5,863 research outputs found
Ultrafast heterogeneous electron transfer reactions Comparative theoretical studies on time and frequency domain data
Recent theoretical studies on linear absorption spectra of dye semiconductor systems perylene attached to nanostructured TiO2, L. Wang et al., J. Phys. Chem. B 109, 9589 2005 are extended here in different respects. Since the systems show ultrafast photoinduced heterogeneous electron transfer the time dependent formulation used to compute the absorbance is also applied to calculate the temporal evolution of the sub 100 fs charge injection dynamics after a 10 fs laser pulse excitation. These studies complement our recent absorption spectra fit for two perylene bridge anchor group TiO2 systems. Moreover, the time dependent formulation of the absorbance is confronted with a frequency domain description. The latter underlines the central importance of the self energy caused by the coupling of the dye levels to the semiconductor band continuum. The used model is further applied to study the effect of different parameters such as 1 the dependence on the reorganization energies of the involved intramolecular transitions, 2 the effect of changing the transfer integral which couples the excited dye state with the band continuum, and 3 the effect of the concrete form of the semiconductor band density of states. Emphasis is also put on the case where the charge injection level of the dye is near or somewhat below the band edge. This nicely demonstrates the change from a structureless absorption to a well resolved vibrational progression including characteristic shifts of the absorption lines which are a direct measure for the dye semiconductor couplin
Health of Philippine Emigrants Study (HoPES): study design and rationale.
BackgroundImmigrants to the United States are usually healthier than their U.S.-born counterparts, yet the health of immigrants declines with duration of stay in the U.S. This pattern is often seen for numerous health problems such as obesity, and is usually attributed to acculturation (the adoption of "American" behaviors and norms). However, an alternative explanation is secular trends, given that rates of obesity have been rising globally. Few studies of immigrants are designed to distinguish the effects of acculturation versus secular trends, in part because most studies of immigrants are cross-sectional, lack baseline data prior to migration, and do not have a comparison group of non-migrants in the country of origin. This paper describes the Health of Philippine Emigrants Study (HoPES), a study designed to address many of these limitations.MethodsHoPES is a dual-cohort, longitudinal, transnational study. The first cohort consisted of Filipinos migrating to the United States (n = 832). The second cohort consisted of non-migrant Filipinos who planned to remain in the Philippines (n = 805). Baseline data were collected from both cohorts in 2017 in the Philippines, with follow-up data collection planned over 3 years in either the U.S. for the migrant cohort or the Philippines for the non-migrant cohort. At baseline, interviewers administered semi-structured questionnaires that assessed demographic characteristics, diet, physical activity, stress, and immigration experiences. Interviewers also measured weight, height, waist and hip circumferences, blood pressure, and collected dried blood spot samples.DiscussionMigrants enrolled in the study appear to be representative of recent Filipino migrants to the U.S. Additionally, migrant and non-migrant study participants are comparable on several characteristics that we attempted to balance at baseline, including age, gender, and education. HoPES is a unique study that approximates a natural experiment from which to study the effects of immigration on obesity and other health problems. A number of innovative methodological strategies were pursued to expand the boundaries of current immigrant health research. Key to accomplishing this research was investment in building collaborative relationships with stakeholders across the U.S. and the Philippines with shared interest in the health of migrants
Probing Cosmology with Weak Lensing Minkowski Functionals
In this paper, we show that Minkowski Functionals (MFs) of weak gravitational
lensing (WL) convergence maps contain significant non-Gaussian,
cosmology-dependent information. To do this, we use a large suite of
cosmological ray-tracing N-body simulations to create mock WL convergence maps,
and study the cosmological information content of MFs derived from these maps.
