2,043 research outputs found
Microstructure-dependent DC set switching behaviors of Ge-Sb-Te-based phase-change random access memory devices accessed by in situ TEM
Phase-change random access memory (PCRAM) is one of the most promising nonvolatile memory devices. However, inability to secure consistent and reliable switching operations in nanometer-scale programing volumes limits its practical use for highdensity applications. Here, we report in situ transmission electron microscopy investigation of the DC set switching of Ge-Sb-Te (GST)-based vertical PCRAM cells. We demonstrate that the microstructure of GST, particularly the passive component surrounding the dome-shaped active switching volume, plays a critical role in determining the local temperature distribution and is therefore responsible for inconsistent cell-to-cell switching behaviors. As demonstrated by a PCRAM cell with a highly crystallized GST matrix, the excessive Joule heat can cause melting and evaporation of the switching volume, resulting in device failure. The failure occurred via two-step void formation due to accelerated phase separation in the molten GST by the polaritydependent atomic migration of constituent elements. The presented real-time observations contribute to the understanding of inconsistent switching and premature failure of GST-based PCRAM cells and can guide future design of reliable PCRAM.1176Ysciescopu
Iron content in forage sorghum (Sorghum bicolor (L.) Moench) measured on different slit widths with atomic absorption spectrometry
Our objective was to know the right slit width for iron (Fe) concentration of forage sorghum, sorghum hybrid (Sorghum bicolor (L.) Moench), and also to discern which water treatment sludge (WTS) were good for ruminant's health with the feeding sorghum on the present study. The present experiment was carried out on a randomized block design with four treatments; Control, alum sludge compost, alum sludge + NPK (nitrogen, phosphorus, potassium fertilizers), alum sludge compost + NPK (nitrogen, phosphorus, potassium fertilizers). Sorghum hybrid was harvested, and iron content of it was analyzed with an atomic absorption spectrophotometer on background correction (BGC) mode. In order to analyze the iron (Fe) content of the sorghum with the spectrophotometer, three different slit widths conditions were used; 0.15, 0.20 and 0.25 nm. Absorbance and background values were obtained during the Fe analyses with the apparatus. When the background value is small, it is preferred for some trace metals’ analyses. Both (AM/BS) ratio (mean of the absorbance values<AM> to the standard deviation of back ground values<BS>) and (AS<standard deviation of the absorbance values>/BS) ratio, were larger on 0.25 nm slit than those on 0.15 and 0.20 nm slit, and, from our experiment, the condition seemed better on the 0.25 nm slit for the iron analysis with the spectrophotometer. Therefore, the sorghum hybrid grown on (Alum+NPK) and on (Compost only) might be dangerous for ruminants because of their higher values than 200 mg Fe/kg DM (dry matter).Key words: Absorbance, alum sludge, atomic absorption spectrophotometer, background, forage sorghum hybrid, iron, slit
Hydrodynamics of R-charged D1-branes
We study the hydrodynamic properties of strongly coupled Yang-Mills
theory of the D1-brane at finite temperature and at a non-zero density of
R-charge in the framework of gauge/gravity duality. The gravity dual
description involves a charged black hole solution of an
Einstein-Maxwell-dilaton system in 3 dimensions which is obtained by a
consistent truncation of the spinning D1-brane in 10 dimensions. We evaluate
thermal and electrical conductivity as well as the bulk viscosity as a function
of the chemical potential conjugate to the R-charges of the D1-brane. We show
that the ratio of bulk viscosity to entropy density is independent of the
chemical potential and is equal to . The thermal conductivity and bulk
viscosity obey a relationship similar to the Wiedemann-Franz law. We show that
at the boundary of thermodynamic stability, the charge diffusion mode becomes
unstable and the transport coefficients exhibit critical behaviour. Our method
for evaluating the transport coefficients relies on expressing the second order
differential equations in terms of a first order equation which dictates the
radial evolution of the transport coefficient. The radial evolution equations
can be solved exactly for the transport coefficients of our interest. We
observe that transport coefficients of the D1-brane theory are related to that
of the M2-brane by an overall proportionality constant which sets the
dimensions.Comment: 57 pages, 12 figure
Domain Wall Holography for Finite Temperature Scaling Solutions
We investigate a class of near-extremal solutions of Einstein-Maxwell-scalar
theory with electric charge and power law scaling, dual to charged IR phases of
relativistic field theories at low temperature. These are exact solutions of
theories with domain wall vacua; hence, we use nonconformal holography to
relate the bulk and boundary theories. We numerically construct a global
interpolating solution between the IR charged solutions and the UV domain wall
vacua for arbitrary physical choices of Lagrangian parameters. By passing to a
conformal frame in which the domain wall metric becomes that of AdS, we uncover
a generalized scale invariance of the IR scaling solution, indicating a
connection to the physics of Lifshitz fixed points. Finally, guided by
effective field theoretic principles and the physics of nonconformal D-branes,
we argue for the applicability of domain wall holography even in theories with
AdS critical points, namely those theories for which a scalar potential is
dominated by a single exponential term over a large range
Fermions and Type IIB Supergravity On Squashed Sasaki-Einstein Manifolds
We discuss the dimensional reduction of fermionic modes in a recently found
class of consistent truncations of type IIB supergravity compactified on
squashed five-dimensional Sasaki-Einstein manifolds. We derive the lower
dimensional equations of motion and effective action, and comment on the
supersymmetry of the resulting theory, which is consistent with N=4 gauged
supergravity in , coupled to two vector multiplets. We compute fermion
masses by linearizing around two vacua of the theory: one that breaks
N=4 down to N=2 spontaneously, and a second one which preserves no
