744 research outputs found
Holographic Gubser-Rocha model does not capture all the transport anomalies of strange metals
In the last decade, motivated by the concept of Planckian relaxation and the
possible existence of a quantum critical point in cuprate materials,
holographic techniques have been extensively used to tackle the problem of
strange metals and high-Tc superconductors. Among the various setups, the
Gubser-Rocha model has often been celebrated as a successful holographic model
for strange metals since endowed with the famous linear in resistivity
property. As fiercely advocated by Phil Anderson, beyond -linear
resistivity, there are several additional anomalies unique to the strange metal
phase, as for example a Fermi liquid like Hall angle -- the famous problem of
the two relaxation scales. In this short note, we show that the holographic
Gubser Rocha model fails in this respect and therefore, at least in its
original and simplest form, is not able to capture the transport phenomenology
of strange metals. We prove our statement by means of a direct numerical
computation, a previously demonstrated scaling analysis and also a hydrodynamic
argument. Finally, we conclude with an optimistic discussion on the possible
improvements and generalizations which could lead to a holographic model for
strange metals in all their glory.Comment: v1: 6 pages, 2 figure
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Inhibition of cAMP/PKA Pathway Protects Optic Nerve Head Astrocytes against Oxidative Stress by Akt/Bax Phosphorylation-Mediated Mfn1/2 Oligomerization.
Glaucoma is characterized by a progressive optic nerve degeneration and retinal ganglion cell loss, but the underlying biological basis for the accompanying neurodegeneration is not known. Accumulating evidence indicates that structural and functional abnormalities of astrocytes within the optic nerve head (ONH) have a role in glaucomatous neurodegeneration. Here, we investigate the impact of activation of cyclic adenosine 3',5'-monophosphate (cAMP)/protein kinase A (PKA) pathway on mitochondrial dynamics of ONH astrocytes exposed to oxidative stress. ONH astrocytes showed a significant loss of astrocytic processes in the glial lamina of glaucomatous DBA/2J mice, accompanied by basement membrane thickening and collagen deposition in blood vessels and axonal degeneration. Serial block-face scanning electron microscopy data analysis demonstrated that numbers of total and branched mitochondria were significantly increased in ONH astrocytes, while mitochondrial length and volume density were significantly decreased. We found that hydrogen peroxide- (H2O2-) induced oxidative stress compromised not only mitochondrial bioenergetics by reducing the basal and maximal respiration but also balance of mitochondrial dynamics by decreasing dynamin-related protein 1 (Drp1) protein expression in rat ONH astrocytes. In contrast, elevated cAMP by dibutyryl-cAMP (dbcAMP) or isobutylmethylxanthine treatment significantly increased Drp1 protein expression in ONH astrocytes. Elevated cAMP exacerbated the impairment of mitochondrial dynamics and reduction of cell viability to oxidative stress in ONH astrocytes by decreasing optic atrophy type 1 (OPA1), and mitofusin (Mfn)1/2 protein expression. Following combined treatment with H2O2 and dbcAMP, PKA inhibition restored mitochondrial dynamics by increasing mitochondrial length and decreasing mitochondrial number, and this promoted cell viability in ONH astrocytes. Also, PKA inhibition significantly promoted Akt/Bax phosphorylation and Mfn1/2 oligomerization in ONH astrocytes. These results suggest that modulation of the cAMP/PKA signaling pathway may have therapeutic potential by activating Akt/Bax phosphorylation and promoting Mfn1/2 oligomerization in glaucomatous ONH astrocytes
Impurity-Driven Metal-Insulator Transitions in Holography
In this work, we study Metal-Insulator transition in a holographic model
containing an interaction between the order parameter and charge-carrier
density. It turns out that the impurity density of this model can drive the
phase transition whose ordered phase corresponds to the insulating phase. The
temperature behavior of DC conductivity distinguishes the insulating phase from
the metal phase. We confirm this behavior by a numerical method and an analytic
calculation. As a byproduct, we show the existence of a `quantum phase
transition' supported by the Breitenlohner-Freedman bound argument.Comment: 22 pages, 21 figure
Pole-skipping points in 2D gravity and SYK model
We represent the first investigation of pole-skipping on both the gravity and
