3,254 research outputs found
Academic precarity as hierarchical dependence in the Max Planck Society
This essay examines the idiosyncratic internal hierarchy of Germany's foremost research organization, the Max Planck Society. It employs Louis Dumont's analytics of paramount value, encompassment, and complementarity to convey the symbolic logic of relations therein. One consequence of this is to show that the organization's paramount values of autonomy and excellence (embodied by its governing community of directors who encompass their departments) produce the complementary value of dependence for subalterns. Ethnographic engagement with three post-PhD scientists demonstrates that dependence is thereby constituted as a âmode of actionâ in James Ferguson's terms, which hinges on their director's support. The essay concludes that the ubiquity of temporary contracts among these actors does not arise simply-as many presume-from a generic neoliberal precariatization of the academy. Instead, precarity of employment in the Max Planck Society is the contemporary expression of dependencies initiated by a far older tradition of intellectual leadership, and the morphologies of German monarchy that preceded it
An ideal mass assignment scheme for measuring the Power Spectrum with FFTs
In measuring the power spectrum of the distribution of large numbers of dark
matter particles in simulations, or galaxies in observations, one has to use
Fast Fourier Transforms (FFT) for calculational efficiency. However, because of
the required mass assignment onto grid points in this method, the measured
power spectrum \la |\delta^f(k)|^2\ra obtained with an FFT is not the true
power spectrum but instead one that is convolved with a window function
in Fourier space. In a recent paper, Jing (2005) proposed an
elegant algorithm to deconvolve the sampling effects of the window function and
to extract the true power spectrum, and tests using N-body simulations show
that this algorithm works very well for the three most commonly used mass
assignment functions, i.e., the Nearest Grid Point (NGP), the Cloud In Cell
(CIC) and the Triangular Shaped Cloud (TSC) methods. In this paper, rather than
trying to deconvolve the sampling effects of the window function, we propose to
select a particular function in performing the mass assignment that can
minimize these effects. An ideal window function should fulfill the following
criteria: (i) compact top-hat like support in Fourier space to minimize the
sampling effects; (ii) compact support in real space to allow a fast and
computationally feasible mass assignment onto grids. We find that the scale
functions of Daubechies wavelet transformations are good candidates for such a
purpose. Our tests using data from the Millennium Simulation show that the true
power spectrum of dark matter can be accurately measured at a level better than
2% up to , without applying any deconvolution processes. The new
scheme is especially valuable for measurements of higher order statistics, e.g.
the bi-spectrum,........Comment: 17 pages, 3 figures, Accepted for publication in ApJ,Matches the
accepte
Refining Finite-Time Lyapunov Exponent Ridges and the Challenges of Classifying Them
While more rigorous and sophisticated methods for identifying Lagrangian based coherent structures exist, the finite-time Lyapunov exponent (FTLE) field remains a straightforward and popular method for gaining some insight into transport by complex, time-dependent two-dimensional flows. In light of its enduring appeal, and in support of good practice, we begin by investigating the effects of discretization and noise on two numerical approaches for calculating the FTLE field. A practical method to extract and refine FTLE ridges in two-dimensional flows, which builds on previous methods, is then presented. Seeking to better ascertain the role of a FTLE ridge in flow transport, we adapt an existing classification scheme and provide a thorough treatment of the challenges of classifying the types of deformation represented by a FTLE ridge. As a practical demonstration, the methods are applied to an ocean surface velocity field data set generated by a numerical model. (C) 2015 AIP Publishing LLC.ONR N000141210665Center for Nonlinear Dynamic
Cluster Correlation in Mixed Models
We evaluate the dependence of the cluster correlation length r_c on the mean
intercluster separation D_c, for three models with critical matter density,
vanishing vacuum energy (Lambda = 0) and COBE normalized: a tilted CDM (tCDM)
model (n=0.8) and two blue mixed models with two light massive neutrinos
yielding Omega_h = 0.26 and 0.14 (MDM1 and MDM2, respectively). All models
approach the observational value of sigma_8 (and, henceforth, the observed
cluster abundance) and are consistent with the observed abundance of Damped
Lyman_alpha systems. Mixed models have a motivation in recent results of
neutrino physics; they also agree with the observed value of the ratio
sigma_8/sigma_25, yielding the spectral slope parameter Gamma, and nicely fit
LCRS reconstructed spectra. We use parallel AP3M simulations, performed in a
wide box (side 360/h Mpc) and with high mass and distance resolution, enabling
us to build artificial samples of clusters, whose total number and mass range
allow to cover the same D_c interval inspected through APM and Abell cluster
clustering data. We find that the tCDM model performs substantially better than
n=1 critical density CDM models. Our main finding, however, is that mixed
models provide a surprisingly good fit of cluster clustering data.Comment: 22 pages + 10 Postscript figures. Accepted for publication in Ap
Constraints on Omega_m and sigma_8 from weak lensing in RCS fields
We have analysed 53 square degrees of imaging data from the Red-Sequence
Cluster Survey (RCS), and measured the excess correlations in the shapes of
galaxies on scales out to ~1.5 degrees. We separate the signal into an ``E''-
