53 research outputs found
Design of a silicon cochlea system with biologically faithful response
This paper presents the design and simulation results of a silicon cochlea system that has closely similar behavior as the real cochlea. A cochlea filter-bank based on the improved three-stage filter cascade structure is used to model the frequency decomposition function of the basilar membrane; a filter tuning block is designed to model the adaptive response of the cochlea; besides, an asynchronous event-triggered spike codec is employed as the system interface with bank-end spiking neural networks. As shown in the simulation results, the system has biologically faithful frequency response, impulse response, and active adaptation behavior; also the system outputs multiple
band-pass channels of spikes from which the original sound input can be recovered. The proposed silicon cochlea is feasible for analog VLSI implementation so that it not only emulates the way that sounds are preprocessed in human ears but also is able match the compact physical size of a real cochlea
Use of high-intensity data to define large river management units: A case study on the lower Waikato River, New Zealand
The importance of environmental heterogeneity in lotic ecosystems is well recognised in river management, and continues to underpin studies of hierarchical patch dynamics, geomorphology and landscape ecology. We evaluated how physical characteristics and water chemistry measurements at high spatiotemporal resolution define channel units of potential ecological importance along 134 km of the lower Waikato River in North Island, New Zealand. We used multivariate hierarchical clustering to classify river reaches in an a priori unstructured manner based on (i) high-frequency, along-river water quality measurements collected in four seasons and (ii) river channel morphology data resolved from aerial photos for 1-km long reaches. Patterns of channel character were shaped by the depth and lateral complexity of constituent river reaches, while water quality patterns were represented by differences in clarity, chlorophyll fluorescence and specific conductance driven by tributary inflows in the mid-section of the river and tidal cycles in the lower section. Management units defined by physical characteristics or water quality did not necessarily align with boundaries typically reflecting clinal processes (e.g. tidal influence) or geomorphic, network or anthropogenic discontinuities. The results highlight the dynamic spatial and temporal properties of large rivers and the need to define clear objectives when deriving spatial units for management and research. Given that actions and targets for physical channel and water quality management may differ, the spatial extent identified for each of these does not necessarily need to directly coincide, although both should be considered in decision making and experimental design
Biomimetic cochlea filters : from modelling, design to analogue VLSI implementation
This thesis presents a novel biomimetic cochlea filter which closely resembles the biological
cochlea behaviour. The filter is highly feasible for analogue very-large-scale integration
(VLSI) circuits, which leads to a micro-watt-power and millimetre-sized hardware implementation.
By virtue of such features, the presented filter contributes to a solid foundation for future
biologically-inspired audio signal processors.
Unlike existing works, the presented filter is developed by taking direct inspirations from the
physiologically measured results of the biological cochlea. Since the biological cochlea has
prominently different characteristics of frequency response from low to high frequencies, the
biomimetic cochlea filter is built by cascading three sub-filters accordingly: a 2nd-order bandpass
filter for the constant gentle low-frequency response, a 2nd-order tunable low-pass filter
for the variable and selective centre frequency response and a 5th-order elliptic filter for the
ultra-steep roll-off at stop-band. As a proof of concept, a biomimetic cochlea filter bank is built
to process audio signals, which demonstrates the highly discriminative spectral decomposition
and high-resolution time-frequency analysis capabilities similar to the biological cochlea.
The filter has simple representation in the Laplace domain which leads to a convenient analogue
circuit realisation. A floating-active-inductor circuit cell is developed to build the corresponding
RLC ladder for each of the three sub-filters. The circuits are designed based on complementary
metal-oxide-semiconductor (CMOS) transistors for VLSI implementation. Non-ideal factors
of CMOS transistors including parasitics, noise and mismatches are extensively analysed and
consciously considered in the circuit design. An analogue VLSI chip is successfully fabricated
using 0.35μ m CMOS process. The chip measurements demonstrate that the centre frequency
response of the filter has about 20 dB wide gain tuning range and a high quality factor reaching
maximally over 19. The filter has a 20 dB/decade constant gentle low-frequency tail and an
over 300 dB/decade sharp stop-band roll-off slope. The measured results agree with the filter
model expectations and are comparable with the biological cochlea characteristics. Each filter
channel consumes as low as 59.5 ~90μ Wpower and occupies only 0.9 mm2 area. Besides, the
biomimetic cochlea filter chip is characterised from a wide range of angles and the experimental
results cover not only the auditory filter specifications but also the integrated circuit design
considerations.
