43,970 research outputs found
A Proton Magnetic Resonance Study of the Association of Lysozyme with Monosaccharide Inhibitors
It has been shown that the acetamido methyl protons of N-acetyl-d-glucosamine undergo a chemical shift to higher fields in their proton magnetic resonance spectrum when the inhibitor is bound to lysozyme. The observed chemical shift in the presence of the enzyme is different for the agr- and ß-anomeric forms of 2-acetamido-2-deoxy-d-glucopyranose indicating either a difference in the affinity of the anomeric forms for lysozyme or different magnetic environments for the methyl protons in their enzyme-bound state. That the agr- and ß-anomeric forms of GlcAc bind to lysozyme in a competitive fashion was indicated by observing the proton magnetic resonance spectra in the presence of 2-acetamido-d3-2-deoxy-agr-d-glucopyranose. The methyl glycosides, methyl-agr-GlcAc and methyl-ß-GlcAc, were also shown to bind competitively with both anomers of GlcAc. Quantitative analysis of the chemical shift data observed for the association of GlcAc with lysozyme was complicated by the mutarotation of GlcAc between its agr- and ß-anomeric forms. However, in the case of the methyl glucosides, where the conformation of each anomer is frozen, it was possible to analyze the chemical shift data in a straightforward manner, and the dissociation constant as well as the chemical shift of the acetamido methyl protons of the enzyme-inhibitor complex was determined for both anomers. The results indicate that the two anomers of methyl-GlcAc bind to lysozyme with slightly different affinities but that the acetamido methyl groups of both anomers experience identical magnetic environments in the enzyme-inhibitor complex
Modeling of secondary organic aerosol yields from laboratory chamber data
Laboratory chamber data serve as the basis for constraining models of secondary organic aerosol (SOA) formation. Current models fall into three categories: empirical two-product (Odum), product-specific, and volatility basis set. The product-specific and volatility basis set models are applied here to represent laboratory data on the ozonolysis of α-pinene under dry, dark, and low-NOx conditions in the presence of ammonium sulfate seed aerosol. Using five major identified products, the model is fit to the chamber data. From the optimal fitting, SOA oxygen-to-carbon (O/C) and hydrogen-to-carbon (H/C) ratios are modeled. The discrepancy between measured H/C ratios and those based on the oxidation products used in the model fitting suggests the potential importance of particle-phase reactions. Data fitting is also carried out using the volatility basis set, wherein oxidation products are parsed into volatility bins. The product-specific model is most likely hindered by lack of explicit inclusion of particle-phase accretion compounds. While prospects for identification of the majority of SOA products for major volatile organic compounds (VOCs) classes remain promising, for the near future empirical product or volatility basis set models remain the approaches of choice
Observation of the single-electron regime in a highly tunable silicon quantum dot
We report on low-temperature electronic transport measurements of a silicon
metal-oxide-semiconductor quantum dot, with independent gate control of
electron densities in the leads and the quantum dot island. This architecture
allows the dot energy levels to be probed without affecting the electron
density in the leads, and vice versa. Appropriate gate biasing enables the dot
occupancy to be reduced to the single-electron level, as evidenced by
magnetospectroscopy measurements of the ground state of the first two charge
transitions. Independent gate control of the electron reservoirs also enables
discrimination between excited states of the dot and density of states
modulations in the leads.Comment: 4 pages, 3 figures, accepted for Applied Physics Letter
Large-Scale Structure in Brane-Induced Gravity II. Numerical Simulations
We use N-body simulations to study the nonlinear structure formation in
brane-induced gravity, developing a new method that requires alternate use of
Fast Fourier Transforms and relaxation. This enables us to compute the
nonlinear matter power spectrum and bispectrum, the halo mass function, and the
halo bias. From the simulation results, we confirm the expectations based on
analytic arguments that the Vainshtein mechanism does operate as anticipated,
with the density power spectrum approaching that of standard gravity within a
modified background evolution in the nonlinear regime. The transition is very
broad and there is no well defined Vainshtein scale, but roughly this
corresponds to k_*~ 2 at redshift z=1 and k_*~ 1 at z=0. We checked that while
extrinsic curvature fluctuations go nonlinear, and the dynamics of the
brane-bending mode C receives important nonlinear corrections, this mode does
get suppressed compared to density perturbations, effectively decoupling from
the standard gravity sector. At the same time, there is no violation of the
weak field limit for metric perturbations associated with C. We find good
agreement between our measurements and the predictions for the nonlinear power
spectrum presented in paper I, that rely on a renormalization of the linear
spectrum due to nonlinearities in the modified gravity sector. A similar
prediction for the mass function shows the right trends. Our simulations also
confirm the induced change in the bispectrum configuration dependence predicted
in paper I.Comment: 19 pages, 13 figures. v2: corrected typos, added more simulations,
better test of predictions in large mass regime. v3: minor changes, published
versio
Scalar Wave Falloff in Asymptotically Anti-de Sitter Backgrounds
Conformally invariant scalar waves in black hole spacetimes which are
asymptotically anti-de Sitter are investigated. We consider both the
-dimensional black hole and -dimensional Schwarzschild-anti-de
Sitter spacetime as backgrounds. Analytical and numerical methods show that the
waves decay exponentially in the dimensional black hole background.
