Anomalies, D-flatness and Small Instantons

Recently, Witten has proposed a mechanism for symmetry enhancement in $SO(32)$ heterotic string theory, where the singularity obtained by shrinking an instanton to zero size is resolved by the appearance of an $Sp(1)$ gauge symmetry. In this short letter, we consider spacetime constraints from anomaly cancellation in six dimensions and D-flatness and demonstrate a subtlety which arises in the moduli space when many instantons are shrunk to zero size.Comment: 8 pages, harvma

Genetic consequences of Quaternary climatic oscillations in the Himalayas: Primula tibetica as a case study based on restriction site-associated DNA sequencing.

The effects of Quaternary climatic oscillations on the demography of organisms vary across regions and continents. In taxa distributed in Europe and North America, several paradigms regarding the distribution of refugia have been identified. By contrast, less is known about the processes that shaped the species' spatial genetic structure in areas such as the Himalayas, which is considered a biodiversity hotspot. Here, we investigated the phylogeographic structure and population dynamics of Primula tibetica by combining genomic phylogeography and species distribution models (SDMs). Genomic data were obtained for 293 samples of P. tibetica using restriction site-associated DNA sequencing (RADseq). Ensemble SDMs were carried out to predict potential present and past distribution ranges. Four distinct lineages were identified. Approximate Bayesian computation analyses showed that each of them have experienced both expansions and bottlenecks since their divergence, which occurred during or across the Quaternary glacial cycles. The two lineages at both edges of the distribution were found to be more vulnerable and responded in different ways to past climatic changes. These results illustrate how past climatic changes affected the demographic history of Himalayan organisms. Our findings highlight the significance of combining genomic approaches with environmental data when evaluating the effects of past climatic changes

Love Letters for Liberatory Futures

This collection of letters serves to explore the narratives of a collective of women of color in academia by examining individual, collective, spiritual, and institutional strategies for surviving and transforming our institutional spaces and the ways that White Supremacy has shaped our journeys. Multiple perspectives are viewed, and we have written to our children, our future social work students, our future selves, our BIPOC faculty siblings, and our feared enemies to envision and embody more liberatory futures. Keywords: liberation, academia, BIPOC faculty, institutional racism, White Supremac

LIQUID XENON FILLED WIRE CHAMBERS FOR MEDICAL IMAGINGAPPLICATIONS

In 1968, Luis Alvarez suggested that a high-resolution multiwire particle detector could be developed using a thin layer of liquified noble gas as the detection medium. After key problems in chamber construction, purification, and readout had been solved, a spatial resolution of 15 {micro} rms was demonstrated. Work is in progress to build high-resolution chambers and measure their properties for particle physics experiments at high-energy accelerators. The liquid xenon multiwire chamber also has potential in nuclear medicine for imaging isotope distributions with an unprecedented combination of gamma-ray detection efficiency and spatial resolution. A preliminary 24-wire chamber has been constructed; this chamber detects 280-keV gamma rays with 65% efficiency and 4-mm FWHM spatial resolution. Initial images of point and distributed sources are very promising, and the liquid purity can be maintained for periods exceeding several days

HIGH-RESOLUTION LIQUID-FILLED MULTI-WIRE CHAMBERS FOR USE INHIGH-ENERGY BEAMS

The authors describe experiments with liquid-xenon-filled wire chambers operating in the proportional mode and the difficulty of achieving useful gain when the anode wires have a spacing < 1 mm. As a result, they have largely turned our attention to chambers with closely spaced wires operated in the ionization mode. They have previously demonstrated a spatial resolution of 15 {micro} rms in this mode, using a 5-wire chamber and a collimated alpha source. They describe the construction of two small high-resolution test chambers to be filled with liquid argon, krypton, or xenon. The chambers consist of two flat cathodes 1 to 2.5 mm apart with a wire plane between them. The wire plane is an array of 24 wires, 5 {micro} in diameter, spaced on 20-{micro} centers, and a charge amplifier is attached to each wire. The space resolution (expected rms < 20 {micro}), time resolution (expected rms < 50 ns), and efficiency will be measured in an accelerator beam. Chambers of this type with only a few hundred wires have sufficient area to cover nearly every beam at NAL

Optimal Radio Window for the Detection of Ultra-High-Energy Cosmic Rays and Neutrinos off the Moon

