3,489 research outputs found
Scaling and trends of hourly precipitation extremes in two different climate zones – Hong Kong and the Netherlands
Hourly precipitation extremes in very long time series from the Hong Kong Observatory and the Netherlands are investigated. Using the 2 m dew point temperature from 4 h before the rainfall event as a measure of near surface absolute humidity, hourly precipitation extremes closely follow a 14% per degree dependency – a scaling twice as large as following from the Clausius-Clapeyron relation. However, for dew point temperatures above 23 °C no significant dependency on humidity was found. Strikingly, in spite of the large difference in climate, results are almost identical in Hong Kong and the Netherlands for the dew point temperature range where both observational sets have sufficient data. Trends in hourly precipitation extremes show substantial increases over the last century for both De Bilt (the Netherlands) and Hong Kong. For De Bilt, not only the long term trend, but also variations in hourly precipitation extremes on an inter-decadal timescale of 30 yr and longer, can be linked very well to the above scaling; there is a very close resemblance between variations in dew point temperature and precipitation intensity with an inferred dependency of hourly precipitation extremes of 10 to 14% per degree. For Hong Kong there is no connection between variations in humidity and those in precipitation intensity in the wet season, May to September. This is consistent with the found zero-dependency of precipitation intensity on humidity for dew points above 23 °C. Yet, outside the wet season humidity changes do appear to explain the positive trend in hourly precipitation extremes, again following a dependency close to twice the Clausius-Clapeyron relation
Decreased expression of the Id3 gene at 1p36.1 in ovarian adenocarcinomas
The molecular events that drive the initiation and progression of ovarian adenocarcinoma are not well defined. We have investigated changes in gene expression in ovarian cancer cell lines compared to an immortalized human ovarian surface epithelial cell line (HOSE) using a cDNA array. We identified 17 genes that were under-expressed and 10 genes that were over-expressed in the cell lines compared to the HOSE cells. One of the genes under-expressed in the ovarian cancer cell lines, Id3, a transcriptional inactivator, was selected for further investigation. Id3 mRNA was expressed at reduced levels in 6 out of 9 ovarian cancer cell lines compared to the HOSE cells while at the protein level, all 7 ovarian cancer cell lines examined expressed the Id3 protein at greatly reduced levels. Expression of Id3 mRNA was also examined in primary ovarian tumours and was found in only 12/38 (32%) cases. A search was conducted for mutations of Id3 in primary ovarian cancers using single stranded conformation polymorphism (SSCP) analysis. Only one nucleotide substitution, present also in the corresponding constitutional DNA, was found in 94 ovarian tumours. Furthermore no association was found between LOH at 1p36 and lack of expression of Id3. These data suggest that Id3 is not the target of LOH at 1p36. © 2001 Cancer Research Campaign http://www.bjcancer.co
N-Body Simulations of Compact Young Clusters near the Galactic Center
We investigate the dynamical evolution of compact young star clusters (CYCs)
near the Galactic center (GC) using Aarseth's Nbody6 codes. The relatively
small number of stars in the cluster (5,000-20,000) makes real-number N-body
simulations for these clusters feasible on current workstations. Using
Fokker-Planck (F-P) models, Kim, Morris, & Lee (1999) have made a survey of
cluster lifetimes for various initial conditions, and have found that clusters
with a mass <~ 2x10^4 Msun evaporate in ~10 Myr. These results were, however,
to be confirmed by N-body simulations because some extreme cluster conditions,
such as strong tidal forces and a large stellar mass range participating in the
dynamical evolution, might violate assumptions made in F-P models. Here we find
that, in most cases, the CYC lifetimes of previous F-P calculations are 5-30%
shorter than those from the present N-body simulations. The comparison of
projected number density profiles and stellar mass functions between N-body
simulations and HST/NICMOS observations by Figer et al. (1999) suggests that
the current tidal radius of the Arches cluster is ~1.0 pc, and the following
parameters for the initial conditions of that cluster: total mass of 2x10^4
Msun and mass function slope for intermediate-to-massive stars of 1.75 (the
Salpeter function has 2.35). We also find that the lower stellar mass limit,
the presence of primordial binaries, the amount of initial mass segregation,
and the choice of initial density profile (King or Plummer models) do not
significantly affect the dynamical evolution of CYCs.Comment: 20 pages including 6 figures, To appear in ApJ, Dec 20 issu
Physical Properties of Tidal Features in Interacting Disk Galaxies
We explore tidal interactions of a galactic disk with Toomre parameter Q ~ 2
embedded in rigid halo/bulge with a point mass companion moving in a prescribed
parabolic orbit. Tidal interactions produce well-defined spiral arms and
extended tidal features such as bridge and tail that are all transient, but
distinct in nature. In the extended disks, strong tidal force is able to lock
the perturbed epicycle phases of the near-side particles to the perturber,
shaping them into a tidal bridge that corotates with the perturber. A tidal
tail develops at the opposite side as strongly-perturbed, near-side particles
overtake mildly-perturbed, far-side particles. The tail is essentially a narrow
material arm with a roughly logarithmic shape, dissolving with time because of
large velocity dispersions. Inside the disks where tidal force is relatively
weak, on the other hand, a two-armed logarithmic spiral pattern emerges due to
the kinematic alignment of perturbed particle orbits. While self-gravity makes
the spiral arms a bit stronger, the arms never become fully self-gravitating,
wind up progressively with time, and decay after the peak almost exponentially
in a time scale of ~ 1 Gyr. The arm pattern speed varying with both radius and
time converges to Omega-kappa/2 at late time, suggesting that the pattern speed
of tidally-driven arms may depend on radius in real galaxies. We present the
parametric dependences of various properties of tidal features on the tidal
strength, and discuss our findings in application to tidal spiral arms in
grand-design spiral galaxies. (Abridged)Comment: 49 pages, 17 figures, 1 table. Accepted for publication in
Astrophysical Journal. PDF version with higher resolution figures is
available at
http://astro.snu.ac.kr/~shoh/research/publications/astroph/Tidally_Induced_Spiral_Structure.pd
The K\"ahler-Ricci flow with positive bisectional curvature
We show that the K\"ahler-Ricci flow on a manifold with positive first Chern
class converges to a K\"ahler-Einstein metric assuming positive bisectional
curvature and certain stability conditions.Comment: 15 page
On The Application of Flow Forming to the Fabrication of Type B Radioactive Material Package Containment Vessels, Rev. 1
Research on classroom practice: A monograph for topic study group 24, ICME 11 - The introductory chapter
published_or_final_versionThe 11th International Congress on Mathematical Education (ICME 11), Monterrey, Mexico, 6-13 July 2008. In Quaderni di Ricerca in Didattica, 2009, n. S4, p. 1-
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