911 research outputs found
Reversible electrowetting and trapping of charge: model and experiments
We derive a model for voltage-induced wetting, so-called electrowetting, from
the principle of virtual displacement. Our model includes the possibility that
charge is trapped in or on the wetted surface. Experimentally, we show
reversible electrowetting for an aqueous droplet on an insulating layer of 10
micrometer thickness. The insulator is coated with a highly fluorinated layer
impregnated with oil, providing a contact-angle hysteresis lower than 2
degrees. Analyzing the data with our model, we find that until a threshold
voltage of 240 V, the induced charge remains in the liquid and is not trapped.
For potentials beyond the threshold, the wetting force and the contact angle
saturate, in line with the occurrence of trapping of charge in or on the
insulating layer. The data are independent of the polarity of the applied
electric field, and of the ion type and molarity. We suggest possible
microscopic origins for charge trapping.Comment: 13 pages & 5 figures; the paper has been accepted for publication in
Langmui
From gas to galaxies
The unsurpassed sensitivity and resolution of the Square Kilometer Array
(SKA) will make it possible for the first time to probe the continuum emission
of normal star forming galaxies out to the edges of the universe. This opens
the possibility for routinely using the radio continuum emission from galaxies
for cosmological research as it offers an independent probe of the evolution of
the star formation density in the universe. In addition it offers the
possibility to detect the first star forming objects and massive black holes.
In deep surveys SKA will be able to detect HI in emission out to redshifts of
and hence be able to trace the conversion of gas into stars
over an era where considerable evolution is taking place. Such surveys will be
able to uniquely determine the respective importance of merging and accreting
gas flows for galaxy formation over this redshift range (i.e. out to when the
universe was only one third its present age). It is obvious that only SKA will
able to see literally where and how gas is turned into stars.
These and other aspects of SKA imaging of galaxies will be discussed.Comment: To be published in New Astronomy Reviews, Elsevier, Amsterdam as part
of "Science with the Square Kilometre Array", eds. C. Carilli and S.
Rawlings. 18 pages + 13 figures; high resolution version and other chapters
of "Science with the Square Kilometre Array" available at
http://www.skatelescope.org/pages/science_gen.ht
Electrodynamics of superconductors
An alternate set of equations to describe the electrodynamics of
superconductors at a macroscopic level is proposed. These equations resemble
equations originally proposed by the London brothers but later discarded by
them. Unlike the conventional London equations the alternate equations are
relativistically covariant, and they can be understood as arising from the
'rigidity' of the superfluid wave function in a relativistically covariant
microscopic theory. They predict that an internal 'spontaneous' electric field
exists in superconductors, and that externally applied electric fields, both
longitudinal and transverse, are screened over a London penetration length, as
magnetic fields are. The associated longitudinal dielectric function predicts a
much steeper plasmon dispersion relation than the conventional theory, and a
blue shift of the minimum plasmon frequency for small samples. It is argued
that the conventional London equations lead to difficulties that are removed in
the present theory, and that the proposed equations do not contradict any known
experimental facts. Experimental tests are discussed.Comment: Small changes following referee's and editor's comments; to be
published in Phys.Rev.
Magnitude and Origin of CO2 Evasion From High-Latitude Lakes
Lakes evade significant amounts of carbon dioxide (CO2) to the atmosphere; yet the magnitude and origin of the evasion are still poorly constrained. We quantified annual CO2 evasion and its origin (in-lake net ecosystem production vs. lateral inputs from terrestrial ecosystems) in 14 high-latitude lakes through high-frequency estimates of open water CO2 flux and ecosystem metabolism and inorganic carbon mass-balance before and after ice breakup. Annual CO2 evasion ranged from 1 to 25 g C m(-2) yr(-1) of which an average of 57% was evaded over a short period at ice-breakup. Annual internal CO2 production ranged from -6 to 21 g C m(-2) yr(-1), of which at least half was produced over winter. The contribution of internal versus external source contribution to annual CO2 evasion varied between lakes, ranging from fully internal to fully external with most lakes having over 75% of the evasion sustained through a single source. Overall, the study stresses the large variability in magnitude and control of CO2 evasion and suggests that environmental change impacts on CO2 evasion from high-latitude lakes are not uniform
WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192
A pilot study with the powerful new backend of the Westerbork Synthesis Radio
Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen
emission from 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4
Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and
the large scale structure in which they are embedded. In Abell 963, a
dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction,
most of the gas-rich galaxies are located between 1 and 3 Mpc in projection,
northeast from the cluster core. Their velocities are slightly redshifted with
respect to the cluster, and this is likely a background group. None of the blue
galaxies in the core of Abell 963 are detected in HI, although they have
similar colors and luminosities as the HI detected galaxies in the cluster
