453 research outputs found
In Praise of Diversity: A Resource Book for Multicultural Education
The unique diversity of our cultural heritage and background is slowly but surely being recognized as a valuable asset for our country, one to be cherished and shared. But the very richness and diversity of our heritage make it difficult for the classroom teacher or the college professor to acquire an understanding of the many groups who have contributed so much to the development of our nation
A Highly Nonlinear Differentially 4 Uniform Power Mapping That Permutes Fields of Even Degree
Functions with low differential uniformity can be used as the s-boxes of
symmetric cryptosystems as they have good resistance to differential attacks.
The AES (Advanced Encryption Standard) uses a differentially-4 uniform function
called the inverse function. Any function used in a symmetric cryptosystem
should be a permutation. Also, it is required that the function is highly
nonlinear so that it is resistant to Matsui's linear attack. In this article we
demonstrate that a highly nonlinear permutation discovered by Hans Dobbertin
has differential uniformity of four and hence, with respect to differential and
linear cryptanalysis, is just as suitable for use in a symmetric cryptosystem
as the inverse function.Comment: 10 pages, submitted to Finite Fields and Their Application
Model Selection for Support Vector Machine Classification
We address the problem of model selection for Support Vector Machine (SVM)
classification. For fixed functional form of the kernel, model selection
amounts to tuning kernel parameters and the slack penalty coefficient . We
begin by reviewing a recently developed probabilistic framework for SVM
classification. An extension to the case of SVMs with quadratic slack penalties
is given and a simple approximation for the evidence is derived, which can be
used as a criterion for model selection. We also derive the exact gradients of
the evidence in terms of posterior averages and describe how they can be
estimated numerically using Hybrid Monte Carlo techniques. Though
computationally demanding, the resulting gradient ascent algorithm is a useful
baseline tool for probabilistic SVM model selection, since it can locate maxima
of the exact (unapproximated) evidence. We then perform extensive experiments
on several benchmark data sets. The aim of these experiments is to compare the
performance of probabilistic model selection criteria with alternatives based
on estimates of the test error, namely the so-called ``span estimate'' and
Wahba's Generalized Approximate Cross-Validation (GACV) error. We find that all
the ``simple'' model criteria (Laplace evidence approximations, and the Span
and GACV error estimates) exhibit multiple local optima with respect to the
hyperparameters. While some of these give performance that is competitive with
results from other approaches in the literature, a significant fraction lead to
rather higher test errors. The results for the evidence gradient ascent method
show that also the exact evidence exhibits local optima, but these give test
errors which are much less variable and also consistently lower than for the
simpler model selection criteria
Inversion Leads to Quantitative, Not Qualitative, Changes in Face Processing
AbstractHumans are remarkably adept at recognizing objects across a wide range of views. A notable exception to this general rule is that turning a face upside down makes it particularly difficult to recognize [1–3]. This striking effect has prompted speculation that inversion qualitatively changes the way faces are processed. Researchers commonly assume that configural cues strongly influence the recognition of upright, but not inverted, faces [3–5]. Indeed, the assumption is so well accepted that the inversion effect itself has been taken as a hallmark of qualitative processing differences [6]. Here, we took a novel approach to understand the inversion effect. We used response classification [7–10] to obtain a direct view of the perceptual strategies underlying face discrimination and to determine whether orientation effects can be explained by differential contributions of nonlinear processes. Inversion significantly impaired performance in our face discrimination task. However, surprisingly, observers utilized similar, local regions of faces for discrimination in both upright and inverted face conditions, and the relative contributions of nonlinear mechanisms to performance were similar across orientations. Our results suggest that upright and inverted face processing differ quantitatively, not qualitatively; information is extracted more efficiently from upright faces, perhaps as a by-product of orientation-dependent expertise
Visual attention and target detection in cluttered natural scenes
Rather than attempting to fully interpret visual scenes in a
