrocycles are of considerable interest as highly specific drug candidates, yet they challenge standard conformer generators with their large number of rotatable bonds and conformational restrictions. Here, we present a molecular dynamics-based routine that bypasses current limitations in conformational sampling and extensively profiles the free energy landscape of peptidic macrocycles in solution. We perform accelerated molecular dynamics simulations to capture a diverse conformational ensemble. By applying an energetic cutoff, followed by geometric clustering, we demonstrate the striking robustness and efficiency of the approach in identifying highly populated conformational states of cyclic peptides. The resulting structural and thermodynamic information is benchmarked against interproton distances from NMR experiments and conformational states identified by X-ray crystallography. Using three different model systems of varying size and flexibility, we show that the method reliably reproduces experimentally determined structural ensembles and is capable of identifying key conformational states that include the bioactive conformation. Thus, the described approach is a robust method to generate conformations of peptidic macrocycles and holds promise for structure-based drug design.

Patterning of ultrathin polymethylmethacrylate films by in-situ photodirecting of the Marangoni flow

NASA Astrophysics Data System (ADS)

Elashnikov, Roman; Fitl, Premysl; Svorcik, Vaclav; Lyutakov, Oleksiy

2017-02-01

Laser heating and Marangoni flow result in the formation of surface structures with different geometries and shape on thin polymer films. By laser beam irradiation combined with a sample movement the solid polymethylmethacrylate (PMMA) films are heated and undergo phase transition which leads to a material flow. Since the laser beam has a non-linear distribution of energy, the PMMA film is heated inhomogeneously and a surface tension gradient in a lateral direction is introduced. During this procedure additional phenomena such as "reversible" or cyclic polymer flow also take place. The careful choice of experimental conditions enables the preparation of patterns with sophisticated geometries and with hierarchical pattern organization. Depending on initial PMMA film thickness and speed of the sample movement line arrays are created, which can subsequently be transformed into the crimped lines or system of circular holes. In addition, the introduction of a constant acceleration in the sample movement or a laser beam distortion enables the preparation of regularly crimped lines, ordered hexagonal holes or overlapped plates.

Plasticity-related genes in brain development and amygdala-dependent learning.

PubMed

Ehrlich, D E; Josselyn, S A

2016-01-01

Learning about motivationally important stimuli involves plasticity in the amygdala, a temporal lobe structure. Amygdala-dependent learning involves a growing number of plasticity-related signaling pathways also implicated in brain development, suggesting that learning-related signaling in juveniles may simultaneously influence development. Here, we review the pleiotropic functions in nervous system development and amygdala-dependent learning of a signaling pathway that includes brain-derived neurotrophic factor (BDNF), extracellular signaling-related kinases (ERKs) and cyclic AMP-response element binding protein (CREB). Using these canonical, plasticity-related genes as an example, we discuss the intersection of learning-related and developmental plasticity in the immature amygdala, when aversive and appetitive learning may influence the developmental trajectory of amygdala function. We propose that learning-dependent activation of BDNF, ERK and CREB signaling in the immature amygdala exaggerates and accelerates neural development, promoting amygdala excitability and environmental sensitivity later in life. © 2015 John Wiley & Sons Ltd and International Behavioural and Neural Genetics Society.

Cyclic electron transfer around Photosystem I mediated by 2,3-dichloro-1,4-naphtoquinone and ascorbate.

PubMed

Petrova, Anastasia A; Trubitsin, Boris V; Boskhomdzhieva, Baina K; Semenov, Alexey Yu; Tikhonov, Alexander N

2018-06-09

In this work, we investigated electron transport around the photosynthetic pigment-protein complex of Photosystem I (PS I) mediated by external high-potential electron carrier 2,3-dichloro-1,4-naphtoquinone (Cl 2 NQ) and ascorbate. It has been demonstrated that the oxidized species of Cl 2 NQ and ascorbate serve as intermediates capable of accepting electrons from the iron-sulfur cluster F X of PS I. Reduced species of Cl 2 NQ and ascorbate are oxidized by photooxidized PS I primary donor P700+ and/or by molecular oxygen. We have found the synergistic effect of Cl 2 NQ and ascorbate on the rate of P700+ reduction. Accelerated electron flow to P700+, observed in the presence of both Cl 2 NQ and ascorbate, is explained by an increase in the reduced species of Cl 2 NQ due to electron transfer from ascorbate. © 2018 Federation of European Biochemical Societies.

Fatigue stress concentration and notch sensitivity in nanocrystalline metals

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

Furnish, Timothy A.; Boyce, Brad L.; Sharon, John A.

Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni–40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension–tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zonesmore » underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. Furthermore, the onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.« less

Stable platinum nanoclusters on genomic DNA–graphene oxide with a high oxygen reduction reaction activity

PubMed Central

Tiwari, Jitendra N.; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N.; Kemp, K. Christian; Le, Nhien H.; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S.

2013-01-01

Nanosize platinum clusters with small diameters of 2–4 nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2 nm). Here we report the synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA–graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA–graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA–graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries. PMID:23900456

Fatigue stress concentration and notch sensitivity in nanocrystalline metals

DOE PAGES

Furnish, Timothy A.; Boyce, Brad L.; Sharon, John A.; ...

2016-03-11

Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni–40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension–tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zonesmore » underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. Furthermore, the onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.« less

Environmentally friendly corrosion preventive compounds for ground support structures

NASA Astrophysics Data System (ADS)

Montgomery, Eliza; Curran, Jerome; Calle, Luz Marina; Kolody, Mark

The need to use environmentally friendly technologies throughout future space-related launch programs prompted a study aimed at replacing current petroleum and solvent-based corrosion preventive compounds (CPCs) with environmentally friendly alternatives. The work in this paper focused on the identification and evaluation of environmentally friendly CPCs for use in protecting flight hardware and ground support equipment from atmospheric corrosion. CPCs are used as temporary protective coatings and must survive in the aggressive coastal marine environment that exists throughout the Kennedy Space Center, Florida. The different protection behaviors of fifteen different oily film CPCs, both common petroleum-based and newer environmentally friendly types, were evaluated on various steel and aluminum substrates. CPC and substrate systems were subjected to atmospheric testing at the Kennedy Space Center's Beachside Atmospheric Corrosion Test Site, as well as cyclic accelerated corrosion testing. Each CPC also underwent physical characterization and launch-related compatibility testing. The results for the fifteen CPC systems are presented in this paper.

The Final Helium Flash Object Sakurai: Photometric Behavior and Physical Characteristics.

NASA Astrophysics Data System (ADS)

Duerbeck, Hilmar W.; Benetti, Stefano; Gautschy, Alfred; van Genderen, Arnout M.; Kemper, Ciska; Liller, William; Thomas, Tom

1997-10-01

Six-color broadband photometry of Sakurai's Object, a star that underwent a final helium flash in late 1994, has been carried out since 1996 February. The light curves show that Sakurai's Object is continuously cooling while it slowly expands and slightly increases its luminosity. The distance is estimated to be 8 kpc, the interstellar extinction EB-V=0.53, and the luminosity in early 1997 is 10 000Lsun. The high luminosity indicates that the white dwarf is quite massive. With the assumption of a slightly accelerated photospheric expansion a realistic description of the outburst light curve is achieved. Superimposed on the gradual brightness changes are variations with amplitudes of up to 0.1 mag and cycle lengths of 63, 23, 14, and 8 days. In spite of the fact that no persistent periodicities could be detected, pulsational studies show that such cyclic changes can be used to constrain stellar parameters such as mass, luminosity, and chemical abundances.

Immobilization of Glucose Oxidase on a Carbon Nanotubes/Dendrimer-Ferrocene Modified Electrode for Reagentless Glucose Biosensing.

PubMed

Zhou, Juan; Li, Huan; Yang, Huasong; Cheng, Hui; Lai, Guosong

2017-01-01

Ferrocene-grafted dendrimer was covalently linked to the surface of a carbon nanotubes (CNTs)-chitosan (CS) nanocomposite modified electrode for immobilizing high-content glucose oxidase (GOx), which resulted in the successful development a novel reagentless glucose biosensor. Electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry were used to characterize the preparation process and the enzymatically catalytic response of this biosensor. Due to the excellent electron transfer acceleration of the CNTs and the high-content loading of the GOx biomolecule and ferrocene mediator on the electrode matrix, this biosensor showed excellent analytical performance such as fast response time less than 10 s, wide linear range from 0.02 to 2.91 mM and low detection limit down to 7.5 μM as well as satisfactory stability and reproducibility toward the amperometric glucose determination. In addition, satisfactory result was obtained when it was used for the glucose measurements in human blood samples. Thus this biosensor provides great potentials for practical applications.

Highly magneto-responsive multilayer microcapsules for controlled release of insulin.

PubMed

Zheng, Chunli; Ding, Yafei; Liu, Xiaoqing; Wu, Yunkai; Ge, Liang

2014-11-20

In this study, magneto-responsive polyelectrolyte multilayer microcapsules were successfully prepared by the formation of shell with biocompatible iron oxide nanoparticles (Fe₃O₄ NPs) and polyallylamine hydrochloride (PAH) by layer-by-layer (LbL) self-assembly technique. The self-assembled microcapsules were characterized by SEM, TEM and zeta-potential analyzer. According to the pH sensitivity of the microcapsule membrane permeability, insulin was encapsulated, with the encapsulation efficiency of 92.08±5.57%. The in vitro release behavior in an external alternating magnetic field indicated that once the magnetic field was applied, the drug release was greatly accelerated. In addition, according to the observed pulse release upon cyclic on-off operations of magnetic field, it could be assumed that the magneto-responsive microcapsules had an excellent "switching on" effect, which might be attributed to the rearrangement of shell structure caused by magnetic nanoparticles twisting and polyelectrolyte chains shaking, hence the increase of microcapsule membrane permeability and the enhancement of insulin release. Copyright © 2014 Elsevier B.V. All rights reserved.

Surface-Accelerated Decomposition of δ-HMX.

PubMed

Sharia, Onise; Tsyshevsky, Roman; Kuklja, Maija M

2013-03-07

Despite extensive efforts to study the explosive decomposition of HMX, a cyclic nitramine widely used as a solid fuel, explosive, and propellant, an understanding of the physicochemical processes, governing the sensitivity of condensed HMX to detonation initiation is not yet achieved. Experimental and theoretical explorations of the initiation of chemistry are equally challenging because of many complex parallel processes, including the β-δ phase transition and the decomposition from both phases. Among four known polymorphs, HMX is produced in the most stable β-phase, which transforms into the most reactive δ-phase under heat or pressure. In this study, the homolytic NO2 loss and HONO elimination precursor reactions of the gas-phase, ideal crystal, and the (100) surface of δ-HMX are explored by first principles modeling. Our calculations revealed that the high sensitivity of δ-HMX is attributed to interactions of surfaces and molecular dipole moments. While both decomposition reactions coexist, the exothermic HONO-isomer formation catalyzes the N-NO2 homolysis, leading to fast violent explosions.

Electrochemical Formation of Multilayer SnO2-Sb x O y Coating in Complex Electrolyte

NASA Astrophysics Data System (ADS)

Maizelis, Antonina; Bairachniy, Boris

2017-02-01

The multilayer antimony-doped tin dioxide coating was obtained by cathodic deposition of multilayer metal-hydroxide coating with near 100-nm thickness layers on the alloy underlayer accompanied by the anodic oxidation of this coating. The potential regions of deposition of tin, antimony, tin-antimony alloy, and mixture of this metals and their hydroxides in the pyrophosphate-tartrate electrolyte were revealed by the cyclic voltammetric method. The possibility of oxidation of cathodic deposit consisting of tin and Sn(II) hydroxide compounds to the hydrated tin dioxide in the same electrolyte was demonstrated. The operations of alloy underlayer deposition and oxidation of multilayer metal-hydroxide coating were proposed to carry out in the diluted pyrophosphate-tartrate electrolyte, similar to the main electrolyte. The accelerated tests showed higher service life of the titanium electrode with multilayer antimony-doped tin dioxide coating compared to both electrode with single-layer electrodeposited coating and the electrode with the coating obtained using prolonged heat treatment step.

Electrochemical Formation of Multilayer SnO2-Sb x O y Coating in Complex Electrolyte.

PubMed

Maizelis, Antonina; Bairachniy, Boris

2017-12-01

The multilayer antimony-doped tin dioxide coating was obtained by cathodic deposition of multilayer metal-hydroxide coating with near 100-nm thickness layers on the alloy underlayer accompanied by the anodic oxidation of this coating. The potential regions of deposition of tin, antimony, tin-antimony alloy, and mixture of this metals and their hydroxides in the pyrophosphate-tartrate electrolyte were revealed by the cyclic voltammetric method. The possibility of oxidation of cathodic deposit consisting of tin and Sn(II) hydroxide compounds to the hydrated tin dioxide in the same electrolyte was demonstrated.The operations of alloy underlayer deposition and oxidation of multilayer metal-hydroxide coating were proposed to carry out in the diluted pyrophosphate-tartrate electrolyte, similar to the main electrolyte.The accelerated tests showed higher service life of the titanium electrode with multilayer antimony-doped tin dioxide coating compared to both electrode with single-layer electrodeposited coating and the electrode with the coating obtained using prolonged heat treatment step.

On the Health Risk of the Lumbar Spine due to Whole-Body VIBRATION—THEORETICAL Approach, Experimental Data and Evaluation of Whole-Body Vibration

NASA Astrophysics Data System (ADS)

Seidel, H.; Blüthner, R.; Hinz, B.; Schust, M.

1998-08-01

The guidance on the effects of vibration on health in standards for whole-body vibration (WBV) does not provide quantitative relationships between WBV and health risk. The paper aims at the elucidation of exposure-response relationships. An analysis of published data on the static and dynamic strength of vertebrae and bone, loaded with various frequencies under different conditions, provided the basis for a theoretical approach to evaluate repetitive loads on the lumbar spine (“internal loads”). The approach enabled the calculation of “equivalent”—with respect to cumulative fatigue failure—combinations of amplitudes and numbers of internal cyclic stress. In order to discover the relation between external peak accelerations at the seat and internal peak loads, biodynamic data of experiments (36 subjects, three somatotypes, two different postures—relaxed and bent forward; random WBV,aw, r.m.s. 1·4 ms-2, containing high transients) were used as input to a biomechanical model. Internal pressure changes were calculated using individual areas of vertebral endplates. The assessment of WBV was based on the quantitative relations between peak accelerations at the seat and pressures predicted for the disk L5/S1. For identical exposures clearly higher rates of pressure rise in the bent forward compared to the relaxed posture were predicted. The risk assessment for internal forces considered the combined internal static and dynamic loads, in relation to the predicted individual strength, and Miner's hypothesis. For exposure durations between 1 min and 8 h, energy equivalent vibration magnitudes (formula B.1, ISO 2631-1, 1997) and equivalent vibration magnitudes according to formula B.2 (time dependence over-energetic) were compared with equivalent combinations of upward peak accelerations and exposure durations according to predicted cumulative fatigue failures of lumbar vertebrae. Formula B.1 seems to underestimate the health risk caused by high magnitudes, formula B.2 is recommended for the evaluation of such conditions.

A dual enzymatic-biosensor for simultaneous determination of glucose and cholesterol in serum and peritoneal macrophages of diabetic mice: evaluation of the diabetes-accelerated atherosclerosis risk.

PubMed

Huang, Qilin; An, Yarui; Tang, Linlin; Jiang, Xiaoli; Chen, Hua; Bi, Wenji; Wang, Zhongchuan; Zhang, Wen

2011-11-30

In this paper, a novel dual enzymatic-biosensor is described for simultaneous determination of glucose and cholesterol in serum and peritoneal macrophages (PMs) of diabetic mice to evaluate the risk of diabetes-accelerated atherosclerosis. The biosensor was constructed by a three-step method. First, a poly-thionine (PTH) film was assembled on the surface of glassy carbon electrode by cyclic voltammetric electropolymerization of thionine, which serves as an electron transfer mediator (ETM). Second, gold nanoparticles (GNPs) were covered on the surface of PTH facilitating the electron transfer between glucose oxidase (GOx), cholesterol oxidase (ChOx) and electrode. Finally, the enzymes, GOx, cholesterol esterase (ChE), and ChOx, were covalently attached to the PTH layer through a chitosan (CH) linker. The PTH coupled with GNPs provides good selectivity, high sensitivity and little crosstalk for the dual enzymatic-biosensor. The developed biosensor had good electrocatalytic activity toward the oxidations of glucose and cholesterol, exhibiting a linear range from 0.008 mM to 6.0 mM for glucose with a detection limit of 2.0 μM, and a linear range from 0.002 mM to 1.0 mM for cholesterol with a detection limit of 0.6 μM. The results of the diabetic mice demonstrated that the cholesterol level did not change obviously with the increase of glucose level in serum, while the cholesterol level was induced with the increase of the glucose level in PMs. Previous studies have shown that the large accumulation of cholesterol in macrophage could lead to macrophage foam cell formation, which is the hallmark of early atherosclerosis. This study provides useful further evidences for the development of diabetes-accelerated atherosclerosis. Copyright © 2011 Elsevier B.V. All rights reserved.

High Energy Molecules of High Symmetry.

DTIC Science & Technology

1987-08-01

concentration. The identity of this derivative is not yet established. Some possibilities are that 1), it is the condensation product of cyclic polyketone ...reduced cyclic polyketone and ammonia, (like Ruhemann’s purple) 31, or 2) it is a cyclic polyketone (1,1,2,2-tetraethylcyclopentane trione is blue) 32

Electrochemical Quartz Crystal Microbalance Monitoring of the Cyclic Voltammetric Deposition of Polyaniline

ERIC Educational Resources Information Center

Xie, Qingji; Li, Zhili; Deng, Chunyan; Liu, Meiling; Zhang, Youyu; Ma, Ming; Xia, Shaoxi; Xiao, Xiaoming; Yin, Dulin; Yao, Shouzhuo

2007-01-01

A real-time, labeled-free and nanogram-sensitive mass sensor, electrochemical quartz crystal microbalance (EQCM) is used to monitor a cyclic voltammetric deposition of polyaniline (PANI). The results determined that the efficiency for PANI deposition and the anion-doping ratio is calculated in one single cyclic voltammetric.

Are Math Grades Cyclical?

ERIC Educational Resources Information Center

Adams, Gerald J.; Dial, Micah

1998-01-01

The cyclical nature of mathematics grades was studied for a cohort of elementary school students from a large metropolitan school district in Texas over six years (average cohort size of 8495). The study used an autoregressive integrated moving average (ARIMA) model. Results indicate that grades do exhibit a significant cyclical pattern. (SLD)

Use of galerina marginata genes and proteins for peptide production

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

Hallen-Adams, Heather E.; Scott-Craig, John S.; Walton, Jonathan D.

The present invention relates to compositions and methods comprising genes and peptides associated with cyclic peptides and cyclic peptide production in mushrooms. In particular, the present invention relates to using genes and proteins from Galerina species encoding peptides specifically relating to amatoxins in addition to proteins involved with processing cyclic peptide toxins. In a preferred embodiment, the present invention also relates to methods for making small peptides and small cyclic peptides including peptides similar to amanitin. Further, the present inventions relate to providing kits for making small peptides.

Use of Galerina marginata genes and proteins for peptide production

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

Hallen-Adams, Heather E.; Scott-Craig, John S.; Walton, Jonathan D.

The present invention relates to compositions and methods comprising genes and peptides associated with cyclic peptides and cyclic peptide production in mushrooms. In particular, the present invention relates to using genes and proteins from Galerina species encoding peptides specifically relating to amatoxins in addition to proteins involved with processing cyclic peptide toxins. In a preferred embodiment, the present invention also relates to methods for making small peptides and small cyclic peptides including peptides similar to amanitin. Further, the present inventions relate to providing kits for making small peptides.

Hierarchical assembly of branched supramolecular polymers from (cyclic Peptide)-polymer conjugates.

