Spin-Isospin Excitations and Muon Capture by Nuclei

By analyzing the energy-weighted moments of the strength function calculated in RPA and beyond it is shown that the explanation of the effect of missing strength of Gamow-Teller transitions requires that residual interaction produce high-excited $1^{+}$ particle-hole collective states. The example of this interaction is presented. The manifestations of spin-isospin nuclear response in nuclear muon capture are discussed.Comment: 16 pages, 5 figures, 2 tables. The talk at the XVI International School on Nuclear Physics, Neutron Physics and Nuclear Energy, September 19-26, Varna, Bulgari

Filaments in observed and mock galaxy catalogues

Context. The main feature of the spatial large-scale galaxy distribution is an intricate network of galaxy filaments. Although many attempts have been made to quantify this network, there is no unique and satisfactory recipe for that yet. Aims. The present paper compares the filaments in the real data and in the numerical models, to see if our best models reproduce statistically the filamentary network of galaxies. Methods. We apply an object point process with interactions (the Bisous process) to trace and describe the filamentary network both in the observed samples (the 2dFGRS catalogue) and in the numerical models that have been prepared to mimic the data.We compare the networks. Results. We find that the properties of filaments in numerical models (mock samples) have a large variance. A few mock samples display filaments that resemble the observed filaments, but usually the model filaments are much shorter and do not form an extended network. Conclusions. We conclude that although we can build numerical models that are similar to observations in many respects, they may fail yet to explain the filamentary structure seen in the data. The Bisous-built filaments are a good test for such a structure.Comment: 13 pages, accepted for publication in Astronomy and Astrophysic

Double-beta decay matrix elements for 76Ge^{76}Ge

Double-beta decay matrix elements (ME) for $^{76}Ge$ are calculated with different quasi random phase approximation (QRPA)-based methods. First, the ME for the two-neutrino mode are computed using two choices for the single particle (s.p.) basis: i) $2-4\hbar\omega$ full shells and ii) $3-4\hbar\omega$ full shells. When calculated with the renormalized QRPA (RQRPA) and full-RQRPA their values are rather dependent on the size of the single particle basis used, while calculated with proton-neutron QRPA (pnQRPA) and second-QRPA approaches such a dependence was found to be small. The Ikeda sum rule was well fulfilled within pnQRPA for both choices of the s.p. basis and with a good approximation within second-QRPA, while the RQRPA and full-RQRPA methods give deviations up to 21%. Further, the ME for the neutrinoless mode are calculated with the pnQRPA, RQRPA and full-RQRPA methods. They all give close results for the calculation with the smaller basis (i), while for the larger basis (ii), the results differ significantly either from one method to another or within the same method. Finally, using the most recent experimental limit for the $0\nu\beta\beta$ decay half-life of $^{76}Ge$ a critical discussion on the upper limits for the neutrino mass parameter obtained with different theoretical approaches is given

In vivo dark-field reflection-mode photoacoustic microscopy

Reflection-mode photoacoustic microscopy with dark-field laser pulse illumination and high-numerical-aperture ultrasonic detection is designed and implemented in noninvasively imaged blood vessels in the skin in vivo. Dark-field optical illumination minimizes the interference caused by strong photoacoustic signals from superficial structures. A high-numerical-aperture acoustic lens provides high lateral resolution, 45–120μm in this system. A broadband ultrasonic detection system provides high axial resolution, estimated to be ∼15μm. The optical illumination and ultrasonic detection are in a coaxial confocal configuration for optimal image quality. The system is capable of imaging optical-absorption contrast as deep as 3mm in biological tissue

In vivo three-dimensional photoacoustic tomography of a whole mouse head

An in vivo photoacoustic imaging system was designed and implemented to image the entire small animal head. A special scanning gantry was designed to enable in vivo imaging in coronal cross sections with high contrast and good spatial resolution for the first time to our knowledge. By use of a 2.25 MHz ultrasonic transducer with a 6 mm diameter active element, an in-plane radial resolution of ∼312  µm was achieved. Deeply seated arterial and venous vessels in the head measuring up to 1.7 cm in diameter were simultaneously imaged in vivo with 804 nm wavelength laser excitation of photoacoustic waves

High-resolution functional photoacoustic tomography

All-optical imaging has high contrast but poor spatial resolution beyond the ballistic and quasiballistic regimes. All-ultrasonic imaging has high spatial resolution but poor contrast for early stage tumors. Photoacoustic tomography combines the high optical contrast and the high ultrasonic resolution. Our work in this emerging area of research will be summarized in this invited talk. In this technology, a diffraction-based inverse-source problem is solved in the image reconstruction, for which our group developed the rigorous reconstruction theory. We developed a prototype and accomplished noninvasive transdermal and transcranial functional imaging of small-animal brains in vivo

Depth-wise differentiation of Jones matrices obtained from Mueller optical coherence tomography

A unique feature of polarization-sensitive Mueller optical coherence tomography (Mueller-OCT) is that it can reveal various polarization properties of biological samples that are not observable using conventional OCT. One of the most important polarization parameters is birefringence, which can be measured in its integrated form using existing Mueller-OCT systems. We present a new method that uses the least squares algorithm to differentiate measured integrated Jones matrices so that the samples can be observed layer-by-layer. We tested the algorithm using simulated data with variable additive white Gaussian noise (AWGN) levels. We further verified the algorithm using in vitro measurements of the porcine tendon and the septum of the rat heart. This least squares-based algorithm has the potential to reveal structures previously hidden by the inherent masking properties of the integrated images and provide localized phase retardation and orientation information