Furthermore, following the progressive development of the acoustic resonator based on microelectro-
mechanical systems (MEMS) technology, a MEMS-CMOS implementation of the proposed
filter becomes possible in the future. A key challenge for such implementation is the
low sensing capacitance of the MEMS resonator which suffers significantly from sensitivity
degradation due to the parasitic capacitance. A novel MEMS capacitive interface circuit chip
is additionally developed to solve this issue. As shown in the chip results, the interface circuit
is able to cancel the parasitic capacitance and increase the sensitivity of capacitive sensors by
35 dB without consuming any extra power. Besides, the chopper-stabilisation technique is employed
which effectively reduces the circuit flicker noise and offsets. Due to these features, the
interface circuit chip is capable of converting a 7.5 fF capacitance change of a 1-Volt-biased
0.5 pF capacitive sensor pair into a 0.745 V signal-conditioned output while consuming only
165.2μ W power
Psychological determinants of whole-body endurance performance
Background: No literature reviews have systematically identified and evaluated research on the psychological determinants of endurance performance, and sport psychology performance-enhancement guidelines for endurance sports are not founded on a systematic appraisal of endurance-specific research.
Objective: A systematic literature review was conducted to identify practical psychological interventions that improve endurance performance and to identify additional psychological factors that affect endurance performance. Additional objectives were to evaluate the research practices of included studies, to suggest theoretical and applied implications, and to guide future research.
Methods: Electronic databases, forward-citation searches, and manual searches of reference lists were used to locate relevant studies. Peer-reviewed studies were included when they chose an experimental or quasi-experimental research design, a psychological manipulation, endurance performance as the dependent variable, and athletes or physically-active, healthy adults as participants.
Results: Consistent support was found for using imagery, self-talk, and goal setting to improve endurance performance, but it is unclear whether learning multiple psychological skills is more beneficial than learning one psychological skill. The results also demonstrated that mental fatigue undermines endurance performance, and verbal encouragement and head-to-head competition can have a beneficial effect. Interventions that influenced perception of effort consistently affected endurance performance.
Conclusions: Psychological skills training could benefit an endurance athlete. Researchers are encouraged to compare different practical psychological interventions, to examine the effects of these interventions for athletes in competition, and to include a placebo control condition or an alternative control treatment. Researchers are also encouraged to explore additional psychological factors that could have a negative effect on endurance performance. Future research should include psychological mediating variables and moderating variables. Implications for theoretical explanations of endurance performance and evidence-based practice are described
Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans
Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have
fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in
25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16
regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of
correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP,
while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in
Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium
(LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region.
Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant
enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the
refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa,
an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of
PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent
signals within the same regio
An open dataset of Plasmodium falciparum genome variation in 7,000 worldwide samples.
MalariaGEN is a data-sharing network that enables groups around the world to work together on the genomic epidemiology of malaria. Here we describe a new release of curated genome variation data on 7,000 Plasmodium falciparum samples from MalariaGEN partner studies in 28 malaria-endemic countries. High-quality genotype calls on 3 million single nucleotide polymorphisms (SNPs) and short indels were produced using a standardised analysis pipeline. Copy number variants associated with drug resistance and structural variants that cause failure of rapid diagnostic tests were also analysed. Almost all samples showed genetic evidence of resistance to at least one antimalarial drug, and some samples from Southeast Asia carried markers of resistance to six commonly-used drugs. Genes expressed during the mosquito stage of the parasite life-cycle are prominent among loci that show strong geographic differentiation. By continuing to enlarge this open data resource we aim to facilitate research into the evolutionary processes affecting malaria control and to accelerate development of the surveillance toolkit required for malaria elimination
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