Negative differential resistance in doped poly(3-methylthiophene) devices

The current density-voltage (J-V) characteristics of poly(3-methylthiophene) devices show a negative differential resistance (NDR) at room temperature with a large peak to valley current ratio (similar to 507). This NDR can be tuned by two orders of magnitude by controlling the carrier density due to the variation of the space-charge region in the device. The temperature and scan rate dependent J-V measurements infer that the NDR is mainly driven by the trapping and de-trapping of carriers. The photo-generation of carriers is observed to reduce the NDR effect.

Negative differential resistance in Gd0.5Sr0.5MnO3: A consequence of Joule heating

Negative differential resistance (NDR) in current-voltage (I-V) characteristics and apparent colossal electroresistance were observed in Gd0.5Sr0.5MnO3 single crystals at low temperatures. The continuous dc I-V measurements showed a marked thermal drift. In addition, temperature of the sample surface was found to be significantly higher than that of the base at high applied currents. Two different strategies namely estimation and diminution of the Joule heating (pulsed I-V measurements) were employed to investigate its role in the electric transport properties. Our experiments reveal that the NDR in Gd0.5Sr0.5MnO3 is a consequence of Joule heating rather than the melting of charge order. (C) 2010 American Institute of Physics. doi:10.1063/1.3486221]

Large low-frequency resistance noise in chemical vapor deposited graphene

We report a detailed investigation of resistance noise in single layer graphene films on Si/SiO2 substrates obtained by chemical vapor deposition (CVD) on copper foils. We find that noise in these systems to be rather large, and when expressed in the form of phenomenological Hooge equation, it corresponds to Hooge parameter as large as 0.1-0.5. We also find the variation in the noise magnitude with the gate voltage (or carrier density) and temperature to be surprisingly weak, which is also unlike the behavior of noise in other forms of graphene, in particular those from exfoliation. (C) 2010 American Institute of Physics. doi:10.1063/1.3493655]

C-H…O hydrogen bond mediated chain reversal in a peptide containing g-amino acid residue, determined directly from powder X-ray diffraction data

The finding that peptides containing -amino acid residues give rise to folding patterns hitherto unobserved in -amino acid peptides[1] has stimulated considerable interest in the conformational properties of peptides built from , and residues,[2] as the introduction of additional methylene (CH2) units into peptide chains provides further degrees of conformational freedom.

A C-H…O hydrogen bond stabilized polypeptide chain reversal motif at the C-terminus helices in proteins.

The serendipitous observation of a C–Hcdots, three dots, centeredO hydrogen bond mediated polypeptide chain reversal in synthetic peptide helices has led to a search for the occurrence of a similar motif in protein structures. From a dataset of 634 proteins, 1304 helices terminating in a Schellman motif have been examined. The C–Hcdots, three dots, centeredO interaction between the T−4 CαH and T+1 C=O group (Ccdots, three dots, centeredO≤3.5 Å) becomes possible only when the T+1 residue adopts an extended β conformation (T is defined as the helix terminating residue adopting an αL conformation). In all, 111 examples of this chain reversal motif have been identified and the compositional and conformational preferences at positions T−4, T, and T+1 determined. A marked preference for residues like Ser, Glu and Gln is observed at T−4 position with the motif being further stabilized by the formation of a side-chain–backbone Ocdots, three dots, centeredH–N hydrogen bond involving the side-chain of residue T−4 and the N–H group of residue T+3. In as many as 57 examples, the segment following the helix was extended with three to four successive residues in β conformation. In a majority of these cases, the succeeding β strand lies approximately antiparallel with the helix, suggesting that the backbone C–Hcdots, three dots, centeredO interactions may provide a means of registering helices and strands in an antiparallel orientation. Two examples were identified in which extended registry was detected with two sets of C–Hcdots, three dots, centeredO hydrogen bonds between (T−4) CαHcdots, three dots, centeredC=O (T+1) and (T−8) CαHcdots, three dots, centeredC=O (T+3).

