The Volume Fraction of Ionized Intergalactic Gas at Redshift z=6.5

The observed number density of Lyman-alpha sources implies a minimum volume of the inter-galactic medium that must be ionized, in order to allow the Lyman-alpha photons to escape attenuation. We estimate this volume by assigning to each Lyman-alpha emitter the minimum Stromgren sphere that would allow half its Lyman-alpha photons to escape. This implies a lower limit to ionized gas volume fraction of 20-50% at redshift z=6.5. This is a lower limit in two ways: First, we conservatively assume that the Lyman-alpha sources seen (at a relatively bright flux limit) are the only ones present; and second, we assume the smallest Stromgren sphere volume that will allow the photons to escape. This limit is completely independent of what ionizing photon sources produced the bubbles. Deeper Lyman-alpha surveys are possible with present technology, and can strengthen these limits by detecting a higher density of Lyman-alpha galaxies.Comment: Submitted to ApJ Letter

Temporoparietal encoding of space and time during vestibular-guided orientation

When we walk in our environment, we readily determine our travelled distance and location using visual cues. In the dark, estimating travelled distance uses a combination of somatosensory and vestibular (i.e., inertial) cues. The observed inability of patients with complete peripheral vestibular failure to update their angular travelled distance during active or passive turns in the dark implies a privileged role for vestibular cues during human angular orientation. As vestibular signals only provide inertial cues of self-motion (e.g., velocity, °/s), the brain must convert motion information to distance information (a process called 'path integration') to maintain our spatial orientation during self-motion in the dark. It is unknown, however, what brain areas are involved in converting vestibular-motion signals to those that enable such vestibular-spatial orientation. Hence, using voxel-based lesion-symptom mapping techniques, we explored the effect of acute right hemisphere lesions in 18 patients on perceived angular position, velocity and motion duration during whole-body angular rotations in the dark. First, compared to healthy controls' spatial orientation performance, we found that of the 18 acute stroke patients tested, only the four patients with damage to the temporoparietal junction showed impaired spatial orientation performance for leftward (contralesional) compared to rightward (ipsilesional) rotations. Second, only patients with temporoparietal junction damage showed a congruent underestimation in both their travelled distance (perceived as shorter) and motion duration (perceived as briefer) for leftward compared to rightward rotations. All 18 lesion patients tested showed normal self-motion perception. These data suggest that the cerebral cortical regions mediating vestibular-motion ('am I moving?') and vestibular-spatial perception ('where am I?') are distinct. Furthermore, the congruent contralesional deficit in time (motion duration) and position perception, seen only in temporoparietal junction patients, may reflect a common neural substrate in the temporoparietal junction that mediates the encoding of motion duration and travelled distance during vestibular-guided navigation. Alternatively, the deficits in timing and spatial orientation with temporoparietal junction lesions could be functionally linked, implying that the temporoparietal junction may act as a cortical temporal integrator, combining estimates of self-motion velocity over time to derive an estimate of travelled distance. This intriguing possibility predicts that timing abnormalities could lead to spatial disorientation

Multiple Components in Narrow Planetary Rings

The phase-space volume of regions of regular or trapped motion, for bounded or scattering systems with two degrees of freedom respectively, displays universal properties. In particular, drastic reductions in the volume (gaps) are observed at specific values of a control parameter. Using the stability resonances we show that they, and not the mean-motion resonances, account for the position of these gaps. For more degrees of freedom, exciting these resonances divides the regions of trapped motion. For planetary rings, we demonstrate that this mechanism yields rings with multiple components.Comment: 4 pages, 7 figures (some in colors

Signatures of Inelastic Scattering in Coulomb-Blockade Quantum Dots

We calculate the finite-temperature conductance peak-height distributions in Coublomb-blockade quantum dots in the limit where the inelastic scattering rate in the dot is large compared with the mean elastic tunneling rate. The relative reduction of the standard deviation of the peak-height distribution by a time-reversal symmetry-breaking magnetic field, which is essentially temperature-independent in the elastic limit, is enhanced by the inclusion of inelastic scattering at finite temperature. We suggest this quantity as an independent experimental probe for inelastic scattering in closed dots.Comment: 4 pages, 3 eps figures, revtex