Our suite consists of 80 independent 512^3 N-body runs, covering seven
different cosmologies, varying three cosmological parameters Omega_m, w, and
sigma_8 one at a time, around a fiducial LambdaCDM model. In each cosmology, we
use ray-tracing to create a thousand pseudo-independent 12 deg^2 convergence
maps, and use these in a Monte Carlo procedure to estimate the joint confidence
contours on the above three parameters. We include redshift tomography at three
different source redshifts z_s=1, 1.5, 2, explore five different smoothing
scales theta_G=1, 2, 3, 5, 10 arcmin, and explicitly compare and combine the
MFs with the WL power spectrum. We find that the MFs capture a substantial
amount of information from non-Gaussian features of convergence maps, i.e.
beyond the power spectrum. The MFs are particularly well suited to break
degeneracies and to constrain the dark energy equation of state parameter w (by
a factor of ~ three better than from the power spectrum alone). The
non-Gaussian information derives partly from the one-point function of the
convergence (through V_0, the "area" MF), and partly through non-linear spatial
information (through combining different smoothing scales for V_0, and through
V_1 and V_2, the boundary length and genus MFs, respectively). In contrast to
the power spectrum, the best constraints from the MFs are obtained only when
multiple smoothing scales are combined.Comment: 19 pages, 9 figures, 5 table
Single-Molecule Study of Metalloregulator CueR-DNA Interactions Using Engineered Holliday Junctions
AbstractTo maintain normal metal metabolism, bacteria use metal-sensing metalloregulators to control transcription of metal resistance genes. Depending on their metal-binding states, the MerR-family metalloregulators change their interactions with DNA to suppress or activate transcription. To understand their functions fundamentally, we study how CueR, a Cu1+-responsive MerR-family metalloregulator, interacts with DNA, using an engineered DNA Holliday junction (HJ) as a protein-DNA interaction reporter in single-molecule fluorescence resonance energy transfer measurements. By analyzing the single-molecule structural dynamics of the engineered HJ in the presence of various concentrations of both apo- and holo-CueR, we show how CueR interacts with the two conformers of the engineered HJ, forming variable protein-DNA complexes at different protein concentrations and changing the HJ structures. We also show how apo- and holo-CueR differ in their interactions with DNA, and discuss their similarities and differences with other MerR-family metalloregulators. The surprising finding that holo-CueR binds more strongly to DNA than to apo-CueR suggests functional differences among MerR-family metalloregulators, in particular in their mechanisms of switching off gene transcription after activation. The study also corroborates the general applicability of engineered HJs as single-molecule reporters for protein-DNA interactions, which are fundamental processes in gene replication, transcription, recombination, and regulation
Infrared Laser Driven Double Proton Transfer. An Optimal Control Theory Study
Laser control of ultrafast double proton transfer is investigated for a
two-dimensional model system describing stepwise and concerted transfer
pathways. The pulse design has been done by employing optimal control theory in
combination with the multiconfiguration time-dependent Hartree wave packet
propagation. The obtained laser fields correspond to multiple pump-dump pulse
sequences. Special emphasis is paid to the relative importance of stepwise and
concerted transfer pathways for the driven wave packet and its dependence on
the parameters of the model Hamiltonian as well as on the propagation time.
While stepwise transfer is dominating in all cases considered, for high barrier
systems concerted transfer proceeding via tunneling can make a contribution.Comment: 9 figure
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Species-Specific Inhibition of RIG-I Ubiquitination and IFN Induction by the Influenza A Virus NS1 Protein
Influenza A viruses can adapt to new host species, leading to the emergence of novel pathogenic strains. There is evidence that highly pathogenic viruses encode for non-structural 1 (NS1) proteins that are more efficient in suppressing the host immune response. The NS1 protein inhibits type-I interferon (IFN) production partly by blocking the TRIM25 ubiquitin E3 ligase-mediated Lys63-linked ubiquitination of the viral RNA sensor RIG-I, required for its optimal downstream signaling. In order to understand possible mechanisms of viral adaptation and host tropism, we examined the ability of NS1 encoded by human (Cal04), avian (HK156), swine (SwTx98) and mouse-adapted (PR8) influenza viruses to interact with TRIM25 orthologues from mammalian and avian species. Using co-immunoprecipitation assays we show that human TRIM25 binds to all tested NS1 proteins, whereas the chicken TRIM25 ortholog binds preferentially