parallel fashion, biological systems appear to employ a serial strategy by
which an attentional spotlight rapidly selects circumscribed regions in the
scene for further analysis. The spatiotemporal deployment of attention
has been shown to be controlled by both bottom-up (image-based) and
top-down (volitional) cues. We describe a detailed neuromimetic computer
implementation of a bottom-up scheme for the control of visual
attention, focusing on the problem of combining information across modalities
(orientation, intensity, and color information) in a purely stimulusdriven
manner. We have applied this model to a wide range of target
detection tasks, using synthetic and natural stimuli. Performance has,
however, remained difficult to objectively evaluate on natural scenes,
because no objective reference was available for comparison. We
present predicted search times for our model on the Search–2 database
of rural scenes containing a military vehicle. Overall, we found a poor
correlation between human and model search times. Further analysis,
however, revealed that in 75% of the images, the model appeared to
detect the target faster than humans (for comparison, we calibrated the
model’s arbitrary internal time frame such that 2 to 4 image locations
were visited per second). It seems that this model, which had originally
been designed not to find small, hidden military vehicles, but rather to
find the few most obviously conspicuous objects in an image, performed
as an efficient target detector on the Search–2 dataset. Further developments
of the model are finally explored, in particular through a more
formal treatment of the difficult problem of extracting suitable low-level
features to be fed into the saliency map
On model-based time trend adjustments in platform trials with non-concurrent controls
Platform trials can evaluate the efficacy of several treatments compared to a
control. The number of treatments is not fixed, as arms may be added or removed
as the trial progresses. Platform trials are more efficient than independent
parallel-group trials because of using shared control groups. For arms entering
the trial later, not all patients in the control group are randomised
concurrently. The control group is then divided into concurrent and
non-concurrent controls. Using non-concurrent controls (NCC) can improve the
trial's efficiency, but can introduce bias due to time trends.
We focus on a platform trial with two treatment arms and a common control
arm. Assuming that the second treatment arm is added later, we assess the
robustness of model-based approaches to adjust for time trends when using NCC.
We consider approaches where time trends are modeled as linear or as a step
function, with steps at times where arms enter or leave the trial. For trials
with continuous or binary outcomes, we investigate the type 1 error (t1e) rate
and power of testing the efficacy of the newly added arm under a range of
scenarios. In addition to scenarios where time trends are equal across arms, we
investigate settings with trends that are different or not additive in the
model scale.
A step function model fitted on data from all arms gives increased power
while controlling the t1e, as long as the time trends are equal for the
different arms and additive on the model scale. This holds even if the trend's
shape deviates from a step function if block randomisation is used. But if
trends differ between arms or are not additive on the model scale, t1e control
may be lost.
The efficiency gained by using step function models to incorporate NCC can
outweigh potential biases. However, the specifics of the trial, plausibility of
different time trends, and robustness of results should be considere
Nano-ADEPT Aeroloads Wind Tunnel Test
A wind tunnel test of the Adaptable Deployable Entry and Placement Technology (ADEPT) was conducted in April 2015 at the US Army's 7 by10 Foot Wind Tunnel located at NASA Ames Research Center. Key geometric features of the fabric test article were a 0.7 meter deployed base diameter, a 70 degree half-angle forebody cone angle, eight ribs, and a nose-to-base radius ratio of 0.7. The primary objective of this wind tunnel test was to obtain static deflected shape and pressure distributions while varying pretension at dynamic pressures and angles of attack relevant to entry conditions at Earth, Mars, and Venus. Other objectives included obtaining aerodynamic force and moment data and determining the presence and magnitude of any dynamic aeroelastic behavior (buzz/flutter) in the fabric trailing edge. All instrumentation systems worked as planned and a rich data set was obtained. This paper describes the test articles, instrumentation systems, data products, and test results. Four notable conclusions are drawn. First, test data support adopting a pre-tension lower bound of 10 foot pounds per inch for Nano-ADEPT mission applications in order to minimize the impact of static deflection. Second, test results indicate that the fabric conditioning process needs to be reevaluated. Third, no flutter/buzz of the fabric was observed for any test condition and should also not occur at hypersonic speeds. Fourth, translating one of the gores caused ADEPT to generate lift without the need for a center of gravity offset. At hypersonic speeds, the lift generated by actuating ADEPT gores could be used for vehicle control
