Parton distributions and new physics searches: the Drell–Yan forward–backward asymmetry as a case study

We present the first unquenched lattice-QCD calculation of the form factors for the decay \(B\rightarrow D^*\ell \nu \) at nonzero recoil. Our analysis includes 15 MILC ensembles with \(N_f=2+1\) flavors of asqtad sea quarks, with a strange quark mass close to its physical mass. The lattice spacings range from \(a\approx 0.15\) fm down to 0.045 fm, while the ratio between the light- and the strange-quark masses ranges from 0.05 to 0.4. The valence b and c quarks are treated using the Wilson-clover action with the Fermilab interpretation, whereas the light sector employs asqtad staggered fermions. We extrapolate our results to the physical point in the continuum limit using rooted staggered heavy-light meson chiral perturbation theory. Then we apply a model-independent parametrization to extend the form factors to the full kinematic range. With this parametrization we perform a joint lattice-QCD/experiment fit using several experimental datasets to determine the CKM matrix element \(|V_{cb}|\). We obtain \(\left| V_{cb}\right| = (38.40 \pm 0.68_{\text {th}} \pm 0.34_{\text {exp}} \pm 0.18_{\text {EM}})\times 10^{-3}\). The first error is theoretical, the second comes from experiment and the last one includes electromagnetic and electroweak uncertainties, with an overall \(\chi ^2\text {/dof} = 126/84\), which illustrates the tensions between the experimental data sets, and between theory and experiment. This result is in agreement with previous exclusive determinations, but the tension with the inclusive determination remains. Finally, we integrate the differential decay rate obtained solely from lattice data to predict \(R(D^*) = 0.265 \pm 0.013\), which confirms the current tension between theory and experiment.

     

Structural anisotropy and internal magnetic fields in trabecular bone: coupling solution and solid dipolar interactions

We investigate the use of intermolecular multiple-quantum coherence to probe structural anisotropy in trabecular bone. Despite the low volume fraction of bone, the bone-water interface produces internal magnetic field gradients which modulate the dipolar field, depending on sample orientation, choice of dipolar correlation length, correlation gradient direction, and evolution time. For this system, the probing of internal magnetic field gradients in the liquid phase permits indirect measurements of the solid phase dipolar field. Our results suggest that measurements of volume-averaged signal intensity as a function of gradient strength and three orthogonal directions could be used to non-invasively measure the orientation of structures inside a sample or their degree of anisotropy. The system is modeled as having two phases, solid and liquid (bone and water), which differ in their magnetization density and magnetic susceptibility. A simple calculation using a priori knowledge of the material geometry and distribution of internal magnetic fields verifies the experimental measurements as a function of gradient strength, direction, and sample orientation.     

The invisible Majorana bound state at the helical edge

The presence of a Majorana bound state in condensed matter systems is often associated to a zero bias peak in conductance measurements. Here, we analyze a system were this paradigm is violated. A Majorana bound state is always present at the interface between a quantum spin Hall system that is magnetically gapped and a quantum spin Hall system gapped by proximity induced s-wave superconductivity. However, the linear conductance could be either zero or non-zero and quantized depending on the energy and length scales of the barriers. The transition between the two values is reminiscent of the topological phase transition in proximitized spin–orbit coupled quantum wires in the presence of an applied magnetic field. We interpret the behavior of the conductance in terms of scattering states at both zero and non-zero energy.     

Simultaneous pH and Temperature Measurements Using Pyranine as a Molecular Probe

Steep variations in concentration and temperature frequently occur in small fluid compartments such as those found in cells or microfluidic devices. A quantitative characterization of concentration and temperature gradients is therefore required before these systems can be fully understood. Although different spatially resolved fluorescence methods have been developed to measure either the temperature or the concentration of ions such as proton or calcium, often concentration measurements depend on temperature and vice versa. Here, we describe a method allowing simultaneous measurement of pH and temperature. This method is based on the detection of the blinking of the fluorescent pH indicator pyranine, a process due to its alternating between a basic form and an acidic form. Fluorescence correlation spectroscopy allows measuring both the protonation and deprotonation rates of pyranine, and each pair of rates can be uniquely related to a pair of pH and temperature values. We show, however, that the relationship between rates, pH and temperature, is very sensitive to the presence of other acid-base molecules in solution. We also show that it is influenced by the overall ionic strength of the solution, in a manner that depends on buffer composition.     

The influence of cell geometry on the Godunov scheme applied to the linear wave equation

By studying the structure of the discrete kernel of the linear acoustic operator discretized with a Godunov scheme, we clearly explain why the behaviour of the Godunov scheme applied to the linear wave equation deeply depends on the space dimension and, especially, on the type of mesh. This approach allows us to explain why, in the periodic case, the Godunov scheme applied to the resolution of the compressible Euler or Navier–Stokes system is accurate at low Mach number when the mesh is triangular or tetrahedral and is not accurate when the mesh is a 2D (or 3D) cartesian mesh. This approach confirms also the fact that a Godunov scheme remains accurate when it is modified by simply centering the discretization of the pressure gradient.     

