1,892 research outputs found
Capacity Bounds for One-Bit MIMO Gaussian Channels with Analog Combining
The use of 1-bit analog-to-digital converters (ADCs) is seen as a promising
approach to significantly reduce the power consumption and hardware cost of
multiple-input multiple-output (MIMO) receivers. However, the nonlinear
distortion due to 1-bit quantization fundamentally changes the optimal
communication strategy and also imposes a capacity penalty to the system. In
this paper, the capacity of a Gaussian MIMO channel in which the antenna
outputs are processed by an analog linear combiner and then quantized by a set
of zero threshold ADCs is studied. A new capacity upper bound for the zero
threshold case is established that is tighter than the bounds available in the
literature. In addition, we propose an achievability scheme which configures
the analog combiner to create parallel Gaussian channels with phase
quantization at the output. Under this class of analog combiners, an algorithm
is presented that identifies the analog combiner and input distribution that
maximize the achievable rate. Numerical results are provided showing that the
rate of the achievability scheme is tight in the low signal-to-noise ratio
(SNR) regime. Finally, a new 1-bit MIMO receiver architecture which employs
analog temporal and spatial processing is proposed. The proposed receiver
attains the capacity in the high SNR regime.Comment: 30 pages, 9 figures, Submitted to IEEE Transactions on Communication
Nanomechanical and thermophoretic analyses of the nucleotide-dependent interactions between the AAA+ subunits of magnesium chelatase
In chlorophyll biosynthesis, the magnesium
chelatase enzyme complex catalyzes the insertion of a Mg2+
ion into protoporphyrin IX. Prior to this event, two of the three
subunits, the AAA+ proteins ChlI and ChlD, form a ChlID−
MgATP complex. We used microscale thermophoresis to
directly determine dissociation constants for the I-D subunits
from Synechocystis, and to show that the formation of a ChlID−
MgADP complex, mediated by the arginine finger and the
sensor II domain on ChlD, is necessary for the assembly of the
catalytically active ChlHID−MgATP complex. The N-terminal
AAA+ domain of ChlD is essential for complex formation, but
some stability is preserved in the absence of the C-terminal
integrin domain of ChlD, particularly if the intervening polyproline linker region is retained. Single molecule force spectroscopy
(SMFS) was used to determine the factors that stabilize formation of the ChlID−MgADP complex at the single molecule level;
ChlD was attached to an atomic force microscope (AFM) probe in two different orientations, and the ChlI subunits were
tethered to a silica surface; the probability of subunits interacting more than doubled in the presence of MgADP, and we show
that the N-terminal AAA+ domain of ChlD mediates this process, in agreement with the microscale thermophoresis data. Analysis
of the unbinding data revealed a most probable interaction force of around 109 pN for formation of single ChlID−MgADP
complexes. These experiments provide a quantitative basis for understanding the assembly and function of the Mg chelatase
complex
Neutral B-meson mixing from three-flavor lattice QCD: Determination of the SU(3)-breaking ratio \xi
We study SU(3)-breaking effects in the neutral B_d-\bar B_d and B_s-\bar B_s
systems with unquenched N_f=2+1 lattice QCD. We calculate the relevant matrix
elements on the MILC collaboration's gauge configurations with asqtad-improved
staggered sea quarks. For the valence light-quarks (u, d, and s) we use the
asqtad action, while for b quarks we use the Fermilab action. We obtain
\xi=f_{B_s}\sqrt{B_{B_s}}/f_{B_d}\sqrt{B_{B_d}}=1.268+-0.063. We also present
results for the ratio of bag parameters B_{B_s}/B_{B_d} and the ratio of CKM
matrix elements |V_{td}|/|V_{ts}|. Although we focus on the calculation of \xi,
the strategy and techniques described here will be employed in future extended
studies of the B mixing parameters \Delta M_{d,s} and \Delta\Gamma_{d,s} in the
Standard Model and beyond.Comment: 36 pages, 7 figure
Simple, Direct Routes to Polymer Brush Traps and Nanostructures for Studies of Diffusional Transport in Supported Lipid Bilayers
Patterned poly(oligo ethylene glycol) methyl ether methacrylate (POEGMEMA) brush structures may be formed by using a combination of atom-transfer radical polymerization (ATRP) and UV photopatterning. UV photolysis is used to selectively dechlorinate films of 4-(chloromethyl)phenyltrichlorosilane (CMPTS) adsorbed on silica surfaces, by exposure either through a mask or using a two-beam interferometer. Exposure through a mask yields patterns of carboxylic acid-terminated adsorbates. POEGMEMA may be grown from intact Cl initiators that were masked during exposure. Corrals, traps, and other structures formed in this way enable the patterning of proteins, vesicles, and, following vesicle rupture, supported lipid bilayers (SLBs). Bilayers adsorbed on the carboxylic acid-terminated surfaces formed by C–Cl bond photolysis in CMPTS exhibit high mobility. SLBs do not form on POEGMEMA. Using traps consisting of carboxylic acid-functionalized regions enclosed by POEGMEMA structures, electrophoresis may be observed in lipid bilayers containing a small amount of a fluorescent dye. Segregation of dye at one end of the traps was measured by fluorescence microscopy. The increase in the fluorescence intensity was found to be proportional to the trap length, while the time taken to reach the maximum value was inversely proportional to the trap length, indicating uniform, rapid diffusion in all of the traps. Nanostructured materials were formed using interferometric lithography. Channels were defined by exposure of CMPTS films to maxima in the interferogram, and POEGMEMA walls were formed by ATRP. As for the micrometer-scale patterns, bilayers did not form on the POEGMEMA structures, and high lipid mobilities were measured in the polymer-free regions of the channels