PubMed

Koh, Ming Liang; Jolliffe, Katrina A; Perrier, Sébastien

2014-11-10

We report the synthesis and assembly of (N-methylated cyclic peptide)-polymer conjugates for which the cyclic peptide is attached to either the α- or both α- and ω- end groups of a polymer. A combination of chromatographic, spectroscopic, and scattering techniques reveals that the assembly of the conjugates follows a two-level hierarchy, initially driven by H-bond formation between two N-methylated cyclic peptides, followed by unspecific, noncovalent aggregation of this peptide into small domains that behave as branching points and lead to the formation of branched supramolecular polymers.

STUDIES ON THE MECHANISM OF ACTION OF CYCLIC 3’,5’-ADENOSINE MONOPHOSPHATE ON STEROID HYDROXYLATIONS IN ADRENAL HOMOGENATES,

DTIC Science & Technology

Cyclic 3’,5’-adenosine monophosphate (cyclic 3’,5’AMP) has recently been shown to stimulate selectively steroid C-11- beta hydroxylase activity in rat...to be mediated via stimulation of alpha- glucan phosphorylase, which in turn led to enhanced production of G-6-P from glycogen and a concomitant...increase in NADPH generation. However, if cyclic 3’,5’-AMP stimulated steroid 11- beta -hydroxylation in adrenal homogenates only by this mechanism, its

Autonomous momentum management for space station

NASA Technical Reports Server (NTRS)

Hahn, E.

1984-01-01

Momentum management for the CDG planar space platform is discussed. It is assumed that the external torques on the space station are gravity gradient and aerodynamic, both have bias and cyclic terms. The integrals of the cyclic torques are the cyclic momenti which will be stored in the momentum storage actuator. Techniques to counteract the bias torques and center the cyclic momentum and gravity gradient desaturation by adjusting vehicle attitude, aerodynamic desaturation using solar panels and radiators and the deployment of flat plates at the end of long booms generating aerodynamic torques are investigated.

Use of Galerina marginata genes and proteins for peptide production

DOEpatents

Hallen-Adams, Heather E.; Scott-Craig, John S.; Walton, Jonathan D.; Luo, Hong

2016-03-01

The present invention relates to compositions and methods comprising genes and peptides associated with cyclic peptides and cyclic peptide production in mushrooms. In particular, the present invention relates to using genes and proteins from Galerina species encoding peptides specifically relating to amatoxins in addition to proteins involved with processing cyclic peptide toxins. In a preferred embodiment, the present invention also relates to methods for making small peptides and small cyclic peptides including peptides similar to amanitin. Further, the present inventions relate to providing kits for making small peptides.

A cyclic peptide derived from alpha-fetoprotein inhibits the proliferative effects of the epidermal growth factor and estradiol in MCF7 cells.

PubMed

Torres, Cristian; Antileo, Elmer; Epuñán, Maráa José; Pino, Ana María; Valladares, Luis Emilio; Sierralta, Walter Daniel

2008-06-01

A cyclic peptide derived from the active domain of alpha-fetoprotein (AFP) significantly inhibited the proliferation of MCF7 cells stimulated with the epidermal growth factor (EGF) or estradiol (E2). The action of these three agents on cell growth was independent of the presence of calf serum in the culture medium. Our results demonstrated that the cyclic peptide interfered markedly with the regulation of MAPK by activated c-erbB2. The cyclic peptide showed no effect on the E2-stimulated release of matrix metalloproteinases 2 and 9 nor on the shedding of heparin-binding EGF into the culture medium. We propose that the AFP-derived cyclic peptide represents a valuable novel antiproliferative agent for treating breast cancer.

Cyclic control stick

DOEpatents

Whitaker, Charles N.; Zimmermann, Richard E.

1989-01-01

A cyclic control stick of the type used in helicopters for reducing the safety hazards associated with such a mechanism in the event of a crewman being thrown violently into contact with the cyclic control stick resulting from a crash or the like. The cyclic control stick is configured to break away upon the exertion of an impact force which exceeds a predetermined value and/or is exerted for more than a momentary time duration. The cyclic control stick is also configured to be adjustable so as to locate the grip thereof as far away from the crewman as possible for safety reasons without comprising the comfort of the crewman or the use of the control stick, and a crushable pad is provided on the top of the grip for impact energy absorbing purposes.

Turnover of cyclic 2,3-diphosphoglycerate in Methanobacterium thermoautotrophicum. Phosphate flux in P1- and H2-limited chemostat cultures.

PubMed

Krueger, R D; Campbell, J W; Fahrney, D E

1986-09-15

The archaebacterium Methanobacterium thermoautotrophicum was grown at 65 degrees C in H2- and Pi-limited chemostat cultures at dilution rates corresponding to 3- and 4-h doubling times, respectively. Under these conditions the steady state concentration of cyclic 2,3-diphosphoglycerate was 44 mM in the H2-limited cells and 13 mM in the cells grown under Pi limitation. Flux of Pi into the cyclic pyrophosphate pool was estimated by two 32P-labeling procedures: approach to isotopic equilibrium and replacement of prelabeled cyclic diphosphoglycerate with unlabeled compound. The results unequivocally demonstrate turnover of the phosphoryl groups; either both phosphoryl groups of the cyclic pyrophosphate leave together or the second leaves at a faster rate. The half-life of the rate-determining step for loss of the phosphoryl groups was approximately equal to the culture doubling time. The Pi flowing into the cyclic diphosphoglycerate pool accounted for 19% of the total Pi flux into Pi-limited cells and 43% of the total for H2-limited cells. The high phosphate flux through the large cyclic diphosphoglycerate pool suggests that this molecule plays an important role in the phosphorus metabolism of this methanogen.

The influence of matrix microstructure

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; Allison, J. E.; Aken, D. C.

1993-11-01

The low-cycle and high-cycle fatigue behavior and cyclic response of naturally aged and artificially aged 2219/TiC/15p and unreinforced 2219 Al were investigated utilizing plastic strain-controlled and stress-controlled testing. The cyclic response of both the reinforced and un-reinforced materials was similar for all plastic strain amplitudes tested except that the saturation stress level for the composite was always greater than that of the unreinforced material. The cyclic response of the naturally aged materials exhibited cyclic hardening and, in some cases, cyclic softening, while the cyclic response for the artificially aged materials showed no evidence of either cyclic hardening or softening. The higher ductility of the unreinforced material made it more resistant to fatigue failure at high strains, and thus, at a given plastic strain, it had longer fatigue life. It should be noted that the tensile ductilities of the 2219/TiC/15p were significantly higher than those previously reported for 2XXX-series composites. During stress-controlled test-ing at stresses below 220 MPa, the presence of TiC particles lead to an improvement in fatigue life. Above 220 MPa, no influence of TiC reinforcement on fatigue life could be detected. In both the composite and unreinforced materials, the low-cycle and high-cycle fatigue lives were found to be virtually independent of matrix microstructure.

Thermoelastic Stress Analysis: An NDE Tool for the Residual Stress Assessment of Metallic Alloys

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.; Baaklini, George Y.

2000-01-01

During manufacturing, certain propulsion components that will be used in a cyclic fatigue environment are fabricated to contain compressive residual stresses on their surfaces because these stresses inhibit the nucleation of cracks. Overloads and elevated temperature excursions cause the induced residual stresses to dissipate while the component is still in service, lowering its resistance to crack initiation. Research at the NASA Glenn Research Center at Lewis Field has focused on employing the Thermoelastic Stress Analysis technique (TSA, also recognized as SPATE: Stress Pattern Analysis by Thermal Emission) as a tool for monitoring the residual stress state of propulsion components. TSA is based on the fact that materials experience small temperature changes when they are compressed or expanded. When a structure is cyclically loaded (i.e., cyclically compressed and expanded), the resulting surface-temperature profile correlates to the stress state of the structure s surface. The surface-temperature variations resulting from a cyclic load are measured with an infrared camera. Traditionally, the temperature amplitude of a TSA signal has been theoretically defined to be linearly dependent on the cyclic stress amplitude. As a result, the temperature amplitude resulting from an applied cyclic stress was assumed to be independent of the cyclic mean stress.

Expansion and diversification of the MSDIN family of cyclic peptide genes in the poisonous agarics Amanita phalloides and A. bisporigera

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

Pulman, Jane A.; Childs, Kevin L.; Sgambelluri, R. Michael

Here, the cyclic peptide toxins of Amanita mushrooms, such as α-amanitin and phalloidin, are encoded by the “MSDIN” gene family and ribosomally biosynthesized. Based on partial genome sequence and PCR analysis, some members of the MSDIN family were previously identified in Amanita bisporigera, and several other members are known from other species of Amanita. However, the complete complement in any one species, and hence the genetic capacity for these fungi to make cyclic peptides, remains unknown. As a result, draft genome sequences of two cyclic peptide-producing mushrooms, the “Death Cap” A. phalloides and the “Destroying Angel” A. bisporigera, were obtained.more » Each species has ~30 MSDIN genes, most of which are predicted to encode unknown cyclic peptides. Some MSDIN genes were duplicated in one or the other species, but only three were common to both species. A gene encoding cycloamanide B, a previously described nontoxic cyclic heptapeptide, was also present in A. phalloides, but genes for antamanide and cycloamanides A, C, and D were not. In A. bisporigera, RNA expression was observed for 20 of the MSDIN family members. Based on their predicted sequences, novel cyclic peptides were searched for by LC/MS/MS in extracts of A. phalloides. The presence of two cyclic peptides, named cycloamanides E and F with structures cyclo(SFFFPVP) and cyclo(IVGILGLP), was thereby demonstrated. Of the MSDIN genes reported earlier from another specimen of A. bisporigera, 9 of 14 were not found in the current genome assembly. Differences between previous and current results for the complement of MSDIN genes and cyclic peptides in the two fungi probably represents natural variation among geographically dispersed isolates of A. phalloides and among the members of the poorly defined A. bisporigera species complex. Both A. phalloides and A. bisporigera contain two prolyl oligopeptidase genes, one of which (POPB) is probably dedicated to cyclic peptide biosynthesis as it is in Galerina marginata. Finally, the MSDIN gene family has expanded and diverged rapidly in Amanita section Phalloideae. Together, A. bisporigera and A. phalloides are predicted to have the capacity to make more than 50 cyclic hexa-, hepta-,octa-, nona- and decapeptides.« less

Proline-Based Cyclic Dipeptides from Korean Fermented Vegetable Kimchi and from Leuconostoc mesenteroides LBP-K06 Have Activities against Multidrug-Resistant Bacteria.

PubMed

Liu, Rui; Kim, Andrew H; Kwak, Min-Kyu; Kang, Sa-Ouk

2017-01-01

Lactobacillus plantarum and Leuconostoc mesenteroides play a prominent role as functional starters and predominant isolates in the production of various types of antimicrobial compound-containing fermented foods, especially including kimchi. In the case of the bioactive cyclic dipeptides, their racemic diastereomers inhibitory to bacteria and fungi have been suggested to come solely from Lactobacillus spp. of these strains. We previously demonstrated the antifungal and antiviral activities of proline-based cyclic dipeptides, which were fractionated from culture filtrates of Lb. plantarum LBP-K10 originated from kimchi. However, cyclic dipeptides have not been identified in the filtrates, either from cultures or fermented subject matter, driven by Ln. mesenteroides , which have been widely used as starter cultures for kimchi fermentation. Most importantly, the experimental verification of cyclic dipeptide-content changes during kimchi fermentation have also not been elucidated. Herein, the antibacterial fractions, including cyclo(Leu-Pro) and cyclo(Phe-Pro), from Ln. mesenteroides LBP-K06 culture filtrates, which exhibited a typical chromatographic retention behavior (t R ), were identified by using semi-preparative high-performance liquid chromatography and gas chromatography-mass spectrometry. Based on this finding, the proline-based cyclic dipeptides, including cyclo(Ser-Pro), cyclo(Tyr-Pro), and cyclo(Leu-Pro), were additionally identified in the filtrates only when fermenting Chinese cabbage produced with Ln. mesenteroides LBP-K06 starter cultures. The detection and isolation of cyclic dipeptides solely in controlled fermented cabbage were conducted under the control of fermentation-process parameters concomitantly with strong CDP selectivity by using a two-consecutive-purification strategy. Interestingly, cyclic dipeptides in the filtrates, when using this strain as a starter, increased with fermentation time. However, no cyclic dipeptides were observed in the filtrates of other fermented products, including other types of kimchi and fermented materials of plant and animal origin. This is the first report to conclusively demonstrate evidence for the existence of antimicrobial cyclic dipeptides produced by Ln. mesenteroides in kimchi. Through filtrates from lactic acid bacterial cultures and from fermented foods, we have also proved a method of combining chromatographic fractionation and mass spectrometry-based analysis for screening cyclic dipeptide profiling, which may allow evaluation of the fermented dairy foods from a new perspective.

Expansion and diversification of the MSDIN family of cyclic peptide genes in the poisonous agarics Amanita phalloides and A. bisporigera

DOE PAGES

Pulman, Jane A.; Childs, Kevin L.; Sgambelluri, R. Michael; ...

2016-12-15

Here, the cyclic peptide toxins of Amanita mushrooms, such as α-amanitin and phalloidin, are encoded by the “MSDIN” gene family and ribosomally biosynthesized. Based on partial genome sequence and PCR analysis, some members of the MSDIN family were previously identified in Amanita bisporigera, and several other members are known from other species of Amanita. However, the complete complement in any one species, and hence the genetic capacity for these fungi to make cyclic peptides, remains unknown. As a result, draft genome sequences of two cyclic peptide-producing mushrooms, the “Death Cap” A. phalloides and the “Destroying Angel” A. bisporigera, were obtained.more » Each species has ~30 MSDIN genes, most of which are predicted to encode unknown cyclic peptides. Some MSDIN genes were duplicated in one or the other species, but only three were common to both species. A gene encoding cycloamanide B, a previously described nontoxic cyclic heptapeptide, was also present in A. phalloides, but genes for antamanide and cycloamanides A, C, and D were not. In A. bisporigera, RNA expression was observed for 20 of the MSDIN family members. Based on their predicted sequences, novel cyclic peptides were searched for by LC/MS/MS in extracts of A. phalloides. The presence of two cyclic peptides, named cycloamanides E and F with structures cyclo(SFFFPVP) and cyclo(IVGILGLP), was thereby demonstrated. Of the MSDIN genes reported earlier from another specimen of A. bisporigera, 9 of 14 were not found in the current genome assembly. Differences between previous and current results for the complement of MSDIN genes and cyclic peptides in the two fungi probably represents natural variation among geographically dispersed isolates of A. phalloides and among the members of the poorly defined A. bisporigera species complex. Both A. phalloides and A. bisporigera contain two prolyl oligopeptidase genes, one of which (POPB) is probably dedicated to cyclic peptide biosynthesis as it is in Galerina marginata. Finally, the MSDIN gene family has expanded and diverged rapidly in Amanita section Phalloideae. Together, A. bisporigera and A. phalloides are predicted to have the capacity to make more than 50 cyclic hexa-, hepta-,octa-, nona- and decapeptides.« less

Ground-based observation of the cyclic nature and temporal variability of planetary-scale UV features at the Venus cloud top level

NASA Astrophysics Data System (ADS)

Imai, Masataka; Takahashi, Yukihiro; Watanabe, Makoto; Kouyama, Toru; Watanabe, Shigeto; Gouda, Shuhei; Gouda, Yuya

2016-11-01

A planetary-scale bright and dark UV feature, known as the ;Y-feature,; rotates around Venus with a period of 4-5 days and has been long-time interpreted as planetary waves. When assuming this, its rotation period and spatial structure might help to understand the propagation of the planetary-scale waves and find out their role in the acceleration-deceleration of the zonal wind speed, which is essential for understanding the super-rotation of the planet. The rotation period of the UV feature varied over the course of observation by the Pioneer Venus orbiter. However, in previous explorations of Venus such as Pioneer Venus and Venus Express, the spacecraft were operated in nearly fixed inertial space. As a result, the periodicity variations on sub-yearly timescales (one Venusian year is ∼224 Earth days) were obscured by the limitations of continuous dayside observations. We newly conducted six periods of ground-based Venus imaging observations at 365 nm from mid-August 2013 to the end of June 2014. Each observation period spanned over half or one month, enabling long-term monitoring of Venus' atmosphere above the equator region. Distributions of the relative brightness were obtained from the equatorial (EQ) to mid-latitudinal regions in both hemispheres, and from the cyclical variations of these distributions we deduced the rotation periods of the UV features of the cloud tops brightness. The relative brightness exhibited periods of 5.2 and 3.5 days above 90% of significance. The relative intensities of these two significant components also seemed subject to temporal variations. Although the 3.5-day component considered persists throughout the observation periods, its dominance over the longer period varied in a cyclic fashion. The prevailing first significant mode seems to change from 5.2-day waves to 3.5-day waves in about nine months, which is clearly inconsistent with the Venusian year. Clear periodic perturbations, indicating stability of the planetary-scale UV-feature, were observed only in the presence of single longer or shorter periodic waves. During the transition periods of dominant-wave changing, the amplitude of the relative brightness was largely changed. This can be explained by the deformation of the Y-shaped UV feature as observed by Pioneer Venus in 1979.

A tissue engineering approach to anterior cruciate ligament regeneration using novel shaped capillary channel polymer fibers

NASA Astrophysics Data System (ADS)

Sinclair, Kristofer D.

2009-12-01

Ruptures of the anterior cruciate ligament (ACL) are the most frequent of injuries to the knee due to its role in preventing anterior translation of the tibia. It is estimated that as many as 200,000 Americans per year will suffer from a ruptured ACL, resulting in management costs on the order of 5 billion dollars. Without treatment these patients are unable to return to normal activity, as a consequence of the joint instability found within the ACL deficient knee. Over the last thirty years, a variety of non-degradable, synthetic fibers have been evaluated for their use in ACL reconstruction; however, a widely accepted prosthesis has been unattainable due to differences in mechanical properties of the synthetic graft relative to the native tissue. Tissue engineering is an interdisciplinary field charged with the task of developing therapeutic solutions for tissue and organ failure by enhancing the natural wound healing process through the use of cellular transplants, biomaterials, and the delivery of bioactive molecules. The capillary channel polymer (CC-P) fibers used in this research were fabricated by melt extrusion from polyethylene terephthalate and polybutylene terephthalate. These fibers possess aligned micrometer scale surface channels that may serve as physical templates for tissue growth and regeneration. This inherent surface topography offers a unique and industrially viable approach for cellular contact guidance on three dimensional constructs. In this fundamental research the ability of these fiber channels to support the adhesion, alignment, and organization of fibroblasts was demonstrated and found to be superior to round fiber controls. The results demonstrated greater uniformity of seeding and accelerated formation of multi-layered three-dimensional biomass for the CC-P fibers relative to those with a circular cross-section. Furthermore, the CC-P geometry induced nuclear elongation consistent with that observed in native ACL tissue. Through the application of uniaxial cyclic strain the mechanical properties of the cell seeded CC-P fiber scaffold systems were shown to improve via the induction of increased cellular proliferation and extracellular matrix synthesis. Finally, unlike many studies examining the effects of cyclic strain on cellular behavior, the CC-P fiber geometry displayed the ability to maintain cellular alignment in the presence of an applied uniaxial cyclic strain.

Purine 3':5'-cyclic nucleotides with the nucleobase in a syn orientation: cAMP, cGMP and cIMP.

