12,348 research outputs found
Continuous volumetric imaging via an optical phase-locked ultrasound lens
In vivo imaging at high spatiotemporal resolution is key to the understanding of complex biological systems. We integrated an optical phase-locked ultrasound lens into a two-photon fluorescence microscope and achieved microsecond-scale axial scanning, thus enabling volumetric imaging at tens of hertz. We applied this system to multicolor volumetric imaging of processes sensitive to motion artifacts, including calcium dynamics in behaving mouse brain and transient morphology changes and trafficking of immune cells
Navigation input to level C OFT navigation functional subsystem software requirements (rendezvous onorbit-2)
Navigation software design requirements are presented for the orbital flight test phase of space shuttle. Computer loads for the entire onorbit-2 operation are documented
The measurement of low pay in the UK labour force survey
Consideration of the National Minimum Wage requires estimates of the distribution of hourly pay. The UK Labour Force Survey (LFS) is a key source of such estimates. The approach most frequently adopted by researchers has been to measure hourly earnings from several questions on pay and hours. The Office for National Statistics is now applying a new approach, based on an alternative more direct measurement introduced in March 1999. These two measures do not produce identical values and this paper investigates sources of discrepancies and concludes that the new variable is more accurate. The difficulty with using the new variable is that it is only available on a subset of respondents. An approach is developed in which missing values of the new variable are replaced by imputed values. The assumptions underlying this imputation approach and results of applying it to LFS data are presented. The relation to weighting approaches is also discussed
Observational evidence of the formation of cyanopolyynes in CRL618 through the polimerization of HCN
The abundance ratio of consecutive members of the cyanopolyynes family has
been explored in CRL618 using data acquired in a complete line survey covering
the frequency range 81-356 GHz. The Jup range explored for the different
molecules is the following: 1 to 4 for HCN and HNC, 9 to 39 for HC3N, 31 to 133
for HC5N, and 72 to 85 for HC7N (not detected beyond Jup=85). The lowest
vibrationally excited state of HC7N (nu_15 at 62 cm^-1) has been tentatively
detected. Data analysis has been performed by extending our previous
geometrical and radiative transfer model of the slowly expanding envelope (SEE)
surrounding the compact central continuum source of CRL 618, that was
established from the study of rotational lines in several vibrationally excited
states of HC_3N. The new lines analyzed here require to model the high velocity
wind (HVW) component and the colder circumstellar gas, remnant of the AGB phase
of CRL618. The derived HC3N/HC5N and HC5N/HC7N abundance ratios from this set
of uniformly calibrated lines are between 3 and 6 in the different regions,
similar to standard values in the CSM and ISM, and consistent with previous
estimates obtained from ISO observations and chemical models. However, the
abundance ratios of HC3N, HC5N and HC7N with respect to HCN are at least two
orders of magnitude larger than those typical for AGB C-rich stars, such as
IRC+10216. This fact indicates that, in the short transition toward the
Planetary Nebula phase, HCN is quickly reprocessed into longer cyanopolyyne
chains. A similar behavior was previously found in this object for the
polyacetylenic chains (C(2n)H2).Comment: 8 figures, accepted in ApJ main journa
Advanced turboprop testbed systems study. Volume 1: Testbed program objectives and priorities, drive system and aircraft design studies, evaluation and recommendations and wind tunnel test plans
The establishment of propfan technology readiness was determined and candidate drive systems for propfan application were identified. Candidate testbed aircraft were investigated for testbed aircraft suitability and four aircraft selected as possible propfan testbed vehicles. An evaluation of the four candidates was performed and the Boeing KC-135A and the Gulfstream American Gulfstream II recommended as the most suitable aircraft for test application. Conceptual designs of the two recommended aircraft were performed and cost and schedule data for the entire testbed program were generated. The program total cost was estimated and a wind tunnel program cost and schedule is generated in support of the testbed program
Rural and urban differences in stage at diagnosis of colorectal and lung cancers
