58 research outputs found
Design and testing of a device for the characterization of gas transfer through soap films and measurement protocol based on color matching
Soap films are interesting for their potential utilization as soft, self-assembled, self-healing and possibly recyclable membranes. The intrinsic possibility of tuning their properties, such as e.g. surface and bulk elasticity or permeability, via tailored chemistry makes them flexible enough for a wide range of physical-chemical applications. Here we introduce a novel device that can serve as a research platform for the detailed experimental characterization of the soap film permeability to gases. The design and manufacturing of the novel platform are discussed, along with a sample characterization protocol based on a color-matching procedure for dioxygen
diffusion through typical soap films. The experimental data is compared with the results obtained from a numerical model, specifically developed for the problem, and good agreement is found. In perspective, the proposed platform can serve for the precise characterization of gas transfer properties of soap films made from different surfactant mixtures and in the presence of different gases
Microscopic unitary description of tidal excitations in high-energy string-brane collisions
The eikonal operator was originally introduced to describe the effect of
tidal excitations on higher-genus elastic string amplitudes at high energy. In
this paper we provide a precise interpretation for this operator through the
explicit tree-level calculation of generic inelastic transitions between closed
strings as they scatter off a stack of parallel Dp-branes. We perform this
analysis both in the light-cone gauge, using the Green-Schwarz vertex, and in
the covariant formalism, using the Reggeon vertex operator. We also present a
detailed discussion of the high energy behaviour of the covariant string
amplitudes, showing how to take into account the energy factors that enhance
the contribution of the longitudinally polarized massive states in a simple
way.Comment: 58 page
Self-gravitating fundamental strings and black-holes
The configuration of typical highly excited (M >> M_s ~ (alpha')^{-1/2})
string states is considered as the string coupling g is adiabatically
increased. The size distribution of very massive single string states is
studied and the mass shift, due to long-range gravitational, dilatonic and
axionic attraction, is estimated. By combining the two effects, in any number
of spatial dimensions d, the most probable size of a string state becomes of
order l_s = sqrt{2 alpha'} when g^2 M / M_s ~ 1. Depending on the dimension d,
the transition between a random-walk-size string state (for low g) and a
compact (~ l_s) string state (when g^2 M / M_s ~ 1) can be very gradual (d=3),
fast but continuous (d=4), or discontinuous (d > 4). Those compact string
states look like nuggets of an ultradense state of string matter, with energy
density rho ~ g^{-2} M_s^{d+1}. Our results extend and clarify previous work by
Susskind, and by Horowitz and Polchinski, on the correspondence between
self-gravitating string states and black holes.Comment: 28 pages, Revtex, minor misprints and references correcte
Compton drag as a mechanism for very high linear polarization in Gamma-Ray Bursts
The recent claim by Coburn & Boggs to have detected a very high degree of
linear polarization in the prompt emission of GRB 021206 has stimulated
interest in how much polarization could arise in gamma-ray bursts from
synchrotron emission. Alternatively, as Shaviv & Dar have shown, GRB
polarization could be produced by inverse Compton scattering in the
point-source limit. We discuss polarization from a fireball that upscatters a
soft radiation field. We show that, after the proper angular integration, the
residual polarization can be large, in some cases approaching the point-source
limit. We discuss the probability of realizing the geometrical conditions in
which a large polarization is obtained showing that, for a particularly bright
burst as GRB 021206, the detection of polarization at the first attempt in the
Compton drag scenario is not unlikely.Comment: Accepted for publication in MNRA
Instanton Calculus and Nonperturbative Relations in N=2 Supersymmetric Gauge Theories
Using instanton calculus we check, in the weak coupling region, the
nonperturbative relation =i\pi\left(\cf-{a\over 2}
{\partial\cf\over\partial a}\right) obtained for a N=2 globally
supersymmetric gauge theory. Our computations are performed for instantons of
winding number k, up to k=2 and turn out to agree with previous nonperturbative
results.Comment: 18 pages, latex file, no figure
Evaluation of an interprofessional education intervention in partnership with patient educators
Background and aim of the work: Patient involvement in interprofessional education is a novel approach to building collaborative and empathic skills in students. However, this area of teaching is lacking in
rigorous studies. The project aimed to evaluate whether an interprofessional education intervention in partnership with patient educators (IPE-PE) would increase readiness for interprofessional learning and empathy