Activity-Based Protein Profiling Reveals That Cephalosporins Selectively Active on Non-replicating Mycobacterium tuberculosis Bind Multiple Protein Families and Spare Peptidoglycan Transpeptidases
This work is licensed under a Creative Commons Attribution 4.0 International License.As β-lactams are reconsidered for the treatment of tuberculosis (TB), their targets are assumed to be peptidoglycan transpeptidases, as verified by adduct formation and kinetic inhibition of Mycobacterium tuberculosis (Mtb) transpeptidases by carbapenems active against replicating Mtb. Here, we investigated the targets of recently described cephalosporins that are selectively active against non-replicating (NR) Mtb. NR-active cephalosporins failed to inhibit recombinant Mtb transpeptidases. Accordingly, we used alkyne analogs of NR-active cephalosporins to pull down potential targets through unbiased activity-based protein profiling and identified over 30 protein binders. None was a transpeptidase. Several of the target candidates are plausibly related to Mtb’s survival in an NR state. However, biochemical tests and studies of loss of function mutants did not identify a unique target that accounts for the bactericidal activity of these beta-lactams against NR Mtb. Instead, NR-active cephalosporins appear to kill Mtb by collective action on multiple targets. These results highlight the ability of these β-lactams to target diverse classes of proteins.NIH U19AI111143Milstein Program in Chemical Biology and Translational MedicineWilliam Randolph Hearst TrustWelch Foundation (A-0015
Steady-state modulation of voltage-gated K+ channels in rat arterial smooth muscle by cyclic AMP-dependent protein kinase and protein phosphatase 2B
Voltage-gated potassium channels (Kv) are important regulators of membrane potential in vascular smooth muscle cells, which is integral to controlling intracellular Ca2+ concentration and regulating vascular tone. Previous work indicates that Kv channels can be modulated by receptor-driven alterations of cyclic AMP-dependent protein kinase (PKA) activity. Here, we demonstrate that Kv channel activity is maintained by tonic activity of PKA. Whole-cell recording was used to assess the effect of manipulating PKA signalling on Kv and ATP-dependent K+ channels of rat mesenteric artery smooth muscle cells. Application of PKA inhibitors, KT5720 or H89, caused a significant inhibition of Kv currents. Tonic PKA-mediated activation of Kv appears maximal as application of isoprenaline (a β-adrenoceptor agonist) or dibutyryl-cAMP failed to enhance Kv currents. We also show that this modulation of Kv by PKA can be reversed by protein phosphatase 2B/calcineurin (PP2B). PKA-dependent inhibition of Kv by KT5720 can be abrogated by pre-treatment with the PP2B inhibitor cyclosporin A, or inclusion of a PP2B auto-inhibitory peptide in the pipette solution. Finally, we demonstrate that tonic PKA-mediated modulation of Kv requires intact caveolae. Pre-treatment of the cells with methyl-β-cyclodextrin to deplete cellular cholesterol, or adding caveolin-scaffolding domain peptide to the pipette solution to disrupt caveolae-dependent signalling each attenuated PKA-mediated modulation of the Kv current. These findings highlight a novel, caveolae-dependent, tonic modulatory role of PKA on Kv channels providing new insight into mechanisms and the potential for pharmacological manipulation of vascular tone
Novel Cephalosporins Selectively Active on Nonreplicating Mycobacterium tuberculosis
We report two series of novel cephalosporins that are bactericidal to Mycobacterium tuberculosis alone of the pathogens tested, which only kill M. tuberculosis when its replication is halted by conditions resembling those believed to pertain in the host, and whose bactericidal activity is not dependent upon or enhanced by clavulanate, a β-lactamase inhibitor. The two classes of cephalosporins bear an ester or alternatively an oxadiazole isostere at C-2 of the cephalosporin ring system, a position that is almost exclusively a carboxylic acid in clinically used agents in the class. Representatives of the series kill M. tuberculosis within macrophages without toxicity to the macrophages or other mammalian cells
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