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Three experiments were conducted to evaluate the effects of feeding 2-hydroxy-4- (methylthio)-butanoic acid (HMTBA) on performance and carcass characteristics of feedlot cattle and on microbial fermentation in a continuous-culture system. In Exp. 1, 160 crossbred steers (initial BW = 385 +/- 10.3 kg) were assigned to 4 treatments consisting of control (0% HMTBA) or 3 diets containing HMTBA (0.069, 0.137, and 0.204%; DM basis) in a randomized complete block design. As the percent of HMTBA increased in the diet, final BW (P = 0.069), final BW adjusted to a constant dressing percent (P = 0.063), and overall ADG (P = 0.099) tended to decrease linearly. Overall DMI decreased linearly (P or = 0.10) were noted for carcass characteristics, except for a tendency (P = 0.078) for a linear increase in the percentage of cattle grading USDA Choice with increasing HMTBA dose. In Exp. 2, 80 crossbred steers (initial BW = 450 +/- 17 kg) in a randomized complete block design were assigned to a control (0% HMTBA) diet or to a diet in which the concentrations of HMTBA were gradually increased from 0.036 to 0.212% of DM over a 50-d period. The HMTBA-containing diet tended to decrease DMI (P = 0.132), but G:F (P = 0.319) for the overall feeding period, carcass measurements, and USDA quality grade (P > or = 0.149) did not differ between treatments. In Exp. 3, continuous culture fermenters (n = 5/treatment) were used to determine the effects of HMTBA (control vs. 0.24% HMTBA) on microbial fermentation. No differences (P > or = 0.31) were detected between treatments in ruminal OM digestibility, microbial N synthesis, pH, ammonia, molar proportions of VFA, or effluent concentration of selected long-chain fatty acids. These results suggest that HMTBA decreased DMI by feedlot steers fed a steam-flaked corn-based diet in a dose-dependent manner; however, gradually increasing the dose over time seemed to moderate effects on DMI. No major changes in microbial fermentation in continuous culture were observed with HMTBA at 0.24% of dietary DM, suggesting effects of HMTBA on DMI were not likely associated with changes in ruminal digestion or fermentation.

Two experiments evaluated effects of ractopamine hydrochloride (RAC) on performance, intake patterns, and acid-base balance of feedlot cattle. In Exp. 1, 360 crossbred steers (Brangus, British, and British x Continental breeding; initial BW = 545 kg) were used in a study with a 3 x 3 factorial design to study the effects of dose [0, 100, or 200 mg/(steer x d) of RAC] and duration (28, 35, or 42 d) of feeding of RAC in a randomized complete block design (9 treatments, 8 pens/treatment). No dose x duration interactions were detected (P > 0.10). As RAC dose increased, final BW (FBW; P = 0.01), ADG (P 0.10) in feedlot performance, urine pH, blood gas measurements, or variation in intake patterns between RAC and control cattle, but steers fed RAC had increased (P = 0.04) LM area, decreased (P = 0.03) yield grade, and increased (P < 0.10) time to consume 50 and 75% of daily intake relative to control steers. Our results suggest that feeding RAC for 35 d at 200 mg/(steer x d) provided optimal performance, and no effects on acid-base balance or variation in intake patterns of finishing steers were noted with RAC fed at 200 mg/(steer x d) over a 30-d period.

We report experimental results on the low-temperature uptake of HCl on H(2)O ice (ice). HCl was deposited on the surface at greater than monolayer amounts at 85 K, and the ice substrate was heated. The temperature dependence of the HCl vapor pressure from this phase was measured from 110 to 150 K, with the nucleation of a bulk hydrate phase observed at 150 K. Measurements were conducted in a closed system by simultaneous application of gas phase mass spectrometry and surface spectroscopy to characterize vapor/solid equilibrium and the nucleation of bulk hydrate phases. Combining the nucleation data reported here with data we reported previously (180 to 200 K) and data from two other laboratories (165 and 170 K), the thermodynamic boundaries for the nucleation of both the metastable bulk solution and bulk hydrate phases subsequent to monolayer adsorption of HCl have been determined. The nucleation of the metastable bulk solution phase occurs promptly at monolayer coverage at the ice/liquid coexistence boundary on the binary bulk phase diagram. The nucleation of the bulk hexahydrate occurs from this metastable solution along a locus of points defining a state of constant solution free energy. This measured free energy is -51.2 +/- 0.9 kJ/mol. Finally, the temperature dependence of the HCl vapor pressure from the low-temperature phase is reported here for the first time and is consistent with that of the metastable solution predicted by this thermodynamic model of uptake, extending the range of validity of this model of adsorption followed by bulk solution and hydrate nucleation to a lower bound in temperature of 110 K.

