3,822 research outputs found
Is the Federal Home Loan Bank system good for banks? a look at evidence on membership, advances and risk
Since the early 1990s, commercial banks have turned to Federal Home Loan Bank (FHLBank) advances to plug the gap between loan and deposit growth. Is this trend worrisome? On the one hand, advances implicitly encourage risk by insulating borrowers from market discipline. On the other, advances give borrowers greater flexibility to managing interest rate and liquidity risk. And access to FHLBank funding encourages members to reshape their balance sheets in ways that could lower credit risk. Using quarterly financial and supervisory data for banks from 1992 to 2000, we assess the effect of FHLBank membership and advances on risk. The evidence suggests liquidity and leverage risks rose modestly, but interest-rate risk declined somewhat. Credit risk and overall failure risk were largely unaffected. Although the evidence suggest FHLBank membership and advances have had, at best, only a modest impact on bank risk, we caution that the 1990s constitute one observation and that moral hazard could be pronounced if leverage ratios revert to historical norms.Government-sponsored enterprises ; Federal home loan banks ; Bank liquidity
Scalable, Time-Responsive, Digital, Energy-Efficient Molecular Circuits using DNA Strand Displacement
We propose a novel theoretical biomolecular design to implement any Boolean
circuit using the mechanism of DNA strand displacement. The design is scalable:
all species of DNA strands can in principle be mixed and prepared in a single
test tube, rather than requiring separate purification of each species, which
is a barrier to large-scale synthesis. The design is time-responsive: the
concentration of output species changes in response to the concentration of
input species, so that time-varying inputs may be continuously processed. The
design is digital: Boolean values of wires in the circuit are represented as
high or low concentrations of certain species, and we show how to construct a
single-input, single-output signal restoration gate that amplifies the
difference between high and low, which can be distributed to each wire in the
circuit to overcome signal degradation. This means we can achieve a digital
abstraction of the analog values of concentrations. Finally, the design is
energy-efficient: if input species are specified ideally (meaning absolutely 0
concentration of unwanted species), then output species converge to their ideal
concentrations at steady-state, and the system at steady-state is in (dynamic)
equilibrium, meaning that no energy is consumed by irreversible reactions until
the input again changes.
Drawbacks of our design include the following. If input is provided
non-ideally (small positive concentration of unwanted species), then energy
must be continually expended to maintain correct output concentrations even at
steady-state. In addition, our fuel species - those species that are
permanently consumed in irreversible reactions - are not "generic"; each gate
in the circuit is powered by its own specific type of fuel species. Hence
different circuits must be powered by different types of fuel. Finally, we
require input to be given according to the dual-rail convention, so that an
input of 0 is specified not only by the absence of a certain species, but by
the presence of another. That is, we do not construct a "true NOT gate" that
sets its output to high concentration if and only if its input's concentration
is low. It remains an open problem to design scalable, time-responsive,
digital, energy-efficient molecular circuits that additionally solve one of
these problems, or to prove that some subset of their resolutions are mutually
incompatible.Comment: version 2: the paper itself is unchanged from version 1, but the
arXiv software stripped some asterisk characters out of the abstract whose
purpose was to highlight words. These characters have been replaced with
underscores in version 2. The arXiv software also removed the second
paragraph of the abstract, which has been (attempted to be) re-inserted.
Also, although the secondary subject is "Soft Condensed Matter", this
classification was chosen by the arXiv moderators after submission, not
chosen by the authors. The authors consider this submission to be a
theoretical computer science paper
Multiple-Resampling Receiver Design for OFDM Over Doppler-Distorted Underwater Acoustic Channels
Cataloged from PDF version of article.In this paper, we focus on orthogonal frequency-divisionmultiplexing
(OFDM) receiver designs for underwater acoustic
(UWA) channels with user- and/or path-specific Doppler scaling
distortions. The scenario is motivated by the cooperative communications
framework, where distributed transmitter/receiver
pairs may experience significantly different Doppler distortions, as
well as by the single-user scenarios, where distinct Doppler scaling
factors may exist among different propagation paths. The conventional
approach of front–end resampling that corrects for common
Doppler scalingmay not be appropriatein such scenarios, rendering
a post-fast-Fourier-transform (FFT) signal that is contaminated by
user- and/or path-specific intercarrier interference. To counteract
this problem, we propose a family of front–end receiver structures
thatutilizemultiple-resampling (MR)branches,eachmatched to the
Doppler scaling factor of a particular user and/or path. Following
resampling, FFT modules transform the Doppler-compensated
signals into the frequency domain for further processing through
linear or nonlinear detection schemes. As part of the overall receiver
structure, a gradient–descent approachis also proposed to refine the
channel estimates obtained by standard sparse channel estimators.
