Studying the scale and q^2 dependence of K^+-->pi^+e^+e^- decay

We extract the K^+-->pi^+e^+e^- amplitude scale at q^2=0 from the recent Brookhaven E865 high-statistics data. We find that the q^2=0 scale is fitted in excellent agreement with the theoretical long-distance amplitude. Lastly, we find that the observed q^2 shape is explained by the combined effect of the pion and kaon form-factor vector-meson-dominance rho, omega and phi poles, and a charged pion loop coupled to a virtual photon-->e^+e^- transition.Comment: 8 pages, 3 figure

Various Forms of Dehydrated Alfalfa in High-concentrate Cattle Finishing Diets

Even though growing and finishing beef cattle have been fed satisfactorily on all-concentrate diets, in many instances weight gains have been improved and management problems reduced by including some conventional form of roughage in the diet. The most efficient level of roughage will likely be a variable factor depending upon a number of things including weight and condition of the cattle and. nature of the roughages and concentrates. It is a well-established fact that .as the energy content of the diet increases the rate of gain increases and the feed required per unit of gain decreases. In addition to rate and efficiency of gain, a feedlot operator must also consider the cost of the grain. A diet that produces the most rapid gain does not necessarily produce the most economical gain. Less cost may result from feeding of lower energy feeds which may not only cost less per unit of weigh but also less per unit of energy as compared to higher energy feeds. Energy consumption depends on the amounts and kinds of feeds consumed, or generally in the case of ruminants, the ratio of concentrates to roughage. Ratios of concentrates to roughage in diets for finishing beef cattle has been the subject of considerable research in the past. Renewed interest in this area has resulted from changes in feed preparation methods, feeding practices and type of diets fed. These factors have been shown to influence the relative value of concentrates and roughages when fed in varying proportions. In a previous experiment at the South Dakota Experiment station (Larson, 1969), weight gains were improved by adding chopped alfalfa hay to an all-concentrate diet composed of corn and supplements. There were essentially no differences in weight gains between levels of hay at 3, 10 or 20% of the diet. However, total feed intake increased with increasing levels of hay resulting in a decrease in concentrates saved per unit of hay as the level was increased. The lower level of hay resulted in a more favorable response than did an equal weight of outer shells. Research with low levels of roughage and with roughage substitutes in cattle diets raises some questions regarding the role performed by the roughage and the importance of its physical form when making up only a small percentage of the diet. The experiment reported here was designed to compare the value of a low level of alfalfa fed in various forms in a corn diet supplemented with protein, minerals, chlortetracycline and vitamin A

Urea vs. Soybean Meal During Feedlot Adaptation and Later Growing and Finishing

Urea is a common ingredient in cattle diets. While this nonprotein nitrogren compound is a satisfactory source of supplemental protein in many cattle diets, there are limitations as to levels in the diet and conditions of use. The primary basis for the use of urea as a substitute for conventional high-protein ingredients is the lower cost for protein supplementation

Investigation of vacuum polarization in t-channel radiative Bhabha scattering

We discuss the possibility of a precision measurement of vacuum polarization in t-channel radiative Bhabha scattering at a high luminosity collider. For illustration, the achievable precision is estimated for the BaBar experiment at PEP-II and for the OPAL experiment at LEP

Spatial Constraint Corrections to the Elasticity of dsDNA Measured with Magnetic Tweezers

In this paper, we have studied, within a discrete WLC model, the spatial constraints in magnetic tweezers used in single molecule experiments. Two elements are involved: first, the fixed plastic slab on which is stuck the initial strand, second, the magnetic bead which pulls (or twists) the attached molecule free end. We have shown that the bead surface can be replaced by its tangent plane at the anchoring point, when it is close to the bead south pole relative to the force. We are led to a model with two parallel repulsive plates: the fixed anchoring plate and a fluctuating plate, simulating the bead, in thermal equilibrium with the system. The bead effect is a slight upper shift of the elongation, about four times smaller than the similar effect induced by the fixed plate. This rather unexpected result, has been qualitatively confirmed within the soluble Gaussian model. A study of the molecule elongation versus the countour length exhibits a significant non-extensive behaviour. The curve for short molecules (with less than 2 kbp) is well fitted by a straight line, with a slope given by the WLC model, but it does not go through the origin. The non-extensive offset gives a 15% upward shift to the elongation of a 2 kbp molecule stretched by a 0.3 pN force.Comment: 28 pages, 6 figures An explanatory figure has been added. The physical interpretation of the results has been made somewhat more transparen

Casimir Forces between Spherical Particles in a Critical Fluid and Conformal Invariance

Mesoscopic particles immersed in a critical fluid experience long-range Casimir forces due to critical fluctuations. Using field theoretical methods, we investigate the Casimir interaction between two spherical particles and between a single particle and a planar boundary of the fluid. We exploit the conformal symmetry at the critical point to map both cases onto a highly symmetric geometry where the fluid is bounded by two concentric spheres with radii R_- and R_+. In this geometry the singular part of the free energy F only depends upon the ratio R_-/R_+, and the stress tensor, which we use to calculate F, has a particularly simple form. Different boundary conditions (surface universality classes) are considered, which either break or preserve the order-parameter symmetry. We also consider profiles of thermodynamic densities in the presence of two spheres. Explicit results are presented for an ordinary critical point to leading order in epsilon=4-d and, in the case of preserved symmetry, for the Gaussian model in arbitrary spatial dimension d. Fundamental short-distance properties, such as profile behavior near a surface or the behavior if a sphere has a `small' radius, are discussed and verified. The relevance for colloidal solutions is pointed out.Comment: 37 pages, 2 postscript figures, REVTEX 3.0, published in Phys. Rev. B 51, 13717 (1995

The SM protein Sly1 accelerates assembly of the ER-Golgi SNARE complex.

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) and Sec1/Munc18 (SM) proteins constitute the core of an ancient vesicle fusion machine that diversified into distinct sets that now function in different trafficking steps in eukaryotic cells. Deciphering their precise mode of action has proved challenging. SM proteins are thought to act primarily through one type of SNARE protein, the syntaxins. Despite high structural similarity, however, contrasting binding modes have been found for different SM proteins and syntaxins. Whereas the secretory SM protein Munc18 binds to the ‟closed conformation" of syntaxin 1, the ER-Golgi SM protein Sly1 interacts only with the N-peptide of Sed5. Recent findings, however, indicate that SM proteins might interact simultaneously with both syntaxin regions. In search for a common mechanism, we now reinvestigated the Sly1/Sed5 interaction. We found that individual Sed5 adopts a tight closed conformation. Sly1 binds to both the closed conformation and the N-peptide of Sed5, suggesting that this is the original binding mode of SM proteins and syntaxins. In contrast to Munc18, however, Sly1 facilitates SNARE complex formation by loosening the closed conformation of Sed5