2,307 research outputs found
"" Singularities and Finite Density ABJM Theory at Strong Coupling
We study non-analytic behavior in the static charge susceptibility in finite
density states of the ABJM theory using its holographic dual. Emphasis is
placed on a particular state characterized by vanishing entropy density at zero
temperature, and Fermi surface-like singularities in various fermionic
correlation functions. The susceptibility exhibits branch points in the complex
momentum plane, with a real part quantitatively very similar to the location of
the Fermi surface singularities.Comment: 29 pages, 5 figures; v2: Minor additions to overview and discussion,
some references added, version to appear in JHE
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Manufacturing Metallic Parts with Designed Mesostructure via Three-Dimensional Printing of Metal Oxide Powder
Cellular materials, metallic bodies with gaseous voids, are a promising class of materials that offer
high strength accompanied by a relatively low mass. In this paper, the authors investigate the use of ThreeDimensional Printing (3DP) to manufacture metallic cellular materials by selectively printing binder into a
bed of metal oxide ceramic powder. The resulting green part undergoes a thermal chemical post-process in
order to convert it to metal. As a result of their investigation, the authors are able to create cellular
materials made of maraging steel that feature wall sizes as small as 400 µm and angled trusses and channels
that are 1 mm in diameter.Mechanical Engineerin
Dynamic critical phenomena at a holographic critical point
We study time-dependent perturbations to a family of five-dimensional black
hole spacetimes constructed as a holographic model of the QCD phase diagram. We
use the results to calculate two transport coefficients, the bulk viscosity and
conductivity, as well as the associated baryon diffusion constant, throughout
the phase diagram. Near the critical point in the T-mu plane, the transport
coefficients remain finite, although their derivatives diverge, and the
diffusion goes to zero. This provides further evidence that large-N_c gauge
theories suppress convective transport. We also find a divergence in the
low-temperature bulk viscosity, outside the region expected to match QCD, and
compare the results to the transport behavior of known R-charged black holes.Comment: 40 pages, 11 figures, LaTe
Charged Schrodinger Black Holes
We construct charged and rotating asymptotically Schrodinger black hole
solutions of IIB supergravity. We begin by obtaining a closed-form expression
for the null Melvin twist of a broad class of type IIB backgrounds, including
solutions of minimal five-dimensional gauged supergravity, and identify the
resulting five-dimensional effective action. We use these results to
demonstrate that the near-horizon physics and thermodynamics of asymptotically
Schrodinger black holes obtained in this way are essentially inherited from
their AdS progenitors, and verify that they admit zero-temperature extremal
limits with AdS_2 near-horizon geometries. Notably, the AdS_2 radius is
parametrically larger than that of the asymptotic Schrodinger space.Comment: 22 pages, LaTe
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Synthesis and Study of Olefin Metathesis Catalysts Supported by Redox-Switchable Diaminocarbene 3 Ferrocenophanes
A redox-switchable ligand, N,N'-dimethyldiaminocarbene[3]ferrocenophane (5), was synthesized and incorporated into a series of Ir- and Ru-based complexes. Electrochemical and spectroscopic analyses of (5) Ir(CO)(2)Cl (15) revealed that 5 displayed a Tolman electronic parameter value of 2050 cm(-1) in the neutral state and 2061 cm(-1) upon oxidation. Moreover, inspection of X-ray crystallography data recorded for (5) Ir(cis,cis-1,5-cyclooctadiene)Cl (13) revealed that 5 was sterically less bulky (%V-Bur = 28.4) than other known diaminocarbene[3]ferrocenophanes, which facilitated the synthesis of (5)(PPh3)Cl2Ru-(3-phenylindenylid-1-ene) (18). Complex 18 exhibited quasi-reversible electrochemical processes at 0.79 and 0.98 V relative to SCE, which were assigned to the Fe and Ru centers in the complex, respectively, based on UV-vis and electron pair resonance spectroscopic measurements. Adding 2,3-dichloro-5,6-dicyanoquinone over the course of a ring-opening metathesis polymerization of cis, cis-1,5-cyclooctadiene catalyzed by 18 ([monomer](0)/[18](0) = 2500) reduced the corresponding rate constant of the reaction by over an order of magnitude (pre-oxidation: k(obs) = 0.045 s(-1); post-oxidation: k(obs) = 0.0012 s(-1)). Subsequent reduction of the oxidized species using decamethylferrocene restored catalytic activity (post-reduction: k(obs) = up to 0.016 s(-1), depending on when the reductant was added). The difference in the polymerization rates was attributed to the relative donating ability of the redox-active ligand (i.e., strongly donating 5 versus weakly donating 5(+)) which ultimately governed the activity displayed by the corresponding catalyst.U. S. Army Research Office W911NF-09-1-0446Chemistr