PubMed

Řlepokura, Katarzyna Anna

2016-06-01

Purine 3':5'-cyclic nucleotides are very well known for their role as the secondary messengers in hormone action and cellular signal transduction. Nonetheless, their solid-state conformational details still require investigation. Five crystals containing purine 3':5'-cyclic nucleotides have been obtained and structurally characterized, namely adenosine 3':5'-cyclic phosphate dihydrate, C10H12N5O6P·2H2O or cAMP·2H2O, (I), adenosine 3':5'-cyclic phosphate 0.3-hydrate, C10H12N5O6P·0.3H2O or cAMP·0.3H2O, (II), guanosine 3':5'-cyclic phosphate pentahydrate, C10H12N5O7P·5H2O or cGMP·5H2O, (III), sodium guanosine 3':5'-cyclic phosphate tetrahydrate, Na(+)·C10H11N5O7P(-)·4H2O or Na(cGMP)·4H2O, (IV), and sodium inosine 3':5'-cyclic phosphate tetrahydrate, Na(+)·C10H10N4O7P(-)·4H2O or Na(cIMP)·4H2O, (V). Most of the cyclic nucleotide zwitterions/anions [two from four cAMP present in total in (I) and (II), cGMP in (III), cGMP(-) in (IV) and cIMP(-) in (V)] are syn conformers about the N-glycosidic bond, and this nucleobase arrangement is accompanied by Crib-H...Npur hydrogen bonds (rib = ribose and pur = purine). The base orientation is tuned by the ribose pucker. An analysis of data obtained from the Cambridge Structural Database made in the context of syn-anti conformational preferences has revealed that among the syn conformers of various purine nucleotides, cyclic nucleotides and dinucleotides predominate significantly. The interactions stabilizing the syn conformation have been indicated. The inter-nucleotide contacts in (I)-(V) have been systematized in terms of the chemical groups involved. All five structures display three-dimensional hydrogen-bonded networks.

Inotropic responses of the frog ventricle to adenosine triphosphate and related changes in endogenous cyclic nucleotides.

PubMed

Flitney, F W; Singh, J

1980-07-01

1. A study has been made of a well documented but poorly understood response of the isolated frog ventricle to treatment with exogenous adenosine 5' triphosphate (ATP). Measurements of membrane potential, isometric twitch tension and levels of endogenous 3',5'-cyclic nucleotides have been made at various times during the ATP-induced response. 2. ATP elicits a characteristic triphasic response, which comprises an initial, abrupt increase in contractility, rising to a maximum within a few beats (first phase); followed by a period when the twitch amplitude falls, sometimes to below the control level (second phase); and superceded by a more slowly developing and longer-lasting increase in contractile force (third phase). The response is unaffected by atropine, propranolol or phentolamine. However, the prostaglandin synthetase inhibitor indomethacin depresses the first phase and entirely suppresses the third phase. 3. The inotropic effects of ATP are accompanied by changes in the shape of the action potential. These effects are dose-related. The duration of the action potential (D-30mV) and its positive overshoot (O) are increased during all phases of the response, for [ATP]o's up to 10(-5) M. However, at higher [ATP]o's, D-30mV and O ar both reduced during the second phase (but not the first or third phase), when isometric twitch tension is also depressed. The relationship between action potential duration and twitch tension (P) for different [ATP]o's is linear for all three phases of the response, but the slopes of the curves (delta P/delta D) are markedly different, indicating that the sensitivity of the contractile system to membrane depolarization is not constant, but varies continuously throughout the response. 4. ATP has a potent stimulatory effect on the metabolism of endogenous 3',5'-cyclic nucleotides. The time courses of the changes in adenosine 3','5-cyclic monophosphate (3',5'-cyclic AMP) and guanosine 3',5'-cyclic monophosphate (3',5'-cyclic GMP) are complex, but the accompanying change in isometric twitch tension is paralleled closely by corresponding changes in the ratio 3',5'cyclic AMP:3',5'-cyclic GMP. 5. It is concluded that ATP exerts a dual effect on the ventricle and that the contractile response is regulated by changes in the metabolism of 3',5'-cyclic nucleotides. The effects of indomethacin indicate a possible involvement of prostaglandins in mediating the ATP response. It is suggested that the initial effect of ATP on the ventricle is to increase the permeability of the fibres to Ca2+. 6. The relationship between 3',5' cyclic nucleotide levels and ventricular contractility is discussed. It is postulated that the antagonistic effects of 3',5'-cyclic AMP and 3',5'-cyclic GMP are expressed at the level of certain phosphoproteins which regulate both the availability of Ca2+ and the sensitivity of the contractile proteins to Ca2+.

High-Temperature Cyclic Oxidation Data, Volume 1

NASA Technical Reports Server (NTRS)

Barrett, C. A.; Garlick, R. G.; Lowell, C. E.

1984-01-01

This first in a series of cyclic oxidation handbooks contains specific-weight-change-versus-time data and X-ray diffraction results derived from high-temperature cyclic tests on high-temperature, high-strength nickel-base gamma/gamma' and cobalt-base turbine alloys. Each page of data summarizes a complete test on a given alloy sample.

A Practical Beginner's Guide to Cyclic Voltammetry

ERIC Educational Resources Information Center

Elgrishi, Noémie; Rountree, Kelley J.; McCarthy, Brian D.; Rountree, Eric S.; Eisenhart, Thomas T.; Dempsey, Jillian L.

2018-01-01

Despite the growing popularity of cyclic voltammetry, many students do not receive formalized training in this technique as part of their coursework. Confronted with self-instruction, students can be left wondering where to start. Here, a short introduction to cyclic voltammetry is provided to help the reader with data acquisition and…

Evaluating cyclic fatigue of sealants during outdoor testing

Treesearch

R. Sam Williams; Steven Lacher; Corey Halpin; Christopher White

2009-01-01

A computer-controlled test apparatus (CCTA) and other instrumentation for subjecting sealant specimens to cyclic fatigue during outdoor exposure was developed. The CCTA enables us to use weather-induced conditions to cyclic fatigue specimens and to conduct controlled tests in-situ during the outdoor exposure. Thermally induced dimensional changes of an aluminum bar...

Understanding the Earth Systems: Expressions of Dynamic and Cyclic Thinking among University Students

ERIC Educational Resources Information Center

Batzri, Or; Ben Zvi Assaraf, Orit; Cohen, Carmit; Orion, Nir

2015-01-01

In this two-part study, we examine undergraduate university students' expression of two important system thinking characteristics--dynamic thinking and cyclic thinking--focusing particularly on students of geology. The study was conducted using an Earth systems questionnaire designed to elicit and reflect either dynamic or cyclic thinking. The…

Cyclic Load Effects on Long Term Behavior of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Shah, A. R.; Chamis, C. C.

1996-01-01

A methodology to compute the fatigue life for different ratios, r, of applied stress to the laminate strength based on first ply failure criteria combined with thermal cyclic loads has been developed and demonstrated. Degradation effects resulting from long term environmental exposure and thermo-mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research Center has been used to account for the degradation of material properties caused by cyclic and aging loads. Effect of variation in the thermal cyclic load amplitude on a quasi-symmetric graphite/epoxy laminate has been studied with respect to the impending failure modes. The results show that, for the laminate under consideration, the fatigue life under combined mechanical and low thermal amplitude cyclic loads is higher than that due to mechanical loads only. However, as the thermal amplitude increases, the life also decreases. The failure mode changes from tensile under mechanical loads only to the compressive and shear at high mechanical and thermal loads. Also, implementation of the developed methodology in the design process has been discussed.

Effects of cyclic-nucleotide derivatives on the growth of human colonic carcinoma xenografts and on cell production in the rat colonic crypt epithelium.

PubMed Central

Tutton, P. J.; Barkla, D. H.

1981-01-01

Previous studies have shown that various amine hormones are able to influence the growth rate of human colorectal carcinomas propagated as xenografts in immune-deprived mice, and it is now well known that the effects of many amine and other hormones are mediated by cyclic nucleotides, acting as second messengers within cells. In the present study the influence of various derivatives of cyclic adenosine monophosphate and cyclic guanosine monophosphate on the growth of two different lines of colorectal cancer growing in immune-deprived mice, and on the cell production rate in the colonic crypt epithelium of the rat, was assessed. Growth of each tumour line, as well as crypt-cell production, was suppressed by treatment wit N6O2' dibutyryl and N6 monobutyryl derivatives of cyclic adenosine monophosphate. Dibutyryl cyclic guanosine monophosphate, on the other hand, was found to promote the growth of Tumour HXK4 and to promote crypt cell production, but to have no significant effect on Tumour HXM2. PMID:6268136

Effects of cyclic-nucleotide derivatives on the growth of human colonic carcinoma xenografts and on cell production in the rat colonic crypt epithelium.

PubMed

Tutton, P J; Barkla, D H

1981-08-01

Previous studies have shown that various amine hormones are able to influence the growth rate of human colorectal carcinomas propagated as xenografts in immune-deprived mice, and it is now well known that the effects of many amine and other hormones are mediated by cyclic nucleotides, acting as second messengers within cells. In the present study the influence of various derivatives of cyclic adenosine monophosphate and cyclic guanosine monophosphate on the growth of two different lines of colorectal cancer growing in immune-deprived mice, and on the cell production rate in the colonic crypt epithelium of the rat, was assessed. Growth of each tumour line, as well as crypt-cell production, was suppressed by treatment wit N6O2' dibutyryl and N6 monobutyryl derivatives of cyclic adenosine monophosphate. Dibutyryl cyclic guanosine monophosphate, on the other hand, was found to promote the growth of Tumour HXK4 and to promote crypt cell production, but to have no significant effect on Tumour HXM2.

Earl Sutherland (1915-1974) [corrected] and the discovery of cyclic AMP.

PubMed

Blumenthal, Stanley A

2012-01-01

In 1945, Earl Sutherland (1915-1974) [corrected] and associates began studies of the mechanism of hormone-induced glycogen breakdown in the liver. In 1956, their efforts culminated in the identification of cyclic AMP, an ancient molecule generated in many cell types in response to hormonal and other extracellular signals. Cyclic AMP, the original "second messenger," transmits such signals through pathways that regulate a diversity of cellular functions and capabilities: metabolic processes such as lipolysis and glycogenolysis; hormone secretion; the permeability of ion channels; gene expression; cell proliferation and survival. Indeed, it can be argued that the discovery of cyclic AMP initiated the study of intracellular signaling pathways, a major focus of contemporary biomedical inquiry. This review presents relevant details of Sutherland's career; summarizes key contributions of his mentors, Carl and Gerti Cori, to the knowledge of glycogen metabolism (contributions that were the foundation for his own research); describes the experiments that led to his identification, isolation, and characterization of cyclic AMP; assesses the significance of his work; and considers some aspects of the impact of cyclic nucleotide research on clinical medicine.

Cyclic Dinucleotides in Oral Bacteria and in Oral Biofilms.

PubMed

Gürsoy, Ulvi K; Gürsoy, Mervi; Könönen, Eija; Sintim, Herman O

2017-01-01

Oral cavity acts as a reservoir of bacterial pathogens for systemic infections and several oral microorganisms have been linked to systemic diseases. Quorum sensing and cyclic dinucleotides, two "decision-making" signaling systems, communicate to regulate physiological process in bacteria. Discovery of cyclic dinucleotides has a long history, but the progress in our understanding of how cyclic dinucleotides regulate bacterial lifestyle is relatively new. Oral microorganisms form some of the most intricate biofilms, yet c-di-GMP, and c-di-AMP signaling have been rarely studied in oral biofilms. Recent studies demonstrated that, with the aid of bacterial messenger molecules and their analogs, it is possible to activate host innate and adaptive immune responses and epithelial integrity with a dose that is relevant to inhibit bacterial virulence mechanisms, such as fimbriae and exopolysaccharide production, biofilm formation, and host cell invasion. The aim of this perspective article is to present available information on cyclic dinucleotides in oral bacteria and in oral biofilms. Moreover, technologies that can be used to detect cyclic dinucleotides in oral biofilms are described. Finally, directions for future research are highlighted.

Evaluation of cyclic flexural fatigue of M-wire nickel-titanium rotary instruments.

PubMed

Al-Hadlaq, Solaiman M S; Aljarbou, Fahad A; AlThumairy, Riyadh I

2010-02-01

This study was conducted to investigate cyclic flexural fatigue resistance of GT series X rotary files made from the newly developed M-wire nickel-titanium alloy compared with GT and Profile nickel-titanium files made from a conventional nickel-titanium alloy. Fifteen files, size 30/0.04, of each type were used to evaluate the cyclic flexural fatigue resistance. A simple device was specifically constructed to measure the time each file type required to fail under cyclic flexural fatigue testing. The results of this experiment indicated that the GT series X files had superior cyclic flexural fatigue resistance than the other 2 file types made from a conventional nickel-titanium alloy (P = .004). On the other hand, the difference between the Profile and the GT files was not statistically significant. The findings of this study suggest that size 30/0.04 nickel-titanium rotary files made from the newly developed M-wire alloy have better cyclic flexural fatigue resistance than files of similar design and size made from the conventional nickel-titanium alloy. Copyright 2010 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Estimation of Cyclic Shift with Delayed Correlation and Matched Filtering in Time Domain Cyclic-SLM for PAPR Reduction

PubMed Central

2016-01-01

Time domain cyclic-selective mapping (TDC-SLM) reduces the peak-to-average power ratio (PAPR) in OFDM systems while the amounts of cyclic shifts are required to recover the transmitted signal in a receiver. One of the critical issues of the SLM scheme is sending the side information (SI) which reduces the throughputs in wireless OFDM systems. The proposed scheme implements delayed correlation and matched filtering (DC-MF) to estimate the amounts of the cyclic shifts in the receiver. In the proposed scheme, the DC-MF is placed after the frequency domain equalization (FDE) to improve the accuracy of cyclic shift estimation. The accuracy rate of the propose scheme reaches 100% at E b/N 0 = 5 dB and the bit error rate (BER) improves by 0.2 dB as compared with the conventional TDC-SLM. The BER performance of the proposed scheme is also better than that of the conventional TDC-SLM even though a nonlinear high power amplifier is assumed. PMID:27752539

Mixed-mode cyclic debonding of adhesively bonded composite joints. M.S. Thesis

NASA Technical Reports Server (NTRS)

Rezaizadeh, M. A.; Mall, S.

1985-01-01

A combined experimental-analytical investigation to characterize the cyclic failure mechanism of a simple composite-to-composite bonded joint is conducted. The cracked lap shear (CLS) specimens of graphite/epoxy adherend bonded with EC-3445 adhesive are tested under combined mode 1 and 2 loading. In all specimens tested, fatigue failure occurs in the form of cyclic debonding. The cyclic debond growth rates are measured. The finite element analysis is employed to compute the mode 1, mode 2, and total strain energy release rates (i.e., GI, GII, and GT). A wide range of mixed-mode loading, i.e., GI/GII ranging from 0.03 to 0.38, is obtained. The total strain energy release rate, G sub T, appeared to be the driving parameter for cyclic debonding in the tested composite bonded system.

Study on stress-strain response of multi-phase TRIP steel under cyclic loading

NASA Astrophysics Data System (ADS)

Dan, W. J.; Hu, Z. G.; Zhang, W. G.; Li, S. H.; Lin, Z. Q.

2013-12-01

The stress-strain response of multi-phase TRIP590 sheet steel is studied in cyclic loading condition at room temperature based on a cyclic phase transformation model and a multi-phase mixed kinematic hardening model. The cyclic martensite transformation model is proposed based on the shear-band intersection, where the repeat number, strain amplitude and cyclic frequency are used to control the phase transformation process. The multi-phase mixed kinematic hardening model is developed based on the non-linear kinematic hardening rule of per-phase. The parameters of transformation model are identified with the relationship between the austenite volume fraction and the repeat number. The parameters in Kinematic hardening model are confirmed by the experimental hysteresis loops in different strain amplitude conditions. The responses of hysteresis loop and stress amplitude are evaluated by tension-compression data.

Effect of laser parameters on surface roughness of laser modified tool steel after thermal cyclic loading

NASA Astrophysics Data System (ADS)

Lau Sheng, Annie; Ismail, Izwan; Nur Aqida, Syarifah

2018-03-01

This study presents the effects of laser parameters on the surface roughness of laser modified tool steel after thermal cyclic loading. Pulse mode Nd:YAG laser was used to perform the laser surface modification process on AISI H13 tool steel samples. Samples were then treated with thermal cyclic loading experiments which involved alternate immersion in molten aluminium (800°C) and water (27°C) for 553 cycles. A full factorial design of experiment (DOE) was developed to perform the investigation. Factors for the DOE are the laser parameter namely overlap rate (η), pulse repetition frequency (f PRF) and peak power (Ppeak ) while the response is the surface roughness after thermal cyclic loading. Results indicate the surface roughness of the laser modified surface after thermal cyclic loading is significantly affected by laser parameter settings.

Experimental Investigation on Deformation Failure Characteristics of Crystalline Marble Under Triaxial Cyclic Loading

NASA Astrophysics Data System (ADS)

Yang, Sheng-Qi; Tian, Wen-Ling; Ranjith, P. G.

2017-11-01

The deformation failure characteristics of marble subjected to triaxial cyclic loading are significant when evaluating the stability and safety of deep excavation damage zones. To date, however, there have been notably few triaxial experimental studies on marble under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic tests was conducted to analyze the mechanical damage characteristics of a marble. The post-peak deformation of the marble changed gradually from strain softening to strain hardening as the confining pressure increased from 0 to 10 MPa. Under uniaxial compression, marble specimens showed brittle failure characteristics with a number axial splitting tensile cracks; in the range of σ 3 = 2.5-7.5 MPa, the marble specimens assumed single shear fracture characteristics with larger fracture angles of about 65°. However, at σ 3 = 10 MPa, the marble specimens showed no obvious shear fracture surfaces. The triaxial cyclic experimental results indicate that in the range of the tested confining pressures, the triaxial strengths of the marble specimens under cyclic loading were approximately equal to those under monotonic loading. With the increase in cycle number, the elastic strains of the marble specimens all increased at first and later decreased, achieving maximum values, but the plastic strains of the marble specimens increased nonlinearly. To evaluate quantitatively the damage extent of the marble under triaxial cyclic loading, a damage variable is defined according to the irreversible deformation for each cycle. The evolutions of the elastic modulus for the marble were characterized by four stages: material strengthening, material degradation, material failure and structure slippage. Based on the experimental results of the marble specimens under complex cyclic loading, the cohesion of the marble decreased linearly, but the internal friction angles did not depend on the damage extent. To describe the peak strength characteristics of the marble specimens under complex cyclic loadings with various deformation positions, a revised strength criterion for damaged rocks is offered.

Cyclic creep and fatigue of TD-NiCr (thoria-dispersion-strengthened nickel-chromium), TD-Ni, and NiCr sheet at 1200 C

NASA Technical Reports Server (NTRS)

Hirschberg, M. H.; Spera, D. A.; Klima, S. J.

1972-01-01

The resistance of thin TD-NiCr sheet to cyclic deformation was compared with that of TD-Ni and a conventional nickel-chromium alloy. Strains were determined by a calibration technique which combines room-temperature strain gage and deflection measurements with high-temperature deflection measurements. Analyses of the cyclic tests using measured tensile and creep-rupture data indicated that the TD-NiCr and NiCr alloy specimens failed by a cyclic creep mechanism. The TD-Ni specimens, on the other hand, failed by a fatigue mechanism.

Cyclic etching of tin-doped indium oxide using hydrogen-induced modified layer

NASA Astrophysics Data System (ADS)

Hirata, Akiko; Fukasawa, Masanaga; Nagahata, Kazunori; Li, Hu; Karahashi, Kazuhiro; Hamaguchi, Satoshi; Tatsumi, Tetsuya

2018-06-01

The rate of etching of tin-doped indium oxide (ITO) and the effects of a hydrogen-induced modified layer on cyclic, multistep thin-layer etching were investigated. It was found that ITO cyclic etching is possible by precisely controlling the hydrogen-induced modified layer. Highly selective etching of ITO/SiO2 was also investigated, and it was suggested that cyclic etching by selective surface adsorption of Si can precisely control the etch rates of ITO and SiO2, resulting in an almost infinite selectivity for ITO over SiO2 and in improved profile controllability.

