6,198 research outputs found
Gravitational Binding, Virialization and the Peculiar Velocity Distribution of the Galaxies
We examine the peculiar velocity distribution function of galaxies in
cosmological many-body gravitational clustering. Our statistical mechanical
approach derives a previous basic assumption and generalizes earlier results to
galaxies with haloes. Comparison with the observed peculiar velocity
distributions indicates that individual massive galaxies are usually surrounded
by their own haloes, rather than being embedded in common haloes. We then
derive the density of energy states, giving the probability that a randomly
chosen configuration of N galaxies in space is bound and virialized.
Gravitational clustering is very efficient. The results agree well with the
observed probabilities for finding nearby groups containing N galaxies. A
consequence is that our local relatively low mass group is quite typical, and
the observed small departures from the local Hubble flow beyond our group are
highly probable.Comment: Paper in aastex 5.0 format and 9 figures. Replace a new version with
figures and typos correcte
High-Performance Bioinstrumentation for Real-Time Neuroelectrochemical Traumatic Brain Injury Monitoring
Traumatic brain injury (TBI) has been identified as an important cause of death and severe disability in all age groups and particularly in children and young adults. Central to TBIs devastation is a delayed secondary injury that occurs in 30–40% of TBI patients each year, while they are in the hospital Intensive Care Unit (ICU). Secondary injuries reduce survival rate after TBI and usually occur within 7 days post-injury. State-of-art monitoring of secondary brain injuries benefits from the acquisition of high-quality and time-aligned electrical data i.e., ElectroCorticoGraphy (ECoG) recorded by means of strip electrodes placed on the brains surface, and neurochemical data obtained via rapid sampling microdialysis and microfluidics-based biosensors measuring brain tissue levels of glucose, lactate and potassium. This article progresses the field of multi-modal monitoring of the injured human brain by presenting the design and realization of a new, compact, medical-grade amperometry, potentiometry and ECoG recording bioinstrumentation. Our combined TBI instrument enables the high-precision, real-time neuroelectrochemical monitoring of TBI patients, who have undergone craniotomy neurosurgery and are treated sedated in the ICU. Electrical and neurochemical test measurements are presented, confirming the high-performance of the reported TBI bioinstrumentation
Entanglement convertibility by sweeping through the quantum phases of the alternating bonds chain
We study the entanglement structure and the topological edge states of the
ground state of the spin-1/2 XXZ model with bond alternation. We employ
parity-density matrix renormalization group with periodic boundary conditions.
The finite-size scaling of R\'enyi entropies and are used to
construct the phase diagram of the system. The phase diagram displays three
possible phases: Haldane type (an example of symmetry protected topological
ordered phases), Classical Dimer and N\'eel phases, the latter bounded by two
continuous quantum phase transitions. The entanglement and non-locality in the
ground state are studied and quantified by the entanglement convertibility. We
found that, at small spatial scales, the ground state is not convertible within
the topological Haldane dimer phase. The phenomenology we observe can be
described in terms of correlations between edge states. We found that the
entanglement spectrum also exhibits a distinctive response in the topological
phase: the effective rank of the reduced density matrix displays a specifically
large "susceptibility" in the topological phase. These findings support the
idea that although the topological order in the ground state cannot be detected
by local inspection, the ground state response at local scale can tell the
topological phases apart from the non-topological phases.Comment: Final versio
Haze in the Klang Valley of Malaysia
Continuous measurements of dry aerosol light scattering (Bsp) were made at two sites in the Klang Valley of Malaysia between December 1998 and December 2000. In addition 24-h PM2.5 samples were collected on a one-day-in-six cycle and the chemical composition of the aerosol was determined. Periods of excessive haze were defined as 24-h average Bsp values greater than 150 Mm-1 and these occurred on a number of occasions, between May and September 1999, during May 2000, and between July and September 2000. The evidence for smoke being a significant contributor to aerosol during periods of excessive haze is discussed and includes features of the aerosol chemistry, the diurnal cycle of Bsp, and the coincidence of forest fires on Sumatra during the southwest (SW) monsoon period, as well as transport modelling for one week of the southwest Monsoon of 2000. The study highlights that whilst transboundary smoke is a major contributor to poor visibility in the Klang Valley, smoke from fires on Peninsular Malaysia is also a contributor, and at all times, the domestic source of secondary particle production is present
The Constraints and Spectra of a Deformed Quantum Mechanics
We examine a deformed quantum mechanics in which the commutator between
coordinates and momenta is a function of momenta. The Jacobi identity
constraint on a two-parameter class of such modified commutation relations
(MCR's) shows that they encode an intrinsic maximum momentum; a sub-class of
which also imply a minimum position uncertainty. Maximum momentum causes the
bound state spectrum of the one-dimensional harmonic oscillator to terminate at