Chandra X-ray Sources in the LALA Cetus Field

The 174 ks Chandra Advanced CCD Imaging Spectrometer exposure of the Large Area Lyman Alpha Survey (LALA) Cetus field is the second of the two deep Chandra images on LALA fields. In this paper we present the Chandra X-ray sources detected in the Cetus field, along with an analysis of X-ray source counts, stacked X-ray spectrum, and optical identifications. A total of 188 X-ray sources were detected: 174 in the 0.5-7.0 keV band, 154 in the 0.5-2.0 keV band, and 113 in the 2.0-7.0 keV band. The X-ray source counts were derived and compared with LALA Bootes field (172 ks exposure). Interestingly, we find consistent hard band X-ray source density, but 36+-12% higher soft band X-ray source density in Cetus field. The weighted stacked spectrum of the detected X-ray sources can be fitted by a powerlaw with photon index Gamma = 1.55. Based on the weighted stacked spectrum, we find that the resolved fraction of the X-ray background drops from 72+-1% at 0.5-1.0 keV to 63+-4% at 6.0-8.0 keV. The unresolved spectrum can be fitted by a powerlaw over the range 0.5-7 keV, with a photon index Gamma = 1.22. We also present optical counterparts for 154 of the X-ray sources, down to a limiting magnitude of r' = 25.9 (Vega), using a deep r' band image obtained with the MMT.Comment: 21 pages, including 6 figures, 1 table, ApJ accepte

Locating Planetesimal Belts in the Multiple-planet Systems HD 128311, HD 202206, HD 82943, and HR 8799

In addition to the Sun, six other stars are known to harbor multiple planets and debris disks: HD 69830, HD 38529, HD 128311, HD 202206, HD 82943, and HR 8799. In this paper, we set constraints on the location of the dust-producing planetesimals around the latter four systems. We use a radiative transfer model to analyze the spectral energy distributions of the dust disks (including two new Spitzer IRS spectra presented in this paper), and a dynamical model to assess the long-term stability of the planetesimals' orbits. As members of a small group of stars that show evidence of harboring a multiple planets and planetesimals, their study can help us learn about the diversity of planetary systems

Effects of Dust Geometry in Lyman Alpha Galaxies at z = 4.4

Equivalent widths (EWs) observed in high-redshift Lyman alpha galaxies could be stronger than the EW intrinsic to the stellar population if dust is present residing in clumps in the inter-stellar medium (ISM). In this scenario, continuum photons could be extinguished while the Lyman alpha photons would be resonantly scattered by the clumps, eventually escaping the galaxy. We investigate this radiative transfer scenario with a new sample of six Lyman alpha galaxy candidates in the GOODS CDF-S, selected at z = 4.4 with ground-based narrow-band imaging obtained at CTIO. Grism spectra from the HST PEARS survey confirm that three objects are at z = 4.4, and that another object contains an active galactic nuclei (AGN). If we assume the other five (non-AGN) objects are at z = 4.4, they have rest-frame EWs from 47 -- 190 A. We present results of stellar population studies of these objects, constraining their rest-frame UV with HST and their rest-frame optical with Spitzer. Out of the four objects which we analyzed, three objects were best-fit to contain stellar populations with ages on the order of 1 Myr and stellar masses from 3 - 10 x 10^8 solar masses, with dust in the amount of A_1200 = 0.9 - 1.8 residing in a quasi-homogeneous distribution. However, one object (with a rest EW ~ 150 A) was best fit by an 800 Myr, 6.6 x 10^9 solar mass stellar population with a smaller amount of dust (A_1200 = 0.4) attenuating the continuum only. In this object, the EW was enhanced ~ 50% due to this dust. This suggests that large EW Lyman alpha galaxies are a diverse population. Preferential extinction of the continuum in a clumpy ISM deserves further investigation as a possible cause of the overabundance of large-EW objects that have been seen in narrow-band surveys in recent years.Comment: Submitted to the Astrophysical Journal. 35 pages, 7 figures and 4 table

Relationships between hyperinsulinaemia, magnesium, vitamin D, thrombosis and COVID-19: rationale for clinical management