We present a model of heterogeneous reactivity based on physical adsorption that describes the observed relative humidity dependence of the ClONO 2 reaction probability with H 2 O and HCl on sulfuric acid tetrahydrate ice surfaces (SAT) and with H 2 O on nitric acid trihydrate (NAT). The laboratory data are modeled using only two parameters for a given system, the measured reaction probability on a neat H 2 O ice surface, and a constant from the BET theory which describes the fraction of an acid hydrate surface covered by H 2 O as a function of relative humidity. The model indicates that ClONO 2 reactivity with both HCl and H 2 O on SAT and with H 2 O on NAT is controlled by the surface coverage of H 2 O. In contrast, the reaction of ClONO 2 + HCl on NAT is better described by an alternative model based on reactivity in solutions formed within a porous ice by capillary liquid absorption.

The high field photoionization cross sections for the (n=2) shell of argon were measured with pulsed 800 nm radiation (27±5 fs duration) at an intensity of 1.5×1019 W/cm2±1×1019 W/cm2. The pondermotive energy for an electron at these field intensities is approximately 1 MeV. The best agreement with a calculated AC tunneling model was at an intensity of 0.6×1019 W/cm2. The difference between experimental and calculated relative charge state yields is less than an order of magnitude for Ar+9 to Ar+14 and Ar+16.

Fundamental processes on the molecular level, such as vibrations and rotations in single molecules, liquids or crystal lattices and the breaking and formation of chemical bonds, occur on timescales of femtoseconds to picoseconds. The electronic changes associated with such processes can be monitored in a time-resolved manner by ultrafast optical spectroscopic techniques1, but the accompanying structural rearrangements have proved more difficult to observe. Time-resolved X-ray diffraction has the potential to probe fast, atomic-scale motions2,3,4,5. This is made possible by the generation of ultrashort X-ray pulses6,7,8,9,10, and several X-ray studies of fast dynamics have been reported6,7,8,11,12,13,14,15. Here we report the direct observation of coherent acoustic phonon propagation in crystalline gallium arsenide using a non-thermal, ultrafast-laser-driven plasma — a high-brightness, laboratory-scale source of subpicosecond X-ray pulses16,17,18,19. We are able to follow a 100-ps coherent acoustic pulse, generated through optical excitation of the crystal surface, as it propagates through the X-ray penetration depth. The time-resolved diffraction data are in excellent agreement with theoretical predictions for coherent phonon excitation20 in solids, demonstrating that it is possible to obtain quantitative information on atomic motions in bulk media during picosecond-scale lattice dynamics.

A new technique, double absorption photofragment spectroscopy (DAPS), has been developed for observing the time evolution of unimolecular processes. Molecules isolated from collisions in a molecular beam are prepared in a well defined intermediate state by an initiation laser pulse. As this state evolves in time, it is monitored by a second probe laser pulse which, after a chosen delay, photodissociates the molecules. Information about the state to which the molecules have evolved by the time of the probe pulse can be extracted from the mass, density, and angular and energy distributions of the recoiling fragments. Simple models are explored for the functional form of the angular distributions which can be expected in DAPS experiments. This new technique is demonstrated on the I2 B state (used as a real rather than virtual intermediate) whose lifetime is found to vary between 770 and 1600 nsec, depending upon the set of B state v′J′ levels prepared by the initiation laser pulse. Future DAPS experiments should be able to observe unimolecular electronic and nuclear change over a time span from 10−12 to 10−3 sec, probing such processes as rearrangement, dissociation, internal vibrational transfer, intersystem crossing, and internal conversion.

Dry matter yields of March–April sown greenfeed oats, measured in a number of trials between 1974 and 1978, reached over 15 t/ha by December. In vitro digestibility was more than 80% at harvests up to November but decreased to less than 60% in December. Mineral levels appeared satisfactory for good animal performance up to October, whereas in November and especially in December N, P, and Cu were deficient. Cattle live-weight gains over the September-mid November period averaged 0.87 kg/day, but declined to 0.39 kg/day between mid November and early December when oats reached the milky-ripe stage of growth. There appeared to be a positive relationship between dry matter on offer and live-weight gain, although results showed that there is a need to find the optimum amount of dry matter to offer animals at each stage of growth of the crop.

Crossed‐beam studies have been made of the reactions of K, Rb, and Cs atoms with Br2 and of K and Cs with I2. It is found that for all these systems: (1) The reaction cross sections are remarkably large, ≳150 A2. (2) Most of the alkali halide product recoils into the forward hemisphere with respect to the incident alkali atom beam, with scattering angle θ≲60° (in the center‐of‐mass system). However, there also appears to be considerable intensity (∼20% of the forward peak) throughout the backward hemisphere, 90°

Crossed‐beam studies have been made of the reactions of Na with CH3I, Br2, and ICl. An approximate kinematic transformation of the measured laboratory angular distributions to the center‐of‐mass coordinate system yields distributions of the recoil angle for elastic and reactive scattering and estimates of the product recoil energies and total reaction cross sections, Qr. The results are qualitatively similar to those found in previous beam studies of the reactions of K, Rb, and Cs and are consistent with the early Polanyi flame experiments. As compared with the analogous K systems, the Na reactions exhibit the following properties: (1) smaller values of Qr (approximately 5, 90, and 100 A2 for CH3I, ICl, and Br2, respectively); (2) most of the reaction exothermicity still appears as product excitation for Br2 and ICl, whereas a considerably larger fraction appears as recoil energy for CH3I; (3) the wide‐angle nonreactive scattering falls off less rapidly; and (4) the Br2 and ICl stripping reactions produce...

