1,394 research outputs found
Heat kernel and number theory on NC-torus
The heat trace asymptotics on the noncommutative torus, where generalized
Laplacians are made out of left and right regular representations, is fully
determined. It turns out that this question is very sensitive to the
number-theoretical aspect of the deformation parameters. The central condition
we use is of a Diophantine type. More generally, the importance of number
theory is made explicit on a few examples. We apply the results to the spectral
action computation and revisit the UV/IR mixing phenomenon for a scalar theory.
Although we find non-local counterterms in the NC theory on \T^4, we
show that this theory can be made renormalizable at least at one loop, and may
be even beyond
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Diffusion of digital innovation in construction: a case study of a UK engineering firm
The UK government is mandating the use of building information modelling (BIM) in large public projects by 2016. As a result, engineering firms are faced with challenges related to embedding new technologies and associated working practices for the digital delivery of major infrastructure projects. Diffusion of innovations theory is used to investigate how digital innovations diffuse across complex firms. A contextualist approach is employed through an in-depth case study of a large, international engineering project-based firm. The analysis of the empirical data, which was collected over a four-year period of close interaction with the firm, reveals parallel paths of diffusion occurring across the firm, where both the innovation and the firm context were continually changing. The diffusion process is traced over three phases: centralization of technology management, standardization of digital working practices, and globalization of digital resources. The findings describe the diffusion of a digital innovation as multiple and partial within a complex social system during times of change and organizational uncertainty, thereby contributing to diffusion of innovations studies in construction by showing a range of activities and dynamics of a non-linear diffusion process
Fertility and gonadal function in female survivors after treatment of early unfavorable Hodgkin lymphoma (HL) within the German Hodgkin Study Group HD14 trial
Background In the HD14 trial, 2× BEACOPPescalated+2× ABVD (2+2) has improved the primary outcome. Compared with 4× ABVD, this benefit might be compromised by more infertility in women. Therefore, we analyzed gonadal function and fertility. Patients and methods Women ≤45 years in ongoing remission at least 1 year after therapy were included. Hormone parameters, menopausal symptoms, measures to preserve fertility, menstrual cycle, pregnancies, and offspring were evaluated. Results Three hundred and thirty one of 579 women addressed participated (57.2%) and 263 per-protocol treated patients qualified (A=ABVD: 137, B=2+2: 126, mean time after therapy 42 and 43 months, respectively). Regular menstrual cycle after treatment (A: 87%, B: 83%) and time to recovery (≤12 months) were not different. Follicle-stimulating hormone and anti-Muellerian hormone were significantly better in arm A. However, pregnancies after therapy favored arm B (A: 15%, B: 26%, P=0.043) and motherhood rates were equivalent to the German normal population. Multivariate analysis revealed prophylactic use of gonadotropin-releasing hormone (GnRH) analogues as highly significant prognostic factor for preservation of fertility (odds ratio=12.87, P=0.001). Severe menopausal symptoms were frequent in women ≥30 years (A: 21%, B: 25%). Conclusions Hormonal levels after 2+2 indicate a reduced ovarian reserve. However, 2+2 in combination with GnRH analogues does not compromise fertility within the evaluated observation tim
Nearby supernova host galaxies from the CALIFA Survey: II. SN environmental metallicity
The metallicity of a supernova (SN) progenitor, together with its mass, is
one of the main parameters that rules their outcome. We present a metallicity
study of 115 nearby SN host galaxies (0.005<z<0.03) which hosted 142 SNe using
Integral Field Spectroscopy (IFS) from the CALIFA survey. Using O3N2 we found
no statistically significant differences between the gas-phase metallicities at
the locations of the three main SN types (Ia, Ib/c and II) all having
~8.500.02 dex. The total galaxy metallicities are also very similar and we
argue that this is because our sample consists only of SNe discovered in
massive galaxies (log(M/Msun)>10 dex) by targeted searches. We also found no
evidence that the metallicity at the SN location differs from the average
metallicity at the GCD of the SNe. By extending our SN sample with published
metallicities at the SN location, we studied the metallicity distributions for
all SN subtypes split into SN discovered in targeted and untargeted searches.
We confirm a bias toward higher host masses and metallicities in the targeted
searches. Combining data from targeted and untargeted searches we found a
sequence from higher to lower local metallicity: SN Ia, Ic, and II show the
highest metallicity, which is significantly higher than SN Ib, IIb, and Ic-BL.