Probing the role of the C-H center dot center dot center dot O hydrogen bond stabilized polypeptide chain reversal at the C-terminus of designed peptide helices. Structural characterization of three decapeptides

The structural characterization in crystals of three designed decapeptides containing a double D-segment at the C-terminus is described. The crystal structures of the peptides Boc-Leu-Aib-Val-Xxx-Leu-Aib-Val- (D)Ala-(D)Leu-Aib-OMe, (Xxx = Gly 2, (D)Ala 3, Aib 4) have been determined and compared with those reported earlier for peptide 1 (Xxx = Ala) and the all L analogue Boc-Leu-Aib-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-OMe, which yielded a perfect right-handed a-helical structure. Peptides 1 and 2 reveal a right-handed helical segment spanning residues 1 to 7, ending in a Schellman motif with Ala(8) functioning as the terminating residue. Polypeptide chain reversal occurs at residue 9, a novel feature that appears to be the consequence of a C-(HO)-O-... hydrogen bond between residue 4 (CH)-H-alpha and residue 9 CO groups. The structures of peptides 3 and 4, which lack the pro R hydrogen at the C-alpha atom of residue 4, are dramatically different. Peptide 3 adopts a right-handed helical conformation over the 1 to 7 segment. Residues 8 and 9 adopt at conformations forming a C-terminus type I' beta-turn, corresponding to an incipient left-handed twist of the polypeptide chain. In peptide 4, helix termination occurs at Aib(6), with residues 6 to 9 forming a left-handed helix, resulting in a structure that accommodates direct fusion of two helical segments of opposite twist. Peptides 3 and 4 provide examples of chiral residues occurring in the less favored sense of helical twist; (D)Ala(4) in peptide 3 adopts an alpha(R) conformation, while (L)Val(7) in 4 adopts an alpha(L) conformation. The structural comparison of the decapeptides reported here provides evidence for the role of specific C-(HO)-O-... hydrogen bonds in stabilizing chain reversals at helix termini, which may be relevant in aligning contiguous helical and strand segments in polypeptide structures.

Scaling theory of quantum resistance distributions in disordered systems

We have derived explicitly, the large scale distribution of quantum Ohmic resistance of a disordered one-dimensional conductor. We show that in the thermodynamic limit this distribution is characterized by two independent parameters for strong disorder, leading to a two-parameter scaling theory of localization. Only in the limit of weak disorder we recover single parameter scaling, consistent with existing theoretical treatments.

Impurity effects on the critical behaviour of the electrical resistance of binary liquid mixtures

The electrical resistance of the binary liquid system cyclohexane + acetic anhydride is measured, in the critical region, both in the pure mixture and when the mixture is doped with small amounts (≈ 100 ppm) of H2O/D2O impurities.T c was approached to aboutt=3×10−6 wheret=(T −T c )/T c . The critical exponentb ≈ 0.35 in the fit of the resistance data to the equationdR/dT ∼t −b does not seem to be affected appreciably by the impurities. There is a sign reversal ofdR/dt in the non-critical region. Binary liquid systems seem to violate the universality of the critical resistivity.

Evaluation of Erosion Resistance of Metallic Materials and the Role of Material Properties in Correlations

A study of the correlations between material properties and normalized erosion resistance (inverse of erosion rates) of various materials tested in the rotating disk and the flow venturi at various intensities indicates that different individual properties influence different stages of erosion. At high and low intensities of erosion, energy properties predominate the phenomenon, whereas at intermediate intensities strength and acoustic properties become more significant. However, both strength and energy properties are significant in the correlations for the entire spectrum of erosion when extensive cavitation and liquid impingement data from several laboratories involving different intensities and hydrodynamic conditions are considered. The use of true material properties improved the statistical parameters by 3 to 37%, depending on the intensity of erosion. It is possible to evaluate qualitatively the erosion resistances of materials based on the true stress-true strain curves.

Critical phenomena in electrical resistance of binary liquids: A study of the frequency dependence

The electrical resistance is measured in two binary liquid systems CS2 + CH3NO2 and n-C7H16 + CH3OH in the critical region as a function of frequency from 10 Hz to 100 kHz. The critical exponent b ≈ 0.35 in the singularity of dR/dT α (T - Tc)−b near Tc has no appreciable dependence upon the frequency. Thus any contribution from dielectric dispersion to the critical resistivity is not appreciable. The universal behaviour of the dR/dT anomaly does not seem to be followed in binary liquid systems.

