New cw far infrared molecular lasers from ClO2, HCCF,FCN, CH3NC,CH3F,and propynal

Many new laser lines between 100 μm and 1 mm have been detected by optically pumping several polyatomic molecules with C¹⁶O₂ and C¹⁸O₂ lasers. Tentative assignment of the lasing transitions has been possible in some cases.     

Infrared spectra of 1-phosphapropyne,CH3CP,and its perdeuteride,CD3CP

The infrared spectra of 1-phosphapropyne, CH₃CP, and its perdeuteride, CD₃CP, have been measured in the gaseous and solid states. The Q_K branches of perpendicular bands have been analyzed in terms of the usual quadratic expression in K. Fermi resonances were identified for the ν₁, ν₂ + ν₃, 2ν₃, 2ν₆⁰; and ν₅, 2ν₃ + ν₈ band systems of CH₃CP and the ν₁, 2ν₃, 2ν₆⁰; ν₆, ν₇ + ν₈; and ν₇, 3ν₈¹ band systems of CD₃CP. The xy Coriolis interaction was also identified between the ν₃ and ν₆ bands of the two species. All the fundamentals were assigned and the normal coordinate treatment was carried out along with the Coriolis constants, ζ^z.     

Finite barrier width effects on exciton states and optical properties in wurtzite InGaN/GaN quantum well

Exciton states and optical properties in wurtzite (WZ) InGaN/GaN quantum well (QW) are investigated theoretically, considering finite barrier width and built-in electric field effects. Numerical results show that when the barrier width increases, the ground-state exciton binding energy, the interband transition energy and the integrated absorption probability increase first and then they are insensitive to the variation of the barrier width. For any barrier width, the ground-state exciton binding energy and the integrated absorption probability have a maximum when the well width is 1 nm; moreover, the integrated absorption probability goes to zero when the well width is larger than 6 nm. In addition, the competition effects between the built-in electric field and quantum confinement are also investigated in the WZ InGaN/GaN QW.     

Resilient quantum computation in correlated environments: a quantum phase transition perspective

We analyze the problem of a quantum computer in a correlated environment protected from decoherence by quantum error correction using a perturbative renormalization group approach. The scaling equation obtained reflects the competition between the dimension of the computer and the scaling dimension of the correlations. For an irrelevant flow, the error probability is reduced to a stochastic form for a long time and/or a large number of qubits; thus, the traditional derivation of the threshold theorem holds for these error models. In this way, the "threshold theorem" of quantum computing is rephrased as a dimensional criterion.     

Chemiluminescence of IF in the gas phase reaction of I2 with F2

Emission from both the state and the previously unreported $\text{A}{}^3\text{Π}{}_1$ state of IF has been observed in the gas phase reaction of I₂ with F₂ at low pressures. For the state the transition moment and vibrational populations were extracted from the spectra by a least-squares method whereby theoretical band shapes were fit to the experimental data. The effect of flow rates of reactants and Ar on the relative emission from the two electronic states, the effect of pressure on the state, and extinction of emission near 470 nm all favor the population of excited electronic states through a four-center reaction complex, rather than association of F and I atoms.It is argued that there is an avoided curve crossing between the lowest two ³Π_0⁺ states of IF, and that the ground state dissociation energy is 23 229 ± 100 cm^?1. The radiative lifetime of the state is estimated to be 10^?3 sec and to be much shorter than that of the $\text{A}{}^3\text{Π}{}_1$ state.     

Evolution of physics-based methodology for exploring the conformational energy landscape of proteins

The evolution of our physics-based computational methods for determining protein conformation without the introduction of secondary-structure predictions, homology modeling, threading, or fragment coupling is described. Initial use of a hard-sphere potential captured much of the structural properties of polypeptide chains, and subsequent more refined force fields, together with efficient methods of global optimization provide indications that progress is being made toward an understanding of the interresidue interactions that underlie protein folding.     