When high-energy cosmic rays impinge on a dense dielectric medium, radio waves are produced through the Askaryan effect. We show that at wavelengths comparable to the length of the shower produced by an Ultra-High Energy cosmic ray or neutrino, radio signals are an extremely efficient way to detect these particles. Through an example it is shown that this new approach offers, for the first time, the realistic possibility of measuring UHE neutrino fluxes below the Waxman-Bahcall limit. It is shown that in only one month of observing with the upcoming LOFAR radio telescope, cosmic-ray events can be measured beyond the GZK-limit, at a sensitivity level of two orders of magnitude below the extrapolated values.Comment: Submitted to Astroparticle Physic

Geometric Phase, Curvature, and Extrapotentials in Constrained Quantum Systems

We derive an effective Hamiltonian for a quantum system constrained to a submanifold (the constraint manifold) of configuration space (the ambient space) by an infinite restoring force. We pay special attention to how this Hamiltonian depends on quantities which are external to the constraint manifold, such as the external curvature of the constraint manifold, the (Riemannian) curvature of the ambient space, and the constraining potential. In particular, we find the remarkable fact that the twisting of the constraining potential appears as a gauge potential in the constrained Hamiltonian. This gauge potential is an example of geometric phase, closely related to that originally discussed by Berry. The constrained Hamiltonian also contains an effective potential depending on the external curvature of the constraint manifold, the curvature of the ambient space, and the twisting of the constraining potential. The general nature of our analysis allows applications to a wide variety of problems, such as rigid molecules, the evolution of molecular systems along reaction paths, and quantum strip waveguides.Comment: 27 pages with 1 figure, submitted to Phys. Rev.

The Impact of Specialist Care on Teenage and Young Adult Patient-Reported Outcomes in England: A BRIGHTLIGHT Study

Purpose: In England, health care policy promotes specialized age-appropriate cancer services for teenagers and young adults (TYA), for those aged 13–24 years at diagnosis. Specialist Principal Treatment Centers (PTCs) provide enhanced age-specific care for TYA, although many still receive all or some of their care in adult or children's cancer services. Our aim was to determine the patient-reported outcomes associated with TYA-PTC based care. Methods: We conducted a multicenter cohort study, recruiting 1114 TYA aged 13–24 years at diagnosis. Data collection involved a bespoke survey at 6,12,18, 24, and 36 months after diagnosis. Confounder adjusted analyses of perceived social support, illness perception, anxiety and depression, and health status, compared patients receiving NO-TYA-PTC care with those receiving ALL-TYA-PTC and SOME-TYA-PTC care. Results: Eight hundred and thirty completed the first survey. There was no difference in perceived social support, anxiety, or depression between the three categories of care. Significantly higher illness perception was observed in the ALL-TYA-PTC and SOME-TYA-PTC group compared to the NO-TYA-PTC group, (adjusted difference in mean (ADM) score on Brief Illness Perception scale 2.28 (95% confidence intervals [CI] 0.48–4.09) and 2.93 [1.27–4.59], respectively, p = 0.002). Similarly, health status was significantly better in the NO-TYA-PTC (ALL-TYA-PTC: ADM −0.011 [95%CI −0.046 to 0.024] and SOME-TYA-PTC: −0.054 [−0.086 to −0.023]; p = 0.006). Conclusion: The reason for the difference in perceived health status is unclear. TYA who accessed a TYA-PTC (all or some care) had higher perceived illness. This may reflect greater education and promotion of self-care by health care professionals in TYA units

Exchange anisotropy, disorder and frustration in diluted, predominantly ferromagnetic, Heisenberg spin systems

Motivated by the recent suggestion of anisotropic effective exchange interactions between Mn spins in Ga$_{1-x}$Mn$_x$As (arising as a result of spin-orbit coupling), we study their effects in diluted Heisenberg spin systems. We perform Monte Carlo simulations on several phenomenological model spin Hamiltonians, and investigate the extent to which frustration induced by anisotropic exchanges can reduce the low temperature magnetization in these models and the interplay of this effect with disorder in the exchange. In a model with low coordination number and purely ferromagnetic (FM) exchanges, we find that the low temperature magnetization is gradually reduced as exchange anisotropy is turned on. However, as the connectivity of the model is increased, the effect of small-to-moderate anisotropy is suppressed, and the magnetization regains its maximum saturation value at low temperatures unless the distribution of exchanges is very wide. To obtain significant suppression of the low temperature magnetization in a model with high connectivity, as is found for long-range interactions, we find it necessary to have both ferromagnetic and antiferromagnetic (AFM) exchanges (e.g. as in the RKKY interaction). This implies that disorder in the sign of the exchange interaction is much more effective in suppressing magnetization at low temperatures than exchange anisotropy.Comment: 9 pages, 8 figure