Microstructural abnormalities in deep and superficial white matter in youths with mild traumatic brain injury

BACKGROUND: Diffusion Tensor Imaging (DTI) studies of traumatic brain injury (TBI) have focused on alterations in microstructural features of deep white matter fibers (DWM), though post-mortem studies have demonstrated that injured axons are often observed at the gray-white matter interface where superficial white matter fibers (SWM) mediate local connectivity. OBJECTIVES: To examine microstructural alterations in SWM and DWM in youths with a history of mild TBI and examine the relationship between white matter alterations and attention. METHODS: Using DTIDWM fractional anisotropy (FA) and SWM FA in youths with mild TBI (TBI, n=63) were compared to typically developing and psychopathology matched control groups (n=63 each). Following tract-based spatial statistics, SWM FA was assessed by applying a probabilistic tractography derived SWM mask, and DWM FA was captured with a white matter fiber tract mask. Voxel-wise z-score calculations were used to derive a count of voxels with abnormally high and low FA for each participant. Analyses examined DWM and SWM FA differences between TBI and control groups, the relationship between attention and DWM and SWM FA and the relative susceptibility of SWM compared to DWM FA to alterations associated with mild TBI. RESULTS: Case-based comparisons revealed more voxels with low FA and fewer voxels with high FA in SWM in youths with mild TBI compared to both control groups. Equivalent comparisons in DWM revealed a similar pattern of results, however, no group differences for low FA in DWM were found between mild TBI and the control group with matched psychopathology. Slower processing speed on the attention task was correlated with the number of voxels with low FA in SWM in youths with mild TBI. CONCLUSIONS: Within a sample of youths with a history of mild TBI, this study identified abnormalities in SWM microstructure associated with processing speed. The majority of DTI studies of TBI have focused on long-range DWM fiber tracts, often overlooking the SWM fiber type

On the Size of Hadrons

The form factor and the mean-square radius of the pion are calculated analytically from a parametrized form of a $q\bar q$ wave function. The numerical wave function was obtained previously by solving numerically an eigenvalue equation for the pion in a particular model. The analytical formulas are of more general interest than just be valid for the pion and can be generalized to the case with unequal quark masses. Two different parametrizations are investigated. Because of the highly relativistic problem, noticable deviations from a non-relativistic formula are obtained.Comment: 14 pages, minor typos corrected, several points clarified, results unchange

On the effective light-cone QCD-Hamiltonian: Application to the pion and other mesons

The effective interaction between a quark and an anti-quark as obtained previously with by the method of iterated resolvents is replaced by the up-down-model and applied to flavor off-diagonal mesons including the positive pion. The only free parameters are the canonical ones, the coupling constant and the masses of the quarks.Comment: 11 pages, 4 figures, 2 tables, 22 reference

Compact Patch Antenna for Automatic Identification System (AIS)

International audienceThis paper presents a radiating element developed for the space AIS application. This element is a compact sized and reduced mass microstrip patch antenna integrating frequency resonant adjustment devices. Theoretical and experimental results with good agreement are presented

Invariant Operators in Collinear Effective Theory

We consider processes which produce final state hadrons whose energy is much greater than their mass. In this limit interactions involving collinear fermions and gluons are constrained by a symmetry, and we give a general set of rules for constructing leading and subleading invariant operators. Wilson coefficients C(mu,P) are functions of a label operator P, and do not commute with collinear fields. The symmetry is used to reproduce a two-loop result for factorization in B -> D pi in a simple way.Comment: 11 pages, 2 figs, journal versio

On the form factor of physical mesons and their distribution function

This work addresses more to the technical rather than to the physical problem, how to calculate analytically the form factor $F(Q)$, the associated mean-square radius $$, and the distribution function $\Phi(x,Q^2)$ for a given light-cone wave function $\Psi_{q\bar q}(x,\vec k_{\perp})$ of the pion. They turn out to be functions of only one dimensionless parameter, which is the ratio of the constituent quark mass and an effective Bohr momentum which measures the width of the wave function in momentum space. Both parameters are subject to change in the future, when the presently used solution for the over simplified $\uparrow\downarrow$-model will be replaced by something better. Their relation to and agreement with experiment is discussed in detail. The procedure can be generalized also to other hadrons.Comment: 19 pages, 8 figures, 1 table, 22 references. Submitted to Nucl.Phys.