Our results support the picture of SN Ib resulting from binary progenitors and,
at least part of, SN Ic being the result of single massive stars stripped of
their outer layers by metallicity driven winds. We studied several proxies of
the local metallicity frequently used in the literature and found that the
total host metallicity allows for the estimation of the metallicity at the SN
location with an accuracy better than 0.08 dex and very small bias. In
addition, weak AGNs not seen in total spectra may only weakly bias (by 0.04
dex) the metallicity estimate from integrated spectra. (abridged)Comment: 24 pages, 16 Figures, 13 Tables, Accepted in A&
The Effect of Lattice Vibrations on Substitutional Alloy Thermodynamics
A longstanding limitation of first-principles calculations of substitutional
alloy phase diagrams is the difficulty to account for lattice vibrations. A
survey of the theoretical and experimental literature seeking to quantify the
impact of lattice vibrations on phase stability indicates that this effect can
be substantial. Typical vibrational entropy differences between phases are of
the order of 0.1 to 0.2 k_B/atom, which is comparable to the typical values of
configurational entropy differences in binary alloys (at most 0.693 k_B/atom).
This paper describes the basic formalism underlying ab initio phase diagram
calculations, along with the generalization required to account for lattice
vibrations. We overview the various techniques allowing the theoretical
calculation and the experimental determination of phonon dispersion curves and
related thermodynamic quantities, such as vibrational entropy or free energy. A
clear picture of the origin of vibrational entropy differences between phases
in an alloy system is presented that goes beyond the traditional bond counting
and volume change arguments. Vibrational entropy change can be attributed to
the changes in chemical bond stiffness associated with the changes in bond
length that take place during a phase transformation. This so-called ``bond
stiffness vs. bond length'' interpretation both summarizes the key phenomenon
driving vibrational entropy changes and provides a practical tool to model
them.Comment: Submitted to Reviews of Modern Physics 44 pages, 6 figure
Multiple reflection expansion and heat kernel coefficients
We propose the multiple reflection expansion as a tool for the calculation of
heat kernel coefficients. As an example, we give the coefficients for a sphere
as a finite sum over reflections, obtaining as a byproduct a relation between
the coefficients for Dirichlet and Neumann boundary conditions. Further, we
calculate the heat kernel coefficients for the most general matching conditions
on the surface of a sphere, including those cases corresponding to the presence
of delta and delta prime background potentials. In the latter case, the
multiple reflection expansion is shown to be non-convergent.Comment: 21 pages, corrected for some misprint
Tracing kinematic (mis)alignments in CALIFA merging galaxies: Stellar and ionized gas kinematic orientations at every merger stage
We present spatially resolved stellar and/or ionized gas kinematic properties
for a sample of 103 interacting galaxies, tracing all merger stages: close
companions, pairs with morphological signatures of interaction, and coalesced
merger remnants. We compare our sample with 80 non-interacting galaxies. We
measure for the stellar and the ionized gas components the major (projected)
kinematic position angles (PA, approaching and receding)
directly from the velocity fields with no assumptions on the internal motions.
This method allow us to derive the deviations of the kinematic PAs from a
straight line (PA). Around half of the interacting
objects show morpho-kinematic PA misalignments that cannot be found in the
control sample. Those misalignments are present mostly in galaxies with
morphological signatures of interaction. Alignment between the kinematic sides
for both samples is similar, with most of the galaxies displaying small
misalignments. Radial deviations of the kinematic PA from a straight line in
the stellar component measured by PA are large for
both samples. However, for a large fraction of interacting galaxies the ionized
gas PA is larger than typical values derived from
isolated galaxies (48%), making this parameter a good indicator to trace the
impact of interaction and mergers in the internal motions of galaxies. By
comparing the stellar and ionized gas kinematic PA, we find that 42% (28/66) of
the interacting galaxies have misalignments larger than 16 degrees, compared to
10% from the control sample. Our results show the impact of interactions in the
internal structure of galaxies as well as the wide variety of their velocity
distributions. This study also provides a local Universe benchmark for
kinematic studies in merging galaxies at high redshift.Comment: 24 pages,11 Figures, Accepted for publication in Astronomy &
Astrophysics. The entire set of stellar and ionized gas velocity fields of
the interacting/merging sample will be available in the electronic version of
the journa
The Mass-Metallicity relation explored with CALIFA: I. Is there a dependence on the star formation rate?
