Radiative Transfer Theory Verified by Controlled Laboratory Experiments

We report the results of high-accuracy controlled laboratory measurements of the Stokes reflection matrix for suspensions of submicrometer-sized latex particles in water and compare them with the results of a numerically exact computer solution of the vector radiative transfer equation (VRTE). The quantitative performance of the VRTE is monitored by increasing the volume packing density of the latex particles from 2 to 10. Our results indicate that the VRTE can be applied safely to random particulate media with packing densities up to 2. VRTE results for packing densities of the order of 5 should be taken with caution, whereas the polarized bidirectional reflectivity of suspensions with larger packing densities cannot be accurately predicted. We demonstrate that a simple modification of the phase matrix entering the VRTE based on the so-called static structure factor can be a promising remedy that deserves further examination

Attracting Manifold for a Viscous Topology Transition

An analytical method is developed describing the approach to a finite-time singularity associated with collapse of a narrow fluid layer in an unstable Hele-Shaw flow. Under the separation of time scales near a bifurcation point, a long-wavelength mode entrains higher-frequency modes, as described by a version of Hill's equation. In the slaved dynamics, the initial-value problem is solved explicitly, yielding the time and analytical structure of a singularity which is associated with the motion of zeroes in the complex plane. This suggests a general mechanism of singularity formation in this system.Comment: 4 pages, RevTeX, 3 ps figs included with text in uuencoded file, accepted in Phys. Rev. Let

Boltzmann-conserving classical dynamics in quantum time-correlation functions: "Matsubara dynamics".

We show that a single change in the derivation of the linearized semiclassical-initial value representation (LSC-IVR or "classical Wigner approximation") results in a classical dynamics which conserves the quantum Boltzmann distribution. We rederive the (standard) LSC-IVR approach by writing the (exact) quantum time-correlation function in terms of the normal modes of a free ring-polymer (i.e., a discrete imaginary-time Feynman path), taking the limit that the number of polymer beads N → ∞, such that the lowest normal-mode frequencies take their "Matsubara" values. The change we propose is to truncate the quantum Liouvillian, not explicitly in powers of ħ(2) at ħ(0) (which gives back the standard LSC-IVR approximation), but in the normal-mode derivatives corresponding to the lowest Matsubara frequencies. The resulting "Matsubara" dynamics is inherently classical (since all terms O(ħ(2)) disappear from the Matsubara Liouvillian in the limit N → ∞) and conserves the quantum Boltzmann distribution because the Matsubara Hamiltonian is symmetric with respect to imaginary-time translation. Numerical tests show that the Matsubara approximation to the quantum time-correlation function converges with respect to the number of modes and gives better agreement than LSC-IVR with the exact quantum result. Matsubara dynamics is too computationally expensive to be applied to complex systems, but its further approximation may lead to practical methods.T.J.H.H., M.J.W., and S.C.A. acknowledge funding from the U.K. Engineering and Physical Sciences Research Council. A.M. acknowledges the European Lifelong Learning Programme (LLP) for an Erasmus student placement scholarship. T.J.H.H. also acknowledges a Research Fellowship from Jesus College, Cambridge and helpful discussions with Dr. Adam Harper.This is the author accepted manuscript. The final version is available from AIP via http://dx.doi.org/10.1063/1.491631

Peptides identify multiple hotspots within the ligand binding domain of the TNF receptor 2

BACKGROUND: Hotspots are defined as the minimal functional domains involved in protein:protein interactions and sufficient to induce a biological response. RESULTS: Here we describe the use of complex and high diversity phage display libraries to isolate peptides (called Hotspot Ligands or HSPLs) which sub-divide the ligand binding domain of the tumor necrosis factor receptor 2 (TNFR2; p75) into multiple hotspots. We have shown that these libraries could generate HSPLs which not only subdivide hotspots on protein and non-protein targets but act as agonists or antagonists. Using this approach, we generated peptides which were specific for human TNFR2, could be competed by the natural ligands, TNFα and TNFβ and induced an unexpected biological response in a TNFR2-specific manner. CONCLUSIONS: To our knowledge, this is the first report describing the dissection of the TNFR2 into biologically active hotspots with the concomitant identification of a novel and unexpected biological activity

