235 research outputs found
Simulation study of the coil-globule transition of a polymer in solvent
No full textMolecular dynamics simulations are used to study the coil-globule transition for a system composed of a bead-spring polymer immersed in an explicitly modeled solvent. Two different versions of the model are used, which are differentiated by the nature of monomer-solvent, solvent-solvent, and nonbonded monomer-monomer interactions. For each case, a model parameter lambda determines the degree of hydrophobicity of the monomers by controlling the degree of energy mismatch between the monomers and solvent particles. We consider a lambda-driven coil-globule transition at constant temperature. The simulations are used to calculate average static structure factors, which are then used to determine the scaling exponents of the system in order to determine the theta-point values lambda(theta) separating the coil from the globule states. For each model we construct coil-globule phase diagrams in terms of lambda and the particle density rho. The results are analyzed in terms of a simple Flory-type theory of the collapse transition. The ratio of lambda(theta) for the two models converges in the high density limit exactly to the value predicted by the theory in the random mixing approximation. Generally, the predicted values of lambda(theta) are in reasonable agreement with the measured values at high rho, though the accuracy improves if the average chain size is calculated using the full probability distribution associated with the polymer-solvent free energy, rather than merely using the value obtained from the minimum of the free energy. (C) 2005 American Institute of Physics.PT: J; CR: ABRAMS CF, 2002, EUROPHYS LETT, V59, P391 ALLEGRA G, 1983, MACROMOLECULES, V16, P1317 ALLEGRA G, 1985, J CHEM PHYS, V83, P397 BAYSAL BM, 2003, MACROMOL THEOR SIMUL, V12, P627 BIRSHTEIN TM, 1991, MACROMOLECULES, V24, P1554 CALVO F, 2002, J CHEM PHYS, V116, P2642 CURRO JG, 1987, J CHEM PHYS, V87, P1842 CURRO JG, 1987, MACROMOLECULES, V20, P1928 CURRO JG, 1991, MACROMOLECULES, V24, P6736 DEGENNES PG, 1975, J PHYS LETT, V36, L55 DESCLOISEAUX J, 1991, POLYM SOLUTION DIJKSTRA M, 1994, J CHEM PHYS, V101, P3179 DIJKSTRA M, 1994, PHYS REV LETT, V72, P298 DIMARZIO EA, 1984, MACROMOLECULES, V17, P969 DOYE JPK, 1998, J CHEM PHYS, V108, P2134 EIZNER EY, 1969, POLYM SCI USSR, V11, P409 FLORY PJ, 1953, PRINCIPLES POLYM CHE FUJIWARA S, 2001, J CHEM PHYS, V114, P6455 GAN HH, 1998, J CHEM PHYS, V109, P2011 GAN HH, 1999, J CHEM PHYS, V110, P3235 GRASSBERGER P, 1995, J CHEM PHYS, V102, P6881 GRASSBERGER P, 1997, PHYS REV E B, V56, P3682 GRAYCE CJ, 1997, J CHEM PHYS, V106, P5171 GROSBERG AY, 1987, SOC SCI REV A, V8, P147 GROSBERG AY, 1992, MACROMOLECULES, V25, P1970 GROSBERG AY, 1992, MACROMOLECULES, V25, P1980 GROSBERG AY, 1992, MACROMOLECULES, V25, P1991 GROSBERG AY, 1992, MACROMOLECULES, V25, P1996 GROSBERG AY, 1994, AIP SERIES POLYM COM HU WB, 1998, J CHEM PHYS, V109, P3686 HUANG L, 2003, J CHEM PHYS, V119, P2432 IRBACK A, 1999, J CHEM PHYS, V110, P12256 IVANOV VA, 1998, J CHEM PHYS, V109, P5659 IVANOV VA, 2000, MACROMOL THEOR SIMUL, V9, P488 KARASAWA N, 1988, J PHYS CHEM-US, V92, P5828 KAVASSALIS TA, 1993, MACROMOLECULES, V26, P4144 KHALATUR PG, 1998, EUR PHYS J B, V5, P881 KHALATUR PG, 1998, MOL PHYS, V93, P555 LAI PY, 1999, MACROMOL THEOR SIMUL, V8, P382 LIANG HJ, 2000, J CHEM PHYS, V113, P4469 LIAO Q, 1999, J CHEM PHYS, V110, P8835 LIFSHITZ IM, 1969, SOV PHYS JETP, V28, P1280 LIFSHITZ IM, 1978, REV MOD PHYS, V50, P683 LUNABARCENAS G, 1997, J CHEM PHYS, V107, P10782 MA JP, 1995, J CHEM