Autonomous momentum management for space station, exhibit A

NASA Technical Reports Server (NTRS)

Hahn, E.

1984-01-01

The report discusses momentum management for the CDG Planar Space Platform. The external torques on the Space Station are assumed to be gravity gradient and aerodynamic with both having bias and cyclic terms. The integrals of the cyclic torques are the cyclic momenti which will be stored in the momentum storage actuator. Various techniques to counteract the bias torques and center the cyclic momentum were investigated including gravity gradient desaturation by adjusting vehicle attitude, aerodynamic desaturation using solar panels and radiators and the deployment of flat plates at the end of long booms generating aerodynamic torques.

Stereoselective synthesis of functionalized cyclic amino acid derivatives via a [2,3]-Stevens rearrangement and ring-closing metathesis.

PubMed

Nash, Aaron; Soheili, Arash; Tambar, Uttam K

2013-09-20

Unnatural cyclic amino acids are valuable tools in biomedical research and drug discovery. A two-step stereoselective strategy for converting simple glycine-derived aminoesters into unnatural cyclic amino acid derivatives has been developed. The process includes a palladium-catalyzed tandem allylic amination/[2,3]-Stevens rearrangement followed by a ruthenium-catalyzed ring-closing metathesis. The [2,3]-rearrangement proceeds with high diastereoselectivity through an exo transition state. Oppolzer's chiral auxiliary was utilized to access an enantiopure cyclic amino acid by this approach, which will enable future biological applications.

Damage evolution analysis of coal samples under cyclic loading based on single-link cluster method

NASA Astrophysics Data System (ADS)

Zhang, Zhibo; Wang, Enyuan; Li, Nan; Li, Xuelong; Wang, Xiaoran; Li, Zhonghui

2018-05-01

In this paper, the acoustic emission (AE) response of coal samples under cyclic loading is measured. The results show that there is good positive relation between AE parameters and stress. The AE signal of coal samples under cyclic loading exhibits an obvious Kaiser Effect. The single-link cluster (SLC) method is applied to analyze the spatial evolution characteristics of AE events and the damage evolution process of coal samples. It is found that a subset scale of the SLC structure becomes smaller and smaller when the number of cyclic loading increases, and there is a negative linear relationship between the subset scale and the degree of damage. The spatial correlation length ξ of an SLC structure is calculated. The results show that ξ fluctuates around a certain value from the second cyclic loading process to the fifth cyclic loading process, but spatial correlation length ξ clearly increases in the sixth loading process. Based on the criterion of microcrack density, the coal sample failure process is the transformation from small-scale damage to large-scale damage, which is the reason for changes in the spatial correlation length. Through a systematic analysis, the SLC method is an effective method to research the damage evolution process of coal samples under cyclic loading, and will provide important reference values for studying coal bursts.

Ventricular fractional shortening in 108 dogs with malignant lymphoma undergoing chemotherapy with a cyclic combination protocol including doxorubicin.

PubMed

Tater, G; Eberle, N; Hungerbuehler, S; Joetzke, A; Nolte, I; Wess, G; Betz, D

2012-01-01

The aim of this study was to evaluate whether changes in the left ventricular fractional shortening (LVFS) can be detected in dogs with malignant lymphoma undergoing a cyclic combination chemotherapy protocol including doxorubicin. Left ventricular fractional shortening as a stand-alone measurement will not show a significant change during the cyclic combination protocol. In this retrospective study, the records of dogs with malignant lymphoma treated between April 2001 and October 2010 were reviewed. Inclusion criteria comprised: a diagnosis of malignant lymphoma, a cyclic combination chemotherapy (including L-asparaginase, vincristine, cyclophosphamide, doxorubicin and prednisolone), and an echocardiographic examination by an experienced examiner before treatment and after each doxorubicin administration. One hundred and eight dogs were included and a total of 446 LVFS measurements had been performed. Patients were divided into four groups according to the number of doxorubicin administrations. Median LVFS did not change significantly during the cyclic combination protocol in all groups. All median LVFS values remained above the lower reference value of 25%. The measurement of LVFS did not show a significant change during the cyclic combination protocol treatment including doxorubicin in this population of dogs. Therefore either this cyclic combination protocol does not cause a systolic dysfunction or LVFS is not sensitive enough to detect early changes. Newer methods that are more sensitive then LVFS might be necessary to detect such changes.

Cyclic Fatigue Resistance of Novel Rotary Files Manufactured from Different Thermal Treated Nickel-Titanium Wires in Artificial Canals.

PubMed

Karataşlıoglu, E; Aydın, U; Yıldırım, C

2018-02-01

The aim of this in vitro study was to compare the static cyclic fatigue resistance of thermal treated rotary files with a conventional nickel-titanium (NiTi) rotary file. Four groups of 60 rotary files with similar file dimensions, geometries, and motion were selected. Groups were set as HyFlex Group [controlled memory wire (CM-Wire)], ProfileVortex Group (M-Wire), Twisted File Group (R-Phase Wire), and OneShape Group (conventional NiTi wire)] and tested using a custom-made static cyclic fatigue testing apparatus. The fracture time and fragment length of the each file was also recorded. Statistical analysis was performed using one-way analysis of variance and Tukey's test at the 95% confidence level (P = 0.05). The HyFlex group had a significantly higher mean cyclic fatigue resistance than the other three groups (P < 0.001). The OneShape groups had the least fatigue resistance. CM-Wire alloy represented the best performance in cyclic fatigue resistance, and NiTi alloy in R-Phase had the second highest fatigue resistance. CM and R-Phase manufacturing technology processed to the conventional NiTi alloy enhance the cyclic fatigue resistance of files that have similar design and size. M-wire alloy did not show any superiority in cyclic fatigue resistance when compared with conventional NiTi wire.

Probabilistic Simulation for Combined Cycle Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2010-01-01

A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multifactor interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Exploring Language Teachers' Perceptions of Cyclical Presentation of Materials in an EFL Context: A Grounded Theory

ERIC Educational Resources Information Center

Ostovar-Namaghi, Seyyed Ali; Gholami, Maryam

2018-01-01

Numerous studies have verified the effect of cyclical presentation of materials on learners' language proficiency and achievement. However, there is a dearth of research exploring language teachers' perceptions of cyclical approach. Since teachers' perceptions may catalyze or nullify the effect of this approach, this study aims at exploring…

Cyclical Grieving: Reocurring Emotions Experienced by Parents Who Have Children with Disabilities.

ERIC Educational Resources Information Center

Blaska, Joan K.

This paper discusses cyclical grieving, which is described as an intermittent reoccurrence of one or more emotions that are part of the grieving process experienced by parents who have children with disabilities. A study to support the concept of cyclical grieving used a naturalistic approach with face-to-face interviews to explore ten parents'…

Evaluation of materials during outdoor testing using a computer-controlled test apparatus

Treesearch

R. Sam Williams; Steven Lacher; Corey Halpin; Christopher White

2006-01-01

Ultraviolet radiation, moisture, heat, and cyclic fatigue are some of the stressors that cause materials to degrade outdoors. Considerable research has addressed the effects of ultraviolet radiation and moisture on the rate of this degradation. An often overlooked stressor on materials, during outdoor testing, is the cyclic fatigue. Cyclic fatigue is caused by self-...

Flexural creep of structural flakeboards under cyclic humidity

Treesearch

M.C. Yeh; R.C. Tang; Chung-Yun Hse

1990-01-01

Flexural creep behavior of randomly oriented structural flakeboards under cyclic humidity is presented. Specimens fabricated with 5 and 7 percent phenol-formaldehyde resin were subjected to constant concentrated load in bending under slow and fast cyclic relative humidity (RH) between 65 and 95 percent for 100 days. The temperature was set at a constant 75°F through...

Catalytic carbene transfer allows the direct customization of cyclic purine dinucleotides.

PubMed

Fei, Na; Häussinger, Daniel; Blümli, Seraina; Laventie, Benoît-Joseph; Bizzini, Lorenzo D; Zimmermann, Kaspar; Jenal, Urs; Gillingham, Dennis

2014-08-11

We describe a simple method for the direct modification of nucleobases in cyclic purine dinucleotides, important signalling molecules in both prokaryotes and eukaryotes. The method tolerates all members of the cyclic dinucleotide family and could be used to modulate their function or introduce useful side-chains such as fluorophores and photo-crosslinking groups.

Analysis of Glenoid Fixation with Anatomic Total Shoulder Arthroplasty in an Extreme Cyclic Loading Scenario.

PubMed

Roche, Christopher P; Staunch, Cameron; Hahn, William; Grey, Sean G; Flurin, Pierre-Henri; Wright, Thomas W; Zuckerman, Joseph D

2015-12-01

ASTM F2028-14 was adopted to recom mend a cyclic eccentric glenoid edge loading test that simulates the rocking horse loading mechanism beleived to cause aTSA glenoid loosening. While this method accurately simulates that failure mechanism, the recommended 750 N load may not be sufficient to simulate worst-case loading magnitudes, and the recommended 100,000 cycles may not be sufficient to simulate device fatigue-related failure modes. Finally, if greater loading magnitude or a larger number of cycles is performed, the recommended substrate density may not be sufficiently strong to support the elevated loads and cycles. To this end, a new test method is proposed to supplement ASTM F2028-14. A series of cyclic tests were performed to evaluate the long-term fixation strength of two different hybrid glenoid designs in both low (15 pcf) and high (30 pcf) density polyurethane blocks at elevated loads relative to ASTM F2028-14. To simulate a worst case clinical condition in which the humeral head is superiorly migrated, a cyclic load was applied to the superior glenoid rim to induce a maximum torque on the fixation pegs for three different cyclic loading tests: 1. 1,250 N load for 0.75 M cycles in a 15 pcf block, 2. 1,250 N load for 1.5 M cycles in a 30 pcf block, and 3. 2,000 N load for 0.65 M cycles in a 30 pcf block. All devices completed cyclic loading without failure, fracture, or loss of fixation regardless of glenoid design, polyurethane density, loading magnitude, or cycle length. No significant difference in post-cyclic displacement was noted between designs in any of the three tests. Post-cyclic radiographs demonstrated that each device maintained fixa - tion with the metal pegs within the bone-substitute blocks with no fatigue related failures. These results demonstrate that both cemented hybrid glenoids maintained fixation when tested according to each cyclic loading scenario, with no difference in post-cyclic displacement observed between designs. The lack of fatigue-related failures in these elevated load and high cycle test scenarios are promising, as are the relatively low displacements given the extreme nature of each test. This cyclic loading method is intended to supplement the ASTM F2028-14 standard that adequately simulates the rocking horse loading mechanism but may not adequately simulate the fatigue-related failure modes.

Characterization of the 2′,3′ cyclic phosphodiesterase activities of Clostridium thermocellum polynucleotide kinase-phosphatase and bacteriophage λ phosphatase

PubMed Central

Keppetipola, Niroshika; Shuman, Stewart

2007-01-01

Clostridium thermocellum polynucleotide kinase-phosphatase (CthPnkp) catalyzes 5′ and 3′ end-healing reactions that prepare broken RNA termini for sealing by RNA ligase. The central phosphatase domain of CthPnkp belongs to the dinuclear metallophosphoesterase superfamily exemplified by bacteriophage λ phosphatase (λ-Pase). CthPnkp is a Ni2+/Mn2+-dependent phosphodiesterase-monoesterase, active on nucleotide and non-nucleotide substrates, that can be transformed toward narrower metal and substrate specificities via mutations of the active site. Here we characterize the Mn2+-dependent 2′,3′ cyclic nucleotide phosphodiesterase activity of CthPnkp, the reaction most relevant to RNA repair pathways. We find that CthPnkp prefers a 2′,3′ cyclic phosphate to a 3′,5′ cyclic phosphate. A single H189D mutation imposes strict specificity for a 2′,3′ cyclic phosphate, which is cleaved to form a single 2′-NMP product. Analysis of the cyclic phosphodiesterase activities of mutated CthPnkp enzymes illuminates the active site and the structural features that affect substrate affinity and kcat. We also characterize a previously unrecognized phosphodiesterase activity of λ-Pase, which catalyzes hydrolysis of bis-p-nitrophenyl phosphate. λ-Pase also has cyclic phosphodiesterase activity with nucleoside 2′,3′ cyclic phosphates, which it hydrolyzes to yield a mixture of 2′-NMP and 3′-NMP products. We discuss our results in light of available structural and functional data for other phosphodiesterase members of the binuclear metallophosphoesterase family and draw inferences about how differences in active site composition influence catalytic repertoire. PMID:17986465

Cyclic strain is a weak inducer of prostacyclin synthase expression in bovine aortic endothelial cells

NASA Technical Reports Server (NTRS)

Segurola, R. J. Jr; Oluwole, B.; Mills, I.; Yokoyama, C.; Tanabe, T.; Kito, H.; Nakajima, N.; Sumpio, B. E.

1997-01-01

Recent studies indicate that hemodynamic forces such as cyclic strain and shear stress can increase prostacyclin (PGI2) secretion by endothelial cells (EC) but the effect of these forces on prostacyclin synthase (PGIS) gene expression remains unclear and is the focus of this study. Bovine aortic EC were seeded onto type I collagen coated flexible membranes and grown to confluence. The membranes and attached EC were subjected to 10% average strain at 60 cpm (0.5 sec deformation alternating with 0.5 sec relaxation) for up to 5 days. PGIS gene expression was determined by Northern blot analysis and protein level by Western blot analysis. The effect of cyclic strain on the PGIS promoter was determined by the transfection of a 1-kb human PGIS gene promoter construct coupled to a luciferase reporter gene into EC, followed by determination of luciferase activity. PGIS gene expression increased 1.7-fold in EC subjected to cyclic strain for 24 hr. Likewise, EC transfected with a pGL3B-PGIS (-1070/-10) construct showed an approximate 1.3-fold elevation in luciferase activity in EC subjected to cyclic strain for 3, 4, 8, and 12 hr. The weak stimulation of PGIS gene expression by cyclic strain was reflected in an inability to detect alterations in PGIS protein levels in EC subjected to cyclic strain for as long as 5 days. These data suggest that strain-induced stimulation of PGIS gene expression plays only a minor role in the ability of cyclic strain to stimulate PGI2 release in EC. These findings coupled with our earlier demonstration of a requisite addition of exogenous arachidonate in order to observe strain-induced PGI2 release, implicates a mechanism that more likely involves strain-induced stimulation of PGIS activity.

Measuring Cyclic Error in Laser Heterodyne Interferometers

NASA Technical Reports Server (NTRS)

Ryan, Daniel; Abramovici, Alexander; Zhao, Feng; Dekens, Frank; An, Xin; Azizi, Alireza; Chapsky, Jacob; Halverson, Peter

2010-01-01

An improved method and apparatus have been devised for measuring cyclic errors in the readouts of laser heterodyne interferometers that are configured and operated as displacement gauges. The cyclic errors arise as a consequence of mixing of spurious optical and electrical signals in beam launchers that are subsystems of such interferometers. The conventional approach to measurement of cyclic error involves phase measurements and yields values precise to within about 10 pm over air optical paths at laser wavelengths in the visible and near infrared. The present approach, which involves amplitude measurements instead of phase measurements, yields values precise to about .0.1 microns . about 100 times the precision of the conventional approach. In a displacement gauge of the type of interest here, the laser heterodyne interferometer is used to measure any change in distance along an optical axis between two corner-cube retroreflectors. One of the corner-cube retroreflectors is mounted on a piezoelectric transducer (see figure), which is used to introduce a low-frequency periodic displacement that can be measured by the gauges. The transducer is excited at a frequency of 9 Hz by a triangular waveform to generate a 9-Hz triangular-wave displacement having an amplitude of 25 microns. The displacement gives rise to both amplitude and phase modulation of the heterodyne signals in the gauges. The modulation includes cyclic error components, and the magnitude of the cyclic-error component of the phase modulation is what one needs to measure in order to determine the magnitude of the cyclic displacement error. The precision attainable in the conventional (phase measurement) approach to measuring cyclic error is limited because the phase measurements are af-

Macromolecular 'size' and 'hardness' drives structure in solvent-swollen blends of linear, cyclic, and star polymers.

PubMed

Gartner, Thomas E; Jayaraman, Arthi

2018-01-17

In this paper, we apply molecular simulation and liquid state theory to uncover the structure and thermodynamics of homopolymer blends of the same chemistry and varying chain architecture in the presence of explicit solvent species. We use hybrid Monte Carlo (MC)/molecular dynamics (MD) simulations in the Gibbs ensemble to study the swelling of ∼12 000 g mol -1 linear, cyclic, and 4-arm star polystyrene chains in toluene. Our simulations show that the macroscopic swelling response is indistinguishable between the various architectures and matches published experimental data for the solvent annealing of linear polystyrene by toluene vapor. We then use standard MD simulations in the NPT ensemble along with polymer reference interaction site model (PRISM) theory to calculate effective polymer-solvent and polymer-polymer Flory-Huggins interaction parameters (χ eff ) in these systems. As seen in the macroscopic swelling results, there are no significant differences in the polymer-solvent and polymer-polymer χ eff between the various architectures. Despite similar macroscopic swelling and effective interaction parameters between various architectures, the pair correlation function between chain centers-of-mass indicates stronger correlations between cyclic or star chains in the linear-cyclic blends and linear-star blends, compared to linear chain-linear chain correlations. Furthermore, we note striking similarities in the chain-level correlations and the radius of gyration of cyclic and 4-arm star architectures of identical molecular weight. Our results indicate that the cyclic and star chains are 'smaller' and 'harder' than their linear counterparts, and through comparison with MD simulations of blends of soft spheres with varying hardness and size we suggest that these macromolecular characteristics are the source of the stronger cyclic-cyclic and star-star correlations.

Cyclization Phenomena in the Sol-Gel Polymerization of a,w-Bis(triethoxysilyl)alkanes and Incorporation of the Cyclic Structures into Network Silsesquioxane Polymers

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

Alam, T.M.; Carpenter, J.P.; Dorhout, P.K.

1999-01-04

Intramolecular cyclizations during acid-catalyzed, sol-gel polymerizations of ct,co- bis(tietioxysilyl)aWmes substintidly lengtien gelties formonomers witietiylene- (l), propylene- (2), and butylene-(3)-bridging groups. These cyclizations reactions were found, using mass spectrometry and %i NMR spectroscopy, to lead preferentially to monomeric and dimeric products based on six and seven membered disilsesquioxane rings. 1,2- Bis(triethoxysilyl)ethane (1) reacts under acidic conditions to give a bicyclic drier (5) that is composed of two annelated seven membered rings. Under the same conditions, 1,3- bis(triethoxysilyl)propane (2), 1,4-bis(triethoxysilyl)butane (3), and z-1,4- bis(triethoxysilyl)but-2-ene (10) undergo an intramolecular condensation reaction to give the six membemd and seven membered cyclic disilsesquioxanes 6, 7,more » and 11. Subsequently, these cyclic monomers slowly react to form the tricyclic dirners 8,9 and 12. With NaOH as polymerization catalyst these cyclic silsesquioxanes readily ~aeted to afford gels that were shown by CP MAS z%i NMR and infr=d spectroscopes to retain some cyclic structures. Comparison of the porosity and microstructwe of xerogels prepared from the cyclic monomers 6 and 7 with gels prepared directly from their acyclic precursors 2 and 3, indicate that the final pore structure of the xerogels is markedly dependent on the nature of the precursor. In addition, despite the fact that the monomeric cyclic disilsesquioxane species can not be isolated from 1-3 under basic conditions due to their rapid rate of gelation, spectroscopic techniques also detected the presence of the cyclic structures in the resulting polymeric gels.« less

Effects of drugs affecting endogenous amines or cyclic nucleotides on ethanol withdrawal head twitches in mice.

