1,054 research outputs found
A Model for Multi-property Galaxy Cluster Statistics
The massive dark matter halos that host groups and clusters of galaxies have
observable properties that appear to be log-normally distributed about
power-law mean scaling relations in halo mass. Coupling this assumption with
either quadratic or cubic approximations to the mass function in log space, we
derive closed-form expressions for the space density of halos as a function of
multiple observables as well as forms for the low-order moments of properties
of observable-selected samples. Using a Tinker mass function in a {\Lambda}CDM
cosmology, we show that the cubic analytic model reproduces results obtained
from direct, numerical convolution at the 10 percent level or better over
nearly the full range of observables covered by current observations and for
redshifts extending to z = 1.5. The model provides an efficient framework for
estimating effects arising from selection and covariance among observable
properties in survey samples.Comment: 9 pages, 4 figures, uses on-line mass function calculator
http://hmf.icrar.org/. Submitted to MNRA
Effects of the bias enhanced nucleation hot-filament chemical-vapor deposition parameters on diamond nucleation on iridium
The effects of the bias current density and the filament-to-substrate distance on the nucleation of diamond on iridium buffer layers were investigated in a hot-filament chemical-vapor deposition (HFCVD) reactor. The nucleation density increased by several orders of magnitude with the raise of the bias current density. According to high-resolution field-emission gun scanning electron microscopy observation, diamond nuclei formed during bias-enhanced nucleation (BEN) did not show any preferred oriented growth. Moreover, the first-nearest-neighbor distance distribution was consistent with a random nucleation mechanism. This occurrence suggested that the diffusion of carbon species at the substrate surface was not the predominant mechanism taking place during BEN in the HFCVD process. This fact was attributed to the formation of a graphitic layer prior to diamond nucleation. We also observed that the reduction of the filament sample distance during BEN was helpful for diamond growth. This nucleation behavior was different from the one previously reported in the case of BEN-microwave chemical-vapor deposition experiments on iridium and has been tentatively explained by taking into account the specific properties and limitations of the HFCVD technique
Conceptual hydrological model calibration using multi-objective optimization techniques over the transboundary Komadugu-Yobe basin, Lake Chad Area, West Africa
Study Area: The discharge of the transboundary Komadugu-Yobe Basin, Lake Chad Area, West Africa is calibrated using multi-objective optimization techniques. Study focus: The GR5J hydrological model parameters are calibrated using six optimization methods i.e. Local Optimization-Multi Start (LOMS), the Differential Evolution (DE), the Multiobjective Particle the Swarm Optimization (MPSO), the Memetic Algorithm with Local Search Chains (MALS), the Shuffled Complex Evolution-Rosenbrockâs function (SCE-R), and the Bayesian Markov Chain Monte Carlo (MCMC) approach. Three combined objective functions i.e. Root Mean Square Error, Nash- Sutcliffe efficiency, Kling-Gupta efficiency are applied. The calibration process is divided into two separate episodes (1974â2000 and 1980â1995) so as to ascertain the robustness of the calibration approaches. Runoff simulation results are analysed with a timefrequency wavelet transform. New hydrological insights for the region: For calibration and validation stages, all optimization methods simulate the base flow and high flow spells with a satisfactory level of accuracy. For calibration period, MCMC underestimate it by -0.07 mm/day. The performance evaluation shows that MCMC has the highest values of mean absolute error (0.28) and mean square error (0.40) while LOMS and MCMC record a low volumetric efficiency of 0.56. In all cases, the DE and the SCE-R methods perform better than others. The combination of multi-objective functions and multi-optimization techniques improve the modelâs parameters stability and the algorithmsâ optimization to represent the runoff in the basin
A Return to âThe Clinicâ for Community Psychology: Lessons from a Clinical Ethnography in Urban American Indian Behavioral Health