PHYS, V103, P2615 MENDEZ S, 2001, J CHEM PHYS, V115, P5669 MILCHEV A, 1993, J CHEM PHYS, V99, P4786 MUTHUKUMAR M, 1984, J CHEM PHYS, V81, P6272 NISHIO I, 1979, NATURE, V281, P208 NOGUCHI H, 1998, J CHEM PHYS, V109, P5070 PAUL W, 2001, J CHEM PHYS, V115, P630 POLSON JM, 1999, PHYS REV E, V60, P3429 POLSON JM, 2000, J CHEM PHYS, V113, P1283 POLSON JM, 2002, J CHEM PHYS, V116, P7244 PTITSYN OB, 1965, BIOFIZIKA, V10, P1 PTITSYN OB, 1968, J POLYMER SCI C, V16, P3509 RUBIO AM, 1995, J CHEM PHYS, V102, P2277 SANCHEZ IC, 1979, MACROMOLECULES, V12, P980 SCHWEIZER KS, 1987, PHYS REV LETT, V58, P246 SCHWEIZER KS, 1994, ADV POLYM SCI, V116, P321 SCHWEIZER KS, 1997, ADV CHEM PHYS, V98, P1 SOKAL A, 1995, MONTE CARLO MOL DYNA STOCKMAYER WH, 1960, MAKROMOL CHEM, V35, P54 SUEN JKC, 1997, J CHEM PHYS, V106, P1288 SWISLOW G, 1980, PHYS REV LETT, V44, P796 SZLEIFER I, 1992, J CHEM PHYS, V97, P6802 TANAKA G, 1995, MACROMOLECULES, V28, P1049 TANAKA G, 1996, MACROMOL THEOR SIMUL, V5, P499 TAYLOR MP, 1995, MOL PHYS, V86, P73 TAYLOR MP, 1996, J CHEM PHYS, V104, P4835 TAYLOR MP, 2001, J CHEM PHYS, V114, P6472 TAYLOR MP, 2003, J CHEM PHYS, V118, P883 VANDERSCHOOT P, 1998, MACROMOLECULES, V31, P4635 VASILEVSKAYA VV, 1998, J CHEM PHYS, V109, P5108 VASILEVSKAYA VV, 1998, J CHEM PHYS, V109, P5119 WITTKOP M, 1996, J CHEM PHYS, V104, P3373 ZHOU YQ, 1997, J CHEM PHYS, V107, P10691; NR: 77; TC: 5; J9: J CHEM PHYS; PG: 11; GA: 893DHSource type: Electronic(1
Therapeutic Efficacy of Vishnu Chakara Mathirai - A Siddha Formulation in the management of Valippu Noi (Convulsive Disorders): A Pre-Clinical study
Get PDFThe Vishnu Chakara Mathirai possess the specified charcters as mentioned by the Pharmacopoeial Laboratory for Indian Medicine, Ministry of AYUSH.
• The phytochemical analysis revealed the presence of alkaloids and phenols which may helpful for the therapeutic efficacy.
• The ICP OES analysis revealed that the toxic elements like mercury, arsenic, cadmium, lead and sulphur were found to be WHO permissible limits.
• The spectral studies revealed the fingerprint of VCM which can be used for its bulk production.
• The SEM and EXAX analysis showed the basic elements present in VCM as well as the external morphology of Vishnu Chakara Mathirai.
• The TLC and HPTLC finger printing is much helpful in identifying the active principle in VCM.
• The drug VCM was found to the safe as the LD50 level was fall above 2000mg/kg.b.wt.
• The NOEAL level was found to be > 200 mg/kg b.wt.
• The subacute and subchronic toxicity study revealed no toxic effects in the animals.
• Efficacy studies revealed good antiepileptic activity as it controls the maximum electro shock in rats, Picrotoxin induced seizures in mice, Picrotoxin induced kindling as well as seizures and N-Methyl-D-Aspartate (NMDA) test in mice.
CONCLUSION:
The present study was undertaken to establish the literature that Vishu Chakara Mathirai (VCM), a herbo mineral formulation of Siddha system of medicine, would be
effectively used against epilepsy (Valippu Noi), through various animal models. The safety as well as efficacy of VCM was studied extensively using standard and recommended scientific techniques. The trial drug VCM was found to be both safe and effective in epilepsy among animal models. The findings are strongly supportive of the traditional claim and use of VCM as an anti-epleptic medicine. From this study findings, it is also recommended that the medicine VCM can be taken for further research in the form of pharmacokinetic and pharmacodynamic studies as well clinical trials among
human subjects to further establish the finding of this study.
