278 research outputs found
Rigid Calabi-Yau threefolds, Picard Eisenstein series and instantons
Type IIA string theory compactified on a rigid Calabi-Yau threefold gives
rise to a classical moduli space that carries an isometric action of U(2,1).
Various quantum corrections break this continuous isometry to a discrete
subgroup. Focussing on the case where the intermediate Jacobian of the
Calabi-Yau admits complex multiplication by the ring of quadratic imaginary
integers O_d, we argue that the remaining quantum duality group is an
arithmetic Picard modular group PU(2,1;O_d). Based on this proposal we
construct an Eisenstein series invariant under this duality group and study its
non-Abelian Fourier expansion. This allows the prediction of non-perturbative
effects, notably the contribution of D2- and NS5-brane instantons. The present
work extends our previous analysis in 0909.4299 which was restricted to the
special case of the Gaussian integers O_1=Z[i].Comment: 8 pages, for the proceedings of Quantum Theories and Symmetries V
Asymmetric collaboration in virtual reality: A taxonomy of asymmetric interfaces for collaborative immersive learning
It has been established that Virtual Reality (VR) possesses certain qualities for educational purposes. These include the ability to place the learner at the location or in the perspective that the desired knowledge exists (e.g., travelling to another planet or shrinking to miniature size to observe internal anatomy). VR is also considered to contribute with enriching the curricular content, promoting active forms of learning, performance assessment of high validity, and provide the opportunity to teach applied academic knowledge in life-like situations. In regards to teaching mathematics and geometry, three key affordances have been identified; interactive manipulation and construction of three-dimensional geometry, comprehension of spatial relationships, and rectification of abstract problems. Safety protocols and practical guidelines from classroom experimentation have also been formulated by various research projects.
In this manuscript, asymmetrical immersive VR in education will be reviewed, as it is relevant for the narrative of learning situations where multiple students use the technology together. As an example, in mathematics, asymmetric VR could be used in contexts where unknown variables must be found in collaboration. The purpose of the narrative literature review is to gain a greater understanding of how asymmetric game mechanics has influence on communication and collaboration between learners. To map the dynamics of this type of learning activity, a taxonomy will be presented. Since VR is still under development in terms of hardware and software, it is important that the current and future technical possibilities are described in a conceptual manner, as well as conclude on optimal coupling between communication dynamics and collaboration mechanics
Instanton Corrections to the Universal Hypermultiplet and Automorphic Forms on SU(2,1)
The hypermultiplet moduli space in Type IIA string theory compactified on a
rigid Calabi-Yau threefold X, corresponding to the "universal hypermultiplet",
is described at tree-level by the symmetric space SU(2,1)/(SU(2) x U(1)). To
determine the quantum corrections to this metric, we posit that a discrete
subgroup of the continuous tree-level isometry group SU(2,1), namely the Picard
modular group SU(2,1;Z[i]), must remain unbroken in the exact metric --
including all perturbative and non perturbative quantum corrections. This
assumption is expected to be valid when X admits complex multiplication by
Z[i]. Based on this hypothesis, we construct an SU(2,1;Z[i])-invariant,
non-holomorphic Eisenstein series, and tentatively propose that this Eisenstein
series provides the exact contact potential on the twistor space over the
universal hypermultiplet moduli space. We analyze its non-Abelian Fourier
expansion, and show that the Abelian and non-Abelian Fourier coefficients take
the required form for instanton corrections due to Euclidean D2-branes wrapping
special Lagrangian submanifolds, and to Euclidean NS5-branes wrapping the
entire Calabi-Yau threefold, respectively. While this tentative proposal fails
to reproduce the correct one-loop correction, the consistency of the Fourier
expansion with physics expectations provides strong support for the utility of
the Picard modular group in constraining the quantum moduli space.Comment: 61 pages, (v2) typos corrected, references added, clarification
regarding the fact that our analysis applies to rigid Calabi-Yau 3-folds that
admit complex multiplication by the Gaussian integers Z[i], (v3) references
added, one-loop discrepancy revised (but still discrepant), other cosmetic
changes, (v4) final version, published in CNT
Hot Spots and Turbulent Initial Conditions of Quark-Gluon Plasmas in Nuclear Collisions
As a result of multiple mini-jet production, initial conditions of the QCD
plasma formed in ultrarelativistic nuclear collisions may be inhomogeneous,
with large fluctuations of the local energy density (hot spots), and turbulent,
with a chaotic initial transverse velocity field. Assuming rapid local
thermalization, the evolution of such plasmas is computed using longitudinal
boost-invariant 3+1-dimensional hydrodynamics. We compare the evolution in case
that the speed of sound in the plasma is constant to one resulting from an
equation of state involving a strong first order transition, with a minimum of
the velocity of sound as a function of energy density. We find that azimuthally
asymmetric fluctuations and correlations of the transverse energy flow can
develop in both cases due to the initial inhomogeneities. Hot spots also
enhance significantly high-transverse momenta direct photon yields. In the case
with a phase transition, the hadronization surface evolves into an unusual
foam-like structure. Also in that case, we find that hadronization is
considerably delayed relative to the ideal gas case, just as previous studies
have found for homogeneous initial conditions. The time-delay signature of a
rapid cross-over transition region in the QCD equation of state (as observable
via meson interferometry) is thus found to be remarkably robust to
uncertainties in the initial conditions in heavy-ion reactions.Comment: 28 pages, LaTeX, 20 figures, available as uucompressed file
(including LaTeX-file) ftp://nt1.phys.columbia.edu/pub/turb/turb2.uu
(username: ftp, password: complete email address
Exploring the Foundation of Genomics: A Northern Blot Reference set for the Comparative Analysis of Transcript Profiling Technologies
In this paper we aim to create a reference data collection of Northern blot results
and demonstrate how such a collection can enable a quantitative comparison of