The use of high aspect ratio photoresist (SU-8) for super-hydrophobic pattern prototyping
In this work we present a reliable technique for the production of large areas of high aspect-ratio patterns and describe their use as model super-hydrophobic systems. The high thickness and straight sidewalls possible with SU-8 were used to generate dense patterns of small pillars. These photoresist patterns could be used directly, without the need for micromoulding. A method is given allowing resist thickness to be varied over a wide range and a bottom antireflective layer was used to simplify patterning on reflective substrates. This patterning technique allows rapid testing of wetting theories, as pattern size and depth can be varied simply and samples can be produced in sufficient numbers for laboratory use. We show how the static contact angle of water varies with pattern height for one sample-pattern and how static and dynamic contact angles vary with dimension using high aspect-ratio patterns
Would raising the total cholesterol diagnostic cut-off from 7.5 mmol/L to 9.3 mmol/L improve detection rate of patients with monogenic familial hypercholesterolaemia?
A previous report suggested that 88% of individuals in the general population with total cholesterol (TC)>9.3mmol/L have familial hypercholesterolaemia (FH). We tested this hypothesis in a cohort of 4896 UK civil servants, mean (SD) age 44 (±6) years, using next generation sequencing to achieve a comprehensive genetic diagnosis. 25 (0.5%) participants (mean age 49.2 years) had baseline TC>9.3mmol/L, and overall we found an FH-causing mutation in the LDLR gene in seven (28%) subjects. The detection rate increased to 39% by excluding eight participants with triglyceride levels over 2.3mmol/L, and reached 75% in those with TC>10.4mmol/L. By extrapolation, the detection rate would be ~25% by including all participants with TC>8.6mmol/L (2.5 standard deviations from the mean). Based on the 1/500 FH frequency, 30% of all FH-cases in this cohort would be missed using the 9.3mmol/L cut-off. Given that an overall detection rate of 25% is considered economically acceptable, these data suggest that a diagnostic TC cut-off of 8.6mmol/L, rather than 9.3mmol/L would be clinically useful for FH in the general population
Evaluation of the impact of a school gardening intervention on children's fruit and vegetable intake: a randomised controlled trial.
Background: Current academic literature suggests that school gardening programmes can provide an interactive environment with the potential to change children’s fruit and vegetable intake. This is the first cluster randomised controlled trial (RCT) designed to evaluate whether a school gardening programme can have an effect on children’s fruit and vegetable intake.
Methods: The trial included children from 23 schools; these schools were randomised into two groups, one to receive the Royal Horticultural Society (RHS)-led intervention and the other to receive the less involved Teacher-led intervention. A 24-hour food diary (CADET) was used to collect baseline and follow-up dietary intake 18 months apart. Questionnaires were also administered to evaluate the intervention implementation.
Results: A total of 641 children completed the trial with a mean age of 8.1 years (95% CI: 8.0, 8.4). The unadjusted results from multilevel regression analysis revealed that for combined daily fruit and vegetable intake the Teacher-led group had a higher daily mean change of 8 g (95% CI: −19, 36) compared to the RHS-led group -32 g (95% CI: −60, −3). However, after adjusting for possible confounders this difference was not significant (intervention effect: −40 g, 95% CI: −88, 1; p = 0.06). The adjusted analysis of process measures identified that if schools improved their gardening score by 3 levels (a measure of school gardening involvement - the scale has 6 levels from 0 ‘no garden’ to 5 ‘community involvement’), irrespective of group allocation, children had, on average, a daily increase of 81 g of fruit and vegetable intake (95% CI: 0, 163; p = 0.05) compared to schools that had no change in gardening score.
Conclusions: This study is the first cluster randomised controlled trial designed to evaluate a school gardening intervention. The results have found very little evidence to support the claims that school gardening alone can improve children’s daily fruit and vegetable intake. However, when a gardening intervention is implemented at a high level within the school it may improve children’s daily fruit and vegetable intake by a portion. Improving children’s fruit and vegetable intake remains a challenging task
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