There is evidence that patients living in outlying areas have poorer survival from cancer. This study set out to investigate whether they have more advanced disease at diagnosis. Case notes of 1323 patients in north and northeast Scotland who were diagnosed with lung or colorectal cancer in 1995 or 1996 were reviewed. Of patients with lung cancer, 42% (69/164) living 58 km or more from a cancer centre had disseminated disease at diagnosis compared to 33% (71/215) living within 5 km. For colorectal cancer the respective figures were 24% (38/161) and 16% (31/193). For both cancers combined, the adjusted odds ratio for disseminated disease at diagnosis in furthest group compared to the closest group was 1.59 (P = 0.037). Of 198 patients with non-small-cell lung cancer in the closest group, 56 (28%) had limited disease (stage I or II) at diagnosis compared to 23 of 165 (14%) of the furthest group (P = 0.002). The respective figures for Dukes A and B colorectal cancer were 101 of 196 (52%) and 67 of 172 (39%) (P = 0.025). These findings suggest that patients who live remote from cities and the associated cancer centres have poorer chances of survival from lung or colorectal cancer because of more advanced disease at diagnosis. This needs to be taken into account when planning investigation and treatment services. © 2001 Cancer Research Campaign http://www.bjcancer.co
The Initial Configuration of Young Stellar Clusters: A K-band Number Counts Analysis of the Surface Density of Stars
We present an analysis of K-band stellar distributions for the young stellar
clusters GGD 12-15, IRAS 20050+2720, and NGC 7129. We find that the two deeply
embedded clusters, GGD 12-15 and IRAS 20050+2720, are not azimuthally symmetric
and show a high degree of structure which traces filamentary structure observed
in 850 micron emission maps. In contrast, the NGC 7129 cluster is circularly
symmetric, less dense, and anti-correlated to 850 micron emission, suggesting
recent gas expulsion and dynamical expansion have occured. We estimate stellar
volume densities from nearest neighbor distances, and discuss the impact of
these densities on the evolution of circumstellar disks and protostellar
envelopes in these regions.Comment: 44 pages, 26 figures, Accepted to ApJ. Changes include extinction
mapping, Monte Carlo field star modeling, and Nyquist sampled azimuthal
stellar distributions. A version with full resolution figures is available at
http://astro.pas.rochester.edu/~rguter/preprints/gutermuth_sd.tar.g
Statistical mechanics of temporal association in neural networks with transmission delays
We study the representation of static patterns and temporal sequences in neural networks with signal delays and a stochastic parallel dynamics. For a wide class of delay distributions, the asymptotic network behavior can be described by a generalized Gibbs distribution, generated by a novel Lyapunov functional for the determination dynamics. We extend techniques of equilibrium statistical mechanics so as to deal with time-dependent phenomena, derive analytic results for both retrieval quality and storage capacity, and compare them with numerical simulations
Magnetohydrodynamics of Cloud Collisions in a Multi-phase Interstellar Medium
We extend previous studies of the physics of interstellar cloud collisions by
beginning investigation of the role of magnetic fields through 2D
magnetohydrodynamic (MHD) numerical simulations. We study head-on collisions
between equal mass, mildly supersonic diffuse clouds. We include a moderate
magnetic field and two limiting field geometries, with the field lines parallel
(aligned) and perpendicular (transverse) to the colliding cloud motion. We
explore both adiabatic and radiative cases, as well as symmetric and asymmetric
ones. We also compute collisions between clouds evolved through prior motion in
the intercloud medium and compare with unevolved cases.
We find that: In the (i) aligned case, adiabatic collisions, like their HD
counterparts, are very disruptive, independent of the cloud symmetry. However,
when radiative processes are taken into account, partial coalescence takes
place even in the asymmetric case, unlike the HD calculations. In the (ii)
transverse case, collisions between initially adjacent unevolved clouds are
almost unaffected by magnetic fields. However, the interaction with the
magnetized intercloud gas during the pre-collision evolution produces a region
of very high magnetic energy in front of the cloud. In collisions between
evolved clouds with transverse field geometry, this region acts like a
``bumper'', preventing direct contact between the clouds, and eventually
reverses their motion. The ``elasticity'', defined as the ratio of the final to
the initial kinetic energy of each cloud, is about 0.5-0.6 in the cases we
considered. This behavior is found both in adiabatic and radiative cases.Comment: 40 pages in AAS LaTeX v4.0, 13 figures (in degraded jpeg format).
Full resolution images as well as mpeg animations are available at
http://www.msi.umn.edu:80/Projects/twj/mhd-cc/ . Accepted for publication in
The Astrophysical Journa
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