771 research outputs found
Physical and geometric constraints explain the labyrinth-like shape of the nasal cavity
The nasal cavity is a vital component of the respiratory system that heats
and humidifies inhaled air in all vertebrates. Despite this common function,
the shapes of nasal cavities vary widely across animals. To understand this
variability, we here connect nasal geometry to its function by theoretically
studying the airflow and the associated scalar exchange that describes heating
and humidification. We find that optimal geometries, which have minimal
resistance for a given exchange efficiency, have a constant gap width between
their side walls, but their overall shape is restricted only by the geometry of
the head. Our theory explains the geometric variations of natural nasal
cavities quantitatively and we hypothesize that the trade-off between high
exchange efficiency and low resistance to airflow is the main driving force
shaping the nasal cavity. Our model further explains why humans, whose nasal
cavities evolved to be smaller than expected for their size, become obligate
oral breathers in aerobically challenging situations.Comment: 7 pages, 4 figure
Untersuchung von Legierungen des Zirkoniums mit Niob und Zinn im Hinblick auf deren Verwendung als HĂĽllmaterial in wassergekĂĽhlten Kernreaktoren. EUR 86.= Examination of zirconium alloys with tin and niobium in terms of their use as a shell material in water-cooled nuclear reactors. EUR 86.
pShuffle: A Plasmid for in vitro Evolution
Multi-gene shuffling is a powerful method used to combine and optimize attributes of various proteins. Here we report on the design and construction of the plasmid “pShuffle” which is suited for a variety of in vitro DNA-recombination techniques. The multiple cloning site (MCS) of pShuffle was designed to allow for the cloning of genes as well as their expression under control of either a lac- or a T7-promoter. As a specific feature, this MCS allows for the fusion of special linker sequences to both ends of cloned genes. After subsequent DNA-recombination steps, these linkers facilitate reamplification of generated gene variants, and thus may be used to construct clone libraries for activity screenings. The suitability of pShuffle for multi-gene shuffling applications was further shown with a set of styrene monooxygenase genes originating from proteo- and actinobacteria
Depth of Field Analysis for Multilayer Automultiscopic Displays
With the re-emergence of stereoscopic displays, through polarized glasses for theatrical presentations and shuttered liquid crystal eyewear in the home, automultiscopic displays have received increased attention. Commercial efforts have predominantly focused on parallax barrier and lenticular architectures applied to LCD panels. Such designs suffer from reduced resolution and brightness. Recently, multilayer LCDs have emerged as an alternative supporting full-resolution imagery with enhanced brightness and depth of field. We present a signal-processing framework for comparing the depth of field for conventional automultiscopic displays and emerging architectures comprising multiple light-attenuating layers. We derive upper bounds for the depths of field, indicating the potential of multilayer configurations to significantly enhance resolution and depth of field, relative to conventional designs.Massachusetts Institute of Technology. Media LaboratoryMIT Camera Culture GroupNational Science Foundation (U.S.) (Grant IIS-1116452)United States. Defense Advanced Research Projects Agency. MOSAIC ProgramUnited States. Defense Advanced Research Projects Agency. SCENICC ProgramAlfred P. Sloan Foundation (Research Fellowship)United States. Defense Advanced Research Projects Agency. (Young Faculty Award
Robust circadian clocks from coupled protein modification and transcription-translation cycles
The cyanobacterium Synechococcus elongatus uses both a protein
phosphorylation cycle and a transcription-translation cycle to generate
circadian rhythms that are highly robust against biochemical noise. We use
stochastic simulations to analyze how these cycles interact to generate stable
rhythms in growing, dividing cells. We find that a protein phosphorylation
cycle by itself is robust when protein turnover is low. For high decay or
dilution rates (and co mpensating synthesis rate), however, the
phosphorylation-based oscillator loses its integrity. Circadian rhythms thus
cannot be generated with a phosphorylation cycle alone when the growth rate,
and consequently the rate of protein dilution, is high enough; in practice, a
purely post-translational clock ceases to function well when the cell doubling
time drops below the 24 hour clock period. At higher growth rates, a
transcription-translation cycle becomes essential for generating robust
circadian rhythms. Interestingly, while a transcription-translation cycle is
necessary to sustain a phosphorylation cycle at high growth rates, a
phosphorylation cycle can dramatically enhance the robustness of a
transcription-translation cycle at lower protein decay or dilution rates. Our
analysis thus predicts that both cycles are required to generate robust
circadian rhythms over the full range of growth conditions.Comment: main text: 7 pages including 5 figures, supplementary information: 13
pages including 9 figure
Frame Theory for Signal Processing in Psychoacoustics
This review chapter aims to strengthen the link between frame theory and
signal processing tasks in psychoacoustics. On the one side, the basic concepts
of frame theory are presented and some proofs are provided to explain those
concepts in some detail. The goal is to reveal to hearing scientists how this
mathematical theory could be relevant for their research. In particular, we
focus on frame theory in a filter bank approach, which is probably the most
relevant view-point for audio signal processing. On the other side, basic
psychoacoustic concepts are presented to stimulate mathematicians to apply
their knowledge in this field
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