Determination of crude protein in animal feed, forage, grain, and oilseeds by using block digestion with a copper catalyst and steam distillation into boric acid: collaborative study

A collaborative study was conducted to evaluate the repeatability and reproducibility of an extension of AOAC Official Method 991.20, Nitrogen (Crude) in Milk, to animal feed, forage (plant tissue), grain, and oilseed materials. Test portions are digested in an aluminum block at 420 degrees C in sulfuric acid with potassium sulfate and a copper catalyst. Digests are cooled and diluted, and concentrated sodium hydroxide is added to neutralize the acid and make the digest basic; the liberated ammonia is distilled by using steam distillation. The liberated ammonia is trapped in a weak boric acid solution and titrated with a stronger standardized acid, hydrochloric acid; colorimetric endpoint detection is used. Fourteen blind samples were sent to 13 collaborators in the United States, Denmark, Sweden, Germany, and the United Kingdom. Recoveries of nitrogen from lysine, tryptophan, and acetanilide were 86.8, 98.8, and 100.1%, respectively. The within-laboratory relative standard deviation (RSDr, repeatability) ranged from 0.40 to 2.38% for crude protein. The among-laboratories (including within-) relative standard deviation (RSD(R), reproducibility) ranged from 0.44 to 2.38%. It is recommended that the method be adopted First Action by AOAC INTERNATIONAL. A lower concentration (1% H3BO3) of trapping solution was compared with the concentration specified in the original protocol (4% H3BO3) and was found comparable for use in an automatic titration system in which titration begins automatically as soon as distillation starts. The Study Directors recommend that 1% H3BO3 as an optional alternative to 4% boric acid trapping solution be allowed for automatic titrators that titrate throughout the distillation.     

The periodic table and the intrinsic barrier in s(n)2 reactions

The identity S(N)2 reactions on nitrogen (see eq 3) with nucleophiles having the general structure H(n)()X(-) where X belongs to the group of nonmetallic elements which do not border the line separating them from the metallic elements (X = F, Cl, Br, I, O, S, Se, N, P, and C) were studied at the G2+ level. The results show that, similarly to the previously observed phenomenon for S(N)2 reaction on carbon (J. Am. Chem. Soc. 1999, 121, 7724), the Periodic Table, through the valence of the element X, controls the intrinsic barrier for the reaction. The average intrinsic barriers obtained for nitrogen substrates were 20, 27, 39, and 57 kcal/mol for the mono-, di-, tri-, and tetravalent X's, respectively. It is also concluded that the intrinsic barriers are similar for N- and C-based substrates and dimethyl substitution on both raises the intrinsic barrier by ca. 10 kcal/mol.     

Pharmacokinetics of the nitroxide PCA measured by in vivo EPR

PCA (2,2,5,5-tetramethylpiperidine-1-oxyl-3-carboxylic acid) is a relatively stable free radical which has been shown to be useful as a contrast agent for nuclear magnetic resonance imaging and as an imaging/spectroscopy agent for EPR. In an effort to determine the role of the liver and kidney in the pharmacokinetics of PCA, using low frequency in vivo EPR spectroscopy, we followed the clearance of PCA after intravenous injection in mice: under normal conditions, with a restricted blood supply to the kidneys, after exposure to an acute hepatotoxin CCl₄, and after exposure to lipopolysaccharide (endotoxin). The observed pharmacokinetics fit a two-component model. The fast component was dramatically affected when the renal vessels were restricted, while CCl₄ and endotoxin had a smaller but significant effect. The half times of the slow components were not significantly different (p>0.05) in the groups treated by renal blood flow occlusion, CCl₄, or LPS, compared with the control group. In conclusion, we find that the pharmacokinetics of PCA need to be completely described in term of a two component model: the fast component of the decay is mainly due to the elimination by the kidneys and also is affected by the time for the initial distribution; the slow component is related to the bioreduction of the nitroxide. In addition to the liver other tissues can also effectively metabolize PCA. The effect of oxygen on the rate of metabolism is modest at most.