Principles of Pituitary Surgery
Key Points
1. Understand the principles of pituitary surgery including the key-elements of surgical planning and decision-making
2. Identify the technical nuances distinguishing the endoscopic from the microscopic transsphenoidal approach
3. Understand the strategies utilized during the nasal, sphenoidal, and sellar stages of surgery that maximize tumor resection while minimizing complications and preserving sino- nasal anatomy/functio
Place, Space, and Motion
(a) Topics and Goals. The Junior Research Group »Place, Space and Motion«
investigates the role of spatial concepts in physical theories in the
millennium from Plato (4th century BCE) through Philoponus and Simplicius (6th
century CE). In particular, we examine the explicit theoretical views of
ancient physicists and philosophers concerning space, the spatial features of
bodies, and the existence of isomorphisms among space, change, and time.
Projects are devoted to issues in Plato’s Timaeus and Aristotle’s Physics, and
to the interwoven reception of these texts in Middle Platonism and Late
Platonism. We trace the evolving answers given to such central questions as
whether space is metaphysically basic or is rather dependent upon bodies or
even non-spatial entities (such as souls); the possibility of empty space; the
causal role of space in nature; how spatial structures make certain kinds of
change possible or necessary. The group aims to produce a series of essays and
commentaries examining key texts of Plato and Aristotle and tracing the
reception and transformation of their views in Middle- and Late Platonism. (b)
Methods. The group engages in close reading and interpretation of ancient
texts, with the aim of constructing a history of engagement with the questions
indicated above. The main areas of expertise brought to bear on the relevant
texts lie in classical philology, history of ideas, history of science, and
systematic philosophy. In a weekly research seminar, individual research
projects and results are presented in detail and discussed in the light of
these varied disciplines and skill sets. (c) State of Discussion. Relevant
texts are interpreted both internally and in the light of their relationships
with earlier sources and later readings. In this way a narrative is emerging
of development and interrelationship among ancient theories of space – a
narrative with some shape and coherence, but without the suppression of
details and uncertainties. The group is also beginning to pay more attention
to epistemological issues, concerning the sources of theoretical knowledge
about space, and the evolving standards of argument, justification, and
presentation of such knowledge
A Pulsational Model for the Orthogonal Polarization Modes in Radio Pulsars
In an earlier paper, we introduced a model for pulsars in which non-radial
oscillations of high spherical degree (\el) aligned to the magnetic axis of a
spinning neutron star were able to reproduce subpulses like those observed in
single-pulse measurements of pulsar intensity. The model did not address
polarization, which is an integral part of pulsar emission. Observations show
that many pulsars emit radio waves that appear to be the superposition of two
linearly polarized emission modes with orthogonal polarization angles. In this
paper, we extend our model to incorporate linear polarization. As before, we
propose that pulsational displacements of stellar material modulate the pulsar
emission, but now we apply this modulation to a linearly-polarized mode of
emission, as might be produced by curvature radiation. We further introduce a
second polarization mode, orthogonal to the first, that is modulated by
pulsational velocities. We combine these modes in superposition to model the
observed Stokes parameters in radio pulsars.Comment: 19 pages, 4 figures accepted Ap
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