Cryogenic combustion laboratory

The objective is to establish a major experimental laboratory for studying fundamental processes such as mixing and combustion under liquid rocket engine conditions. The capability of this laboratory will include operation using a variety of fuel and oxidizer systems including liquid oxygen and liquid hydrocarbons. In addition to providing the proper facilities for supplying and controlling these fuels and oxidizers, a specific effort is being made to provide a state-of-the-art diagnostic capability for combustion measurements. In particular, optical and laser-based techniques are being emphasized for measurements of species, velocities, and spray characteristics

Enantiomeric separation and quantitative determination of propranolol enantiomers in pharmaceutical preparations by chiral liquid chromatography

Neste trabalho é descrito um método validado empregando a cromatografia líquida de alta eficiência com fase estacionária quiral para a separação e determinação quantitativa dos enantiômeros do propranolol em formulações farmacêuticas. A separação foi obtida em meio orgânico polar empregando a coluna ±-Burke 2® como fase estacionária quiral (250 x 4,6 mm, 5 µm) e fase móvel constituída por diclorometano: metanol (90:10 v/v) juntamente com 12 mM de acetato de amônio e vazão de 0,9 mL/min. A detecção foi efetuada por absorção no ultravioleta a 280 nm. Em todos casos o tempo de corrida foi menor do que 10 min. O coeficiente de correlação obtido pelo método de regressão linear foi de 0,9995 para o R-prop e de 0,9998 para o S-prop. A precisão intra-dia, expressa como desvio padrão relativo, foi menor do que 2%. A exatidão, determinada pela recuperação média de R- e S-prop nas amostras foi de 97,3% e 100,1% para a amostra comercial e de 99,5% e 100,4% para a amostra simulada, respectivamente. Excelentes níveis para os limites de detecção (1,34 ng) e de quantificação (4,47 ng), além do tempo rápido de eluição dos enantiômeros do propranolol, confirmam a aplicabilidade do método no controle de qualidade de preparações farmacêuticas contendo este fármaco.This paper describes validated direct liquid chromatographic chiral methods for enantiomeric separation and quantitative determination of clinically significant ²-blocking agent, propranolol. A liquid chromatographic method was validated and applied for enantiomeric determination of propranolol enantiomers in pharmaceutical formulations. Separation were obtained in polar organic mode on a ±-Burke 2® chiral stationary phase (250 x 4.6 mm, 5µm) with mobile phase composed of dichloromethane:methanol (90:10 v/v), along with 12 mM of ammonium acetate, at a flow rate of 0.9 mL/min. Detection was made by ultraviolet absorption at 280 nm. In all cases the run time was less than 10 min. The correlation coefficient for linear regression curves of R-propranolol and S-propranolol were 0.9995 and 0.9998 respectively. The intra-day precision, expressed as RSD was less than 2%. The accuracy determined by average recovery of R-propranolol and S-propranolol from sample matrices were 97.3% and 100.1% in commercial sample and 99.5% and 100.4% in simulated samples, respectively. Excellent levels of limit of detection (mean value = 1.34 ng) and limit of quantitation (mean value = 4.47 ng), along with rapid elution time of both enantiomers, makes the method useful for routine enantiomeric quality control applications

Negative Impurity Magnetic Susceptibility and Heat Capacity in a Kondo Model with Narrow Peaks in the Local Density of Electron States

Temperature dependencies of the impurity magnetic susceptibility, entropy, and heat capacity have been obtained by the method of numerical renormalization group and exact diagonalization for the Kondo model with peaks in the electron density of states near the Fermi energy (in particular, with logarithmic Van Hove singularities). It is shown that these quantities can be {\it negative}. A new effect has been predicted (which, in principle, can be observed experimentally), namely, the decrease in the magnetic susceptibility and heat capacity of a nonmagnetic sample upon the addition of magnetic impurities into it

Dynamic correlations in symmetric electron-electron and electron-hole bilayers

The ground-state behavior of the symmetric electron-electron and electron-hole bilayers is studied by including dynamic correlation effects within the quantum version of Singwi, Tosi, Land, and Sjolander (qSTLS) theory. The static pair-correlation functions, the local-field correction factors, and the ground-state energy are calculated over a wide range of carrier density and layer spacing. The possibility of a phase transition into a density-modulated ground state is also investigated. Results for both the electron-electron and electron-hole bilayers are compared with those of recent diffusion Monte Carlo (DMC) simulation studies. We find that the qSTLS results differ markedly from those of the conventional STLS approach and compare in the overall more favorably with the DMC predictions. An important result is that the qSTLS theory signals a phase transition from the liquid to the coupled Wigner crystal ground state, in both the electron-electron and electron-hole bilayers, below a critical density and in the close proximity of layers (d <~ r_sa_0^*), in qualitative agreement with the findings of the DMC simulations.Comment: 13 pages, 11 figures, 2 table