Stability of valence alternation pairs across the substoichiometric region at Ge/GeO2 interfaces

Through hybrid density functional calculations, we compare the Ge–Ge bond energy with the formation energy of a valence alternation pair as the O concentration varies across the Ge/GeO₂ interface. First, hole trapping energies are calculated for three atomistic models with different O concentrations: bulk Ge with isolated O atoms, amorphous GeO, and amorphous GeO₂ with an O vacancy. The reaction is then broken down in three steps involving the breaking of a Ge–Ge bond, charge transfer processes involving dangling bonds, and the formation of a threefold coordinated O atom. The energy of each elemental reaction is estimated through suitable model calculations. The charge transition levels resulting from this analysis agree with those obtained for the atomistic models. Our estimates indicate that hole trapping at low O concentrations occurs at no energy cost for p-type germanium owing to the formation of threefold-coordinated O atoms. Applied to n-type Ge, our analysis indicates that electron trapping in dangling bonds obtained from the breaking of Ge–Ge bonds is unfavorable. The formation energy of a valence alternation pair is evaluated and discussed in relation to previous results.     

Enhancement of high harmonics generated by field steering of electrons in a two-color orthogonally polarized laser field

We demonstrate enhancement by 1 order of magnitude of the high-order harmonics generated in argon by combining a fundamental field at 1300 nm (10(14) W cm(-2)) and its orthogonally polarized second harmonic at 650 nm (2 × 10(13) W cm(-2)) and by controlling the relative phase between them. This extends earlier work by ensuring that the main effect is the combined field steering the electron trajectory with negligible contribution from multiphoton effects compared to the previous schemes with 800/400 nm fields. We access a broad energy range of harmonics (from 20 eV to 80 eV) at a low laser intensity (far below the ionization saturation limit) and observe deep modulation of the harmonic yield with a period of π in the relative phase. Strong field theoretical analysis reveals that this is principally due to the steering of the recolliding electron wave packet by the two-color field. Our modeling also shows that the atto chirp can be controlled, leading to production of shorter pulses.     

Physical and Chemical Characterization of Therapeutic Iron Containing Materials: A Study of Several Superparamagnetic Drug Formulations with the β-FeOOH or Ferrihydrite Structure

The effectiveness of therapeutically used iron compounds is related to their physical and chemical properties. Four different iron compounds used in oral, intravenous, and intramuscular therapy have been examined by X-ray powder diffraction, iron-57 Mössbauer spectroscopy, transmission electron microscopy, BET surface area measurement, potentiometric titration and studied through dissolution kinetics determinations using acid, reducing and chelating agents. All compounds are nanosized with particle diameters, as determined by X-ray diffraction, ranging from 1 to 4.1 nm. The superparamagnetic blocking temperatures, as determined by Mössbauer spectroscopy, indicate that the relative diameters of the aggregates range from 2.5 to 4.1 nm. Three of the iron compounds have an akaganeite-like structure, whereas one has a ferrihydrite-like structure. As powders the particles form large and dense aggregates which have a very low surface area on the order of 1 m²?g^?1. There is evidence, however, that in a colloidal solution the surface area is increased by two to three orders of magnitude, presumably as a result of the break up of the aggregates. Iron release kinetics by acid, chelating and reducing agents reflect the high surface area, the size and crystallinity of the particles, and the presence of the protective carbohydrate layer coating the iron compound. Within a physiologically relevant time period, the iron release produced by acid or large chelating ligands is small. In contrast, iron is rapidly mobilized by small organic chelating agents, such as oxalate, or by chelate-forming reductants, such as thioglycolate.

     

A non-ideal portal frame energy harvester controlled using a pendulum

A model of energy harvester based on a simple portal frame structure is presented. The system is considered to be non-ideal system (NIS) due to interaction with the energy source, a DC motor with limited power supply and the system structure. The nonlinearities present in the piezoelectric material are considered in the piezoelectric coupling mathematical model. The system is a bi-stable Duffing oscillator presenting a chaotic behavior. Analyzing the average power variation, and bifurcation diagrams, the value of the control variable that optimizes power or average value that stabilizes the chaotic system in the periodic orbit is determined. The control sensitivity is determined to parametric errors in the damping and stiffness parameters of the portal frame. The proposed passive control technique uses a simple pendulum to tuned to the vibration of the structure to improve the energy harvesting. The results show that with the implementation of the control strategy it is possible to eliminate the need for active or semi active control, usually more complex. The control also provides a way to regulate the energy captured to a desired operating frequency.