11,505 research outputs found
Ingestive behaviour and physiology of the medicinal leech
Ingestion lasts 25 min in Hirudo medicinalis and is characterized by pharyngeal peristalsis which fills the crop. This peristalsis has an initial rate of 2.4 Hz which decays smoothly to 1.2 Hz at termination of ingestion. During ingestion, the leech body wall undergoes peristalsis which appears to aid in filling the crop diverticula. Body peristalsis begins at a rate of 10 min^(-1) and decreases linearly to 2 min^(-1) at termination. The body also undergoes dorsoventral flexions when blood flow is occluded. Blood meal size increases slightly with leech size: 8.4 g for 1-g leeches and 9.7 g for 2-g leeches. However, relative meal size decreases markedly with increasing animal size; from 8.15 times body mass for 1-g to 4.80 times for 2-g leeches. When intact leeches were exposed to micromolar concentrations of serotonin, there was an increase in the rate of pharyngeal peristalsis and the size of the blood meals. Leeches excrete the plasma from their ingested blood meals. Excretion is activated during ingestion, which increases feeding efficiency by increasing the proportion of blood cells in the ingestate. Excretion continues for 4–6 days following ingestion, removing all the remaining plasma from the ingestate. Leech ingestion comprises stereotyped muscular movements, secretion of saliva and excretion of plasma. A strikingly similar feeding physiology is seen in the blood-sucking insect Rhodnius, and we suggest that efficient sanguivory may require the convergent evolution of similar ingestive mechanisms
Near-IR imaging of moderate redshift galaxy clusters
We have obtained near-IR imaging of 3 moderate-z clusters on the 1.3 m at KPNO with SQIID, a new camera offering wide-field (5.5 arcmin) simultaneous JHK band imaging. Our photometry on a sample of approximately 100 likely member galaxies in one of the clusters, Abell 370 at z = 0.37, shows that we can obtain magnitudes good to 20 percent down to K = 18, considerably below the estimated K* = 16.5 at this redshift. These data indicate that there are no systematic problems in obtaining photometry at faint levels with SQIID. With the development of larger arrays, the field is open to progress. The resulting J, H, and K data for three clusters are combined with previously obtained multiband optical photometry. We present an investigation of the spectral properties and evolution of the dominant cold stellar populations by comparing optical-to-IR colors and color-magnitude diagrams to predictions from population synthesis models and galaxy spectral evolution codes
Rectenna system design
The function of the rectenna in the solar power satellite system is described and the basic design choices based on the desired microwave field concentration and ground clearance requirements are given. One important area of concern, from the EMI point of view, harmonic reradiation and scattering from the rectenna is also designed. An optimization of a rectenna system design to minimize costs was performed. The rectenna cost breakdown for a 56 w installation is given as an example
The lack of intense Lyman~alpha in ultradeep spectra of z=7 candidates in GOODS-S: imprint of reionization?
We present ultradeep optical spectroscopy obtained with FORS2 on VLT of seven
Lyman-break galaxy (LBG) candidates at z>6.5 selected in the GOODS-S field from
Hawk-I/VLT and WFC3/HST imaging. For one galaxy we detect a low significance
emission line (S/N< 7), located at 9691.5 +/- 0.5A and with flux 3.4 x
10^(-18)erg/cm^2/s. If identified as Lyman alpha, it places the LBG at redshift
z=6.972+/- 0.002, with a rest-frame equivalent width EW}=13A. Using Monte Carlo
simulations and conservative EW distribution functions at 2<z<6, we estimate
that the probability of observing no galaxies in our data with S/N>10 is ~ 2%,
and that of observing only one galaxy out of seven with S/N=5 is ~4%, but these
can be as small as ~1E-3, depending on the details of the EW distribution. We
conclude that either a significant fraction of the candidates is not at high
redshift or that some physical mechanism quenches the Lyman alpha emission
emerging from the galaxies at z>6.5, abruptly reversing the trend of the
increasing fraction of strong emitters with increasing redshift observed up to
z~ 6.5. We discuss the possibility that an increasingly neutral intergalactic
medium is responsible for such quenching.Comment: Submitted to ApJL: re-submitted version after modification responding
to the referee's repor
Sixth Sense Transport : Challenges in Supporting Flexible Time Travel
In this paper, we consider the challenges associated with providing a mobile computing system that helps users enjoy a
more flexible relationship between time and travel. Current
travel plans, especially in Western cultures, are dominated
by a strict notion of time. The need to conform to schedules
leads to increased pressures for travellers and inefficiencies when these schedules cannot be met. We are interested in exploring the extent to which mobile computing can be used to help travellers relax these schedules and adopt a more opportunistic approach to travel – potentially helping to reduce the environmental, financial and societal costs of modern travel
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