PubMed Central

Collier, H O; Hammond, M D; Schneider, C

1976-01-01

1 Twenty-four hours after ethanol withdrawal, dependent mice exhibited frequent head twitching. Naive mice exhibited similar twitching 15 min after treatment with 5-hydroxytryptophan (5-HTP) or 6 h after alpha-methyl-p-tyrosine (AMPT). Ethanol lessened the incidence of head twitches induced by any of these treatments. 5-HTP and AMPT each increased the incidence of head twitches induced by withdrawal of ethanol from dependent mice. 2 Drugs that affect the amount or activity of endogenous amines or cyclic nucleotides modified the incidence of head twitches. Nearly all drugs acted in the same direction on twitching elicited by any of these three treatments. 3 The incidence was lessened by: (a) methysergide, methergoline, MA 1420, p-chlorophenylalanine and p-chloroamphetamine; (b) dopamine, noradrenaline, L-DOPA, amphetamine and apomorphine; (c) hyoscine and nicotine; and (d) adenosine triphosphate, dibutyryl cyclic adenosine-3',5'-monophosphate (db cyclic AMP) and prostaglandins E1 and E2. 4 The incidence was increased by: (a) acetylcholine, carbachol and physostigmine; and (b) guanosine triphosphate, dibutyryl cyclic guanosine monophosphate (db cyclic GMP), theophylline and 3-isobutyl-1-methyl-xanthine. 5 These findings suggest that head twitching induced by these three treatments arises from a common biochemical mechanism, which may ultimately be a change in favour of cyclic GMP of the balance between this nucleotide and cyclic AMP within appropriate neurones. This imbalance appears to be elicited or increased by 5-hydroxytryptamine and acetylcholine and to be decreased by dopamine, noradrenaline and E prostaglandins. 6 Neither actinomycin D nor cycloheximide, given during the induction of ethanol dependence, altered the incidence of head twitches after ethanol withdrawal. PMID:987821

Phosphatidylinositol-specific phospholipase C from Bacillus cereus combines intrinsic phosphotransferase and cyclic phosphodiesterase activities: A sup 31 P NMR study

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

Shashidhar, M.S.; Kuppe, A.; Volwerk, J.J.

1990-09-04

The inositol phosphate products formed during the cleavage of phosphatidylinositol by phosphatidylinositol-specific phospholipase C from Bacillus cereus were analyzed by {sup 31}P NMR. {sup 31}P NMR spectroscopy can distinguish between the inositol phosphate species and phosphatidylinositol. Chemical shift values (with reference to phosphoric acid) observed are {minus}0.41, 3.62, 4.45, and 16.30 ppm for phosphatidylinositol, myo-inositol 1-monophosphate, myo-inositol 2-monophosphate, and myo-inositol 1,2-cyclic monophosphate, respectively. It is shown that under a variety of experimental conditions this phospholipase C cleaves phosphatidylinositol via an intramolecular phosphotransfer reaction producing diacylglycerol and D-myo-inositol 1,2-cyclic monophosphate. The authors also report the new and unexpected observation that themore » phosphatidylinositol-specific phospholipase C from B. cereus is able to hydrolyze the inositol cyclic phosphate to form D-myo-inositol 1-monophosphate. The enzyme, therefore, possesses phosphotransferase and cyclic phosphodiesterase activities. The second reaction requires thousandfold higher enzyme concentrations to be observed by {sup 31}P NMR. This reaction was shown to be regiospecific in that only the 1-phosphate was produced and stereospecific in that only D-myo-inositol 1,2-cyclic monophosphate was hydrolyzed. Inhibition with a monoclonal antibody specific for the B.cereus phospholipase C showed that the cyclic phosphodiesterase activity is intrinsic to the bacterial enzyme. They propose a two-step mechanism for the phosphatidyl-inositol-specific phospholipase C from B. cereus involving sequential phosphotransferase and cyclic phosphodiesterase activities. This mechanism bears a resemblance to the well-known two-step mechanism of pancreatic ribonuclease, RNase A.« less

Sources of Water to Wells for Transient Cyclic Systems

USGS Publications Warehouse

Reilly, T.E.; Pollock, D.W.

1996-01-01

Many state agencies are currently (1995) developing wellhead protection programs. The thrust of some of these programs is to protect water supplies by determining the areas contributing recharge to water-supply wells and by specifying regulations to minimize the opportunity for contamination of the recharge water by activities at the land surface. The area contributing recharge to a discharging well is the surface area at the water table through which the water flowing to the well entered the ground-water system. In the analyses of ground-water flow systems, steady-state average conditions are commonly used to simplify the problem and make a solution tractable. However, recharge is usually cyclic in nature, with seasonal cycles and longer term climatic cycles. The effect of these cyclic stresses on the area contributing recharge to wells is quantitatively analyzed for a hypothetical alluvial valley aquifer system that is representative of a large class of ground-water systems that are extensively developed for water supply. The analysis shows that, in many cases, these cyclic changes in the recharge rates do not significantly affect the location and size of the areas contributing recharge to wells. The ratio of the mean travel time to the length of the cyclic stress period appears to be an indicator of whether the transient effects of the cyclic stress must be explicitly represented in the analysis of contributing areas to wells. For the cases examined, if the ratio of the mean travel time to the period of the cyclic stress was much greater than one, then the transient area contributing recharge to wells was similar to the area calculated using an average steady-state condition. However, cyclic stresses on systems with ratios less than one do have an effect on the location and size of the areas contributing recharge to wells.

Systemic Administration of a Cyclic Signal Transducer and Activator of Transcription 3 (STAT3) Decoy Oligonucleotide Inhibits Tumor Growth without Inducing Toxicological Effects

PubMed Central

Sen, Malabika; Paul, Kathleen; Freilino, Maria L; Li, Hua; Li, Changyou; Johnson, Daniel E; Wang, Lin; Eiseman, Julie; Grandis, Jennifer R

2014-01-01

Hyperactivation of signal transducer and activator of transcription 3 (STAT3) has been linked to tumorigenesis in most malignancies, including head and neck squamous cell carcinoma. Intravenous delivery of a chemically modified cyclic STAT3 decoy oligonucleotide with improved serum and thermal stability demonstrated antitumor efficacy in conjunction with downmodulation of STAT3 target gene expression such as cyclin D1 and Bcl-XL in a mouse model of head and neck squamous cell carcinoma. The purpose of the present study was to determine the toxicity and dose-dependent antitumor efficacy of the cyclic STAT3 decoy after multiple intravenous doses in Foxn1 nu mice in anticipation of clinical translation. The two doses (5 and 10 mg/kg) of cyclic STAT3 decoy demonstrated a significant decrease in tumor volume compared with the control groups (mutant cyclic STAT3 decoy or saline) in conjunction with downmodulation of STAT3 target gene expression. There was no dose-dependent effect of cyclic STAT3 decoy on tumor volume or STAT3 target gene expression. There were no significant changes in body weights between the groups during the dosing period, after the dosing interval or on the day of euthanasia. No hematology or clinical chemistry parameters suggested toxicity of the cyclic STAT3 decoy compared with saline control. No gross or histological pathological abnormalities were noted at necropsy in any of the animals. These findings suggest a lack of toxicity of intravenous administration of a cyclic STAT3 decoy oligonucleotide. In addition, comparable antitumor effects indicate a lack of dose response at the two dose levels investigated. PMID:24395569

A Material Model for the Cyclic Behavior of Nitinol

NASA Astrophysics Data System (ADS)

Rebelo, Nuno; Zipse, Achim; Schlun, Martin; Dreher, Gael

2011-07-01

The uniaxial behavior of Nitinol in different forms and at different temperatures has been well documented in the literature. Mathematical models for the three-dimensional behavior of this class of materials, covering superelasticity, plasticity, and shape memory effects have been previously developed. Phenomenological models embedded in FEA analysis are part of common practice today in the development of devices made out of Nitinol. In vivo loading of medical devices has cyclic characteristics. There have been some indications in the literature that cyclic loading of Nitinol modifies substantially its behavior. A consortium of several stent manufacturers, Safe Technology and Dassault Systèmes Simulia Corp., dedicated to the development of fatigue laws suitable for life prediction of Nitinol devices, has conducted an extensive experimental study of the modifications in uniaxial behavior of both Nitinol wire and tubing due to cyclic loading. The Abaqus Nitinol material model has been extended to capture some of the phenomena observed and is described in this article. Namely, a preload beyond 6% strain alters the transformation plateaus; if the cyclic load amplitude is large enough, permanent deformations (residual martensite) are observed; the lower plateau increases; and the upper plateau changes. The modifications to the upper plateau are very interesting in the sense that it appears broken: its start stress gets lowered creating a new plateau up to the highest level of cyclic strain, followed by resuming the original plateau until full transformation. Since quite often the geometry of a device at the point at which it is subjected to cyclic loading is very much dependent on the manufacturing, deployment, and preloading sequence, it is important that analyses be conducted with the original material behavior up to that point, and then with the cyclic behavior thereafter.

Study of CO2 cyclic absorption stability of CaO-based sorbents derived from lime mud purified by sucrose method.

PubMed

Ma, AiHua; Jia, QingMing; Su, HongYing; Zhi, YunFei; Tian, Na; Wu, Jing; Shan, ShaoYun

2016-02-01

Using lime mud (LM) purified by sucrose method, derived from paper-making industry, as calcium precursor, and using mineral rejects-bauxite-tailings (BTs) from aluminum production as dopant, the CaO-based sorbents for high-temperature CO2 capture were prepared. Effects of BTs content, precalcining time, and temperature on CO2 cyclic absorption stability were illustrated. The cyclic carbonation behavior was investigated in a thermogravimetric analyzer (TGA). Phase composition and morphologies were analyzed by XRD and SEM. The results reflected that the as-synthesized CaO-based sorbent doped with 10 wt% BTs showed a superior CO2 cyclic absorption-desorption conversion during multiple cycles, with conversion being >38 % after 50 cycles. Occurrence of Ca12Al14O33 phase during precalcination was probably responsible for the excellent CO2 cyclic stability.

Comparison of cyclic fatigue resistance of original and counterfeit rotary instruments.

PubMed

Ertas, Huseyin; Capar, Ismail Davut; Arslan, Hakan; Akan, Ender

2014-05-31

In recent years, with the advances in counterfeiting methods, counterfeit products have reached the dental market. The purpose of this study was to compare the cyclic fatigue resistance of original and counterfeit rotary root canal instruments. The cyclic fatigue of original and counterfeit ProTaper F2 endodontic instruments was tested (n = 20) in 3 mm radius steel canals with a 60° angle of curvature. The number of cycles to fracture (NCF) was calculated, and the data were subjected to the Student's t-test (α = 0.05). The original instruments showed better cyclic fatigue resistance than the counterfeit ones (p < .001). The mean NCF was 483 ± 84 for the original files and 186 ± 86 for the counterfeit files. The cyclic fatigue resistance of the counterfeit instruments was very low. As a result, clinicians should be careful not to purchase counterfeit products.

Influence of surface treatment of yttria-stabilized tetragonal zirconia polycrystal with hot isostatic pressing on cyclic fatigue strength.

PubMed

Iijima, Toshihiko; Homma, Shinya; Sekine, Hideshi; Sasaki, Hodaka; Yajima, Yasutomo; Yoshinari, Masao

2013-01-01

Hot isostatic pressing processed yttria-stabilized tetragonal zirconia polycrystal (HIP Y-TZP) has the potential for application to implants due to its high mechanical performance. The aim of this study was to investigate the influence of surface treatment of HIP Y-TZP on cyclic fatigue strength. HIP Y-TZP specimens were subjected to different surface treatments. Biaxial flexural strength was determined by both static and cyclic fatigue testing. In the cyclic fatigue test, the load was applied at a frequency of 10 Hz for 10(6) cycles in distilled water at 37°C. The surface morphology, roughness, and crystal phase of the surfaces were also evaluated. The cyclic fatigue strength (888 MPa) of HIP Y-TZP with sandblasting and acid-etching was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the clinical potential of this material.

Experimental investigation of steel fiber-reinforced concrete beams under cyclic loading

NASA Astrophysics Data System (ADS)

Ranjbaran, Fariman; Rezayfar, Omid; Mirzababai, Rahmatollah

2018-03-01

An experimental study has been conducted to study the cyclic behavior of reinforced concrete beams in which steel fibers were added to the concrete mix. Seven similar geometrically specimens in full scale were studied under four- point bending test in the form of slow cyclic loading. One sample as a control specimen was made without steel fibers or 0% volume fraction (vf) and six other samples with 1, 2 and 4% vf of steel fibers in twin models. The maximum and ultimate resistance, ductility, degradation of loading and unloading stiffness, absorption and dissipation of energy and equivalent viscous damping were studied in this investigation and the effect of steel fibers on the cyclic behavior was compared with each other. Generally, the addition of steel fibers up to a certain limit value (vf = 2%) improves the cyclic behavior of reinforced concrete beams and results in the increase of maximum strength and ultimate displacement.

Endogenous and exogenous cyclicity and temperament in bipolar disorder: review, new data and hypotheses.

PubMed

Koukopoulos, Athanasios; Sani, Gabriele; Koukopoulos, Alexia E; Albert, Matthew J; Girardi, Paolo; Tatarelli, Roberto

2006-12-01

In this special issue dedicated to Falret and the French contributions to the concept of cyclicity in manic depressive illness, we begin with a historical overview of the development of the concept of cyclicity and its fundamental significance in manic-depressive illness and we underscore how the concept fell into neglect only to reemerge in recent years. We then look at the intimate relationship between mania and depression. The hypothesis of the primacy of mania is discussed. The thesis is presented, supported by the examination of 100 consecutive index manias, that in most cases mania is triggered by external factors acting upon hyperthymic patients, determining an exogenous cyclicity. On the other hand, in BPII patients the temperamental mood instability (cyclothymia) is an inherent and decisive factor in determining the cyclic autonomous course of the disorder. Finally, a new distinction of Bipolar Disorders, based on premorbid temperament and course of the illness, is considered.

Binding of the cyclic AMP receptor protein of Escherichia coli to RNA polymerase.

PubMed Central

Pinkney, M; Hoggett, J G

1988-01-01

Fluorescence polarization studies were used to study the interaction of a fluorescein-labelled conjugate of the Escherichia coli cyclic AMP receptor protein (F-CRP) and RNA polymerase. Under conditions of physiological ionic strength, F-CRP binds to RNA polymerase holoenzyme in a cyclic AMP-dependent manner; the dissociation constant was about 3 microM in the presence of cyclic AMP and about 100 microM in its absence. Binding to core RNA polymerase under the same conditions was weak (Kdiss. approx. 80-100 microM) and independent of cyclic AMP. Competition experiments established that native CRP and F-CRP compete for the same binding site on RNA polymerase holoenzyme and that the native protein binds about 3 times more strongly than does F-CRP. Analytical ultracentrifuge studies showed that CRP binds predominantly to the monomeric rather than the dimeric form of RNA polymerase. PMID:2839152

Binding of the cyclic AMP receptor protein of Escherichia coli to RNA polymerase.

PubMed

Pinkney, M; Hoggett, J G

1988-03-15

Fluorescence polarization studies were used to study the interaction of a fluorescein-labelled conjugate of the Escherichia coli cyclic AMP receptor protein (F-CRP) and RNA polymerase. Under conditions of physiological ionic strength, F-CRP binds to RNA polymerase holoenzyme in a cyclic AMP-dependent manner; the dissociation constant was about 3 microM in the presence of cyclic AMP and about 100 microM in its absence. Binding to core RNA polymerase under the same conditions was weak (Kdiss. approx. 80-100 microM) and independent of cyclic AMP. Competition experiments established that native CRP and F-CRP compete for the same binding site on RNA polymerase holoenzyme and that the native protein binds about 3 times more strongly than does F-CRP. Analytical ultracentrifuge studies showed that CRP binds predominantly to the monomeric rather than the dimeric form of RNA polymerase.

Regulation of Endothelial Barrier Function by Cyclic Nucleotides: The Role of Phosphodiesterases

PubMed Central

Surapisitchat, James

2014-01-01

The endothelium plays an important role in maintaining normal vascular function. Endothelial barrier dysfunction leading to increased permeability and vascular leakage is associated with several pathological conditions such as edema and sepsis. Thus, the development of drugs that improve endothelial barrier function is an active area of research. In this chapter, the current knowledge concerning the signaling pathways regulating endothelial barrier function is discussed with a focus on cyclic nucleotide second messengers (cAMP and cGMP) and cyclic nucleotide phosphodiesterases (PDEs). Both cAMP and cGMP have been shown to have differential effects on endothelial permeability in part due to the various effector molecules, crosstalk, and compartmentalization of cyclic nucleotide signaling. PDEs, by controlling the amplitude, duration, and localization of cyclic nucleotides, have been shown to play a critical role in regulating endothelial barrier function. Thus, PDEs are attractive drug targets for the treatment of disease states involving endothelial barrier dysfunction. PMID:21695641

Regulation of endothelial barrier function by cyclic nucleotides: the role of phosphodiesterases.

PubMed

Surapisitchat, James; Beavo, Joseph A

2011-01-01

The endothelium plays an important role in maintaining normal vascular function. Endothelial barrier dysfunction leading to increased permeability and vascular leakage is associated with several pathological conditions such as edema and sepsis. Thus, the development of drugs that improve endothelial barrier function is an active area of research. In this chapter, the current knowledge concerning the signaling pathways regulating endothelial barrier function is discussed with a focus on cyclic nucleotide second messengers (cAMP and cGMP) and cyclic nucleotide phosphodiesterases (PDEs). Both cAMP and cGMP have been shown to have differential effects on endothelial permeability in part due to the various effector molecules, crosstalk, and compartmentalization of cyclic nucleotide signaling. PDEs, by controlling the amplitude, duration, and localization of cyclic nucleotides, have been shown to play a critical role in regulating endothelial barrier function. Thus, PDEs are attractive drug targets for the treatment of disease states involving endothelial barrier dysfunction.

iCVD Cyclic Polysiloxane and Polysilazane as Nanoscale Thin-Film Electrolyte: Synthesis and Properties.

PubMed

Chen, Nan; Reeja-Jayan, B; Liu, Andong; Lau, Jonathan; Dunn, Bruce; Gleason, Karen K

2016-03-01

A group of crosslinked cyclic siloxane (Si-O) and silazane (Si-N) polymers are synthesized via solvent-free initiated chemical vapor deposition (iCVD). Notably, this is the first report of cyclic polysilazanes synthesized via the gas-phase iCVD method. The deposited nanoscale thin films are thermally stable and chemically inert. By iCVD, they can uniformly and conformally cover nonplanar surfaces having complex geometry. Although polysiloxanes are traditionally utilized as dielectric materials and insulators, our research shows these cyclic organosilicon polymers can conduct lithium ions (Li(+) ) at room temperature. The conformal coating and the room temperature ionic conductivity make these cyclic organosilicon polymers attractive for use as thin-film electrolytes in solid-state batteries. Also, their synthesis process and properties have been systemically studied and discussed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cyclic Multiblock Copolymers via Combination of Iterative Cu(0)-Mediated Radical Polymerization and Cu(I)-Catalyzed Azide-Alkyne Cycloaddition Reaction.

PubMed

Xiao, Lifen; Zhu, Wen; Chen, Jiqiang; Zhang, Ke

2017-02-01

Cyclic multiblock polymers with high-order blocks are synthesized via the combination of single-electron transfer living radical polymerization (SET-LRP) and copper-catalyzed azide-alkyne cycloaddition (CuAAC). The linear α,ω-telechelic multiblock copolymer is prepared via SET-LRP by sequential addition of different monomers. The SET-LRP approach allows well control of the block length and sequence as A-B-C-D-E, etc. The CuAAC is then performed to intramolecularly couple the azide and alkyne end groups of the linear copolymer and produce the corresponding cyclic copolymer. The block sequence and the cyclic topology of the resultant cyclic copolymer are confirmed by the characterization of 1 H nuclear magnetic resonance spectroscopy, gel permeation chromatography, Fourier transform infrared spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cyclic softening based on dislocation annihilation at sub-cell boundary for SA333 Grade-6 C-Mn steel

NASA Astrophysics Data System (ADS)

Bhattacharjee, S.; Dhar, S.; Acharyya, S. K.; Gupta, S. K.

