Rensselaer Polytechnic Institute

About: Rensselaer Polytechnic Institute is a education organization based out in Troy, New York, United States. It is known for research contribution in the topics: Terahertz radiation & Finite element method. The organization has 19024 authors who have published 39922 publications receiving 1414699 citations. The organization is also known as: RPI & Rensselaer Institute.

Bloch Electrons in a Uniform Magnetic Field

Abstract: The physical periodicity of a space lattice is not destroyed by the presence of a uniform magnetic field. It is shown that a ray group of unitary operators, isomorphic to pure translations, commutes with the Hamiltonian in this case. Such a group has the characteristic property that $AB=\mathrm{exp}[i\ensuremath{\varphi}(A,B)]C$, where $A$, $B$, and $C$ are elements of the group and $\ensuremath{\varphi}$ is a numerical factor. Representation theory applied to this group yields the characteristic degeneracies of levels in magnetic fields, as well as the transformation properties of eigenfunctions. By means of these it is possible to construct an effective Hamiltonian appropriate to finite magnetic fields in crystals.

Conformationally restrained analogues of pravadoline: nanomolar potent, enantioselective, (aminoalkyl)indole agonists of the cannabinoid receptor.

Abstract: Pravadoline (1) is an (aminoalkyl)indole analgesic agent which is an inhibitor of cyclooxygenase and, in contrast to other NSAIDs, inhibits neuronally stimulated contractions in mouse vas deferens (MVD) preparations (IC50 = 0.45 microM). A number of conformationally restrained heterocyclic analogues of pravadoline were synthesized in which the morpholinoethyl side chain was tethered to the indole nucleus. Restraining the morpholine diminished the ability of these pravadoline analogues to inhibit prostaglandin synthesis in vitro. In contrast, mouse vas deferens inhibitory activity was enhanced in [2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl] pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-(4-methoxyphenyl)methano ne (20). Only the R enantiomer of 20 was active (IC50 = 0.044 microM). An optimal orientation of the morpholine nitrogen for MVD inhibitory activity within the analogues studied was in the lower right quadrant, below the plane defined by the indole ring. A subseries of analogues of 20 and a radioligand of the most potent analogue, (R)-(+)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo [1,2,3-de]-1,4-benzoxazin-6-yl](1-naphthalenyl)methanone (21) were prepared. Inhibition of radioligand binding in rat cerebellar membranes was observed to correlate with functional activity in mouse vas deferens preparations. Binding studies with this ligand (Win 55212-2) have helped demonstrate that the (aminoalkyl)indole binding site is functionally equivalent with the CP-55,940 cannabinoid binding site. These compounds represent a new class of cannabinoid receptor agonists.

Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover.

Abstract: Small and large hydrophobic solutes exhibit remarkably different hydration thermodynamics. Small solutes are accommodated in water with minor perturbations to water structure, and their hydration is captured accurately by theories that describe density fluctuations in pure water. In contrast, hydration of large solutes is accompanied by dewetting of their surfaces and requires a macroscopic thermodynamic description. A unified theoretical description of these lengthscale dependencies was presented by Lum, Chandler, and Weeks [(1999) J. Phys. Chem. B 103, 4570–4577]. Here, we use molecular simulations to study lengthscale-dependent hydrophobic hydration under various thermodynamic conditions. We show that the hydration of small and large solutes displays disparate dependencies on thermodynamic variables, including pressure, temperature, and additive concentration. Understanding these dependencies allows manipulation of the small-to-large crossover lengthscale, which is nanoscopic under ambient conditions. Specifically, applying hydrostatic tension or adding ethanol decreases the crossover length to molecular sizes, making it accessible to atomistic simulations. With detailed temperature-dependent studies, we further demonstrate that hydration thermodynamics changes gradually from entropic to enthalpic near the crossover. The nanoscopic lengthscale of the crossover and its sensitivity to thermodynamic variables imply that quantitative modeling of biomolecular self-assembly in aqueous solutions requires elements of both molecular and macroscopic hydration physics. We also show that the small-to-large crossover is directly related to the Egelstaff-Widom lengthscale, the product of surface tension and isothermal compressibility, which is another fundamental lengthscale in liquids.

Fatigue resistance of aligned carbon nanotube arrays under cyclic compression.

Abstract: Structural components subject to cyclic stress can succumb to fatigue, causing them to fail at stress levels much lower than if they were under static mechanical loading1 However, despite extensive research into the mechanical properties of carbon nanotube structures2,3,4,5,6,7,8,9 for more than a decade, data on the fatigue behaviour of such devices have never been reported We show that under repeated high compressive strains, long, vertically aligned multiwalled nanotubes exhibit viscoelastic behaviour similar to that observed in soft-tissue membranes10,11 Under compressive cyclic loading, the mechanical response of the nanotube arrays shows preconditioning, characteristic viscoelasticity-induced hysteresis, nonlinear elasticity and stress relaxation, and large deformations Furthermore, no fatigue failure is observed at high strain amplitudes up to half a million cycles This combination of soft-tissue-like behaviour and outstanding fatigue resistance suggests that properly engineered nanotube structures could mimic artificial tissues, and that their good electrical conductivity could lead to their use as compliant electrical contacts in a variety of applications

Risk factor paradox in wasting diseases.

Abstract: Purpose of reviewEmerging data indicate that conventional cardiovascular risk factors (e.g. hypercholesterolemia and obesity) are paradoxically associated with better survival in distinct populations with wasting. We identify these populations and review survival paradoxes and common pathophysiologi