However the falloff pattern of the conformal scalar waves in the
Schwarzschild-anti-de Sitter background is generally neither exponential nor an
inverse power rate, although the approximate falloff of the maximal peak is
weakly exponential. We discuss the implications of these results for mass
inflation.Comment: 34 pages, Latex, 26 figures, uses psfi
Mapping of serotype-specific, immunodominant epitopes in the NS-4 region of hepatitis C virus (HCV):use of type-specific peptides to serologically differentiate infections with HCV types 1, 2, and 3
The effect of sequence variability between different types of hepatitis C virus (HCV) on the antigenicity of the NS-4 protein was investigated by epitope mapping and by enzyme-linked immunosorbent assay with branched oligopeptides. Epitope mapping of the region between amino acid residues 1679 and 1768 in the HCV polyprotein revealed two major antigenic regions (1961 to 1708 and 1710 to 1728) that were recognized by antibody elicited upon natural infection of HCV. The antigenic regions were highly variable between variants of HCV, with only 50 to 60% amino acid sequence similarity between types 1, 2, and 3. Although limited serological cross-reactivity between HCV types was detected between peptides, particularly in the first antigenic region of NS-4, type-specific reactivity formed the principal component of the natural humoral immune response to NS-4. Type-specific antibody to particular HCV types was detected in 89% of the samples from anti-HCV-positive blood donors and correlated almost exactly with genotypic analysis of HCV sequences amplified from the samples by polymerase chain reaction. Whereas almost all blood donors appeared to be infected with a single virus type (97%), a higher proportion of samples (40%) from hemophiliacs infected from transfusion of non-heat-inactivated clotting factor contained antibody to two or even all three HCV types, providing evidence that long-term exposure may lead to multiple infection with different variants of HCV
Rotating Black Holes at Future Colliders. III. Determination of Black Hole Evolution
TeV scale gravity scenario predicts that the black hole production dominates
over all other interactions above the scale and that the Large Hadron Collider
will be a black hole factory. Such higher dimensional black holes mainly decay
into the standard model fields via the Hawking radiation whose spectrum can be
computed from the greybody factor. Here we complete the series of our work by
showing the greybody factors and the resultant spectra for the brane localized
spinor and vector field emissions for arbitrary frequencies. Combining these
results with the previous works, we determine the complete radiation spectra
and the subsequent time evolution of the black hole. We find that, for a
typical event, well more than half a black hole mass is emitted when the hole
is still highly rotating, confirming our previous claim that it is important to
take into account the angular momentum of black holes.Comment: typoes in eqs(82)-(84) corrected; version to appear in Phys. Rev. D;
references and a footnote added; same manuscript with high resolution
embedded figures available on
http://www.gakushuin.ac.jp/univ/sci/phys/ida/paper
Entropy of Rotating Misner String Spacetimes
Using a boundary counterterm prescription motivated by the AdS/CFT
conjecture, I evaluate the energy, entropy and angular momentum of the class of
Kerr-NUT/bolt-AdS spacetimes. As in the non-rotating case, when the NUT charge
is nonzero the entropy is no longer equal to one-quarter of the area due to the
presence of the Misner string. When the cosmological constant is also non-zero,
the entropy is bounded from above.Comment: Revtex, 9 pages, 3 figure
Density fluctuations in -deformed inflationary universe
We study the spectrum of metric fluctuation in -deformed inflationary
universe. We write the theory of scalar metric fluctuations in the
deformed Robertson-Walker space, which is represented as a non-local
theory in the conventional Robertson-Walker space. One important consequence of
the deformation is that the mode generation time is naturally determined by the
structure of the deformation.
We expand the non-local action in , with being the Hubble
parameter and the deformation parameter, and then compute the power
spectra of scalar metric fluctuations both for the cases of exponential and
power law inflations up to the first order in . We show that the
power spectra of the metric fluctuation have non-trivial corrections on the
time dependence and on the momentum dependence compared to the commutative
space results. Especially for the power law inflation case, the power spectrum
for UV modes is weakly blue shifted early in the inflation and its strength
decreases in time. The power spectrum of far-IR modes has cutoff proportional
to which may explain the low CMB quadrupole moment.Comment: final revision; 19 pages, 3 figures; to appear in Phys. Rev.
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