Community psychology (CP) abandoned the clinic and disengaged from movements for community mental health (CMH) to escape clinical convention and pursue growing aspirations as an independent field of contextâoriented, communityâengaged, and valuesâdriven research and action. In doing so, however, CP positioned itself on the sidelines of influential contemporary movements that promote potentially harmful, reductionist biomedical narratives in mental health. We advocate for a return to the clinicâthe seat of institutional power in mental healthâusing critical clinicâbased inquiry to open sites for clinicalâcommunity dialogue that can instigate transformative change locally and nationally. To inform such works within the collaborative and emancipatory traditions of CP, we detail a recently completed clinical ethnography and offer âlessons learnedâ regarding challenges likely to reâemerge in similar efforts. Conducted with an urban American Indian community behavioral health clinic, this ethnography examined how culture and culture concepts (e.g., cultural competence) shaped clinical practice with socioâpolitical implications for American Indian peoples and the pursuit of transformative change in CMH. Lessons learned identify exceptional clinicians versed in ecological thinking and contextualist discourses of human suffering as ideal partners for this work; encourage intense contextualization and constraining critique to areas of mutual interest; and support relational approaches to clinic collaborations.HighlightsCommunity psychology (CP) must reengage the clinic setting to address problems in mental health.Clinical ethnography represents one promising approach to clinicâbased critical CP research.Clinicians versed in ecological thinking and contextualist discourses make ideal collaborators.Intense contextualism and mutual interests can guide a collaborative CP critique of the clinic.Relationallyâdriven and contextually specific approaches to collaboration are helpful in this work.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142553/1/ajcp12212.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142553/2/ajcp12212_am.pd
An Efficient State Recovery Attack on X-FCSR-256
We describe a state recovery attack on the X-FCSR-256 stream cipher of total complexity at most . This complexity is achievable by requiring output blocks with an amortized calculation effort of at most table lookups per output block using no more than table entries of precomputational storage
Microwave single-photon detection using a hybrid spin-optomechanical quantum interface
While infrared and optical single-photon detectors exist at high quantum
efficiencies, detecting single microwave photons has been an ongoing challenge.
Specifically, microwave photon detection is challenging compared to its optical
counterpart as its energy scale is four to five orders of magnitude smaller,
necessitating lower operating temperatures. Here, we propose a hybrid
spin-optomechanical interface to detect single microwave photons. The microwave
photons are coupled to a phononic resonator via piezoelectric actuation. This
phononic cavity also acts as a photonic cavity with an embedded Silicon-Vacancy
(SiV) center in diamond. Phonons mediate the quantum state transfer of the
microwave cavity to the SiV spin, in order to allow for high spin-mechanical
coupling at the single quantum level. From this, the optical cavity is used to
perform a cavity-enhanced single-shot readout of the spin-state. Here, starting
with a set of experimentally realizable parameters, we simulate the complete
protocol and estimate an overall detection success probability of
, Shannon's mutual information of , and a total
detection time of . We also talk about the experimental regimes
in which tends to near unity and tends to
indicating exactly one bit of information retrieval about the presence or
absence of a microwave photon
Wolf-Rayet Galaxies in the Sloan Digital Sky Survey: the metallicity dependence of the initial mass function
We use a large sample of 174 Wolf-Rayet (WR) galaxies drawn from the Sloan
Digital Sky Survey to study whether and how the slope of the stellar initial
mass function depends on metallicity. We calculate for each object its oxygen
abundance according to which we divide our sample into four metallicity
subsamples. For each subsample, we then measure three quantities: the
equivalent width of \hb emission line, the equivalent width of WR bump around
4650\AA, and the WR bump-to-\hb intensity ratio, and compare to the predictions
of the same quantities by evolutionary synthesis models of Schaerer & Vacca.
Such comparisons lead to a clear dependence of the slope of initial mass
function () on metallicity in that galaxies at higher metallicities
tend to have steeper initial mass functions, with the slope index ranging from
1.00 for the lowest metallicity of to 3.30
for the highest metallicity . We have carefully examined the possible
sources of systematic error either in models or in our observational
measurements and shown that these sources do not change this result.Comment: 12 pages, 6 figures, ApJ accepte
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