2018-01-01

In this work, the response of SA333 Grade-6 C-Mn steel subjected to uniaxial and in-phase biaxial tension-torsion cyclic loading is experimented and an attempt is made to model the material behaviour. Experimentally observed cyclic softening is modelled based on ‘dislocation annihilation at low angle grain boundary’, while Ohno-Wang kinematic hardening rule is used to simulate the stress-strain hysteresis loops. The relevant material parameters are extracted from the appropriate experimental results and metallurgical investigations. The material model is plugged as user material subroutine into ABAQUS FE platform to simulate pre-saturation low cycle fatigue loops with cyclic softening and other cyclic plastic behaviour under prescribed loading. The stress-strain hysteresis loops and peak stress with cycles were compared with the experimental results and good agreements between experimental and simulated results validated the material model.

On the no-boundary proposal for ekpyrotic and cyclic cosmologies

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

Battarra, Lorenzo; Lehners, Jean-Luc, E-mail: lorenzo.battarra@aei.mpg.de, E-mail: jlehners@aei.mpg.de

2014-12-01

The no-boundary proposal provides a compelling theory for the initial conditions of our universe. We study the implications of such initial conditions for ekpyrotic and cyclic cosmologies. These cosmologies allow for the existence of a new type of ''ekpyrotic instanton'', which describes the creation of a universe in the ekpyrotic contraction phase. Remarkably, we find that the ekpyrotic attractor can explain how the universe became classical. In a cyclic context, in addition to the ekpyrotic instantons there exist de Sitter-like instantons describing the emergence of the universe in the dark energy phase. Our results show that typically the ekpyrotic instantonsmore » yield a higher probability. In fact, in a potential energy landscape allowing both inflationary and cyclic cosmologies, the no-boundary proposal implies that the probability for ekpyrotic and cyclic initial conditions is vastly higher than that for inflationary ones.« less

Cyclic electron flow is redox-controlled but independent of state transition.

PubMed

Takahashi, Hiroko; Clowez, Sophie; Wollman, Francis-André; Vallon, Olivier; Rappaport, Fabrice

2013-01-01

Photosynthesis is the biological process that feeds the biosphere with reduced carbon. The assimilation of CO2 requires the fine tuning of two co-existing functional modes: linear electron flow, which provides NADPH and ATP, and cyclic electron flow, which only sustains ATP synthesis. Although the importance of this fine tuning is appreciated, its mechanism remains equivocal. Here we show that cyclic electron flow as well as formation of supercomplexes, thought to contribute to the enhancement of cyclic electron flow, are promoted in reducing conditions with no correlation with the reorganization of the thylakoid membranes associated with the migration of antenna proteins towards Photosystems I or II, a process known as state transition. We show that cyclic electron flow is tuned by the redox power and this provides a mechanistic model applying to the entire green lineage including the vast majority of the cases in which state transition only involves a moderate fraction of the antenna.

Supramolecular polymer formation by cyclic dinucleotides and intercalators affects dinucleotide enzymatic processing

PubMed Central

Nakayama, Shizuka; Zhou, Jie; Zheng, Yue; Szmacinski, Henryk; Sintim, Herman O

2016-01-01

Background: Cyclic dinucleotides form supramolecular aggregates with intercalators, and this property could be utilized in nanotechnology and medicine. Methods & results: Atomic force microscopy and electrophoretic mobility shift assays were used to show that cyclic diguanylic acid (c-di-GMP) forms G-wires in the presence of intercalators. The average fluorescence lifetime of thiazole orange, when bound to c-di-GMP was greater than when bound to DNA G-quadruplexes or dsDNA. The stability of c-di-GMP supramolecular polymers is dependent on both the nature of the cation present and the intercalator. C-di-GMP or cyclic diadenylic acid/intercalator complexes are more resistant to cleavage by YybT, a phosphodiesterase, than the uncomplexed nucleotides. Conclusion: Cleavage of bacterial cyclic dinucleotides could be slowed down via complexation with small molecules and that this could be utilized for diverse applications in nanotechnology and medicine. PMID:28031943

Gonadotropin level abnormalities in women with cyclic mastalgia.

PubMed

Ecochard, R; Marret, H; Rabilloud, M; Boehringer, H; Mathieu, C; Guerin, J F

2001-01-01

Women with cyclic mastalgia seem to be at risk of fibrocystic breast disease and/or breast cancer. We studied the relationships between mastalgia and hormone levels throughout the menstrual cycle. Ostensibly healthy women were monitored during a sum of 326 cycles. A case-control study compared personal and hormonal variables of 30 women experiencing cyclic mastalgia with those of 77 women without this symptom. Except sleeping times, no significant differences were found in personal variables. Cyclic mastalgia and symptoms of fluid retention were slightly associated. Menses and the luteal phase were significantly longer in cases than in controls. Gonadotropin but not ovarian hormone levels were also significantly higher in cases throughout the cycle. Cyclic mastalgia is less related to symptoms of fluid retention or to ovarian hormone levels than to regularly high gonadotropin levels, specific inhibitors might thus be used to alleviate the symptom.

Particle loading time and humidity effects on the efficiency of an N95 filtering facepiece respirator model under constant and inhalation cyclic flows.

PubMed

Mahdavi, Alireza; Haghighat, Fariborz; Bahloul, Ali; Brochot, Clothilde; Ostiguy, Claude

2015-06-01

It is necessary to investigate the efficiencies of filtering facepiece respirators (FFRs) exposed to ultrafine particles (UFPs) for long periods of time, since the particle loading time may potentially affect the efficiency of FFRs. This article aims to investigate the filtration efficiency for a model of electrostatic N95 FFRs with constant and 'inhalation-only' cyclic flows, in terms of particle loading time effect, using different humidity conditions. Filters were exposed to generated polydisperse NaCl particles. Experiments were performed mimicking an 'inhalation-only' scenario with a cyclic flow of 85 l min(-1) as the minute volume [or 170 l min(-1) as mean inhalation flow (MIF)] and for two constant flows of 85 and 170 l min(-1), under three relative humidity (RH) levels of 10, 50, and 80%. Each test was performed for loading time periods of 6h and the particle penetration (10-205.4nm in electrical mobility diameter) was measured once every 2h. For a 10% RH, the penetration of smaller size particles (<80nm), including the most penetrating particle size (MPPS), decreased over time for both constant and cyclic flows. For 50 and 80% RH levels, the changes in penetration were typically observed in an opposite direction with less magnitude. The penetrations at MPPS increased with respect to loading time under constant flow conditions (85 and 170 l min(-1)): it did not substantially increase under cyclic flows. The comparison of the cyclic flow (85 l min(-1) as minute volume) and constant flow equal to the cyclic flow minute volume indicated that, for all conditions the penetration was significantly less for the constant flow than that of cyclic flow. The comparison between the cyclic (170 l min(-1) as MIF) and constant flow equal to cyclic flow MIF indicated that, for the initial stage of loading, the penetrations were almost equal, but they were different for the final stages of the loading time. For a 10% RH, the penetration of a wide range of sizes was observed to be higher with the cyclic flow (170 as MIF) than with the equivalent constant flow (170 l min(-1)). For 50 and 80% RH levels, the penetrations were usually greater with a constant flow (170 l min(-1)) than with a cyclic flow (170 l min(-1) as MIF). It is concluded that, for the tested electrostatic N95 filters, the change in penetration as a function of the loading time does not necessarily take place with the same rate under constant (MIF) and cyclic flow. Moreover, for all tested flow rates, the penetration is not only affected by the loading time but also by the RH level. Lower RH levels (10%) have decreasing penetration rates in terms of loading time, while higher RH levels (50 and 80%) have increasing penetration rates. Also, the loading of the filter is normally accompanied with a shift of MPPS towards larger sizes. © The Author 2015. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

Thermal-Mechanical Cyclic Test of a Composite Cryogenic Tank for Reusable Launch Vehicles

NASA Technical Reports Server (NTRS)

Messinger, Ross; Pulley, John

2003-01-01

This viewgraph presentation provides an overview of thermal-mechanical cyclic tests conducted on a composite cryogenic tank designed for reusable launch vehicles. Topics covered include: a structural analysis of the composite cryogenic tank, a description of Marshall Space Flight Center's Cryogenic Structure Test Facility, cyclic test plans and accomplishments, burst test and analysis and post-testing evaluation.

Environmental Compliance Assessment and Management Program

DTIC Science & Technology

1994-04-01

following classes: 1. cyclic, branched, or linear, completely fluorinated alkanes 2. cyclic, branched, or linear, completely fluorinated ethers with no...unsaturations 3. cyclic, branched, or linear, completely fluorinated tertiary amines with no unsaturations 4. sulfur containing perfluorocarbons with no...unsaturations and with sulfur bonds only to carbon and fluorine . 2.58. VOC Water Separator - a tank, box, or other container which is primarily

Cyclic plasticity models and application in fatigue analysis

NASA Technical Reports Server (NTRS)

Kalev, I.

1981-01-01

An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a crack plane stress panel under several cyclic loading conditions.

Doping effect of polyaniline/MWCNT composites on capacitance and cyclic stability of supercapacitors.

PubMed

Karthikeyan, G; Sahoo, S; Nayak, G C; Das, C K

2012-03-01

Polyaniline doped by Zn2+ ions was synthesized as nanocomposites with multiwalled carbon nanotubes (MWCNT) by in-situ oxidative polymerization and investigated as electrode material for supercapacitors. The uniform coating of polyaniline on MWCNT was characterized by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). The effect of Zn2+ ions on nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy. The electrochemical performances were investigated by cyclic voltammetry (CV), constant current charging/discharging cyclic test (CC) and electrochemical impedance spectroscopy (EIS) using a three-electrode system. The doped polyaniline composites show higher specific capacitance and better cyclic stability.

The mycotoxin definition reconsidered towards fungal cyclic depsipeptides.

PubMed

Taevernier, Lien; Wynendaele, Evelien; De Vreese, Leen; Burvenich, Christian; De Spiegeleer, Bart

2016-04-02

Currently, next to the major classes, cyclic depsipeptides beauvericin and enniatins are also positioned as mycotoxins. However, as there are hundreds more fungal cyclic depsipeptides already identified, should these not be considered as mycotoxins as well? The current status of the mycotoxin definition revealed a lack of consistency, leading to confusion about what compounds should be called mycotoxins. Because this is of pivotal importance in risk assessment prioritization, a clear and quantitatively expressed mycotoxin definition is proposed, based on data of widely accepted mycotoxins. Finally, this definition is applied to a set of fungal cyclic depsipeptides, revealing that some of these should indeed be considered as mycotoxins.

Cyclical Annealing Technique To Enhance Reliability of Amorphous Metal Oxide Thin Film Transistors.

PubMed

Chen, Hong-Chih; Chang, Ting-Chang; Lai, Wei-Chih; Chen, Guan-Fu; Chen, Bo-Wei; Hung, Yu-Ju; Chang, Kuo-Jui; Cheng, Kai-Chung; Huang, Chen-Shuo; Chen, Kuo-Kuang; Lu, Hsueh-Hsing; Lin, Yu-Hsin

2018-02-26

This study introduces a cyclical annealing technique that enhances the reliability of amorphous indium-gallium-zinc-oxide (a-IGZO) via-type structure thin film transistors (TFTs). By utilizing this treatment, negative gate-bias illumination stress (NBIS)-induced instabilities can be effectively alleviated. The cyclical annealing provides several cooling steps, which are exothermic processes that can form stronger ionic bonds. An additional advantage is that the total annealing time is much shorter than when using conventional long-term annealing. With the use of cyclical annealing, the reliability of the a-IGZO can be effectively optimized, and the shorter process time can increase fabrication efficiency.

Intramolecular cascade rearrangements of enynamine derived ketenimines: access to acyclic and cyclic amidines.

PubMed

Chauhan, Dinesh Pratapsinh; Varma, Sreejith J; Gudem, Mahesh; Panigrahi, Nihar; Singh, Khushboo; Hazra, Anirban; Talukdar, Pinaki

2017-06-07

Copper-catalyzed reaction of enynamines with sulfonylazides provides acyclic and cyclic amidines. Nucleophilic addition of the tethered amino group on the in situ generated ketenimine forms a six-membered cyclic zwitterionic intermediate which facilitates migration of the tethered amino group to the C 5 -center giving the acyclic amidine. On the other hand, migration of a substituent on the amino group to C 2 - and C 4 -centers results in the formation of cyclic amidines. Computational studies were carried out to validate the mechanism which indicates that the product distribution of the process depends on the substitutions on the enynamine backbone.

Cyclic behavior at quasi-parallel collisionless shocks

NASA Technical Reports Server (NTRS)

Burgess, D.

1989-01-01

Large scale one-dimensional hybrid simulations with resistive electrons have been carried out of a quasi-parallel high-Mach-number collisionless shock. The shock initially appears stable, but then exhibits cyclic behavior. For the magnetic field, the cycle consists of a period when the transition from upstream to downstream is steep and well defined, followed by a period when the shock transition is extended and perturbed. This cyclic shock solution results from upstream perturbations caused by backstreaming gyrating ions convecting into the shock. The cyclic reformation of a sharp shock transition can allow ions, at one time upstream because of reflection or leakage, to contribute to the shock thermalization.

Prediction and verification of creep behavior in metallic materials and components, for the space shuttle thermal protection system. Volume 1, phase 1: Cyclic materials creep predictions

NASA Technical Reports Server (NTRS)

Davis, J. W.; Cramer, B. A.

1974-01-01

Cyclic creep response was investigated and design methods applicable to thermal protection system structures were developed. The steady-state (constant temperature and load) and cyclic creep response characteristics of four alloys were studied. Steady-state creep data were gathered through a literature survey to establish reference data bases. These data bases were used to develop empirical equations describing creep as a function of time, temperature, and stress and as a basis of comparison for test data. Steady-state creep tests and tensile cyclic tests were conducted. The following factors were investigated: material thickness and rolling direction; material cyclic creep response under varying loads and temperatures; constant stress and temperature cycles representing flight conditions; changing stresses present in a creeping beam as a result of stress redistribution; and complex stress and temperature profiles representative of space shuttle orbiter trajectories. A computer program was written, applying creep hardening theories and empirical equations for creep, to aid in analysis of test data. Results are considered applicable to a variety of structures which are cyclicly exposed to creep producing thermal environments.

Quantifying effects of cyclic stretch on cell-collagen substrate adhesiveness of vascular endothelial cells.

PubMed

Omidvar, Ramin; Tafazzoli-Shadpour, Mohammad; Mahmoodi-Nobar, Farbod; Azadi, Shohreh; Khani, Mohammad-Mehdi

2018-05-01

Vascular endothelium is continuously subjected to mechanical stimulation in the form of shear forces due to blood flow as well as tensile forces as a consequence of blood pressure. Such stimuli influence endothelial behavior and regulate cell-tissue interaction for an optimized functionality. This study aimed to quantify influence of cyclic stretch on the adhesive property and stiffness of endothelial cells. The 10% cyclic stretch with frequency of 1 Hz was applied to a layer of endothelial cells cultured on a polydimethylsiloxane substrate. Cell-substrate adhesion of endothelial cells was examined by the novel approach of atomic force microscope-based single-cell force spectroscopy and cell stiffness was measured by atomic force microscopy. Furthermore, the adhesive molecular bonds were evaluated using modified Hertz contact theory. Our results show that overall adhesion of endothelial cells with substrate decreased after cyclic stretch while they became stiffer. Based on the experimental results and theoretical modeling, the decrease in the number of molecular bonds after cyclic stretch was quantified. In conclusion, in vitro cyclic stretch caused alterations in both adhesive capacity and elastic modulus of endothelial cells through mechanotransductive pathways as two major determinants of the function of these cells within the cardiovascular system.

Finite element analysis of the biaxial cyclic tensile loading of the elastoplastic plate with the central hole: asymptotic regimes

NASA Astrophysics Data System (ADS)

Turkova, Vera; Stepanova, Larisa

2018-03-01

For elastistoplastic structure elements under cyclic loading three types of asymptotic behavior are well known: shakedown, cyclic plasticity or ratcheting. In structure elements operating in real conditions ratcheting must always be excluded since it caused the incremental fracture of structure by means of the accumulation of plastic strains. In the present study results of finite-element (FEM) calculations of the asymptotical behavior of an elastoplastic plate with the central circular and elliptic holes under the biaxial cyclic loading for three different materials are presented. Incremental cyclic loading of the sample with stress concentrator (the central hole) is performed in the multifunctional finite-element package SIMULIA Abaqus. The ranges of loads found for shakedown, cyclic plasticity and ratcheting are presented. The results obtained are generalized and analyzed. Convenient normalization is suggested. The chosen normalization allows us to present all computed results, corresponding to separate materials, within one common curve with minimum scattering of the points. Convenience of the generalized diagram consists in a possibility to find an asymptotical behavior of an inelastic structure for materials for which computer calculations were not made.

Comparative effects of vinpocetine and 8-Br-cyclic GMP on the contraction and /sup 45/Ca-fluxes in the rabbit aorta

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

Chiu, P.J.; Tetzloff, G.; Ahn, H.S.

1988-07-01

Vinpocetine is a highly specific inhibitor of calmodulin-dependent phosphodiesterase (CaM-PDE) with an IC50 of 19 microM and produces a significant accumulation of cyclic GMP but not cyclic AMP in rabbit aorta. In isolated rabbit aortic strips, vinpocetine (0.01 and 0.1 mM) inhibited the contraction and /sup 45/Ca uptake due to both phenylephrine (1 microM) and KCl (40 mM), whereas 8-Br-cyclic GMP (0.1-1mM) selectively impaired phenylephrine-induced responses. Furthermore, the KCl-stimulated /sup 45/Ca efflux in normal Ca2+ buffer, which reflects elevated cytosolic Ca2+, was greatly diminished by vinpocetine but not by 8-Br-cyclic GMP. However, phenylephrine-induced /sup 45/Ca efflux and contraction in Ca2+-freemore » buffer, which reflect Ca2+ release from intracellular sites, were similarly inhibited by both vinpocetine and 8-Br-cyclic GMP. The results suggest that vinpocetine may effect vasodilatation through blockade of the slow channel and selective inhibition of CaM-PDE in the vascular smooth muscle.« less

Involvement of plasma membrane-located calmodulin in the response decay of cyclic nucleotide-gated cation channel of cultured carrot cells.

PubMed

Kurosaki, F; Kaburaki, H; Nishi, A

1994-03-07

Increase in cytoplasmic cyclic AMP concentration stimulates Ca2+ influx through the cyclic AMP-gated cation channel in the plasma membrane of cultured carrot cells. However, the Ca2+ current terminated after a few minutes even in the presence of high concentrations of cyclic AMP indicating that hydrolysis of the nucleotide is not responsible for stop of the Ca2+ influx. Cyclic AMP evoked discharge of Ca2+ from inside-out sealed vesicles of carrot plasma membrane, and it was strongly inhibited when the suspension of the vesicles was supplemented with 1 microM of free Ca2+, while Ca2+ lower than 0.1 microM did not affect the Ca(2+)-release. The Ca2+ flux across plasma membrane was restored from this Ca(2+)-induced inhibition by the addition of calmodulin inhibitors or anti-calmodulin. These results suggest that Ca2+ influx initiated by the increase in intracellular cAMP in cultured carrot cells is terminated when the cytosolic Ca2+ concentration reaches the excitatory level in the cells, and calmodulin located in the plasma membrane plays an important role in the response decay of the cyclic nucleotide-gated Ca2+ channel.

