One-loop Correction and the Dilaton Runaway Problem

We examine the one-loop vacuum structure of an effective theory of gaugino condensation coupled to the dilaton for string models in which the gauge coupling constant does not receive string threshold corrections. The new ingredients in our treatment are that we take into account the one-loop correction to the dilaton K\"ahler potential and we use a formulation which includes a chiral field $H$ corresponding to the gaugino bilinear. We find through explicit calculation that supersymmetry in the Yang-Mills sector is broken by gaugino condensation. The dilaton and $H$ field have masses on the order of the gaugino condensation scale independently of the dilaton VEV. Although the calculation performed here is at best a model of the full gaugino condensation dynamics, the result shows that the one-loop correction to the dilaton K\"ahler potential as well as the detailed dynamics at the gaugino condensation scale may play an important role in solving the dilaton runaway problem.Comment: 19 page

Non-Abelian Born-Infeld Action and Type I - Heterotic Duality (II): Nonrenormalization Theorems

Type I - heterotic duality in D=10 predicts various relations and constraints on higher order F^n couplings at different string loop levels on both sides. We prove the vanishing of two-loop corrections to the heterotic F^4 terms, which is one of the basic predictions from this duality. Furthermore, we show that the heterotic F^5 and (CP even) F^6 couplings are not renormalized at one loop. These results strengthen the conjecture that in D=10 any Tr F^(2n) coupling appears only at the disc tree-level on type I side and at (n-1)-loop level on the heterotic side. Our non-renormalization theorems are valid in any heterotic string vacuum with sixteen supercharges.Comment: 35 pages, harvmac; cosmetic changes; final version to appear in NP

Direct Production of Lightest Regge Resonances

We discuss direct production of Regge excitations in the collisions of massless four-dimensional superstring states, focusing on the first excited level of open strings ending on D-branes extending into higher dimensions. We construct covariant vertex operators and identify ``universal'' Regge states with the internal parts either trivial or determined by the world-sheet SCFT describing superstrings propagating on an arbitrary Calabi-Yau manifold. We evaluate the amplitudes involving one such massive state and up to three massless ones and express them in the helicity basis. The most important phenomenological applications of our results are in the context of low-mass string (and large extra dimensions) scenarios in which excited string states are expected to be produced at the LHC as soon as the string mass threshold is reached in the center-of-mass energies of the colliding partons. In order to facilitate the use of partonic cross sections, we evaluate them and tabulate for all production processes: gluon fusion, quark absorbing a gluon, quark-antiquark annihilation and quark-quark scattering.Comment: 43 pages, RevTeX 4.

Study of the three-dimensional shape and dynamics of coronal loops observed by Hinode/EIS

We study plasma flows along selected coronal loops in NOAA Active Region 10926, observed on 3 December 2006 with Hinode's EUV Imaging Spectrograph (EIS). From the shape of the loops traced on intensity images and the Doppler shifts measured along their length we compute their three-dimensional (3D) shape and plasma flow velocity using a simple geometrical model. This calculation was performed for loops visible in the Fe VIII 185 Ang., Fe X 184 Ang., Fe XII 195 Ang., Fe XIII 202 Ang., and Fe XV 284 Ang. spectral lines. In most cases the flow is unidirectional from one footpoint to the other but there are also cases of draining motions from the top of the loops to their footpoints. Our results indicate that the same loop may show different flow patterns when observed in different spectral lines, suggesting a dynamically complex rather than a monolithic structure. We have also carried out magnetic extrapolations in the linear force-free field approximation using SOHO/MDI magnetograms, aiming toward a first-order identification of extrapolated magnetic field lines corresponding to the reconstructed loops. In all cases, the best-fit extrapolated lines exhibit left-handed twist (alpha < 0), in agreement with the dominant twist of the region.Comment: 17 pages, 6 figure

Axion Couplings and Effective Cut-Offs in Superstring Compactifications

We use the linear supermultiplet formalism of supergravity to study axion couplings and chiral anomalies in the context of field-theoretical Lagrangians describing orbifold compactifications beyond the classical approximation. By matching amplitudes computed in the effective low energy theory with the results of string loop calculations we determine the appropriate counterterm in this effective theory that assures modular invariance to all loop order. We use supersymmetry consistency constraints to identify the correct ultra-violet cut-offs for the effective low energy theory. Our results have a simple interpretation in terms of two-loop unification of gauge coupling constants at the string scale.Comment: 25 page