(lensing) and ``B''-mode (systematics), which allows us to study residual
systematics. On scales larger than 10 arcminutes, we find no ``B''-mode. On
smaller scales we find a small, but significant ``B''-mode. This signal is also
present when we select a sample of bright galaxies. These galaxies are rather
insensitive to observational distortions, and we therefore conclude that the
oberved ``B''-mode is likely to be caused by intrinsic alignments. We therefore
limit the cosmic shear analysis to galaxies with 22<R_C<24. We derive joint
constraints on Omega_m and sigma_8, by marginalizing over Gamma, Omega_Lambda
and the source redshift distribution, using different priors. We obtain a
conservative constraint of
(95% confidence). A better constraint is derived when we use Gaussian priors
redshift distribution. For this choice of priors, we find
(95% confidence). Using our
setof Gaussian priors, we find that we can place a lower bound on Gamma:
Gamma>0.1+0.16\Omega_m$ (95% confidence). Comparison of the RCS results with
three other recent cosmic shear measurements shows excellent agreement. The
current weak lensing results are also in good agreement with CMB measurements,
when we allow the reionization optical depth tau and the spectral index n_s to
vary. We present a simple demonstration of how the weak lensing results can be
used as a prior in the parameter estimation from CMB measurements to derive
constraints on the reionization optical depth tau. (abridged)Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
A new measure of using the lensing dispersion in high- type Ia SNe
The gravitational lensing magnification or demagnification due to large-scale
structures induces a scatter in peak magnitudes of high redshift type Ia
supernovae (SNe Ia). The amplitude of the lensing dispersion strongly depends
on that of density fluctuations characterized by the parameter.
Therefore the value of is constrained by measuring the dispersion in
the peak magnitudes. We examine how well SN Ia data will provide a constraint
on the value of using a likelihood analysis method. It is found that
the number and quality of SN Ia data needed for placing a useful constraint on
is attainable with Next Generation Space Telescope.Comment: 9 pages, 3 figures. Accepted for publication in The Astrophysical
Journa
Optical characterisation of germanium optical fibres
Semiconductor core optical fibres are currently generating great interest as they promise to be a platform for the seamless incorporation of optoelectronic functionality into a new generation of all-fibre networks [1,2]. Although recent attentions have primarily focused on silicon as the material of choice for semiconductor photonics applications, germanium has some advantages over its counterpart. For example, it has higher nonlinearity, extended infrared transparency and has recently been demonstrated as a direct band gap laser medium [3]. Here we present the first optical characterisation of a germanium core optical fibre. The fibre was fabricated using a chemical micro fluidic deposition process [1] that uses GeH4 (germane) as a precursor to deposit amorphous germanium into the hole of a silica capillary. Figure 1 (a) shows an optical microscope image of the polished end face of a germanium fibre, with a 5.6 ”m core diameter, which has been completely filled with the semiconductor material. Optical transmission measurements have been conducted over the wavelength range 2 ”m to 11 ”m, to confirm the broad mid-infrared operational window, and the guided output at 2.4 ”m, imaged using a Spiricon Pyrocam III pyroelectric array camera, is shown in Figure 1 (b). At this wavelength the optical loss has been measured to be 20 dB/cm, which is comparable to losses measured for amorphous silicon fibres in the infrared. The potential for these germanium optical fibres to be used as optical modulators and infrared detectors will be discussed
âMirror, mirrorâŠâ A preliminary investigation of skin tone dissatisfaction and its impact among British adults
This study examined skin tone dissatisfaction, measured using a skin tone chart, among a multiethnic sample of British adults. A total of 648 British White individuals, 292 British South Asians, and 260 British African Caribbean participants completed a visual task in which they were asked to indicate their actual and ideal skin tones. They also completed measures of body appreciation, self-esteem, and ethnic identity attachment. Results showed that Asians had a lighter skin tone ideal than White and African Caribbean participants. Conversely, White participants had higher skin tone dissatisfaction (preferring a darker skin tone) than Asian and African Caribbean participants, who preferred a lighter skin tone. Results also showed that skin tone dissatisfaction predicted body appreciation once the effects of participant ethnicity, age, ethnic identity attachment, and self-esteem had been accounted for. Implications of our findings and suggestions for future research are discussed
The Evolution of Radio Galaxies at Intermediate Redshift
We describe a new estimate of the radio galaxy 1.4 GHz luminosity function
and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and
color selection have been used to select Bj<23.5 early-type galaxies from the
Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields.
Approximately 230 radio galaxies have then been selected by matching early-type
galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz
luminosity function of radio galaxies measure significant evolution over the
observed redshift range. For an Omega_M=1 cosmology the evolution of the radio
power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and
3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray
selected AGN and is consistent with the same physical process being responsible
for the optical and radio luminosity evolution of AGN.Comment: 26 pages, 9 Figures, Accepted for Publication in A
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