The effectiveness and robustness of the proposed receivers are
demonstrated via simulations, as well as emulations based on real
data collected during the 2010 Mobile Acoustic Communications
Experiment (MACE10, Martha’s Vineyard, MA) and the 2008
Kauai Acomms MURI (KAM08, Kauai, HI) experiment
Effect of reinforcement on mechanical characteristics of A356 alloy nanocomposites
© Published under licence by IOP Publishing Ltd. Nanocomposites with aluminum base reinforced with nanoparticles, have wide application in many industries, for example, aerospace, marine, automobile, due to its lightweight, high tensile strength and high wear resistance, etc. The study of the microstructure, mechanical and tribological properties of the nanocomposite is very important in order to reliably and optimally carry out the design of new materials. In this study for the mechanical characterization of the A356 composites with a ceramic particle reinforcements nanoindentation was performed. Nanoindentaion is largely used for the analysis of mechanical properties. The samples of the nanocomposites were developed using 0, 0.2, 0.3 and 0.5 wt.% SiC, with an average size of particles of about 50 nm, produced by a compocasting process with pre-processing mechanical alloying. Nanoindentation was carried out based on Berkovich's test method with the indenter in shape of three sided diamond pyramid. The nanocomposite testing showed that the nanocomposites containing 0.5 wt.% of the reinforcement have slightly higher tensile strength and a lower value of the elastic modulus compared to the aluminum alloy base
Catch-up growth in children with chronic kidney disease started on enteral feeding after 2 years of age
BACKGROUND: Enteral feeding by tube in chronic kidney disease (CKD) before 2 years of age improves growth. Whether it is effective after this age is unknown. We assessed whether height and weight SDS changed after tube feeding was started in children with CKD above 2 years of age. METHODS: Retrospective study of pre-transplant, pre-pubertal children (< 11 years) with CKD stages 2–5 started on nasogastric tube or gastrostomy feeds for the first time after age 2 years. Children were identified by searching dietetic records and the renal database. Children on growth hormone were excluded. Height, weight, and BMI were documented 1 year prior to and at the start of tube feeds, and after 1 and 2 years. Data collection ceased at transplantation. RESULTS: Fifty children (25 male) were included. The median (range) age at start of tube feeds was 5.6 (2.1–10.9) years. Sixteen children were dialysed (1 haemodialysis, 15 peritoneal dialysis); 34 predialysis patients had a median (range) eGFR of 22 (6–88) ml/min/1.73 m2. Overall height SDS (Ht SDS) improved from − 2.39 to − 2.27 at 1 year and − 2.18 after 2 years (p = 0.02). BMI SDS improved from − 0.72 to 0.23 after 1 year and was 0.09 after 2 years of enteral feeding (p < 0.0001). Height SDS improved more in children aged 2–6 years (− 2.13 to − 1.68, p = 0.03) and in children not on dialysis (− 2.33 to − 1.99, p = 0.002). CONCLUSIONS: Enteral tube feeding commenced after 2 years of age in prepubertal children with CKD improves height and weight SDS, with stability of BMI during the second year. Younger children and those not on dialysis had the greatest benefit
Adaptive OFDM Modulation for Underwater Acoustic Communications: Design Considerations and Experimental Results
Cataloged from PDF version of article.In this paper, we explore design aspects of adaptive modulation based on orthogonal frequency-division multiplexing (OFDM) for underwater acoustic (UWA) communications, and study its performance using real-time at-sea experiments. Our design criterion is to maximize the system throughput under a target average bit error rate (BER). We consider two different schemes based on the level of adaptivity: in the first scheme, only the modulation levels are adjusted while the power is allocated uniformly across the subcarriers, whereas in the second scheme, both the modulation levels and the power are adjusted adaptively. For both schemes we linearly predict the channel one travel time ahead so as to improve the performance in the presence of a long propagation delay. The system design assumes a feedback link from the receiver that is exploited in two forms: one that conveys the modulation alphabet and quantized power levels to be used for each subcarrier, and the other that conveys a quantized estimate of the sparse channel impulse response. The second approach is shown to be advantageous, as it requires significantly fewer feedback bits for the same system throughput. The effectiveness of the proposed adaptive schemes is demonstrated using computer simulations, real channel measurements recorded in shallow water off the western coast of Kauai, HI, USA, in June 2008, and real-time at-sea experiments conducted at the same location in July 2011. We note that this is the first paper that presents adaptive modulation results for UWA links with real-time at-sea experiments. © 2013 IEEE
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