262 research outputs found
Diffusion and consensus on weakly connected directed graphs
Let be a weakly connected directed graph with asymmetric graph Laplacian
. Consensus and diffusion are dual dynamical processes defined on
by for consensus and for diffusion. We
consider both these processes as well their discrete time analogues. We define
a basis of row vectors of the left null-space of
and a basis of column vectors of the right
null-space of in terms of the partition of into strongly
connected components. This allows for complete characterization of the
asymptotic behavior of both diffusion and consensus --- discrete and continuous
--- in terms of these eigenvectors.
As an application of these ideas, we present a treatment of the pagerank
algorithm that is dual to the usual one. We further show that the teleporting
feature usually included in the algorithm is not strictly necessary.
This is a complete and self-contained treatment of the asymptotics of
consensus and diffusion on digraphs. Many of the ideas presented here can be
found scattered in the literature, though mostly outside mainstream mathematics
and not always with complete proofs. This paper seeks to remedy this by
providing a compact and accessible survey.Comment: 19 pages, Survey Article, 1 figur
J- and Ks-band Galaxy Counts and Color Distributions in the AKARI North Ecliptic Pole Field
We present the J- and Ks-band galaxy counts and galaxy colors covering 750
square arcminutes in the deep AKARI North Ecliptic Pole (NEP) field, using the
FLoridA Multi-object Imaging Near-ir Grism Observational Spectrometer
(FLAMINGOS) on the Kitt Peak National Observatory (KPNO) 2.1m telescope. The
limiting magnitudes with a signal-to-noise ratio of three in the deepest
regions are 21.85 and 20.15 in the J- and Ks-bands respectively in the Vega
magnitude system. The J- and Ks-band galaxy counts in the AKARI NEP field are
broadly in good agreement with those of other results in the literature,
however we find some indication of a change in the galaxy number count slope at
J~19.5 and over the magnitude range 18.0 < Ks < 19.5. We interpret this feature
as a change in the dominant population at these magnitudes because we also find
an associated change in the B - Ks color distribution at these magnitudes where
the number of blue samples in the magnitude range 18.5 < Ks < 19.5 is
significantly larger than that of Ks < 17.5
A systematic review and meta-analysis on the effect of neoadjuvant chemotherapy on complications following immediate breast reconstruction
Background
The impact of neoadjuvant chemotherapy (NACT) on surgical outcomes following immediate breast reconstruction (IBR) remains unclear. While it is generally considered safe practice to perform an IBR post NACT, reported complication rates in published data are highly variable with the majority of studies including fewer than 50 patients in the NACT and IBR arm. To evaluate this further, we conducted a systematic review and meta-analysis on the effect of NACT on autologous and implant based immediate breast reconstructions. We aimed to assess for differences in the post-operative course following IBR between patients who received NACT with those who did not.
Methods
PubMed, EMBASE, and Cochrane Library were searched from 1995 to Sept 2, 2020 to identify articles that assessed the impact of NACT on IBR. All included studies assessed outcomes following IBR. Only studies comparing reconstructed patients receiving NACT to a control group of women who did not receive NACT were included. Unadjusted relative risk of outcomes between patients who received or did not receive NACT were synthesized using a fixed-effect meta-analysis. The evidence was assessed using the Newcastle Ottawa Scale scores and GRADE. Primary effect measures were risk ratios (RRs) with 95% confidence intervals.
Results
A total 17 studies comprising 3249 patients were included in the meta-analyses. Overall, NACT did not increase the risk of complications after immediate breast reconstructions (risk ratio [RR]: 0.91, 95% CI 0.74 to 1.11, p = 0.34). There was a moderate, but not significant, increase in flap loss following NACT compared with controls (RR: 1.23, 95% CI 0.70 to 2.18, p = 0.47; I2 = 0%). Most notably, there was a statistically significant increase in implant/expander loss after NACT (RR: 1.54, 95% CI 1.04 to 2.29, p = 0.03; I2 = 34%). NACT was not shown to significantly increase the incidence of hematomas, seromas or wound complications, or result in a significant delay to commencing adjuvant therapy (RR: 1.59, 95% CI 0.66 to 3.87, p = 0.30).
Conclusion
Immediate breast reconstruction after NACT is a safe procedure with an acceptable post-operative complication profile. It may result in a slight increase in implant loss rates, but it does not delay commencing adjuvant therapy
Inelastic Quantum Transport
We solve a Schrodinger equation for inelastic quantum transport that retains
full quantum coherence, in contrast to previous rate or Boltzmann equation
approaches. The model Hamiltonian is the zero temperature 1d Holstein model for
an electron coupled to optical phonons (polaron), in a strong electric field.