Exact, E=0, Solutions for General Power-Law Potentials. I. Classical Orbits

For zero energy, $E=0$, we derive exact, classical solutions for {\em all} power-law potentials, $V(r)=-\gamma/r^\nu$, with $\gamma>0$ and $-\infty <\nu<\infty$. When the angular momentum is non-zero, these solutions lead to the orbits $\r(t)= [\cos \mu (\th(t)-\th_0(t))]^{1/\mu}$, for all $\mu \equiv \nu/2-1 \ne 0$. When $\nu>2$, the orbits are bound and go through the origin. This leads to discrete discontinuities in the functional dependence of $\th(t)$ and $\th_0(t)$, as functions of $t$, as the orbits pass through the origin. We describe a procedure to connect different analytic solutions for successive orbits at the origin. We calculate the periods and precessions of these bound orbits, and graph a number of specific examples. Also, we explain why they all must violate the virial theorem. The unbound orbits are also discussed in detail. This includes the unusual orbits which have finite travel times to infinity and also the special $\nu = 2$ case.Comment: LaTeX, 27 pages with 12 figures available from the authors or can be generated from Mathematica instructions at end of the fil

Parsing cyclothymic disorder and other specified bipolar spectrum disorders in youth

© 2018 Elsevier B.V. Objective: Most studies of pediatric bipolar disorder (BP) combine youth who have manic symptoms, but do not meet criteria for BP I/II, into one “not otherwise specified” (NOS) group. Consequently, little is known about how youth with cyclothymic disorder (CycD) differ from youth with BP NOS. The objective of this study was to determine whether youth with a research diagnosis of CycD (RDCyc) differ from youth with operationalized BP NOS. Method: Participants from the Course and Outcome of Bipolar Youth study were evaluated to determine whether they met RDCyc criteria. Characteristics of RDCyc youth and BP NOS youth were compared at baseline, and over eight-years follow-up. Results: Of 154 youth (average age 11.96 (3.3), 42% female), 29 met RDCyc criteria. RDCyc youth were younger (p =.04) at baseline. Over follow-up, RDCyc youth were more likely to have a disruptive behavior disorder (p =.01), and were more likely to experience irritability (p =.03), mood reactivity (p =.02), and rejection sensitivity (p =.03). BP NOS youth were more likely to develop hypomania (p =.02), or depression (p =.02), and tended to have mood episodes earlier in the eight-year follow-up period. Limitations: RDCyc diagnoses were made retrospectively and followed stringent criteria, which may highlight differences that, under typical clinical conditions and more vague criteria, would not be evident. Conclusion: There were few differences between RDCyc and BP NOS youth. However, the ways in which the groups diverged could have implications; chronic subsyndromal mood symptoms may portend a severe, but ultimately non-bipolar, course. Longer follow-up is necessary to determine the trajectory and outcomes of CycD symptoms

Pseudoscalar and Scalar Meson Photoproduction Interpreted by Regge Phenomenology

We have evaluated pseudoscalar and scalar neutral pion photoproduction in $\vec{\gamma}p\to\pi^0p$ and $\vec{\gamma}p\to a_0^0p$ above the resonance region and within Regge phenomenology. Our fit, including GlueX $\Sigma$ pseudoscalar photoproduction data, shows that previous SLAC $\Sigma$ measurements for $\vec{\gamma}p \to \pi^0p$ above $E_\gamma = 4~\mathrm{GeV}$ are at variance with SLAC data with more recent measurements made by GlueX in vicinity of $E_\gamma = 9~\mathrm{GeV}$. The Regge model predicts that the beam polarization asymmetry $\Sigma$ of the scalar meson is opposite to that of pseudoscalar meson photoproduction, however, the cross sections are similar. While the vector natural parity meson exchange is dominant in both cases, the contribution of the pseudovector unnatural parity meson exchange is very small. Using Regge phenomenology, we predicted high energy behavior for double polarized observables $\mathbb{E}$, $\mathbb{F}$, $\mathbb{G}$, and $\mathbb{H}$ for the reactions $\gamma p\to \pi^0p$ and $\gamma p\to a_0^0p$.Comment: 8 pages, 5 figures, several small glitches were fixe

A surrogate-based approach for post-genomic partner identification

BACKGROUND: Modern drug discovery is concerned with identification and validation of novel protein targets from among the 30,000 genes or more postulated to be present in the human genome. While protein-protein interactions may be central to many disease indications, it has been difficult to identify new chemical entities capable of regulating these interactions as either agonists or antagonists. RESULTS: In this paper, we show that peptide complements (or surrogates) derived from highly diverse random phage display libraries can be used for the identification of the expected natural biological partners for protein and non-protein targets. Our examples include surrogates isolated against both an extracellular secreted protein (TNFβ) and intracellular disease related mRNAs. In each case, surrogates binding to these targets were obtained and found to contain partner information embedded in their amino acid sequences. Furthermore, this information was able to identify the correct biological partners from large human genome databases by rapid and integrated computer based searches. CONCLUSIONS: Modified versions of these surrogates should provide agents capable of modifying the activity of these targets and enable one to study their involvement in specific biological processes as a means of target validation for downstream drug discovery