Mechanical annealing under low-amplitude cyclic loading in micropillars

NASA Astrophysics Data System (ADS)

Cui, Yi-nan; Liu, Zhan-li; Wang, Zhang-jie; Zhuang, Zhuo

2016-04-01

Mechanical annealing has been demonstrated to be an effective method for decreasing the overall dislocation density in submicron single crystal. However, simultaneously significant shape change always unexpectedly happens under extremely high monotonic loading to drive the pre-existing dislocations out of the free surfaces. In the present work, through in situ TEM experiments it is found that cyclic loading with low stress amplitude can drive most dislocations out of the submicron sample with virtually little change of the shape. The underlying dislocation mechanism is revealed by carrying out discrete dislocation dynamic (DDD) simulations. The simulation results indicate that the dislocation density decreases within cycles, while the accumulated plastic strain is small. By comparing the evolution of dislocation junction under monotonic, cyclic and relaxation deformation, the cumulative irreversible slip is found to be the key factor of promoting junction destruction and dislocation annihilation at free surface under low-amplitude cyclic loading condition. By introducing this mechanics into dislocation density evolution equations, the critical conditions for mechanical annealing under cyclic and monotonic loadings are discussed. Low-amplitude cyclic loading which strengthens the single crystal without seriously disturbing the structure has the potential applications in the manufacture of defect-free nano-devices.

Isotopic Exchange HPLC-HRMS/MS Applied to Cyclic Proanthocyanidins in Wine and Cranberries

NASA Astrophysics Data System (ADS)

Longo, Edoardo; Rossetti, Fabrizio; Scampicchio, Matteo; Boselli, Emanuele

2018-01-01

Cyclic B-type proanthocyanidins in red wines and grapes have been discovered recently. However, proanthocyanidins of a different chemical structure (non-cyclic A-type proanthocyanidins) already known to be present in cranberries and wine possess an identical theoretical mass. As a matter of fact, the retention times and the MS/MS fragmentations found for the proposed novel cyclic B-type tetrameric proanthocyanidin in red wine and the known tetrameric proanthocyanidin in a cranberry extract are herein shown to be identical. Thus, hydrogen/deuterium (H/D) exchange was applied to HPLC-HRMS/MS to confirm the actual chemical structure of the new oligomeric proanthocyanidins. The comparison of the results in water and deuterium oxide and between wine and cranberry extract indicates that the cyclic B-type tetrameric proanthocyanidin is the actual constituent of the recently proposed novel tetrameric species ([C60H49O24]+, m/z 1153.2608). Surprisingly, the same compound was also identified as the main tetrameric proanthocyanidin in cranberries. Finally, a totally new cyclic B-type hexameric proanthocyanidin ([C90H73O36]+, m/z 1729.3876) belonging to this novel class was identified for the first time in red wine. [Figure not available: see fulltext.

Possible mechanisms of stimulatory action of papaverine on calcium-uptake by rat uterine microsomal fraction.

PubMed

Koike, K; Takayanagi, I

1981-10-01

Effects of papaverine and cyclic AMP on Ca-uptake by the microsomal fraction from rat uterus were studied. Papaverine (3 x 10(-5) M) potentiated Ca-uptake by the microsomal fraction in the presence of potassium oxalate. However, cyclic AMP and MIX (3-isobutyl-1-methylxanthine; 1 mM), a potent phosphodiesterase inhibitor, did not influence Ca-uptake by the microsomal fraction in the presence of potassium oxalate. Cyclic AMP in concentrations of 10(-8) to 10(-4) M did not influence Ca-uptake by the microsomal fraction in the presence of potassium oxalate. In the absence of potassium oxalate, papaverine and Aspaminol (1,1,-diphenyl-3-piperidinobutanol hydrochloride), a nonspecific smooth muscle relaxant, inhibited Ca-uptake by the microsomal fraction and cyclic AMP had no influence on this uptake. These results suggest that papaverine potentiated Ca-uptake by membranes such as sarcoplasmic reticulum, in the presence of potassium oxalate and inhibited Ca-uptake by the plasma membrane-derived vesicles in the absence of potassium oxalate. These results suggest that relaxation of smooth muscle by papaverine is related to a cyclic AMP-independent mechanism as well as to a mechanism mediated via cyclic AMP.

Creep crack growth by grain boundary cavitation under monotonic and cyclic loading

NASA Astrophysics Data System (ADS)

Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan

2017-11-01

Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.

Long-term cyclicities in Phanerozoic sea-level sedimentary record and their potential drivers

NASA Astrophysics Data System (ADS)

Boulila, Slah; Laskar, Jacques; Haq, Bilal U.; Galbrun, Bruno; Hara, Nathan

2018-06-01

Cyclic sedimentation has varied at several timescales and this variability has been geologically well documented at Milankovitch timescales, controlled in part by climatically (insolation) driven sea-level changes. At the longer (tens of Myr) timescales connection between astronomical parameters and sedimentation via cyclic solar-system motions within the Milky Way has also been proposed, but this hypothesis remains controversial because of the lack of long geological records. In addition, the absence of a meaningful physical mechanism that could explain the connection between climate and astronomy at these longer timescales led to the more plausible explanation of plate motions as the main driver of climate and sedimentation through changes in ocean and continent mass distribution on Earth. Here we statistically show a prominent and persistent 36 Myr sedimentary cyclicity superimposed on two megacycles ( 250 Myr) in a relatively well-constrained sea-level (SL) record of the past 542 Myr (Phanerozoic eon). We also show two other significant 9.3 and 91 Myr periodicities, but with lower amplitudes. The 9.3 Myr cyclicity was previously attributed to long-period Milankovitch band based on the Cenozoic record. However, the 91 Myr cyclicity has never been observed before in the geologic record. The 250 Myr cyclicity was attributed to the Wilson tectonic (supercontinent) cycle. The 36 Myr periodicity, also detected for the first time in SL record, has previously been ascribed either to tectonics or to astronomical cyclicity. Given the possible link between amplitudes of the 36 and 250 Myr cyclicities in SL record and the potential that these periodicities fall into the frequency band of solar system motions, we suggest an astronomical origin, and model these periodicities as originating from the path of the solar system in the Milky Way as vertical and radial periods that modulate the flux of cosmic rays on Earth. Our finding of the 36 Myr SL cyclicity lends credibility to the existing hypothesis about the imprint of solar-system vertical period on the geological record. The 250 Myr megacycles are tentatively attributed to a radial period. However, tectonic causal mechanisms remain equally plausible. The potential existence of a correlation between the modeled astronomical signal and the geological record may offer an indirect proxy to understand the structure and history of the Milky Way by providing a 542 Myr long record of the path of the Sun in our Galaxy.

Comparison between the effects of inhaled isoprenaline and fenoterol on plasma cyclic AMP and heart rate in normal subjects.

PubMed Central

Fairfax, A J; Rehahn, M; Jones, D; O'Malley, B

1984-01-01

The time course of changes in plasma cyclic AMP, heart rate and bronchial tone after inhalation of fenoterol or isoprenaline from a dose-metered aerosol are reported in a group of normal subjects. After isoprenaline, plasma cyclic AMP increased rapidly reaching a peak by 10 min and returned to basal levels within 60 min. A rapid, transient rise in heart rate occurred that was maximal by 5 min and returned to a basal level by 45 min. After fenoterol, the changes in cyclic AMP and heart rate were of much longer duration. The rise in plasma cyclic AMP was slower in onset and of greater magnitude than for isoprenaline, reaching a peak by 20 min and remaining above basal level for more than 6 h. The maximum increase in heart rate after fenoterol was less than that observed with isoprenaline but an elevated rate persisted for 4 h after inhalation of fenoterol. Fenoterol is known to have a longer duration of action as a bronchodilator in comparison with isoprenaline. The prolonged rise in plasma cyclic AMP in normal subjects given inhaled fenoterol may reflect this long duration of action. The concomitant rise in heart rate, however, suggests that the duration of plasma cyclic AMP response may in part be due to the systemic effect of the fraction of inhaled fenoterol known to be absorbed via the buccal and intestinal routes. PMID:6322828

C-Terminal β9-Strand of the Cyclic Nucleotide-Binding Homology Domain Stabilizes Activated States of Kv11.1 Channels

PubMed Central

Ng, Chai Ann; Ke, Ying; Perry, Matthew D.; Tan, Peter S.; Hill, Adam P.; Vandenberg, Jamie I.

2013-01-01

Kv11.1 potassium channels are important for regulation of the normal rhythm of the heartbeat. Reduced activity of Kv11.1 channels causes long QT syndrome type 2, a disorder that increases the risk of cardiac arrhythmias and sudden cardiac arrest. Kv11.1 channels are members of the KCNH subfamily of voltage-gated K+ channels. However, they also share many similarities with the cyclic nucleotide gated ion channel family, including having a cyclic nucleotide-binding homology (cNBH) domain. Kv11.1 channels, however, are not directly regulated by cyclic nucleotides. Recently, crystal structures of the cNBH domain from mEAG and zELK channels, both members of the KCNH family of voltage-gated potassium channels, revealed that a C-terminal β9-strand in the cNBH domain occupied the putative cyclic nucleotide-binding site thereby precluding binding of cyclic nucleotides. Here we show that mutations to residues in the β9-strand affect the stability of the open state relative to the closed state of Kv11.1 channels. We also show that disrupting the structure of the β9-strand reduces the stability of the inactivated state relative to the open state. Clinical mutations located in this β9-strand result in reduced trafficking efficiency, which suggests that binding of the C-terminal β9-strand to the putative cyclic nucleotide-binding pocket is also important for assembly and trafficking of Kv11.1 channels. PMID:24204727

Astressin B, a corticotropin-releasing hormone receptor antagonist, accelerates the return to normal luteal function after an inflammatory-like stress challenge in the rhesus monkey.

PubMed

Xiao, Ennian; Xia-Zhang, Linna; Vulliemoz, Nicolas; Rivier, Jean; Ferin, Michel

2007-02-01

Endogenous release of CRH in stress has been associated with a dysfunctional reproductive endocrine axis. In the rhesus monkey, an inflammatory-like stress challenge in the luteal phase decreases luteal secretory function. Here, we tested the effectiveness of astressin B, a nonspecific CRH receptor antagonist, in constraining the deleterious impact of a 10-d lipopolysaccharide (LPS) challenge on the menstrual cycle. Two protocols were carried out in nine animals. In the first, the animals, after showing two normal consecutive control cycles, were injected daily for 10 days with LPS (75-125 mug/d) during the luteal phase of the cycle. The animals were followed through the two postchallenge cycles. The second protocol, carried out in the following year, was identical with protocol 1, except that the animals were treated with astressin B (0.45 mg/kg) 1 h before each daily LPS challenge during the luteal phase. Blood samples were obtained daily to document cyclic hormones levels. The LPS challenge significantly decreased luteal progesterone and LH release during the challenge cycle. Inhibition of luteal progesterone extended to the two successive postchallenge cycles. Astressin B treatment prevented luteal LH but not luteal progesterone decrease during the treatment cycle and restored normal progesterone secretion during the two posttreatment cycles. We conclude that the deleterious impact of a short-term inflammatory stress challenge on luteal function is far longer than the stress period itself. Systemic administration of astressin B accelerates the return to normal luteal function, presumably by restoring normal neuroendocrine regulation of gonadotropin secretion.

Seismic characterization and dynamic site response of a municipal solid waste landfill in Bangalore, India.

PubMed

Anbazhagan, P; SivakumarBabu, G L; Lakshmikanthan, P; VivekAnand, K S

2016-03-01

Seismic design of landfills requires an understanding of the dynamic properties of municipal solid waste (MSW) and the dynamic site response of landfill waste during seismic events. The dynamic response of the Mavallipura landfill situated in Bangalore, India, is investigated using field measurements, laboratory studies and recorded ground motions from the intraplate region. The dynamic shear modulus values for the MSW were established on the basis of field measurements of shear wave velocities. Cyclic triaxial testing was performed on reconstituted MSW samples and the shear modulus reduction and damping characteristics of MSW were studied. Ten ground motions were selected based on regional seismicity and site response parameters have been obtained considering one-dimensional non-linear analysis in the DEEPSOIL program. The surface spectral response varied from 0.6 to 2 g and persisted only for a period of 1 s for most of the ground motions. The maximum peak ground acceleration (PGA) obtained was 0.5 g and the minimum and maximum amplifications are 1.35 and 4.05. Amplification of the base acceleration was observed at the top surface of the landfill underlined by a composite soil layer and bedrock for all ground motions. Dynamic seismic properties with amplification and site response parameters for MSW landfill in Bangalore, India, are presented in this paper. This study shows that MSW has less shear stiffness and more amplification due to loose filling and damping, which need to be accounted for seismic design of MSW landfills in India. © The Author(s) 2016.

Coupled transport of p-aminohippurate by rat kidney basolateral membrane vesicles

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

Pritchard, J.B.

p-Aminohippuric acid (PAH) transport by basolateral membrane (BLM) vesicles isolated from rat renal cortex was stimulated very little by a Na{sup +} gradient (out > in). However, when micromolar concentrations of glutaric acid or {alpha}-ketoglutaric acid were added in the presence of a out > in Na{sup +} gradient, PAH uptake was accelerated >20-fold and an overshoot of greater than fivefold was produced. Other anions, e.g., fumarate, stimulated PAH uptake very modestly under these conditions, and that stimulation was totally prevented by short circuiting, i.e., with K{sup +} (in = out) and valinomycin. Glutarate-stimulated uptake was inhibited by 4-acetamide-4{prime}-({sup 14}C)-isothiocyanostilbene-2,2{prime}-disulfonicmore » acid (SITS) and probenecid and was slightly stimulated by the imposition of an inside-negative membrane potential. Furthermore, even in the absence of a Na{sup +} gradient, glutarate-loaded vesicles exhibited a marked acceleration of ({sup 3}H)-PAH uptake (5-fold) and a modest overshoot (2.5-fold). These results suggest an indirect coupling of BLM PAH uptake to the Na{sup +} gradient by a cyclic accumulation (Na{sup +}-dependent) of glutarate followed by its efflux from the vesicle in exchange for PAH. This coupled system was absent in apical membranes. Thus net secretory transport of PAH may entail Na{sup +}-dependent, glutarate-driven PAH uptake at the BLM, followed by the exit of PAH into the lumen down its electrochemical gradient, probably in exchange for other anions, e.g., {sup 36}Cl{sup {minus}}, HCO{sub 3}{sup {minus}}, or OH{sup {minus}}.« less

An exposition on Friedmann cosmology with negative energy densities

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

Nemiroff, Robert J.; Joshi, Ravi; Patla, Bijunath R., E-mail: nemiroff@mtu.edu, E-mail: rjoshimtu@gmail.com, E-mail: bijunath.patla@nist.gov

2015-06-01

How would negative energy density affect a classic Friedmann cosmology? Although never measured and possibly unphysical, certain realizations of quantum field theories leaves the door open for such a possibility. In this paper we analyze the evolution of a universe comprising varying amounts of negative energy forms. Negative energy components have negative normalized energy densities, Ω < 0. They include negative phantom energy with an equation of state parameter w < −1, negative cosmological constant: w=−1, negative domain walls: w = −2/3, negative cosmic strings: w=−1/3, negative mass: w = 0, negative radiation: w = 1/3 and negative ultralight: w > 1/3. Assuming that such energy forms generate pressure like perfect fluids,more » the attractive or repulsive nature of negative energy components are reviewed. The Friedmann equation is satisfied only when negative energy forms are coupled to a greater magnitude of positive energy forms or positive curvature. We show that the solutions exhibit cyclic evolution with bounces and turnovers.The future and fate of such universes in terms of curvature, temperature, acceleration, and energy density are reviewed. The end states are dubbed ''big crunch,' '' big void,' or ''big rip' and further qualified as ''warped',''curved', or ''flat',''hot' versus ''cold', ''accelerating' versus ''decelerating' versus ''coasting'. A universe that ends by contracting to zero energy density is termed ''big poof.' Which contracting universes ''bounce' in expansion and which expanding universes ''turnover' into contraction are also reviewed.« less

Palladium-Catalyzed Direct C–H Arylation of Cyclic Enaminones with Aryl Iodides

PubMed Central

Yu, Yi-Yun; Bi, Lei

2013-01-01

A ligand-free method for the Pd-catalyzed direct arylation of cyclic enaminones using aryl iodides was developed. This method can be applied to a wide range of cyclic enaminones and aryl iodides with excellent C5-regioselectivity. Using widely available aryl iodides, the generality of this transformation provides easy access to a variety of 3-arylpiperidine structural motifs. PMID:23750615

A computer program for cyclic plasticity and structural fatigue analysis

NASA Technical Reports Server (NTRS)

Kalev, I.

1980-01-01

A computerized tool for the analysis of time independent cyclic plasticity structural response, life to crack initiation prediction, and crack growth rate prediction for metallic materials is described. Three analytical items are combined: the finite element method with its associated numerical techniques for idealization of the structural component, cyclic plasticity models for idealization of the material behavior, and damage accumulation criteria for the fatigue failure.

Functionalized linear and cyclic polyolefins

DOEpatents

Tuba, Robert; Grubbs, Robert H.

2018-02-13

This invention relates to methods and compositions for preparing linear and cyclic polyolefins. More particularly, the invention relates to methods and compositions for preparing functionalized linear and cyclic polyolefins via olefin metathesis reactions. Polymer products produced via the olefin metathesis reactions of the invention may be utilized for a wide range of materials applications. The invention has utility in the fields of polymer and materials chemistry and manufacture.

Efficient synthesis of cysteine-rich cyclic peptides through intramolecular native chemical ligation of N-Hnb-Cys peptide crypto-thioesters.

PubMed

Terrier, Victor P; Delmas, Agnès F; Aucagne, Vincent

2017-01-04

We herein introduce a straightforward synthetic route to cysteine-containing cyclic peptides based on the intramolecular native chemical ligation of in situ generated thioesters. Key precursors are N-Hnb-Cys crypto-thioesters, easily synthesized by Fmoc-based SPPS. The strategy is applied to a representative range of naturally occurring cyclic disulfide-rich peptide sequences.

Computer Simulation Of Cyclic Oxidation

NASA Technical Reports Server (NTRS)

Probst, H. B.; Lowell, C. E.

1990-01-01

Computer model developed to simulate cyclic oxidation of metals. With relatively few input parameters, kinetics of cyclic oxidation simulated for wide variety of temperatures, durations of cycles, and total numbers of cycles. Program written in BASICA and run on any IBM-compatible microcomputer. Used in variety of ways to aid experimental research. In minutes, effects of duration of cycle and/or number of cycles on oxidation kinetics of material surveyed.

Control Strategies for Guided Collective Motion

DTIC Science & Technology

2015-01-30

Control, Atlanta, GA, USA, December 2010, pp. 5468-5473. [19] C. Rorres and H. Anton , “ Elementary linear algebra applications version,” 9th Edition...work addresses and analyses deviated linear cyclic pursuit in which an Distribution Code A: Approved for public release, distribution is unlimited...Pursuit 6. D. Mukherjee and D. Ghose: Deviated Linear Cyclic Pursuit 7. D. Mukherjee and D. Ghose; On Synchronous and Asynchronous Heterogeneous Cyclic

Cyclic Fatigue of Brittle Materials with an Indentation-Induced Flaw System

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Salem, Jonathan A.

1996-01-01

The ratio of static to cyclic fatigue life, or 'h ratio', was obtained numerically for an indentation flaw system subjected to sinusoidal loading conditions. Emphasis was placed on developing a simple, quick lifetime prediction tool. The solution for the h ratio was compared with experimental static and cyclic fatigue data obtained from as-indented 96 wt.% alumina specimens tested in room-temperature distilled water.