Epigenetic Engineering of Ribosomal RNA Genes Enhances Protein Production

Selection of mammalian high-producer cell lines remains a major challenge for the biopharmaceutical manufacturing industry. Ribosomal RNA (rRNA) genes encode the major component of the ribosome but many rRNA gene copies are not transcribed [1]–[5] due to epigenetic silencing by the nucleolar remodelling complex (NoRC) [6], which may limit the cell's full production capacity. Here we show that the knockdown of TIP5, a subunit of NoRC, decreases the number of silent rRNA genes, upregulates rRNA transcription, enhances ribosome synthesis and increases production of recombinant proteins. However, general enhancement of rRNA transcription rate did not stimulate protein synthesis. Our data demonstrates that the number of transcriptionally competent rRNA genes limits efficient ribosome synthesis. Epigenetic engineering of ribosomal RNA genes offers new possibilities for improving biopharmaceutical manufacturing and provides novel insights into the complex regulatory network which governs the translation machinery in normal cellular processes as well as in pathological conditions like cancer

Convergence theorems for quantum annealing

We prove several theorems to give sufficient conditions for convergence of quantum annealing, which is a protocol to solve generic optimization problems by quantum dynamics. In particular the property of strong ergodicity is proved for the path-integral Monte Carlo implementation of quantum annealing for the transverse Ising model under a power decay of the transverse field. This result is to be compared with the much slower inverse-log decay of temperature in the conventional simulated annealing. Similar results are proved for the Green's function Monte Carlo approach. Optimization problems in continuous space of particle configurations are also discussed.Comment: 19 page

Working group written presentation: Trapped radiation effects

The results of the Trapped Radiation Effects Panel for the Space Environmental Effects on Materials Workshop are presented. The needs of the space community for new data regarding effects of the space environment on materials, including electronics are listed. A series of questions asked of each of the panels at the workshop are addressed. Areas of research which should be pursued to satisfy the requirements for better knowledge of the environment and better understanding of the effects of the energetic charged particle environment on new materials and advanced electronics technology are suggested

Valence-bond states in dynamical Jahn-Teller molecular systems

We discuss a hopping model of electrons between idealized molecular sites with local orbital degeneracy and dynamical Jahn-Teller effect, for crystal field environments of sufficiently high symmetry. For the Mott-insulating case (one electron per site and large Coulomb repulsions), in the simplest two-fold degenerate situation, we are led to consider a particular exchange hamiltonian, describing two isotropic spin-1/2 Heisenberg problems coupled by a quartic term on equivalent bonds. This twin-exchange hamiltonian applies to a physical regime in which the inter-orbital singlet is the lowest-energy intermediate state available for hopping. This regime is favored by a relatively strong electron-phonon coupling. Using variational arguments, a large-N limit, and exact diagonalization data, we find that the ground state, in the one dimensional case, is a solid valence bond state. The situation in the two dimensional case is less clear. Finally, the behavior of the system upon hole doping is studied in one dimension.Comment: 11 pages, 5 figure

Surface Contribution to Raman Scattering from Layered Superconductors

Generalizing recent work, the Raman scattering intensity from a semi-infinite superconducting superlattice is calculated taking into account the surface contribution to the density response functions. Our work makes use of the formalism of Jain and Allen developed for normal superlattices. The surface contributions are shown to strongly modify the bulk contribution to the Raman-spectrum line shape below $2\Delta$, and also may give rise to additional surface plasmon modes above $2\Delta$. The interplay between the bulk and surface contribution is strongly dependent on the momentum transfer $q_\parallel$ parallel to layers. However, we argue that the scattering cross-section for the out-of-phase phase modes (which arise from interlayer Cooper pair tunneling) will not be affected and thus should be the only structure exhibited in the Raman spectrum below $2\Delta$ for relatively large $q_\parallel\sim 0.1\Delta/v_F$. The intensity is small but perhaps observable.Comment: 14 pages, RevTex, 6 figure