to the NS1 from the avian virus. Strikingly, none of the NS1 proteins were able to bind mouse TRIM25. Since NS1 can inhibit IFN production in mouse, we tested the impact of TRIM25 and NS1 on RIG-I ubiquitination in mouse cells. While NS1 efficiently suppressed human TRIM25-dependent ubiquitination of RIG-I 2CARD, NS1 inhibited the ubiquitination of full-length mouse RIG-I in a mouse TRIM25-independent manner. Therefore, we tested if the ubiquitin E3 ligase Riplet, which has also been shown to ubiquitinate RIG-I, interacts with NS1. We found that NS1 binds mouse Riplet and inhibits its activity to induce IFN-β in murine cells. Furthermore, NS1 proteins of human but not swine or avian viruses were able to interact with human Riplet, thereby suppressing RIG-I ubiquitination. In conclusion, our results indicate that influenza NS1 protein targets TRIM25 and Riplet ubiquitin E3 ligases in a species-specific manner for the inhibition of RIG-I ubiquitination and antiviral IFN production
3-Carbamoylquinoxalin-1-ium chloride
The title compound, C9H8N3O+·Cl−, was isolated from a liquid culture of streptomyces sp. In the cation, the ring system makes a dihedral angle of 0.2 (2)° with the amide group. The protonation creating the cation occurs at ome of the N atoms in the quinoxaline ring system. In the crystal, the ions are linked through N—H⋯O and N—H⋯Cl hydrogen bonds, forming a two-dimensional network parallel to (10)
Quasiparticle Spectrum of d-wave Superconductors in the Mixed State
The quasiparticle spectrum of a two-dimensional d-wave superconductor in the
mixed state, H_{c1} << H << H_{c2}, is studied both analytically and
numerically using the linearized Bogoliubov-de Gennes equation. We consider
various values of the "anisotropy ratio" v_F/v_Delta for the quasiparticle
velocities at the Dirac points, and we examine the implications of symmetry.
For a Bravais lattice of vortices, we find there is always an isolated
energy-zero (Dirac point) at the center of the Brillouin zone, but for a
non-Bravais lattice with two vortices per unit cell there is generally an
energy gap. In both of these cases, the density of states should vanish at zero
energy, in contrast with the semiclassical prediction of a constant density of
states, though the latter may hold down to very low energies for large
anisotropy ratios. This result is closely related to the particle-hole symmetry
of the band structures in lattices with two vortices per unit cell. More
complicated non-Bravais vortex lattice configurations with at least four
vortices per unit cell can break the particle-hole symmetry of the linearized
energy spectrum and lead to a finite density of states at zero energy.Comment: 16 pages, 14 figures, RevTe
Two-photon Lithography for 3D Magnetic Nanostructure Fabrication
Ferromagnetic materials have been utilised as recording media within data
storage devices for many decades. Confinement of the material to a two
dimensional plane is a significant bottleneck in achieving ultra-high recording
densities and this has led to the proposition of three dimensional (3D)
racetrack memories that utilise domain wall propagation along nanowires.
However, the fabrication of 3D magnetic nanostructures of complex geometry is
highly challenging and not easily achievable with standard lithography
techniques. Here, by using a combination of two-photon lithography and
electrochemical deposition, we show a new approach to construct 3D magnetic
nanostructures of complex geometry. The magnetic properties are found to be
intimately related to the 3D geometry of the structure and magnetic imaging
experiments provide evidence of domain wall pinning at a 3D nanostructured
junction
Dirac Nodes and Quantized Thermal Hall Effect in the Mixed State of d-wave Superconductors
We consider the vortex state of d-wave superconductors in the clean limit.
Within the linearized approximation the quasiparticle bands obtained are found
to posess Dirac cone dispersion (band touchings) at special points in the
Brillouin zone. They are protected by a symmetry of the linearized Hamiltonian
that we call T_Dirac. Moreover, for vortex lattices that posess inversion
symmetry, it is shown that there is always a Dirac cone centered at zero energy
within the linearized theory. On going beyond the linearized approximation and
including the effect of the smaller curvature terms (that break T_Dirac), the
Dirac cone dispersions are found to acquire small gaps (0.5 K/Tesla in YBCO)
that scale linearly with the applied magnetic field. When the chemical
potential for quasiparticles lies within the gap, quantization of the
thermal-Hall conductivity is expected at low temperatures i.e. kappa_{xy}/T =
n[(pi k_B)^2/(3h)] with the integer `n' taking on values n=+2, -2, 0. This
quantization could be seen in low temperature thermal transport measurements of
clean d-wave superconductors with good vortex lattices.Comment: (23 pages in all [7 pages in appendices], 9 figures
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