RECOMMENDATIONS:
As VCM shows very good anti epileptic activity in animal models, therefore it is recommended for a pharmacokinetic and pharmacodynamic study. The drug is also be recommended for a clinical trial in epileptic patients
WITHDRAWN: J point elevation on electrocardiogram – An uncommon etiology
No full textThis article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy
Gutzwiller-RVB theory of high temperature superconductivity : results from renormalized mean field theory and variational Monte Carlo calculations
No full textWe consider the theory of high temperature superconductivity from the viewpoint of a strongly correlated electron system. In particular, we discuss Gutzwiller projected wave functions, which incorporate strong correlations by prohibiting double occupancy in orbitals with strong on-site repulsion. After a general overview on high temperature superconductivity, we discuss Anderson’s resonating valence bond (RVB) picture and its implementation by renormalized mean field theory (RMFT) and variational Monte Carlo (VMC) techniques. In the following, we present a detailed review on RMFT and VMC results with emphasis on our recent contributions. Especially, we are interested in spectral features of Gutzwiller-Bogoliubov quasiparticles obtained by extending VMC and RMFT techniques to excited states. We explicitly illustrate this method to determine the quasiparticle weight and provide a comparison with angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). We conclude by summarizing recent successes and by discussing open questions, which must be solved for a thorough understanding of high temperature superconductivity by Gutzwiller projected wave functions
Numerical study of the Wheatley-Hsu-Anderson interlayer tunneling mechanism of high-T<SUB>c</SUB> superconductivity
No full textWe present results obtained (by exact diagonalization) for the problem of two t-J planes with an interlayer coupling t⊥. Our results for small hole concentrations show that in-plane superconducting correlations are enhanced by t⊥. When the constraint on double occupancy in the t-J model is relaxed, the enhancement disappears. These results illustrate the interlayer tunneling mechanism for superconductivity
Spectral function of the electron in a superconducting resonating valence-band state
No full textWe present a model calculation of the spectral function of an electron in a superconducting resonating valence-bond (RVB) state. The RVB state, described by the phase-string mean-field theory of the t-J model, is characterized by three important features: (i) spin-charge separation, (ii) short-range antiferromagnetic correlations, and (iii) holon condensation. We show that when a bare hole is created, as in photoemission spectroscopy for instance, the RVB background responds with an antiferromagnetic oscillation of the local spin density surrounding the hole. This leads to matrix element effects with definite experimental consequences. We compare our results with data obtained from angle resolved photoemission spectroscopy in superconducting Bi2Sr2CaCu2O8+?? at optimal doping concentration
Modeling Method for Semicrystalline Polymers Controlling Aspects of the Morphology at the Molecular Scale for the Study of Mechanical and Physicochemical Properties
No full textInternational audienceA novel method is presented to build semi-crystalline polymer models used in molecular dynamics simulations. The method allows controlling certain aspects of the molecu- lar morphology of the material. It relies on the generation of the polymer sections in the amorphous phase of the semi-crystalline structure according to the statistical polymer physics theory proposed by Adhikari and Muthukumar [Adhikari S. and Muthukumar M., J. Chem. Phys., 2019 151, 114905]. The amorphous phase is first built based on the method initially developed by Theodorou and Suter [Theodorou D. N. and Suter U. W., Macromolecules 1985 18 (7), 1467-1478]. Then, the amorphous phase is stacked between crystallites, and a connection algorithm proposed by Rigby et al. [Rigby, D., Saxe, P.W., Freeman, C.M., Leblanc, B. Advanced Composites for Aerospace, Marine, and Land Applications. 2014 Springer, Cham], initially developed to build polymer thermosets, is employed to link the two phases. For a given set of degree of crystallinity, semi-crystalline long period, densities of the crystalline and amorphous phases and polymer molecular weight, the characteristic ratio is used to control the relative fractions of different types of polymer sections in the amorphous phase as well as the distribution of their lengths. There are three types of amorphous polymer sections: the ones that are reentering in the same crystallite called loops, those that are bonding two different crystallites called tie chains, and the chain tails ending in the amorphous region. The higher the imposed characteristic ratio is, the higher the fraction of tie chains is. The full implementation of the theory is described and then applied to High-Density PolyEthylene (HDPE). Several samples are generated. The obtained structures are characterized. Their elastic coeffcients are computed, and high uniaxial deformations are performed. It is shown that the higher the degree of crystallinity, the higher the elastic coeffcients. An entanglement analysis shows that the quantity of tie chains is more decisive than the entanglements in acting as stress transmitters to rigidify the structure