Conformational studies of the triphenylphosphazenyl side chain in cyclophosphazenes. I. Crystal and molecular structure of N3P3C15(NPPh3)

The title compound, C t8H~sC15NaP4, crystallizes in the monoclinic space group P2~/n with a = 20.14 (2), b = 8.69 (1), c = 14.92 (2) A, fl = 98.8 (3) ° , Z = 4. The structure was determined from visual data and refined to R = 0-069 for 1450 reflections. The cyclophosphazene ring is non-planar. The exocyclic NPPh 3 group exhibits type I conformation [R. A. Shaw (1975). Pure Appl. Chem. 44, 317-341] in which the N-P bond is perpendicular to the adjacent P-CI bond.

Analysis of side-chain conformation in proteins

The crystal structures of a number of globular proteins are currently available. An analysis of the distribution of side-chains among different allowed conformations in these proteins has been carried out. The observed conformations of individual residues are discussed on the basis of well-known stereochemical criteria. The population distribution of side-chains in different allowed regions in conformational space can be explained largely on the basis of simple steric considerations. In addition to examining the conformational behaviour of individual residues, some population distributions of conformational angles of general interest involving groups of residues have also been analyzed.

Alloy design for fracture resistance

Several methods for improving the strength of metallic materials are available and correlations between strength and various microstructural features have been established. The purpose of this paper is to review parallel developments favouring improved fracture resistance. Resistance to fracture in monotonie loading, cyclic loading and when fracture is environment-aided have been considered in steels, aluminium alloys and anisotropic materials. Finally, the question of optimising alloy behaviour is discussed.

Uncoupling Protein 2 and 3 Gene Polymorphisms and Their Association with Type 2 Diabetes in Asian Indians

Background: This study examined the association of -866G/A, Ala55Val, 45bpI/D, and -55C/T polymorphisms at the uncoupling protein (UCP) 3-2 loci with type 2 diabetes in Asian Indians. Methods: A case-control study was performed among 1,406 unrelated subjects (487 with type 2 diabetes and 919 normal glucose-tolerant NGT]), chosen from the Chennai Urban Rural Epidemiology Study, an ongoing population-based study in Southern India. The polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism and direct sequencing. Haplotype frequencies were estimated using an expectation-maximization algorithm. Linkage disequilibrium was estimated from the estimates of haplotypic frequencies. Results: The genotype (P = 0.00006) and the allele (P = 0.00007) frequencies of Ala55Val of the UCP2 gene showed a significant protective effect against the development of type 2 diabetes. The odds ratios (adjusted for age, sex, and body mass index) for diabetes for individuals carrying Ala/Val was 0.72, and that for individuals carrying Val/Val was 0.37. Homeostasis insulin resistance model assessment and 2-h plasma glucose were significantly lower among Val-allele carriers compared to the Ala/Ala genotype within the NGT group. The genotype (P = 0.02) and the allele (P = 0.002) frequencies of -55C/T of the UCP3 gene showed a significant protective effect against the development of diabetes. The odds ratio for diabetes for individuals carrying CT was 0.79, and that for individuals carrying TT was 0.61. The haplotype analyses further confirmed the association of Ala55Val with diabetes, where the haplotypes carrying the Ala allele were significantly higher in the cases compared to controls. Conclusions: Ala55Val and -55C/T polymorphisms at the UCP3-2 loci are associated with a significantly reduced risk of developing type 2 diabetes in Asian Indians.

Covalent attachment of two important dicopper(II) systems in a one-dimensional polymeric chain: An x-ray structure of [Cu2(en)2(OH)2·Cu2(O2CMe)4](PF6)2·0.5EtOH]α showing the shortest Cucdots, three dots, centeredCu Distance in the tetraacetato core

Reaction of Cu2(O2CMe)4(H2O)2 with 1,2-diaminoethane(en) in ethanol, followed by the addition of NH4PF6, led to the formation of a covalently linked 1D polymeric copper(II) title complex showing alternating [Cu2(en)2(OH)22+] and [Cu2(O2CMe)4] units in the chain and the shortest Cucdots, three dots, centeredCu separation of 2.558(2) Å in the tetraacetato core.