modern expression profiling techniques, a central component of functional genomics
studies. Historically, Northern blots were the de facto standard for determining RNA
transcript levels. However, driven by the demand for analysis of large sets of genes in
parallel, high-throughput methods, such as microarrays, dominate modern profiling
efforts. To facilitate assessment of these methods, in comparison to Northern blots,
we created a database of published Northern results obtained with a standardized
commercial multiple tissue blot (dbMTN). In order to demonstrate the utility of the
dbMTN collection for technology comparison, we also generated expression profiles
for genes across a set of human tissues, using multiple profiling techniques. No method
produced profiles that were strongly correlated with the Northern blot data. The
highest correlations to the Northern blot data were determined with microarrays
for the subset of genes observed to be specifically expressed in a single tissue in
the Northern analyses. The database and expression profiling data are available
via the project website (http://www.cisreg.ca). We believe that emphasis on multitechnique
validation of expression profiles is justified, as the correlation results
between platforms are not encouraging on the whole. Supplementary material for this
article can be found at: http://www.interscience.wiley.com/jpages/1531-6912/suppma
Home-Based Work and Home-Based Workers (1800-2021)
Home-Based Work and Home-Based Workers (1800-2021) is about the past and present of home-based work and homebased workers between 1800 and 2021 from a global perspective.; Readership: All interested in social and economic history, and especially in the past and present of home-based work and homebased workers
Remote Electrical Stimulation by Means of Implanted Rectifiers
Miniaturization of active implantable medical devices is currently compromised by the available means for electrically powering them. Most common energy supply techniques for implants – batteries and inductive couplers – comprise bulky parts which, in most cases, are significantly larger than the circuitry they feed. Here, for overcoming such miniaturization bottleneck in the case of implants for electrical stimulation, it is proposed to make those implants act as rectifiers of high frequency bursts supplied by remote electrodes. In this way, low frequency currents will be generated locally around the implant and these low frequency currents will perform stimulation of excitable tissues whereas the high frequency currents will cause only innocuous heating. The present study numerically demonstrates that low frequency currents capable of stimulation can be produced by a miniature device behaving as a diode when high frequency currents, neither capable of thermal damage nor of stimulation, flow through the tissue where the device is implanted. Moreover, experimental evidence is provided by an in vivo proof of concept model consisting of an anesthetized earthworm in which a commercial diode was implanted. With currently available microelectronic techniques, very thin stimulation capsules (diameter <500 µm) deliverable by injection are easily conceivable
The Role of pH Fronts in Reversible Electroporation
We present experimental measurements and theoretical predictions of ion transport in agar gels during reversible electroporation (ECT) for conditions typical to many clinical studies found in the literature, revealing the presence of pH fronts emerging from both electrodes. These results suggest that pH fronts are immediate and substantial. Since they might give rise to tissue necrosis, an unwanted condition in clinical applications of ECT as well as in irreversible electroporation (IRE) and in electrogenetherapy (EGT), it is important to quantify their extent and evolution. Here, a tracking technique is used to follow the space-time evolution of these pH fronts. It is found that they scale in time as , characteristic of a predominantly diffusive process. Comparing ECT pH fronts with those arising in electrotherapy (EChT), another treatment applying constant electric fields whose main goal is tissue necrosis, a striking result is observed: anodic acidification is larger in ECT than in EChT, suggesting that tissue necrosis could also be greater. Ways to minimize these adverse effects in ECT are suggested
Do Fleas Affect Energy Expenditure of Their Free-Living Hosts?
Parasites can cause energetically costly behavioural and immunological responses which potentially can reduce host fitness. However, although most laboratory studies indicate that the metabolic rate of the host increases with parasite infestation, this has never been shown in free-living host populations. In fact, studies thus far have shown no effect of parasitism on field metabolic rate (FMR).We tested the effect of parasites on the energy expenditure of a host by measuring FMR using doubly-labelled water in free-living Baluchistan gerbils (Gerbillus nanus) infested by naturally occurring fleas during winter, spring and summer. We showed for the first time that FMR of free-living G. nanus was significantly and positively correlated with parasite load in spring when parasite load was highest; this relationship approached significance in summer when parasite load was lowest but was insignificant in winter. Among seasons, winter FMRs were highest and summer FMRs were lowest in G. nanus.The lack of parasite effect on FMR in winter could be related to the fact that FMR rates were highest among seasons. In this season, thermoregulatory costs are high which may indicate that less energy could be allocated to defend against parasites or to compensate for other costly activities. The question about the cost of parasitism in nature is now one of the major themes in ecological physiology. Our study supports the hypothesis that parasites can elevate FMR of their hosts, at least under certain conditions. However, the effect is complex and factors such as season and parasite load are involved
Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC
The average transverse momentum versus the charged-particle multiplicity was measured in p-Pb collisions at a collision energy per nucleon-nucleon pair = 5.02 TeV and in pp collisions at collision energies of = 0.9, 2.76, and 7 Tev in the kinematic range 0.15 with is observed, which is much stronger than that measured in Pb-Pb collisions. For pp collisions, this could be attributed, within a model of hadronizing strings, to multiple-parton interactions and to a final-state color reconnection mechanism. The data in p-Pb and Pb-Pb collisions cannot be described by an incoherent superposition of nucleon-nucleon collisions and pose a challenge to most of the event generators.publishedVersio
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