Domain decomposition improvement of quark propagator estimation

Applying domain decomposition to the lattice Dirac operator and the associated quark propagator, we arrive at expressions which, with the proper insertion of random sources therein, can provide improvement to the estimation of the propagator. Schemes are presented for both open and closed (or loop) propagators. In the end, our technique for improving open contributions is similar to the ``maximal variance reduction'' approach of Michael and Peisa, but contains the advantage, especially for improved actions, of dealing directly with the Dirac operator. Using these improved open propagators for the Chirally Improved operator, we present preliminary results for the static-light meson spectrum. The improvement of closed propagators is modest: on some configurations there are signs of significant noise reduction of disconnected correlators; on others, the improvement amounts to a smoothening of the same correlators.Comment: 19 pages, 8 figures, version to appear in Computer Physics Communication

A proof of factorization for B -> D pi

We prove that the matrix elements of four fermion operators mediating the decay B^0 -> D^+ \pi^- and B^- -> D^0 \pi^- factor into the product of a form factor describing the B -> D transition and a convolution of a short distance coefficient with the nonperturbative pion light-cone wave function. This is shown to all orders in alpha_s, up to corrections suppressed by factors of 1/mb, 1/mc, and 1/E_pi. It is not necessary to assume that the pion state is dominated by the q-qbar Fock state.Comment: 4 pages, 3 figs, PRL versio

Effect of Zero Modes on the Bound-State Spectrum in Light-Cone Quantisation

We study the role of bosonic zero modes in light-cone quantisation on the invariant mass spectrum for the simplified setting of two-dimensional SU(2) Yang-Mills theory coupled to massive scalar adjoint matter. Specifically, we use discretised light-cone quantisation where the momentum modes become discrete. Two types of zero momentum mode appear -- constrained and dynamical zero modes. In fact only the latter type of modes turn out to mix with the Fock vacuum. Omission of the constrained modes leads to the dynamical zero modes being controlled by an infinite square-well potential. We find that taking into account the wavefunctions for these modes in the computation of the full bound state spectrum of the two dimensional theory leads to 21% shifts in the masses of the lowest lying states.Comment: LaTeX with 5 postscript file

Widely tunable 23 μm III-V-on-silicon Vernier lasers for broadband spectroscopic sensing

Heterogeneously integrating III-V materials on silicon photonic integrated circuits has emerged as a promising approach to make advanced laser sources for optical communication and sensing applications. Tunable semiconductor lasers operating in the 2-2.5 mu m range are of great interest for industrial and medical applications since many gases (e.g., CO2, CO, CH4) and biomolecules (such as blood glucose) have strong absorption features in this wavelength region. The development of integrated tunable laser sources in this wavelength range enables low-cost and miniature spectroscopic sensors. Here we report heterogeneously integrated widely tunable III-V-on-silicon Vernier lasers using two silicon microring resonators as the wavelength tuning components. The laser has a wavelength tuning range of more than 40 nm near 2.35 mu m. By combining two lasers with different distributed Bragg reflectors, a tuning range of more than 70 nm is achieved. Over the whole tuning range, the side-mode suppression ratio is higher than 35 dB. As a proof-of-principle, this III-V-on-silicon Vernier laser is used to measure the absorption lines of CO. The measurement results match very well with the high-resolution transmission molecular absorption (HITRAN) database and indicate that this laser is suitable for broadband spectroscopy. (C) 2018 Chinese Laser Pres