supersymmetries. The truncations under consideration are noteworthy in that
they retain massive modes which are charged under a U(1) subgroup of the
-symmetry, a feature that makes them interesting for applications to
condensed matter phenomena via gauge/gravity duality. In this light, as an
application of our general results we exhibit the coupling of the fermions to
the type IIB holographic superconductor, and find a consistent further
truncation of the fermion sector that retains a single spin-1/2 mode.Comment: 43 pages, 2 figures, PDFLaTeX; v2: added references, typos corrected,
minor change
Lifshitz-like space-time from intersecting branes in string/M theory
We construct 1/4 BPS, threshold F-D bound states (with )
of type II string theories by applying S- and T-dualities to the D1-D5 system
of type IIB string theory. These are different from the known 1/2 BPS,
non-threshold F-D bound states. The near horizon limits of these solutions
yield Lifshitz-like space-times with varying dynamical critical exponent
, for , along with the hyperscaling violation exponent
, showing how Lifshitz-like space-time can be
obtained from string theory. The dilatons are in general non-constant (except
for ). We discuss the holographic RG flows and the phase structures of
these solutions. For , we do not get a Lifshitz-like space-time, but the
near horizon limit in this case leads to an AdS space.Comment: 20 pages, no figure, v2: proper identification of hyperscaling
violation exponent has been made, abstract and the text has been changed
accordingly, note added, v3: minor changes, refs added, version to appear in
JHE
Supercritical Fluid Deposition of Conformal SrTiO3 Films with Composition Uniformity in Nanocontact Holes
SrTiO3 with a high dielectric constant is considered a promising capacitor dielectric for dynamic random access memory. Until now, a SrTiO3 deposition with compositional uniformity and perfect conformality inside high-aspect nanoscale holes has been difficult by chemical vapor deposition (CVD) and atomic layer deposition (ALD). In this study, we report a supercritical fluid deposition (SCFD) of SrTiO3. Compared to CVD SrTiO3, the SCFD SrTiO3 showed perfect conformality and compositional uniformity inside nanosize holes. From these results, the SCFD is expected to be a solution for the stoichiometry and conformality issues of the CVD and ALD SrTiO3.open111411sciescopu
Holography for chiral scale-invariant models
Deformation of any d-dimensional conformal field theory by a constant null
source for a vector operator of dimension (d + z -1) is exactly marginal with
respect to anisotropic scale invariance, of dynamical exponent z. The
holographic duals to such deformations are AdS plane waves, with z=2 being the
Schrodinger geometry. In this paper we explore holography for such chiral
scale-invariant models. The special case of z=0 can be realized with gravity
coupled to a scalar, and is of particular interest since it is related to a
Lifshitz theory with dynamical exponent two upon dimensional reduction. We show
however that the corresponding reduction of the dual field theory is along a
null circle, and thus the Lifshitz theory arises upon discrete light cone
quantization of an anisotropic scale invariant field theory.Comment: 62 pages; v2, published version, minor improvements and references
adde
QCD with Chemical Potential in a Small Hyperspherical Box
To leading order in perturbation theory, we solve QCD, defined on a small
three sphere in the large N and Nf limit, at finite chemical potential and map
out the phase diagram in the (mu,T) plane. The action of QCD is complex in the
presence of a non-zero quark chemical potential which results in the sign
problem for lattice simulations. In the large N theory, which at low
temperatures becomes a conventional unitary matrix model with a complex action,
we find that the dominant contribution to the functional integral comes from
complexified gauge field configurations. For this reason the eigenvalues of the
Polyakov line lie off the unit circle on a contour in the complex plane. We
find at low temperatures that as mu passes one of the quark energy levels there
is a third-order Gross-Witten transition from a confined to a deconfined phase
and back again giving rise to a rich phase structure. We compare a range of
physical observables in the large N theory to those calculated numerically in
the theory with N=3. In the latter case there are no genuine phase transitions
in a finite volume but nevertheless the observables are remarkably similar to
the large N theory.Comment: 44 pages, 18 figures, jhep3 format. Small corrections and
clarifications added in v3. Conclusions cleaned up. Published versio
Universality and exactness of Schrodinger geometries in string and M-theory
We propose an organizing principle for classifying and constructing
Schrodinger-invariant solutions within string theory and M-theory, based on the
idea that such solutions represent nonlinear completions of linearized vector
and graviton Kaluza-Klein excitations of AdS compactifications. A crucial
simplification, derived from the symmetry of AdS, is that the nonlinearities
appear only quadratically. Accordingly, every AdS vacuum admits infinite
families of Schrodinger deformations parameterized by the dynamical exponent z.
We exhibit the ease of finding these solutions by presenting three new
constructions: two from M5 branes, both wrapped and extended, and one from the
D1-D5 (and S-dual F1-NS5) system. From the boundary perspective, perturbing a
CFT by a null vector operator can lead to nonzero beta-functions for spin-2
operators; however, symmetry restricts them to be at most quadratic in
couplings. This point of view also allows us to easily prove nonrenormalization
theorems: for any Sch(z) solution of two-derivative supergravity constructed in
the above manner, z is uncorrected to all orders in higher derivative
corrections if the deforming KK mode lies in a short multiplet of an AdS
supergroup. Furthermore, we find infinite classes of 1/4 BPS solutions with
4-,5- and 7-dimensional Schrodinger symmetry that are exact.Comment: 31 pages, plus appendices; v2, minor corrections, added refs, slight
change in interpretation in section 2.3, new Schrodinger and Lifshitz
solutions included; v3, clarifications in sections 2 and 3 regarding
existence of solutions and multi-trace operator
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