finite energy, whereby classical characteristics are observed for the studied
cases. We then use a semi-classical analysis to discuss general concave
potentials in one dimension and isotropic power-law potentials in higher
dimensions. Among other conclusions, we find that in a subset of the studied
MCR's, the leading order energy shifts of bound states are of opposite sign
compared to those obtained using string-theory motivated MCR's, and thus these
two cases are more easily distinguishable in potential experiments.Comment: 30 pages inclusive of 7 figure
Measurement of Resonant Frequency and Quality Factor of Microwave Resonators: Comparison of Methods
Precise microwave measurements of sample conductivity, dielectric, and
magnetic properties are routinely performed with cavity perturbation
measurements. These methods require the accurate determination of quality
factor and resonant frequency of microwave resonators. Seven different methods
to determine the resonant frequency and quality factor from complex
transmission coefficient data are discussed and compared to find which is most
accurate and precise when tested using identical data. We find that the
nonlinear least-squares fit to the phase vs. frequency is the most accurate and
precise when the signal-to-noise ratio is greater than 65. For noisier data,
the nonlinear least squares fit to a Lorentzian curve is more accurate and
precise. The results are general and can be applied to the analysis of many
kinds of resonant phenomena.Comment: 29 pages, 11 figure
Necrotising colitis related to clozapine? A rare but life threatening side effect
We report here a case of a 34-year-old gentleman who developed right-sided necrotising colitis after clozapine usage. Anticholinergic activity is believed to the cause. We believe that in patients who have been consuming medications known to have an association with necrotising colitis, constipation with concomitant increasing abdominal pain, distension and fever should be treated with a strong index of suspicion. Consideration of necrotising colitis should prompt expeditious resection of the affected colonic segment
Design and fabrication of 3D-printed anatomically shaped lumbar cage for intervertebra disc (IVD) degeneration treatment
Spinal fusion is the gold standard surgical procedure for degenerative spinal conditions when conservative therapies have been unsuccessful in rehabilitation of patients. Novel strategies are required to improve biocompatibility and osseointegration of traditionally used materials for lumbar cages. Furthermore, new design and technologies are needed to bridge the gap due to the shortage of optimal implant sizes to fill the intervertebral disc defect. Within this context, additive manufacturing technology presents an excellent opportunity to fabricate ergonomic shape medical implants. The goal of this study is to design and manufacture a 3D-printed lumbar cage for lumbar interbody fusion. Optimisations of the proposed implant design and its printing parameters were achieved via in silico analysis. The final construct was characterised via scanning electron microscopy, contact angle, x-ray micro computed tomography (μCT), atomic force microscopy, and compressive test. Preliminary in vitro cell culture tests such as morphological assessment and metabolic activities were performed to access biocompatibility of 3D-printed constructs. Results of in silico analysis provided a useful platform to test preliminary cage design and to find an optimal value of filling density for 3D printing process. Surface characterisation confirmed a uniform coating of nHAp with nanoscale topography. Mechanical evaluation showed mechanical properties of final cage design similar to that of trabecular bone. Preliminary cell culture results showed promising results in terms of cell growth and activity confirming biocompatibility of constructs. Thus for the first time, design optimisation based on computational and experimental analysis combined with the 3D-printing technique for intervertebral fusion cage has been reported in a single study. 3D-printing is a promising technique for medical applications and this study paves the way for future development of customised implants in spinal surgical applications
Charting the research course for sustainable aquaculture in Sabah, Malaysia
Due to arising needs and demands, aquaculture is currently the fastest growing food production sector. In order to increase yield and yet to remain sustainable, the challenges would be to minimise impact on the environment and ecosystem services. Aquaculture activity contributes significantly to Malaysia and also the state of Sabah’s economy and food security. Hence, the future changes in the environment as a result of rapid population growth and development would pose as threats to this industry in terms of quality, quantity and sustainability. Unforeseen environmental changes such as environmental pollution from other sources, climate change and the changes in policies would jeopardize the sustainability of this industry. In order to anticipate such impacts to the aquaculture activities, this paper set to chart a sustainable course for its development. Four important research courses were proposed: establishment of a sustainable framework, assessment of impacts of climate change, viability and vulnerability assessment due to future environmental changes and food security. Such findings would eventually allow the stakeholders to plan and manage the resources and aquaculture activities in such a way that foster sustainable food security and resilient aquatic ecosystems
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