field theory sides. In contrast to the higher dimensional models, there is no
momentum degree of freedom in dimensional bulk theory. Thus, we then
consider a scalar field mass as our degree of freedom for the pole-skipping
phenomenon instead of momentum. The pole-skipping frequencies of the scalar
field in 2D gravity are the same as higher dimensional cases: for positive integer . At each of these frequencies, there is a
corresponding pole-skipping mass, so the pole-skipping points exist in the
space. We also compute the pole-skipping points of the SYK model
in space where is the dimension of the bilinear primary
operator. We find that there is a one-to-one correspondence of the
pole-skipping points between the JT gravity and the SYK model. To obtain the
pole-skipping points, we need to consider the parameter related to
chemical potential on the horizon of charged JT gravity and the particle-hole
asymmetric parameter of the complex SYK model as shift
parameters. This highlights the correspondence in
relation to pole-skipping
Proto-type installation of a double-station system for the optical-video-detection and orbital characterisation of a meteor/fireball in South Korea
We give a detailed description of the installation and operation of a
double-station meteor detection system which formed part of a research &
education project between Korea Astronomy Space Science Institute and Daejeon
Science Highschool. A total of six light-sensitive CCD cameras were installed
with three cameras at SOAO and three cameras at BOAO observatory. A
double-station observation of a meteor event enables the determination of the
three-dimensional orbit in space. This project was initiated in response to the
Jinju fireball event in March 2014. The cameras were installed in
October/November 2014. The two stations are identical in hardware as well as
software. Each station employes sensitive Watec-902H2 cameras in combination
with relatively fast f/1.2 lenses. Various fields of views were used for
measuring differences in detection rates of meteor events. We employed the
SonotaCo UFO software suite for meteor detection and their subsequent analysis.
The system setup as well as installation/operation experience is described and
first results are presented. We also give a brief overview of historic as well
as recent meteor (fall) detections in South Korea. For more information please
consult http://meteor.kasi.re.kr .Comment: Technical/instrumentation description of a professional meteor
detection system, 23 pages, 20 figures (color/monochrome), 5 tables,
submitted to the Journal of Korean Astronomical Society (JKAS,
http://jkas.kas.org/, http://jkas.kas.org/history.html
Neck control after definitive radiochemotherapy without planned neck dissection in node-positive head and neck cancers
<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to evaluate neck control outcomes after definitive radiochemotherapy without planned neck dissection in node-positive head and neck cancer.</p> <p>Methods</p> <p>We retrospectively reviewed medical records of fifty patients with node-positive head and neck cancer who received definitive radiochemotherapy. Twelve patients subsequently underwent neck dissection for suspicious recurrent or persistent disease. A median dose of 70 Gy (range 60-70.6) was delivered to involved nodes. Response evaluation was performed at a median of 5 weeks after completion of radiotherapy.</p> <p>Results</p> <p>Neck failure was observed in 11 patients and the 3-year regional control (RC) rate was 77.1%. Neck dissection was performed in 10 of the 11 patients; seven of these cases were successfully salvaged, and the ultimate rate of neck control was 92%. The remaining two patients who received neck dissection had negative pathologic results. On univariate analysis, initial nodal size > 2 cm, a less-than-complete response at the primary site, post-radiotherapy nodal size > 1.5 cm, and post-radiotherapy nodal necrosis were associated with RC. On multivariate analysis, less-than-complete primary site response and post-radiotherapy nodal necrosis were identified as independent prognostic factors for RC.</p> <p>Conclusions</p> <p>The neck failure rate after definitive radiochemotherapy without planned neck dissection was 22%. Two-thirds of these were successfully salvaged with neck dissection and the ultimate neck control rate was 92%. Our results suggest that planned neck dissection might not be necessary in patients with complete response of primary site, no evidence of residual lesion > 1.5 cm, or no necrotic lymph nodes at the 1-2 months follow-up evaluation after radiotherapy.</p
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