Components of the ubiquitin-proteasome pathway compete for surfaces on Rad23 family proteins

Background  

The delivery of ubiquitinated proteins to the proteasome for degradation is a key step in the regulation of the ubiquitin-proteasome pathway, yet the mechanisms underlying this step are not understood in detail. The Rad23 family of proteins is known to bind ubiquitinated proteins through its two ubiquitin-associated (UBA) domains, and may participate in the delivery of ubiquitinated proteins to the proteasome through docking via the Rad23 ubiquitin-like (UBL) domain.     

Determination of the heats of gasification of polymers using differential scanning calorimetry

The amount of heat that is required to gasify unit mass of material is one of the key properties that define its ignition resistance and fire response. Knowledge of this property is necessary to assess a material's fire hazard in a particular fire scenario. Nevertheless, even for the most common polymers the values of this property are not well established. Here we present a method for determining the heat of gasification using differential scanning calorimetry and apply this method to a set of ten common plastics and engineering polymers.     

New states in heavy Cd isotopes and evidence for weakening of the N = 82 shell structure

A chemically selective laser ion source has been used in a β-decay study of heavy Ag isotopes into even-even Cd nuclides. Gamma-spectroscopic techniques in time-resolving event-by-event and multiscaling modes have permitted the identification of the first 2⁺ and 4⁺ levels in ¹²⁶Cd₇₈, ¹²⁸Cd₈₀, and tentatively the 2⁺ state in ¹³⁰Cd₈₂. From a comparison of these new states in ₄₈Cd with the E(2⁺) and E(4⁺)/E(2⁺) level systematics of ₄₆Pd and ₅₂Te isotopes and several recent model predictions, possible evidence for a weakening of the spherical N = 82 neutron-shell below double-magic ¹³²Sn is obtained. Received: 13 July 2000 / Accepted: 12 October 2000     

Filtering databases and chemical libraries

Molecular Diversity -     

An unstructured grid,three‐dimensional model based on the shallow water equations

A semi‐implicit finite difference model based on the three‐dimensional shallow water equations is modified to use unstructured grids. There are obvious advantages in using unstructured grids in problems with a complicated geometry. In this development, the concept of unstructured orthogonal grids is introduced and applied to this model. The governing differential equations are discretized by means of a semi‐implicit algorithm that is robust, stable and very efficient. The resulting model is relatively simple, conserves mass, can fit complicated boundaries and yet is sufficiently flexible to permit local mesh refinements in areas of interest. Moreover, the simulation of the flooding and drying is included in a natural and straightforward manner. These features are illustrated by a test case for studies of convergence rates and by examples of flooding on a river plain and flow in a shallow estuary. Copyright © 2000 John Wiley & Sons, Ltd.     

COMPARISON OF H AND P FINITE ELEMENT APPROXIMATIONS OF THE SHALLOW WATER EQUATIONS

A p-type finite element scheme is introduced for the three-dimensional shallow water equations with a harmonic expansion in time. The wave continuity equation formulation is used which decouples the problem into a Helmholtz equation for surface elevation and a momentum equation for horizontal velocity. An exploration of the applicability of p methods to this form of the shallow water problem is presented, with a consideration of the problem of continuity errors. The convergence rates and relative computational efficiency between h- and p- type methods are compared with the use of three test cases representing various degrees of difficulty. A channel test case establishes convergence rates, a continental shelf test case examines a problem with accuracy difficulties at the shelf break, and a field-scale test case examines problems with highly irregular grids. For the irregular grids, adaptive h combined with uniform p refinement was necessary to retain high convergence rates. © 1997 John Wiley & Sons, Ltd.     

The dark reactions F2 + CF3I,C2F5I,and n-C3F7I

The reactions between F₂ and the lowest members of the homologous series of perfluoroalkyl iodides (CF₃I, C₂F₅I, and n-C₃F₇I) have been studied. For these compounds, an exponential decrease in the alkyl iodide concentration over time following an induction period is observed for certain experimental conditions. Other conditions lead to chaotic-like kinetic behavior where the rate of alkyl iodide consumption continually changes. Kinetic rate data with CF₃I show that the disappearance rate depends upon both the type of surface and surface preparation. For all three compounds, Arrhenius plots reveal activation energies on the order of 10 kcal/mol, consistent with effective initiation steps of F₂ + RI → RIF + F, where R represents the CF₃, C₂F₅, or n-C₃F₇ radical respectively. The end products of the F₂ + RI reactions are RF, R₂, and IF₅, suggesting that the R radicals play an important kinetic role. Introducing O₂ into the F₂ + RI reaction systems results in successive oxidation of R by O₂, leading to the formation of CF₂O as an additional end product. IF(B → X) emission is observed from the RI-rich F₂ + RI reactions, confirming the existence of IF as an intermediate. © 1996 John Wiley & Sons, Inc.     

Solution Crystallization Analysis by Laser Light Scattering (SCALLS)

Summary: Solution crystallization analysis by laser light scattering offers a direct way of studying the solution crystallization of polyolefins. The technique yields similar results to Crystaf, but in a shorter time and with apparently greater sensitivity in some cases. The use of SCALLS is demonstrated for the study of selected propylene/higher α-olefin copolymers. Some conclusions are also drawn regarding the effect of molecular weight on the solution crystallization of polyolefins.     

Rectangles as sums of squares

In this paper we examine generalisations of the following problem posed by Laczkovich: Given an n×m rectangle with n and m integers, it can be written as a disjoint union of squares; what is the smallest number of squares that can be used? He also asked the corresponding higher dimensional analogue. For the two dimensional case Kenyon proved a tight logarithmic bound but left open the higher dimensional case. Using completely different methods we prove good upper and lower bounds for this case as well as some other variants.     

The effect of high dose of gamma-irradiation on residual radicals concentration in ultra-high molecular weight polyethylene (UHMWPE) in the presence of vitamin E

Powder samples of UHMWPE (GUR 1020) containing 0.1% by wt. vitamin E (??-tocopherol, ??-T) were irradiated at room temperature in air for doses of 30-kGy, 65-kGy or 100-kGy (⁶⁰Co). After irradiation, they were stored at ?78.5°C (dry ice temperature) for one year and then opened to air at room temperature. Following the decay of the primary alkyl and allyl radicals (at room temperature in air), growth of the carbon-centered polyenyl R1 (?^·CH?CH=CH?, m ?? 3), and the oxygen-centered dior tri-enyl R2 (?^·OCH?CH=CH? _m , m ?? 3) residual radicals were measured for eight weeks. An X-band electron spin resonance (ESR) spectrometer was used for radical measurements. The initial relative radical concentrations (R2/R1) were found to be 10.13, 4.6 and 3.7 for the 65-kGy, 30-kGy and 100-kGy samples, respectively. R1 and R2 were both found to grow significantly in the 65-kGy samples while they grew only slightly in the 30-kGy and 100-kGy samples. In 65-kGy sample, R1 grew faster than R2 and the relative concentration R2/R1 was reduced from 10.13 to 2.9 for the 65-kGy sample while that for the 30-kGy and 100-kGy samples reduced only slightly, from 4.6 to 3.5 and 3.7 to 3.2, respectively. The behavior of the residual radicals can be explained by Raman spectroscopic data which suggest that the 65-kGy samples had a higher percentage of amorphous regions when compared to the 30-kGy or 100-kGy (21.7% compared to 15.7% or 17.9%) and also suggest a lower percentage of inter-phase regions (16.4% compared to 25.6% or 17.5%) and a lower level of structural disorder (0.26% compared to 0.44% or 0.27%).