Risk factors for COVID-19 patients with poorer outcomes include pre-existing conditions: obesity, type 2 diabetes mellitus, cardiovascular disease (CVD), heart failure, hypertension, low oxygen saturation capacity, cancer, elevated: ferritin, C reactive protein (CRP) and D-dimer. A common denominator, hyperinsulinaemia, provides a plausible mechanism of action, underlying CVD, hypertension and strokes, all conditions typified with thrombi. The underlying science provides a theoretical management algorithm for the frontline practitioners. Vitamin D activation requires magnesium. Hyperinsulinaemia promotes: magnesium depletion via increased renal excretion, reduced intracellular levels, lowers vitamin D status via sequestration into adipocytes and hydroxylation activation inhibition. Hyperinsulinaemia mediates thrombi development via: fibrinolysis inhibition, anticoagulation production dysregulation, increasing reactive oxygen species, decreased antioxidant capacity via nicotinamide adenine dinucleotide depletion, haem oxidation and catabolism, producing carbon monoxide, increasing deep vein thrombosis risk and pulmonary emboli. Increased haem-synthesis demand upregulates carbon dioxide production, decreasing oxygen saturation capacity. Hyperinsulinaemia decreases cholesterol sulfurylation to cholesterol sulfate, as low vitamin D regulation due to magnesium depletion and/or vitamin D sequestration and/or diminished activation capacity decreases sulfotransferase enzyme SULT2B1b activity, consequently decreasing plasma membrane negative charge between red blood cells, platelets and endothelial cells, thus increasing agglutination and thrombosis. Patients with COVID-19 admitted with hyperglycaemia and/or hyperinsulinaemia should be placed on a restricted refined carbohydrate diet, with limited use of intravenous dextrose solutions. Degree/level of restriction is determined by serial testing of blood glucose, insulin and ketones. Supplemental magnesium, vitamin D and zinc should be administered. By implementing refined carbohydrate restriction, three primary risk factors, hyperinsulinaemia, hyperglycaemia and hypertension, that increase inflammation, coagulation and thrombosis risk are rapidly managed

Analysis of acoustic emission during the melting of embedded indium particles in an aluminum matrix: a study of plastic strain accommodation during phase transformation

Acoustic emission is used here to study melting and solidification of embedded indium particles in the size range of 0.2 to 3 um in diameter and to show that dislocation generation occurs in the aluminum matrix to accommodate a 2.5% volume change. The volume averaged acoustic energy produced by indium particle melting is similar to that reported for bainite formation upon continuous cooling. A mechanism of prismatic loop generation is proposed to accommodate the volume change and an upper limit to the geometrically necessary increase in dislocation density is calculated as 4.1 x 10^9 cm^-2 for the Al-17In alloy. Thermomechanical processing is also used to change the size and distribution of the indium particles within the aluminum matrix. Dislocation generation with accompanied acoustic emission occurs when the melting indium particles are associated with grain boundaries or upon solidification where the solid-liquid interfaces act as free surfaces to facilitate dislocation generation. Acoustic emission is not observed for indium particles that require super heating and exhibit elevated melting temperatures. The acoustic emission work corroborates previously proposed relaxation mechanisms from prior internal friction studies and that the superheat observed for melting of these micron-sized particles is a result of matrix constraint.Comment: Presented at "Atomistic Effects in Migrating Interphase Interfaces - Recent Progress and Future Study" TMS 201

Asteroid Belts in Debris Disk Twins: VEGA and FOMALHAUT

Vega and Fomalhaut, are similar in terms of mass, ages, and global debris disk properties; therefore, they are often referred as "debris disk twins". We present Spitzer 10-35 um spectroscopic data centered at both stars, and identify warm, unresolved excess emission in the close vicinity of Vega for the first time. The properties of the warm excess in Vega are further characterized with ancillary photometry in the mid infrared and resolved images in the far-infrared and submillimeter wavelengths. The Vega warm excess shares many similar properties with the one found around Fomalhaut. The emission shortward of ~30 um from both warm components is well described as a blackbody emission of ~170 K. Interestingly, two other systems, eps Eri and HR 8799, also show such an unresolved warm dust using the same approach. These warm components may be analogous to the solar system's zodiacal dust cloud, but of far greater. The dust temperature and tentative detections in the submillimeter suggest the warm excess arises from dust associated with a planetesimal ring located near the water-frost line and presumably created by processes occurring at similar locations in other debris systems as well. We also review the properties of the 2 um hot excess around Vega and Fomalhaut, showing that the dust responsible for the hot excess is not spatially associated with the dust we detected in the warm belt. We suggest it may arise from hot nano grains trapped in the magnetic field of the star. Finally, the separation between the warm and cold belt is rather large with an orbital ratio >~10 in all four systems. In light of the current upper limits on the masses of planetary objects and the large gap, we discuss the possible implications for their underlying planetary architecture, and suggest that multiple, low-mass planets likely reside between the two belts in Vega and Fomalhaut.Comment: 14 pages, accepted for publication in Ap