On the homology spectral sequence for topological Hochschild homology

Marcel Bökstedt has computed the homotopy type of the topological Hochschild homology of using his definition of topological Hochschild homology for a functor with smash product. Here we show that easy conceptual proofs of his main technical result of are possible in the context of the homotopy theory of -algebras as introduced by Elmendorf, Kriz, Mandell and May. We give algebraic arguments based on naturality properties of the topological Hochschild homology spectral sequence. In the process we demonstrate the utility of the unstable ``lower' notation for the Dyer-Lashof algebra.

     

Powder diffraction from a continuous microjet of submicrometer protein crystals

Atomic‐resolution structures from small proteins have recently been determined from high‐quality powder diffraction patterns using a combination of stereochemical restraints and Rietveld refinement [Von Dreele (2007), J. Appl. Cryst. 40 , 133–143; Margiolaki et al. (2007), J. Am. Chem. Soc. 129 , 11865–11871]. While powder diffraction data have been obtained from batch samples of small crystal‐suspensions, which are exposed to X‐rays for long periods of time and undergo significant radiation damage, the proof‐of‐concept that protein powder diffraction data from nanocrystals of a membrane protein can be obtained using a continuous microjet is shown. This flow‐focusing aerojet has been developed to deliver a solution of hydrated protein nanocrystals to an X‐ray beam for diffraction analysis. This method requires neither the crushing of larger polycrystalline samples nor any techniques to avoid radiation damage such as cryocooling. Apparatus to record protein powder diffraction in this manner has been commissioned, and in this paper the first powder diffraction patterns from a membrane protein, photosystem I, with crystallite sizes of less than 500 nm are presented. These preliminary patterns show the lowest‐order reflections, which agree quantitatively with theoretical calculations of the powder profile. The results also serve to test our aerojet injector system, with future application to femtosecond diffraction in free‐electron X‐ray laser schemes, and for serial crystallography using a single‐file beam of aligned hydrated molecules.     

Chemical triple-mutant boxes for quantifying cooperativity in intermolecular interactions

Chemical double-mutant cycles have been used to quantify intermolecular functional-group interactions in H-bonded zipper complexes in chloroform. If the same interaction is measured in zippers of different overall stability, the double-mutant cycles can be combined to produce a triple-mutant box. This construct quantifies cooperativity between the functional group interaction of interest and the other interactions that are used to change the overall stability of the complexes. The sum of two edge-to-face aromatic interactions (-2.9 +/- 0.5 kJ mol-1) is shown to be insensitive to changes of up to 13.7 +/- 0.2 kJ mol-1 in the overall stability of the complex. In principle, enthalpic cooperative effects caused by entropy-enthalpy compensation could perturb the measurement of intermolecular interactions when using the double-mutant cycle approach, but these experiments show that, for this system, the magnitude of the effect lies within the error of the measurements.     

Vibrational-translational/rotational and vibrational-vibrational processes in methane/inert-gas mixtures: Optoacoustic phase measurements

We consider the model with kinetic excitation into the quasicontinuum (KEQ) for resonant polyatomic molecules which absorb laser radiation and are surrounded by buffer molecules. KEQ takes place when the resonant molecules in the lower part of the energy spectrum interact weakly with the laser radiation, but the molecules in the quasicontinuum are rapidly excited to still higher energy and dissociate. Under these conditions the collisions of the resonant and buffer molecules lead to excitation of resonant molecules into the quasicontinuum because the population of the quasicontinuum is much less than its thermodynamical equilibrium value. It is found, that the smaller the V-T relaxation time τ_VT, the larger the rate of KEQ and the dissociation rate (if only τ_VT is not too small). Thus, if we change the experimental conditions and decrease τ_VT (for instance, by passing from the heavy buffer gas Xe to the light buffer gas He), for some resonant molecules we may observe that the probability of dissociation increases.     

The construction of irreducible normalized representations of the general linear group

A method is described for constructing in an explicit form an irreducible representation T of M_n(F), the set of all n × n matrices over the real or complex field F, satisfying the condition T(A^*)=T^*(A) for all A∈M_n(F).     

Photoelasto-plastic analysis of notched-bar configuration subjected to bending

Knowledge of the three-dimensional stress distribution near a notch for a strain-hardening material in an elasto-plastic state is limited, to say the least. This experimental investigation is concerned with obtaining some insight concerning the three0dimensional elastoplastic stress distributions and the associated plastic-zone sizes. A notched-bar configuration (scaled-up Charpy specimen) subjected to flexure was selected for this purpose. The three-dimensional elasto-plastic stress distributions were determined along the plane of symmetry adjacent to the notch for two levels of applied bending moment. The experimental-stress-analysis method utilizes the creep and frozen-stress characteristics of an epoxy resin when subjected to a thermal cycle whose maximum temperature is significantly less than the critical temperature of the model material. The resulting frozenstress-strain behavior is characterized by the generation of a nonlinear effective stress-strain curve. This effective stress-strain curve was generated by subjecting uniaxial tensile specimens to constant stress and the appropriate thermal cycle. Also, an effective birefringence-stress curve was obtained from these tensile specimens (calibration). Then the notched-bar configuration was subjected to the thermal cycle and an applied bending moment which would develop a plastic zone (determined by using a distortion-energy-yield criteria). The stress distributions were determined from photomechanical analysis of the slices removed from the model.     

Observation of a parity violation in cesium

We have measured a parity violation in the 6S–7S transition of Cs in an electric field. Our result is Im $\text{E}{}_1{}^{\mathrm{<mtext>pv</mtext>}}\text{β}\text{= -1.34 ± 0.22}$$\text{(}\text{rms statistical deviation}\text{) ± ～0.11 (}\text{systematic uncertainty}\text{)}\text{mV}\text{cm;}\text{E}{}_1{}^{\mathrm{<mtext>pv</mtext>}}$ is the parity violating electric dipole amplitude, ß is the vector polarizability. This result is consistent with the Weinberg-Salam prediction.     

Quantifying intermolecular interactions: guidelines for the molecular recognition toolbox

Molecular recognition events in solution are affected by many different factors that have hampered the development of an understanding of intermolecular interactions at a quantitative level. Our tendency is to partition these effects into discrete phenomenological fields that are classified, named, and divorced: aromatic interactions, cation-pi interactions, CH-O hydrogen bonds, short strong hydrogen bonds, and hydrophobic interactions to name a few.1 To progress in the field, we need to develop an integrated quantitative appreciation of the relative magnitudes of all of the different effects that might influence the molecular recognition behavior of a given system. In an effort to navigate undergraduates through the vast and sometimes contradictory literature on the subject, I have developed an approach that treats theoretical ideas and experimental observations about intermolecular interactions in the gas phase, the solid state, and solution from a single simplistic viewpoint. The key features are outlined here, and although many of the ideas will be familiar, the aim is to provide a semiquantitative thermodynamic ranking of these effects in solution at room temperature.