We present the results on the study of the global and local M-Z relation
based on the first data available from the CALIFA survey (150 galaxies). This
survey provides integral field spectroscopy of the complete optical extent of
each galaxy (up to 2-3 effective radii), with enough resolution to separate
individual HII regions and/or aggregations. Nearly 3000 individual HII
regions have been detected. The spectra cover the wavelength range between
[OII]3727 and [SII]6731, with a sufficient signal-to-noise to derive the oxygen
abundance and star-formation rate associated with each region. In addition, we
have computed the integrated and spatially resolved stellar masses (and surface
densities), based on SDSS photometric data. We explore the relations between
the stellar mass, oxygen abundance and star-formation rate using this dataset.
We derive a tight relation between the integrated stellar mass and the
gas-phase abundance, with a dispersion smaller than the one already reported in
the literature (0.07 dex). Indeed, this
dispersion is only slightly larger than the typical error derived for our
oxygen abundances. However, we do not find any secondary relation with the
star-formation rate, other than the one induced due to the primary relation of
this quantity with the stellar mass. We confirm the result using the 3000
individual HII regions, for the corresponding local relations.
Our results agree with the scenario in which gas recycling in galaxies, both
locally and globally, is much faster than other typical timescales, like that
of gas accretion by inflow and/or metal loss due to outflows. In essence,
late-type/disk dominated galaxies seem to be in a quasi-steady situation, with
a behavior similar to the one expected from an instantaneous
recycling/closed-box model.Comment: 19 Pages, 8 figures, Accepted for Publishing in Astronomy and
Astrophysics (A&A
Strangeness enhancements at central rapidity in 40 A GeV/c Pb-Pb collisions
Results are presented on neutral kaon, hyperon and antihyperon production in
Pb-Pb and p-Be interactions at 40 GeV/c per nucleon. The enhancement pattern
follows the same hierarchy as seen in the higher energy data - the enhancement
increases with the strangeness content of the hyperons and with the centrality
of collision. The centrality dependence of the Pb-Pb yields and enhancements is
steeper at 40 than at 158 A GeV/c. The energy dependence of strangeness
enhancements at mid-rapidity is discussed.Comment: 15 pages, 10 figures and 3 tables. Presented at International
Conference on Strangeness in Quark Matter (SQM2009), Buzios, Rio de Janeiro,
Brazil, 27 Sept - 2 Oct 2009. Submitted to J.Phys.G: Nucl.Part.Phys, one
reference adde
Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503
Measuring the relative mass contributions of luminous and dark matter in
spiral galaxies is important for understanding their formation and evolution.
The combination of a galaxy rotation curve and strong lensing is a powerful way
to break the disk-halo degeneracy that is inherent in each of the methods
individually. We present an analysis of the 10-image radio spiral lens
B1933+503 at z_l=0.755, incorporating (1) new global VLBI observations, (2) new
adaptive-optics assisted K-band imaging, (3) new spectroscopic observations for
the lens galaxy rotation curve and the source redshift. We construct a
three-dimensionally axisymmetric mass distribution with 3 components: an
exponential profile for the disk, a point mass for the bulge, and an NFW
profile for the halo. The mass model is simultaneously fitted to the kinematics
and the lensing data. The NFW halo needs to be oblate with a flattening of
a/c=0.33^{+0.07}_{-0.05} to be consistent with the radio data. This suggests
that baryons are effective at making the halos oblate near the center. The
lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we
obtain a lower limit on the halo scale radius of 16 kpc (95% CI). The dark
matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is
f_{DM,2.2}=0.43^{+0.10}_{-0.09}. The contribution of the disk to the total
circular velocity at 2.2 disk scale lengths is 0.76^{+0.05}_{-0.06}, suggesting
that the disk is marginally submaximal. The stellar mass of the disk from our
modeling is log_{10}(M_{*}/M_{sun}) = 11.06^{+0.09}_{-0.11} assuming that the
cold gas contributes ~20% to the total disk mass. In comparison to the stellar
masses estimated from stellar population synthesis models, the stellar initial
mass function of Chabrier is preferred to that of Salpeter by a probability
factor of 7.2.Comment: 16 pages, 13 figures, minor revisions based on referee's comments,
accepted for publication in Ap
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