Magnetic resonance spectroscopy assessment of brain injury after moderate hypothermia in neonatal encephalopathy: a prospective multicentre cohort study
Get PDFCopyright \ua9 2019 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. Published by Elsevier Ltd.. All rights reserved. BACKGROUND: In neonatal encephalopathy, the clinical manifestations of injury can only be reliably assessed several years after an intervention, complicating early prognostication and rendering trials of promising neuroprotectants slow and expensive. We aimed to determine the accuracy of thalamic proton magnetic resonance (MR) spectroscopy (MRS) biomarkers as early predictors of the neurodevelopmental abnormalities observed years after neonatal encephalopathy. METHODS: We did a prospective multicentre cohort study across eight neonatal intensive care units in the UK and USA, recruiting term and near-term neonates who received therapeutic hypothermia for neonatal encephalopathy. We excluded infants with life-threatening congenital malformations, syndromic disorders, neurometabolic diseases, or any alternative diagnoses for encephalopathy that were apparent within 6 h of birth. We obtained T1-weighted, T2-weighted, and diffusion-weighted MRI and thalamic proton MRS 4-14 days after birth. Clinical neurodevelopmental tests were done 18-24 months later. The primary outcome was the association between MR biomarkers and an adverse neurodevelopmental outcome, defined as death or moderate or severe disability, measured using a multivariable prognostic model. We used receiver operating characteristic (ROC) curves to examine the prognostic accuracy of the individual biomarkers. This trial is registered with ClinicalTrials.gov, number NCT01309711. FINDINGS: Between Jan 29, 2013, and June 25, 2016, we recruited 223 infants who all underwent MRI and MRS at a median age of 7 days (IQR 5-10), with 190 (85%) followed up for neurological examination at a median age of 23 months (20-25). Of those followed up, 31 (16%) had moderate or severe disability, including one death. Multiple logistic regression analysis could not be done because thalamic N-acetylaspartate (NAA) concentration alone accurately predicted an adverse neurodevelopmental outcome (area under the curve [AUC] of 0\ub799 [95% CI 0\ub794-1\ub700]; sensitivity 100% [74-100]; specificity 97% [90-100]; n=82); the models would not converge when any additional variable was examined. The AUC (95% CI) of clinical examination at 6 h (n=190) and at discharge (n=167) were 0\ub772 (0\ub765-0\ub778) and 0\ub760 (0\ub753-0\ub768), respectively, and the AUC of abnormal amplitude integrated EEG at 6 h (n=169) was 0\ub773 (0\ub765-0\ub779). On conventional MRI (n=190), cortical injury had an AUC of 0\ub767 (0\ub760-0\ub773), basal ganglia or thalamic injury had an AUC of 0\ub781 (0\ub775-0\ub787), and abnormal signal in the posterior limb of internal capsule (PLIC) had an AUC of 0\ub782 (0\ub776-0\ub787). Fractional anisotropy of PLIC (n=65) had an AUC of 0\ub782 (0\ub776-0\ub787). MRS metabolite peak-area ratios (n=160) of NAA-creatine (<1\ub729) had an AUC of 0\ub779 (0\ub772-0\ub785), of NAA-choline had an AUC of 0\ub774 (0\ub766-0\ub780), and of lactate-NAA (>0\ub722) had an AUC of 0\ub794 (0\ub789-0\ub797). INTERPRETATION: Thalamic proton MRS measures acquired soon after birth in neonatal encephalopathy had the highest accuracy to predict neurdevelopment 2 years later. These methods could be applied to increase the power of neuroprotection trials while reducing their duration. FUNDING: National Institute for Health Research UK
(R)-2,3,4,5-Tetrahydro-2,2,4-trimethyl-1,5-benzothiazepine and rac-5-benzoyl-2,3,4,5-tetrahydro-2,2,4-trimethyl-1,5-benzothiazepine: chains built from N-H center dot center dot center dot S and C-H center dot center dot center dot pi(arene)hydrogen bonds
No full textMolecules of (R)-2,3,4,5-tetrahydro-2,2,4-trimethyl-1,5-benzothiazepine, C12H17NS, are linked into spiral C(5) chains by a single N-H...S hydrogen bond, while molecules of rac-5-benzoyl-2,3,4,5-tetrahydro-2,2,4-trimethyl-1,5-benzothiazepine, C19H21NOS, are linked into zigzag chains by a C-H...pi(arene) hydrogen bond.</p
Spectral function of the electron in a superconducting resonating valence-band state
Get PDFWe present a model calculation of the spectral function of an electron in a superconducting resonating valence-bond (RVB) state. The RVB state, described by the phase-string mean-field theory of the t-J model, is characterized by three important features: (i) spin-charge separation, (ii) short-range antiferromagnetic correlations, and (iii) holon condensation. We show that when a bare hole is created, as in photoemission spectroscopy for instance, the RVB background responds with an antiferromagnetic oscillation of the local spin density surrounding the hole. This leads to matrix element effects with definite experimental consequences. We compare our results with data obtained from angle resolved photoemission spectroscopy in superconducting Bi2Sr2CaCu2O8+δ at optimal doping concentration.Physical Review B 65(21), 214522. (2002)0163-182
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