The Hilbert space grows exponentially with electron position, forming a
non-standard Bethe lattice. We calculate nonperturbatively the transport
current, electron-phonon correlations, and quantum diffusion. This system is a
toy model for the constantly branching ``wavefunction of the universe''.Comment: revtex, 13 pages, 4 figure
Local Electronic Structure of a Single Magnetic Impurity in a Superconductor
The electronic structure near a single classical magnetic impurity in a
superconductor is determined using a fully self-consistent Koster-Slater
algorithm. Localized excited states are found within the energy gap which are
half electron and half hole. Within a jellium model we find the new result that
the spatial structure of the positive-frequency (electron-like) spectral weight
(or local density of states), can differ strongly from that of the negative
frequency (hole-like) spectral weight. The effect of the impurity on the
continuum states above the energy gap is calculated with good spectral
resolution for the first time. This is also the first three-dimensional
self-consistent calculation for a strong magnetic impurity potential.Comment: 13 pages, RevTex, change in heuristic picture, no change in numerical
result
Local Electronic Structure of Defects in Superconductors
The electronic structure near defects (such as impurities) in superconductors
is explored using a new, fully self-consistent technique. This technique
exploits the short-range nature of the impurity potential and the induced
change in the superconducting order parameter to calculate features in the
electronic structure down to the atomic scale with unprecedented spectral
resolution. Magnetic and non-magnetic static impurity potentials are
considered, as well as local alterations in the pairing interaction. Extensions
to strong-coupling superconductors and superconductors with anisotropic order
parameters are formulated.Comment: RevTex source, 20 pages including 22 figures in text with eps
The First Measurements of Galaxy Clustering from IRAC Data of the Spitzer First Look Survey
We present the first results of the angular auto-correlation function of the
galaxies detected by the Infrared Array Camera (IRAC) instrument in the First
Look Survey (FLS) of the Spitzer Space Telescope. We detect significant signals
of galaxy clustering within the survey area. The angular auto-correlation
function of the galaxies detected in each of the four IRAC instrument channels
is consistent with a power-law form out to
\theta = 0.2\arcdeg, with the slope ranging from to 1.8. We
estimate the correlation amplitudes to be , , , and at
\theta=1\arcdeg for galaxies detected in the IRAC 3.6m, 4.5m,
5.8m, and 8.0m instrument channels, respectively. We compare our
measurements at 3.6m with the previous K-band measurements, and discuss
the implications of these results.Comment: Accepted for publication in the ApJ Supplements Spitzer Special
Issue; 12 pages including 3 figures and 1 tabl
Evidence for a Massive Post-Starburst Galaxy at z ~ 6.5
We present results from a search for high-redshift J--band ``dropout''
galaxies in the portion of the GOODS southern field that is covered by
extremely deep imaging from the Hubble Ultradeep Field (HUDF).Using
observations at optical, near-infrared and mid-infrared wavelengths from the
Hubble and Spitzer Space Telescopes and the ESO-VLT, we search for very massive
galaxies at high redshifts and find one particularly remarkable candidate. Its
spectral energy distribution is consistent with a galaxy at z ~ 6.5 and a
stellar mass of 6x10e11 M(sun) (for a Salpeter IMF). We interpret a prominent
photometric break between the near-infrared and Spitzer bandpasses as the 3646A
Balmer discontinuity. The best-fitting models have low reddening and ages of
several hundred Myr, placing the formation of the bulk of the stars at z > 9.
Alternative models of dusty galaxies at z ~ 2.5 are possible but provide
significantly poorer fits. The object is detected with Spitzer at 24 micron.
This emission originats from an obscured active nucleus or star formation. We
present optical and near-infrared spectroscopy which has, thus far, failed to
detect any spectral features. This helps limit the solution in which the galaxy
is a starburst or active galaxy at z ~ 2.5. If the high-redshift interpretation
is correct, this object would be an example of a galaxy that formed by a
process strongly resembling traditional models of monolithic collapse, in a way
which a very large mass of stars formed within a remarkably short period of
time, at very high redshift.Comment: Accepted for publication in Ap.J. 31 pages, 6 diagram
Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding
Within the broad class of multiferroics (compounds showing a coexistence of
magnetism and ferroelectricity), we focus on the subclass of "improper
electronic ferroelectrics", i.e. correlated materials where electronic degrees
of freedom (such as spin, charge or orbital) drive ferroelectricity. In
particular, in spin-induced ferroelectrics, there is not only a {\em
coexistence} of the two intriguing magnetic and dipolar orders; rather, there
is such an intimate link that one drives the other, suggesting a giant
magnetoelectric coupling. Via first-principles approaches based on density
functional theory, we review the microscopic mechanisms at the basis of
multiferroicity in several compounds, ranging from transition metal oxides to
organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic
frameworks, MOFs)Comment: 22 pages, 9 figure
A Redshift z=5.4 Lyman alpha Emitting Galaxy with Linear Morphology in the GRAPES/UDF Field
We have discovered an extended Lyman alpha plume associated with a compact
source at redshift 5.4 in slitless spectroscopic data from the Grism ACS
Program for Extragalactic Science (GRAPES) project. The spatial extent of the
emission is about 6 x 1.5 kpc (1 x 0.25 arcsec). Combining our grism data and
the broadband images from the Hubble UltraDeep Field (UDF) images, we find a
Lyman alpha line flux of 2e-17 erg/cm2/s and surface brightness 7e-17
erg/cm2/s/arcsec2. The UDF images show diffuse continuum emission associated
with the Lyman alpha plume (hereafter UDF 5225), with three embedded knots. The
morphology of UDF 5225 is highly suggestive of a galaxy in assembly. It is
moreover possible that the prominent Lyman alpha emission from this object is
due to an active nucleus, and that we are seeing the simultaneous growth
through accretion of a galaxy and its central black hole. Followup observations
at higher spectral resolution could test this hypothesis.Comment: 14 pages, accepted for publication in the Astrophysical Journa
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