outskirts and field. Abell 2192 is less massive and more diffuse. Here, the
gas-rich galaxies are more uniformly distributed. The detected HI masses range
from 5x10^9 to 4x10^10 Msun. Some galaxies are spatially resolved, providing
rudimentary rotation curves useful for detailed kinematic studies of galaxies
in various environments. This is a pilot for ultra-deep integrations down to HI
masses of 8x10^8 Msun, providing a complete survey of the gas content of
galaxies at z=0.2, probing environments ranging from cluster cores to voids.Comment: 5 pages, 6 figures + 1 Plate, accepted for publication in the
Astrophysical Journal Letter
Geometry-dependent electrostatics near contact lines
Long-ranged electrostatic interactions in electrolytes modify their contact
angles on charged substrates in a scale and geometry dependent manner. For
angles measured at scales smaller than the typical Debye screening length, the
wetting geometry near the contact line must be explicitly considered. Using
variational and asymptotic methods, we derive new transcendental equations for
the contact angle that depend on the electrostatic potential only at the three
phase contact line. Analytic expressions are found in certain limits and
compared with predictions for contact angles measured with lower resolution. An
estimate for electrostatic contributions to {\it line} tension is also given.Comment: 3 .eps figures, 5p
Identification and in vitro reconstitution of lysosomal neuraminidase from human placenta
Lysosomal neuraminidase from human placenta has been obtained in its active form by association of an inactive neuraminidase polypeptide with β-galactosidase and the protective protein. Using a specific antiserum, we have now identified a 66-kDa protein as the inactive neuraminidase polypeptide. It is specifically recognized on immunoblots only in its nonreduced state, and it coprecipitates with neuraminidase activity. The 66-kDa polypeptide is substantially glycosylated (38-kDa protein core with 7-14 N-linked oligosaccharide chains), a feature characteristic of lysosomal integral membrane proteins. Specific removal of the 66-kDa neuraminidase polypeptide from glycoprotein preparations prevents the generation of neuraminidase activity. Removal of β-galactosidase or destruction of the protective protein also hinders the formation of active neuraminidase. Reconstitution of neuraminidase activity is observed after mixing glycoprotein preparations, depleted in different components of the β-galactosidase-neuraminidase-protective protein complex, indicating that all three components of the complex are required for neuraminidase activity. Association of the neuraminidase polypeptide and the protective protein generates unstables neuraminidase activity, whereas association with β-galactosidase is required for stability.</p
Identification and in vitro reconstitution of lysosomal neuraminidase from human placenta
Lysosomal neuraminidase from human placenta has been obtained in its active form by association of an inactive neuraminidase polypeptide with β-galactosidase and the protective protein. Using a specific antiserum, we have now identified a 66-kDa protein as the inactive neuraminidase polypeptide. It is specifically recognized on immunoblots only in its nonreduced state, and it coprecipitates with neuraminidase activity. The 66-kDa polypeptide is substantially glycosylated (38-kDa protein core with 7-14 N-linked oligosaccharide chains), a feature characteristic of lysosomal integral membrane proteins. Specific removal of the 66-kDa neuraminidase polypeptide from glycoprotein preparations prevents the generation of neuraminidase activity. Removal of β-galactosidase or destruction of the protective protein also hinders the formation of active neuraminidase. Reconstitution of neuraminidase activity is observed after mixing glycoprotein preparations, depleted in different components of the β-galactosidase-neuraminidase-protective protein complex, indicating that all three components of the complex are required for neuraminidase activity. Association of the neuraminidase polypeptide and the protective protein generates unstables neuraminidase activity, whereas association with β-galactosidase is required for stability.</p
Incidence and survival rate of women with cervical cancer in the Greater Amsterdam area
To evaluate the effect of population-based cervical cancer screening on the occurrence of cervical cancer in The Netherlands, we investigated the incidence and survival of cervical cancer registered by a cancer registry in the Greater Amsterdam area. The incidence rate of squamous cell carcinoma decreased significantly from 9.2/100,000 women in 1988 to 5.9/100,000 in 2000 (P<0.001). The incidence rate of adenocarcinomas remained stable. After adjustment for age, stage and lymph node involvement, the relative risk of death was 1.6 times higher for patients with adenocarcinomas than for patients with squamous cell carcinoma (95% CI 1.2-2.1). The decreased survival was related to histological type, as the effect remained significant after correction for confounding factors. Over time, the prognosis of women with squamous cell carcinoma improved significantly. No significant change was observed for women diagnosed with adenocarcinoma. These results suggest that the screening programme in The Netherlands as executed in the Greater Amsterdam area is associated with a decreased incidence and increased survival of patients with squamous cell carcinoma, but fails to detect (pre)malignant lesions of adenocarcinoma. Since more than 92% of adenocarcinomas and its precursors contain high-risk HPV, adding HPV testing to cytologic screening might improve the present screening programme in detecting adenocarcinoma and its precursor lesions
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