Angular distribution measurements have been made for reactive and elastic scattering of K, Rb, or Cs atoms from two series of polyhalide molecules (listed in order of decreasing reaction yield): PBr3>PCl3≫ BBr3; and CBr4>SnCl4>CCl4>CHCl3>SiCl4. For PBr3, PCl3, CBr4, and SnCl4 the reaction cross sections are very large (>150 A2) and stripping behavior is predominant: most of the alkali halide recoils into the forward hemisphere with respect to the incident alkali‐atom beam. For CCl4 the laboratory alkali halide distributions are bimodal, corresponding in the center‐of‐mass system to conical, sideways‐peaked distributions of the recoil velocity vectors. The half‐angle of the cone is roughly 50° for Cs, 70° for Rb, and 90° for K. For CHCl3 the alkali halide distribution favors the backward hemisphere. The angular distribution of alkali atoms scattered without reaction likewise shows a strong correlation with the reaction yield. As compared with the much less reactive reference systems BBr3 and SiCl4, the e...

1. Isolated renal tubules were prepared from vitamin D-deficient chicks. The effects of added prostaglandin E2 (PGE2) and agents which modify prostaglandin metabolism on the metabolism of 25-hydroxy-vitamin D3 were studied. 2. Frusemide (0.1 mmol/l) raised the prostaglandin E (PGE) content of the tubule incubation medium; it significantly increased 1,25-dihydroxy-vitamin D3 [1,25-(OH)2D3] production from 25-hydroxy-vitamin D3 [25-(OH)D3] and significantly inhibited the net production of 24,25-dihydroxy-vitamin D3 [24,25-(OH)2D3]. 3. Acetylsalicylic acid (aspirin; 0.1 mmol/l) decreased the PGE content of the tubule incubation medium and significantly inhibited 1,25-(OH)2D3 production. 4. In the presence of 1,25-(OH)2D3, 4 h exposure of tubules from vitamin D-deficient chicks to concentrations of PGE2 between 2.8 × 10−6 and 2.8 × 10−8 mol/l significantly enhanced 1,25-(OH)2D3 production. 5. It is concluded that, in view of the effects of modulation of endogenous prostaglandin levels by frusemide in aspirin, and the stimulatory effect of exogenous PGE2, prostaglandins should be considered potential regulators of the renal 25-hydroxy-vitamin D-1α-hydroxylase [25-(OH)D-1α-hydroxylase] enzyme.

The accessible time range for picosecond experimental measurements is now short enough, and that for molecular dynamics theoretical computation is now long enough, to significantly overlap. This overlap of theory and experiment can, at least in principle, be exploited to discover the trajectories of atoms during chemical processes in solution, for example rotational and vibrational relaxation [1], rotational and vibrational dephasing [2], and chemical reactions. This is significant in that our understanding of the microscopic basis of processes in liquids has fallen far behind our understanding of the gas phase. In fact, the atomic motions which form the microscopic mechanisms for solution processes are hardly understood at all, even though most processes of interest to most chemists occur in solution.

Summary form only given. We present the first optical-pump X-ray probe study on coherent lattice dynamics in semiconductor heterostructures. We have observed propagation of optically generated picosecond acoustic pulses within crystalline Ge films and into the underlying Si substrate, where 20 femtometer lattice compression was observed.

THE classic Polanyi flame work1,2 explored the reactions of sodium atoms with a very wide range of halogen compounds. For some of these the rate constants were found to be extremely large (∼ 1014 c.c. mole−1 sec−1), corresponding to “reaction on more than every gas-kinetic collision”. This was attributed to an electron-jump mechanism, Here essentially all collision trajectories that pass within the radius rc at which formation of the ion-pair becomes possible lead to reaction3. This radius is given by e2/rc = I(Na) − Eν(X − R), where I denotes the ionization potential of the alkali atom and Eν the vertical electron affinity of the halogen molecule. Recently, several alkali atom reactions of this type (with X − R = Br2, ICl, PBr3, CBr4, SnCl4, SF6, etc.) have been examined in molecular beam scattering experiments4. The form of the angular distributions of elastic and reactive scattering and other detailed dynamical properties observed in these experiments can be very plausibly interpreted in terms of the electron-jump mechanism.