Lectures on Heterotic-Type I Duality

We present a review of heterotic-type I string duality. In particular, we discuss the effective field theory of six- and four-dimensional compactifications with N>1 supersymmetries. We then describe various duality tests by comparing gauge couplings, N=2 prepotentials, as well as higher-derivative F-terms. Based on invited lectures delivered at: 33rd Karpacz Winter School of Theoretical Physics ``Duality, Strings and Fields,'' Przesieka, Poland, 13 - 22 February 1997; Trieste Conference on Duality Symmetries in String Theory, Trieste, Italy, 1 - 4 April 1997; Cargese Summer School ``Strings, Branes and Dualities,'' Cargese, France, 26 May - 14 June 1997.Comment: 14 pages, LaTeX, espcrc2.st

Fast evaluation of appointment schedules for outpatients in health care

We consider the problem of evaluating an appointment schedule for outpatients in a hospital. Given a fixed-length session during which a physician sees K patients, each patient has to be given an appointment time during this session in advance. When a patient arrives on its appointment, the consultations of the previous patients are either already finished or are still going on, which respectively means that the physician has been standing idle or that the patient has to wait, both of which are undesirable. Optimising a schedule according to performance criteria such as patient waiting times, physician idle times, session overtime, etc. usually requires a heuristic search method involving a huge number of repeated schedule evaluations. Hence, the aim of our evaluation approach is to obtain accurate predictions as fast as possible, i.e. at a very low computational cost. This is achieved by (1) using Lindley's recursion to allow for explicit expressions and (2) choosing a discrete-time (slotted) setting to make those expression easy to compute. We assume general, possibly distinct, distributions for the patient's consultation times, which allows us to account for multiple treatment types, as well as patient no-shows. The moments of waiting and idle times are obtained. For each slot, we also calculate the moments of waiting and idle time of an additional patient, should it be appointed to that slot. As we demonstrate, a graphical representation of these quantities can be used to assist a sequential scheduling strategy, as often used in practice

Ghost D-branes

We define a ghost D-brane in superstring theories as an object that cancels the effects of an ordinary D-brane. The supergroups U(N|M) and OSp(N|M) arise as gauge symmetries in the supersymmetric world-volume theory of D-branes and ghost D-branes. A system with a pair of D-brane and ghost D-brane located at the same location is physically equivalent to the closed string vacuum. When they are separated, the system becomes a new brane configuration. We generalize the type I/heterotic duality by including n ghost D9-branes on the type I side and by considering the heterotic string whose gauge group is OSp(32+2n|2n). Motivated by the type IIB S-duality applied to D9- and ghost D9-branes, we also find type II-like closed superstrings with U(n|n) gauge symmetry.Comment: 49 pages, 6 figures, harvmac. v2: references and acknowledgements adde

Professional Identity Formation Through a Peer Learning, Integrated Clinical Experience

Purpose: The purpose of this study was to explore the experiences and perceptions of first-year DPT students related to professional behaviors and professional identity formation after an integrated clinical experience facilitated by peers. Methods: Forty-one first-year DPT students from an accredited Doctor of Physical Therapy program participated in a class assignment designed to collect qualitative data regarding their experiences with professional behaviors and professional identity formation after completing an integrated clinical experience. Incident coding processes analyzed responses to open-ended assignment prompts. Results: The most frequent professional behaviors students felt they could demonstrate during the integrated clinical experience were “communication” and “PT skills and values.” The most frequently coded categories for professional identity formation were “Self-development” and “Relationships/Connection.” Conclusion: DPT students’ perspectives on professional behaviors and identity can be formulated with on-campus integrated clinical experiences. As such, innovative means for improving the clinical experience and developing professional behavior and identity are warranted

A 15.7-minAM CVn binary discovered in K2

We present the discovery of SDSS J135154.46−064309.0, a short-period variable observed using 30-mincadence photometry in K2 Campaign 6. Follow-up spectroscopy and high-speed photometry support a classification as a new member of the rare class of ultracompact accreting binaries known as AM CVn stars. The spectroscopic orbital period of 15.65 ± 0.12 min makes this system the fourth-shortest-period AM CVn known, and the second system of this type to be discovered by the Kepler spacecraft. The K2 data show photometric periods at 15.7306 ± 0.0003 min, 16.1121 ± 0.0004 min, and 664.82 ± 0.06 min, which we identify as the orbital period, superhump period, and disc precession period, respectively. From the superhump and orbital periods we estimate the binary mass ratio q = M2/M1= 0.111 ± 0.005, though this method of mass ratio determination may not be well calibrated for helium-dominated binaries. This system is likely to be a bright foreground source of gravitational waves in the frequency range detectable by Laser Interferometer Space Antenna, and may be of use as a calibration source if future studies are able to constrain the masses of its stellar components