in health sciences students. Methods: This is the report of a didactic innovation project. Participants included
310 undergraduate health sciences students who took part in an IPE-PE intervention. Data were collected
before and after the training, using the Readiness for Interprofessional Learning Scale (RIPLS) and the
Jefferson Scale of Empathy-Health Professions Student version ( JSE-HPS). Only at the end of the intervention, a data collection form was administered to explore the value of the patient educator in the training and
to investigate the socio-demographic variables. Results: The mean age of participants was 21±3.2 SD years and
76% were female. The Wilcoxon signed-rank test showed significant changes from before to after the IPE-PE
in the RIPLS total score (m=42.7±5.8 SD vs 44.62±5.9 SD, z=-4.168, P<0.001) and in the JSE-HPS total
score (m=112.7±12.5 SD vs 116.03±12.8 SD, z=-4.052, P<0.001). Conclusions: Our students reported that
IPE-PE had helped them to become more effective healthcare team members, to think positively about other
professionals, and to gain an empathic understanding of the perspective of the person being cared for. The
results of the project confirm that the intervention promoted the development of empathy, fostering a better
understanding of the patient-centred perspective
Regge behavior saves string theory from causality violations
Higher-derivative corrections to the Einstein-Hilbert action are present in bosonic string theory leading to the potential causality violations recently pointed out by Camanho et al. [1]. We analyze in detail this question by considering high-energy string-brane collisions at impact parameters b ≤ l s (the string-length parameter) with l s ≫ R p (the characteristic scale of the D p -brane geometry). If we keep only the contribution of the massless states causality is violated for a set of initial states whose polarization is suitably chosen with respect to the impact parameter vector. Such violations are instead neatly avoided when the full structure of string theory — and in particular its Regge behavior — is taken into account
Black holes from high-energy beam--beam collisions
Using a recent technique, proposed by Eardley and Giddings, we extend their
results to the high-energy collision of two beams of massless particles, i.e.
of two finite-front shock waves. Closed (marginally) trapped surfaces can be
determined analytically in several cases even for collisions at non-vanishing
impact parameter in D\ge 4 space-time dimensions. We are able to confirm and
extend earlier conjectures by Yurtsever, and to deal with arbitrary
axisymmetric profiles, including an amusing case of ``fractal'' beams. We
finally discuss some implications of our results in high-energy experiments and
in cosmology.Comment: 17 pages Revtex, 1 figure, references adde
On the role of extinction in failed gamma-ray burst optical/IR afterglows
While all but one Gamma-Ray Bursts observed in the X-ray band showed an X-ray
afterglow, about 60 per cent of them have not been detected in the optical
band. We demonstrate that in many cases this is not due to adverse observing
conditions, or delay in performing the observations. We also show that the
optically non-detected afterglows are not affected by particularly large
Galactic absorbing columns, since its distribution is similar for both the
detected and non-detected burst subclasses. We then investigate the hypothesis
that the failure of detecting the optical afterglow is due to absorption at the
source location. We find that this is a marginally viable interpretation, but
only if the X-ray burst and afterglow emission and the possible optical/UV
flash do not destroy the dust responsible for absorption in the optical band.
If dust is efficiently destroyed, we are led to conclude that bursts with no
detected optical afterglow are intrinsically different. Prompt infrared
observations are the key to solve this issue.Comment: Accepted for publication in MNRAS, changes in the tables and in the
statistical analysi
Notes on Noncommutative Instantons
We study in detail the ADHM construction of U(N) instantons on noncommutative
Euclidean space-time R_{NC}^4 and noncommutative space R_{NC}^2 x R^2. We point
out that the completeness condition in the ADHM construction could be
invalidated in certain circumstances. When this happens, regular instanton
configuration may not exist even if the ADHM constraints are satisfied. Some of
the existing solutions in the literature indeed violate the completeness
condition and hence are not correct. We present alternative solutions for these
cases. In particular, we show for the first time how to construct explicitly
regular U(N) instanton solutions on R_{NC}^4 and on R_{NC}^2 x R^2. We also
give a simple general argument based on the Corrigan's identity that the
topological charge of noncommutative regular instantons is always an integer.Comment: Regular instanton solutions are now explicitly constructed also for
the case of space-space noncommutativit
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