Unimodular Loop Quantum Cosmology

Unimodular gravity is based on a modification of the usual Einstein-Hilbert action that allows one to recover general relativity with a dynamical cosmological constant. It also has the interesting property of providing, as the momentum conjugate to the cosmological constant, an emergent clock variable. In this paper we investigate the cosmological reduction of unimodular gravity, and its quantization within the framework of flat homogeneous and isotropic loop quantum cosmology. It is shown that the unimodular clock can be used to construct the physical state space, and that the fundamental features of the previous models featuring scalar field clocks are reproduced. In particular, the classical singularity is replaced by a quantum bounce, which takes place in the same condition as obtained previously. We also find that requirement of semi-classicality demands the expectation value of the cosmological constant to be small (in Planck units). The relation to spin foam models is also studied, and we show that the use of the unimodular time variable leads to a unique vertex expansion.Comment: 26 pages. Revised version taking into account referee's comment

ASTROD, ASTROD I and their gravitational-wave sensitivities

ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) is a mission concept with three spacecraft -- one near L1/L2 point, one with an inner solar orbit and one with an outer solar orbit, ranging coherently with one another using lasers to test relativistic gravity, to measure the solar system and to detect gravitational waves. ASTROD I with one spacecraft ranging optically with ground stations is the first step toward the ASTROD mission. In this paper, we present the ASTROD I payload and accelerometer requirements, discuss the gravitational-wave sensitivities for ASTROD and ASTROD I, and compare them with LISA and radio-wave PDoppler-tracking of spacecraft.Comment: presented to the 5th Edoardo Amaldi Conference (July 6-11, 2003) and submitted to Classical and Quantum Gravit

Breast cancer–secreted factors perturb murine bone growth in regions prone to metastasis

Breast cancer frequently metastasizes to bone, causing osteolytic lesions. However, how factors secreted by primary tumors affect the bone microenvironment before the osteolytic phase of metastatic tumor growth remains unclear. Understanding these changes is critical as they may regulate metastatic dissemination and progression. To mimic premetastatic bone adaptation, immunocompromised mice were injected with MDA-MB-231–conditioned medium [tumor-conditioned media (TCM)]. Subsequently, the bones of these mice were subjected to multiscale, correlative analysis including RNA sequencing, histology, micro–computed tomography, x-ray scattering analysis, and Raman imaging. In contrast to overt metastasis causing osteolysis, TCM treatment induced new bone formation that was characterized by increased mineral apposition rate relative to control bones, altered bone quality with less matrix and more carbonate substitution, and the deposition of disoriented mineral near the growth plate. Our study suggests that breast cancer–secreted factors may promote perturbed bone growth before metastasis, which could affect initial seeding of tumor cells

Nitrogen-Functionalized Graphene Nanoflakes (GNFs:N): Tunable Photoluminescence and Electronic Structures

This study investigates the strong photoluminescence (PL) and X-ray excited optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes (GNFs:N), which arise from the significantly enhanced density of states in the region of {\pi} states and the gap between {\pi} and {\pi}* states. The increase in the number of the sp2 clusters in the form of pyridine-like N-C, graphite-N-like, and the C=O bonding and the resonant energy transfer from the N and O atoms to the sp2 clusters were found to be responsible for the blue shift and the enhancement of the main PL emission feature. The enhanced PL is strongly related to the induced changes of the electronic structures and bonding properties, which were revealed by the X-ray absorption near-edge structure, X-ray emission spectroscopy, and resonance inelastic X-ray scattering. The study demonstrates that PL emission can be tailored through appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way for new optoelectronic devices.Comment: 8 pages, 6 figures (including toc figure

Backpropagation neural network as earthquake early warning tool using a new modified elementary Levenberg–Marquardt Algorithm to minimise backpropagation errors

A new modified elementary Levenberg–Marquardt Algorithm (M-LMA) was used to minimise backpropagation errors in training a backpropagation neural network (BPNN) to predict the records related to the Chi-Chi earthquake from four seismic stations: Station-TAP003, Station-TAP005, Station-TCU084, and Station-TCU078 belonging to the Free Field Strong Earthquake Observation Network, with the learning rates of 0.3, 0.05, 0.2, and 0.28, respectively. For these four recording stations, the M-LMA has been shown to produce smaller predicted errors compared to the Levenberg–Marquardt Algorithm (LMA). A sudden predicted error could be an indicator for Early Earthquake Warning (EEW), which indicated the initiation of strong motion due to large earthquakes. A trade-Off decision-making process with BPNN (TDPB), using two alarms, adjusted the threshold of the magnitude of predicted error without a mistaken alarm. With this approach, it is unnecessary to consider the problems of characterising the wave phases and pre-processing, and does not require complex hardware; an existing seismic monitoring network-covered research area was already sufficient for these purposes.</p

Nondestructive characterization of UHMWPE armor materials

Ultra-high molecular weight polyethylene (UHMWPE) is a material increasingly used for fabricating helmet and body armor. In this work, plate specimens consolidated from thin fiber sheets in series 3124 and 3130 were examined with ultrasound, X-ray and terahertz radiation. Ultrasonic through-transmission scans using both air-coupled and immersion modes revealed that the 3130 series material generally had much lower attenuation than the 3124 series, and that certain 3124 plates had extremely high attenuation. Due to the relatively low inspection frequencies used, pulse-echo immersion ultrasonic testing could not detect distinct flaw echoes from the interior. To characterize the nature of the defective condition that was responsible for the high ultrasonic attenuation, terahertz radiation in the time-domain spectroscopy mode were used to image the flaws. Terahertz scan images obtained on the high attenuation samples clearly showed a distribution of a large number of defects, possibly small planar delaminations, throughout the volume of the interior. Their precise nature and morphology are to be verified by optical microscopy of the sectioned surface