THERMALLY STABLE PERFLUORINATED POLYMERS

DTIC Science & Technology

structure to cyclic product from perfluoroglutaronitrile and N2H4, opening of this cyclic product with polymerization to poly(N2-imidoyl perfluoroglutar ...Work on the 1,2,4-triazole polymer system, in which these heterocyclic groups are connected by perfluoroalkylene chains, included assignment of...hydrazidine), and synthesis of poly( perfluoropropylene - 1,2,4- triazole) both from the poly(imidoyl hydrazidine) and directly from the original cyclic

Colour cyclic code for Brillouin distributed sensors

NASA Astrophysics Data System (ADS)

Le Floch, Sébastien; Sauser, Florian; Llera, Miguel; Rochat, Etienne

2015-09-01

For the first time, a colour cyclic coding (CCC) is theoretically and experimentally demonstrated for Brillouin optical time-domain analysis (BOTDA) distributed sensors. Compared to traditional intensity-modulated cyclic codes, the code presents an additional gain of √2 while keeping the same number of sequences as for a colour coding. A comparison with a standard BOTDA sensor is realized and validates the theoretical coding gain.

Abnormal regulation of adenosine 3′,5′-monophosphate and corticosterone formation in an adrenocortical carcinoma

PubMed Central

Ney, R. L.; Hochella, N. J.; Grahame-Smith, D. G.; Dexter, R. N.; Butcher, R. W.

1969-01-01

A spontaneously occurring rat adrenocortical carcinoma which produces corticosterone was maintained by transplantation. The carcinoma appeared to utilize corticosterone biosynthetic steps similar to those of the normal adrenal, but the tumor produced only about 1-10% as much corticosterone per unit tissue weight as nontumorous adrenal glands. The tumor demonstrated little or no increase in corticosterone production in response to adrenocorticotropic hormone (ACTH) either in vivo or in vitro. In normal adrenals, ACTH increases the activity of adenyl cyclase which catalyzes the conversion of adenosine triphosphate (ATP) to adenosine-3′,5′-monophosphate (cyclic AMP), the latter then serving as an intracellular regulator of steroidogenesis. ACTH failed to increase cyclic AMP levels in the tumor in vivo or in slices in vitro, conditions under which there were 50- and 20-fold increases in nontumorous adrenals. However, in homogenates fortified with exogenous ATP, adenyl cyclase activity was comparable in the tumor and adrenals, and cyclic AMP formation was increased 3-fold by ACTH in each. As measured in homogenates, the tumor did not possess a greater ability to destroy cyclic AMP than did normal adrenals. Although ATP levels in the carcinoma were found to be considerably lower than those in normal adrenals, it was not clear that this finding can explain the inability of ACTH to increase cyclic AMP levels in intact tumor cells. While the failure to normally influence cyclic AMP levels in the carcinoma cells could be an important factor in the lack of a steroid response to ACTH, several lines of evidence suggest that the tumor possesses one or more additional abnormalities in the regulation of steroidogenesis. First, in the absence of ACTH stimulation, the tissue concentrations of cyclic AMP were comparable in the tumor and in nontumorous adrenals, but these cyclic AMP levels were associated with a lower level of steroidogenesis in the tumor. Second, tumor slices failed to increase corticosterone production when incubated with cyclic AMP, in contrast to 5-fold increases observed with nontumorous adrenals. PMID:4390412

Cyclic Axial-Torsional Deformation Behavior of a Cobalt-Base Superalloy

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

1995-01-01

The cyclic, high-temperature deformation behavior of a wrought cobalt-base super-alloy, Haynes 188, is investigated under combined axial and torsional loads. This is accomplished through the examination of hysteresis loops generated from a biaxial fatigue test program. A high-temperature axial, torsional, and combined axial-torsional fatigue database has been generated on Haynes 188 at 760 C. Cyclic loading tests have been conducted on uniform gage section tubular specimens in a servohydraulic axial-torsional test rig. Test control and data acquisition were accomplished with a minicomputer. The fatigue behavior of Haynes 188 at 760 C under axial, torsional, and combined axial-torsional loads and the monotonic and cyclic deformation behaviors under axial and torsional loads have been previously reported. In this paper, the cyclic hardening characteristics and typical hysteresis loops in the axial stress versus axial strain, shear stress ,versus engineering shear strain, axial strain versus engineering shear strain. and axial stress versus shear stress spaces are presented for cyclic in-phase and out-of-phase axial-torsional tests. For in-phase tests, three different values of the proportionality constant lambda (the ratio of engineering shear strain amplitude to axial strain amplitude, are examined, viz. 0.86, 1.73, and 3.46. In the out-of-phase tests, three different values of the phase angle, phi (between the axial and engineering shear strain waveforms), are studied, viz., 30, 60, and 90 degrees with lambda equals 1.73. The cyclic hardening behaviors of all the tests conducted on Haynes 188 at 760 C are evaluated using the von Mises equivalent stress-strain and the maximum shear stress-maximum engineering shear strain (Tresca) curves. Comparisons are also made between the hardening behaviors of cyclic axial, torsional, and combined in-phase (lambda = 1.73 and phi = 0) and out-of-phase (lambda = 1.73 and phi = 90') axial-torsional fatigue tests. These comparisons are accomplished through simple Ramberg-Osgood type stress-strain functions for cyclic, axial stress-strain and shear stress-engineering shear strain curves.

Cyclic AMP system in muscle tissue during prolonged hypokinesia

NASA Technical Reports Server (NTRS)

Antipenko, Y. A.; Bubeyev, Y. A.; Korovkin, B. F.; Mikhaleva, N. P.

1980-01-01

Components of the cyclic Adenosine-cyclic-35-monophosphate (AMP) system in the muscle tissue of white rats were studied during 70-75 days of hypokinesia, created by placing the animals in small booths which restricted their movements, and during the readaptation period. In the initial period, cyclic AMP levels and the activities of phosphodiesterase and adenylate cyclase in muscle tissue were increased. The values for these indices were roughly equal for controls and experimental animals during the adaptation period, but on the 70th day of the experiment cAMP levels dropped, phosphodiesterase activity increased, and the stimulative effect of epinephrine on the activity of adenylate cyclase decreased. The indices under study normalized during the readaptation period.

Mechanical Stimulation of Adipose-Derived Stem Cells for Functional Tissue Engineering of the Musculoskeletal System via Cyclic Hydrostatic Pressure, Simulated Microgravity, and Cyclic Tensile Strain.

PubMed

Nordberg, Rachel C; Bodle, Josie C; Loboa, Elizabeth G

2018-01-01

It is critical that human adipose stem cell (hASC) tissue-engineering therapies possess appropriate mechanical properties in order to restore function of the load bearing tissues of the musculoskeletal system. In an effort to elucidate the hASC response to mechanical stimulation and develop mechanically robust tissue engineered constructs, recent research has utilized a variety of mechanical loading paradigms including cyclic tensile strain, cyclic hydrostatic pressure, and mechanical unloading in simulated microgravity. This chapter describes methods for applying these mechanical stimuli to hASC to direct differentiation for functional tissue engineering of the musculoskeletal system.

A constitutive model for AS4/PEEK thermoplastic composites under cyclic loading

NASA Technical Reports Server (NTRS)

Rui, Yuting; Sun, C. T.

1990-01-01

Based on the basic and essential features of the elastic-plastic response of the AS4/PEEK thermoplastic composite subjected to off-axis cyclic loadings, a simple rate-independent constitutive model is proposed to describe the orthotropic material behavior for cyclic loadings. A one-parameter memory surface is introduced to distinguish the virgin deformation and the subsequent deformation process and to characterize the loading range effect. Cyclic softening is characterized by the change of generalized plastic modulus. By the vanishing yield surface assumption, a yield criterion is not needed and it is not necessary to consider loading and unloading separately. The model is compared with experimental results and good agreement is obtained.

Population cycles: generalities, exceptions and remaining mysteries

PubMed Central

2018-01-01

Population cycles are one of nature's great mysteries. For almost a hundred years, innumerable studies have probed the causes of cyclic dynamics in snowshoe hares, voles and lemmings, forest Lepidoptera and grouse. Even though cyclic species have very different life histories, similarities in mechanisms related to their dynamics are apparent. In addition to high reproductive rates and density-related mortality from predators, pathogens or parasitoids, other characteristics include transgenerational reduced reproduction and dispersal with increasing-peak densities, and genetic similarity among populations. Experiments to stop cyclic dynamics and comparisons of cyclic and noncyclic populations provide some understanding but both reproduction and mortality must be considered. What determines variation in amplitude and periodicity of population outbreaks remains a mystery. PMID:29563267

Identification of cytidine 2',3'-cyclic monophosphate and uridine 2',3'-cyclic monophosphate in Pseudomonas fluorescens pfo-1 culture.

PubMed

Bordeleau, Emily; Oberc, Christopher; Ameen, Eve; da Silva, Amanda Mendes; Yan, Hongbin

2014-09-15

Cytidine 2',3'-cyclic monophosphate (2',3'-cCMP) and uridine 2',3'-cyclic monophosphate (2',3'-cUMP) were isolated from Pseudomonas fluorescens pfo-1 cell extracts by semi-preparative reverse phase HPLC. The structures of the two compounds were confirmed by NMR and mass spectroscopy against commercially available authentic samples. Concentrations of both intracellular and extracellular 2',3'-cCMP and 2',3'-cUMP were determined. Addition of 2',3'-cCMP and 2',3'-cUMP to P. fluorescens pfo-1 culture did not significantly affect the level of biofilm formation in static liquid cultures. Copyright © 2014 Elsevier Ltd. All rights reserved.

Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system. Volume 2: Phase 2 subsize panel cyclic creep predictions

NASA Technical Reports Server (NTRS)

Cramer, B. A.; Davis, J. W.

1975-01-01

A method for predicting permanent cyclic creep deflections in stiffened panel structures was developed. The resulting computer program may be applied to either the time-hardening or strain-hardening theories of creep accumulation. Iterative techniques were used to determine structural rotations, creep strains, and stresses as a function of time. Deflections were determined by numerical integration of structural rotations along the panel length. The analytical approach was developed for analyzing thin-gage entry vehicle metallic-thermal-protection system panels subjected to cyclic bending loads at high temperatures, but may be applied to any panel subjected to bending loads. Predicted panel creep deflections were compared with results from cyclic tests of subsize corrugation and rib-stiffened panels. Empirical equations were developed for each material based on correlation with tensile cyclic creep data and both the subsize panels and tensile specimens were fabricated from the same sheet material. For Vol. 1, see N75-21431.

A statistical analysis of elevated temperature gravimetric cyclic oxidation data of 36 Ni- and Co-base superalloys based on an oxidation attack parameter

NASA Technical Reports Server (NTRS)

Barrett, Charles A.

1992-01-01

A large body of high temperature cyclic oxidation data generated from tests at NASA Lewis Research Center involving gravimetric/time values for 36 Ni- and Co-base superalloys was reduced to a single attack parameter, K(sub a), for each run. This K(sub a) value was used to rank the cyclic oxidation resistance of each alloy at 1000, 1100, and 1150 C. These K(sub a) values were also used to derive an estimating equation using multiple linear regression involving log(sub 10)K(sub a) as a function of alloy chemistry and test temperature. This estimating equation has a high degree of fit and could be used to predict cyclic oxidation behavior for similar alloys and to design an optimum high strength Ni-base superalloy with maximum high temperature cyclic oxidation resistance. The critical alloy elements found to be beneficial were Al, Cr, and Ta.

Antifungal and Antiviral Cyclic Peptides from the Deep-Sea-Derived Fungus Simplicillium obclavatum EIODSF 020.

PubMed

Liang, Xiao; Nong, Xu-Hua; Huang, Zhong-Hui; Qi, Shu-Hua

2017-06-28

A new linear peptide simplicilliumtide I (1) and four new cyclic peptides simplicilliumtides J-M (2-5) together with known analogues verlamelins A and B (6 and 7) were isolated from the deep-sea-derived fungal strain Simplicillium obclavatum EIODSF 020. Their structures were elucidated by spectroscopic analysis, and their absolute configurations were further confirmed by chemical structural modification, Marfey's and Mosher's methods. Compounds 2, 6, and 7 showed significant antifungal activity toward Aspergillus versicolor and Curvularia australiensis and also had obvious antiviral activity toward HSV-1 with IC 50 values of 14.0, 16.7, and 15.6 μM, respectively. The structure-bioactivity relationship of this type of cyclic peptide was also discussed. This is the first time to discuss the effects of the lactone linkage and the substituent group of the fatty acid chain fragment on the bioactivity of this type of cyclic peptides. This is also the first time to report the antiviral activity of these cyclic peptides.

Computational Design of Self-Assembling Cyclic Protein Homo-oligomers

PubMed Central

Fallas, Jorge A.; Ueda, George; Sheffler, William; Nguyen, Vanessa; McNamara, Dan E.; Sankaran, Banumathi; Pereira, Jose Henrique; Parmeggiani, Fabio; Brunette, TJ; Cascio, Duilio; Yeates, Todd R.; Zwart, Peter; Baker, David

2016-01-01

Self-assembling cyclic protein homo-oligomers play important roles in biology and the ability to generate custom homo-oligomeric structures could enable new approaches to probe biological function. Here we report a general approach to design cyclic homo-oligomers that employs a new residue pair transform method for assessing the design ability of a protein-protein interface. This method is sufficiently rapid to enable systematic enumeration of cyclically docked arrangements of a monomer followed by sequence design of the newly formed interfaces. We use this method to design interfaces onto idealized repeat proteins that direct their assembly into complexes that possess cyclic symmetry. Of 96 designs that were experimentally characterized, 21 were found to form stable monodisperse homo-oligomers in solution, and 15 (4 homodimers, 6 homotrimers, 6 homotetramers and 1 homopentamer) had solution small angle X-ray scattering data consistent with the design models. X-ray crystal structures were obtained for five of the designs and each of these were shown to be very close to their design model. PMID:28338692

Regulation of Phosphorylation of a Specific Protein in Toad-Bladder Membrane by Antidiuretic Hormone and Cyclic AMP, and Its Possible Relationship to Membrane Permeability Changes

PubMed Central

DeLorenzo, Robert J.; Walton, Kenneth G.; Curran, Peter F.; Greengard, Paul

1973-01-01

Phosphorylation of a specific protein was decreased in intact toad bladders by exposure to either antidiuretic hormone or monobutyryl cyclic AMP. The decrease in phosphorylation caused by these agents preceded the change in electrical potential difference (an indicator of the rate of sodium ion transport) observed in response to the same compounds. The addition of cyclic AMP to homogenates of toad bladder led to a decrease in phosphorylation of the same, or a similar, protein. In subcellular fractionation studies, the effect of cyclic AMP on the phosphorylation of this protein was observed in those fractions rich in membrane fragments, but not in the nuclear or cell-sap fractions. These and other results are compatible with the possibility that the regulation by vasopressin and cyclic AMP of sodium and/or water transport in toad bladder may be mediated through regulation of the phosphorylation of this specific protein. Images PMID:4351809

Cyclic peptides as potential therapeutic agents for skin disorders.

PubMed

Namjoshi, Sarika; Benson, Heather A E

2010-01-01

There is an increasing understanding of the role of peptides in normal skin function and skin disease. With this knowledge, there is significant interest in the application of peptides as therapeutics in skin disease or as cosmeceuticals to enhance skin appearance. In particular, antimicrobial peptides and those involved in inflammatory processes provide options for the development of new therapeutic directions in chronic skin conditions such as psoriasis and dermatitis. To exploit their potential, it is essential that these peptides are delivered to their site of action in active form and in sufficient quantity to provide the desired effect. Many polymers permeate the skin poorly and are vulnerable to enzymatic degradation. Synthesis of cyclic peptide derivatives can substantially alter the physicochemical characteristics of the peptide with the potential to improve its skin permeation. In addition, cyclization can stabilize the peptide structure and thereby increase its stability. This review describes the role of cyclic peptides in the skin, examples of current cyclic peptide therapeutic products, and the potential for cyclic peptides as dermatological therapeutics and cosmeceuticals.

A short review on structure and role of cyclic-3',5'-adenosine monophosphate-specific phosphodiesterase 4 as a treatment tool.

PubMed

Eskandari, Nahid; Mirmosayyeb, Omid; Bordbari, Gazaleh; Bastan, Reza; Yousefi, Zahra; Andalib, Alireza

2015-01-01

Cyclic nucleotide phosphodiesterases (PDEs) are known as a super-family of enzymes which catalyze the metabolism of the intracellular cyclic nucleotides, cyclic-3',5'-adenosine monophosphate (cAMP), and cyclic-3',5'-guanosine monophosphate that are expressed in a variety of cell types that can exert various functions based on their cells distribution. The PDE4 family has been the focus of vast research efforts over recent years because this family is considered as a prime target for therapeutic intervention in a number of inflammatory diseases such as asthma, chronic obstructive pulmonary disease, and rheumatoid arthritis, and it should be used and researched by pharmacists. This is because the major isoform of PDE that regulates inflammatory cell activity is the cAMP-specific PDE, PDE4. This review discusses the relationship between PDE4 and its inhibitor drugs based on structures, cells distribution, and pharmacological properties of PDE4 which can be informative for all pharmacy specialists.

Strain controlled cyclic tests on miniaturized specimens

NASA Astrophysics Data System (ADS)

Procházka, R.; Džugan, J.

2017-02-01

The paper is dealing with strain controlled cyclic tests using a non-contact strain measurement based on digital image correlation techniques on proportional sizes of conventional specimens. The cyclic behaviour of 34CrNiMo6 high-strength steel was investigated on miniaturized round specimens with diameter of 2mm that were compared with specimens in accordance with ASTM E606 standards. The cycle asymmetry coefficient was R= -1. This application is intended to be used for life time assessment of in service components in future work which enables to carried out a group of mechanical tests from a limited amount of the experimental material. The attention was paid to confirm the suitability of the proposed size miniaturization geometry, testing set up and procedure. The test results obtained enabled to construct Manson-Coffin curves and assess fatigue parameters. The purpose of this study is to present differences between cyclic curves and cyclic parameters which have been evaluated based on conventional and miniaturized specimens.

Cyclic strain rate effects in fatigued face-centred and body-centred cubic metals

NASA Astrophysics Data System (ADS)

Mughrabi, Haël

2013-09-01

The present work deals mainly with the effect and the use of strain rate and temperature changes during cyclic deformation as a means to obtain valuable information on the thermally activated dislocation glide processes, based on the assessment of reversible changes of the thermal effective stress and of transient changes of the athermal stress. The importance of closed-loop testing in true plastic strain control with constant cyclic plastic strain rate throughout the cycle is explained and emphasized, especially with respect to the case of strain rate sensitive materials. Stress responses of face-centred cubic and body-centred cubic (bcc) metals to cyclic strain rate changes are presented to illustrate that the deformation modes of these two classes of materials differ characteristically at temperatures below that the so-called knee temperature of bcc metals. When such tests are performed in cyclic saturation, the temperature and strain rate dependence of bcc metals can be measured very accurately on one and the same specimen, permitting a thorough analysis of thermal activation.

The Presence of Two Cyclase Thioesterases Expands the Conformational Freedom of the Cyclic Peptide Occidiofungin

PubMed Central

Ravichandran, Akshaya; Gu, Ganyu; Escano, Jerome; Lu, Shi-En; Smith, Leif

2014-01-01

Occidiofungin is a cyclic nonribosomally synthesized antifungal peptide with submicromolar activity produced by Gram-negative bacterium Burkholderia contaminans. The biosynthetic gene cluster was confirmed to contain two cyclase thioesterases. NMR analysis revealed that the presence of both thioesterases is used to increase the conformational repertoire of the cyclic peptide. The loss of the OcfN cyclic thioesterase by mutagenesis results in a reduction of conformational variants and an appreciable decrease in bioactivity against Candida species. Presumably, the presence of both asparagine and β-hydroxyasparagine variants coordinate the enzymatic function of both of the cyclase thioesterases. OcfN has presumably evolved to be part of the biosynthetic gene cluster due to its ability to produce structural variants that enhance antifungal activity against some fungi. The enhancement of the antifungal activity from the incorporation of an additional cyclase thioesterase into the biosynthetic gene cluster of occidiofungin supports the need to explore new conformational variants of other therapeutic or potentially therapeutic cyclic peptides. PMID:23394257