1,399 research outputs found
Accumulation of driver and passenger mutations during tumor progression
Major efforts to sequence cancer genomes are now occurring throughout the
world. Though the emerging data from these studies are illuminating, their
reconciliation with epidemiologic and clinical observations poses a major
challenge. In the current study, we provide a novel mathematical model that
begins to address this challenge. We model tumors as a discrete time branching
process that starts with a single driver mutation and proceeds as each new
driver mutation leads to a slightly increased rate of clonal expansion. Using
the model, we observe tremendous variation in the rate of tumor development -
providing an understanding of the heterogeneity in tumor sizes and development
times that have been observed by epidemiologists and clinicians. Furthermore,
the model provides a simple formula for the number of driver mutations as a
function of the total number of mutations in the tumor. Finally, when applied
to recent experimental data, the model allows us to calculate, for the first
time, the actual selective advantage provided by typical somatic mutations in
human tumors in situ. This selective advantage is surprisingly small, 0.005 +-
0.0005, and has major implications for experimental cancer research
Analytically Derived Switching-Functions For Exact H-2(+) Eigenstates
Electron translation factors (ETF\u27s) appropriate for slow atomic collisions may be constructed using switching functions. In this paper we derive a set of switching functions for the H2+ system by an analytical two-center decomposition of the exact molecular eigenstates. These switching functions are closely approximated by the simple form f=bη, where η is the angle variable of prolate spheroidal coordinates. For given united atom angular momentum quantum numbers (l,m), the characteristic parameter blm depends only on the quantity c2=-âR22, where â is the electronic binding energy and R the internuclear distance in a.u. The resulting parameters are in excellent agreement with those found in our earlier work by a heuristic optimization scheme based on a study of coupling matrix-element behavior for a number of H2+ states. An approximate extension to asymmetric cases (HeH2+) has also been made. Nonadiabatic couplings based on these switching functions have been used in recent close-coupling calculations for H+-H(1s) collisions and He2+-H(1s) collisions at energies 1.0-20 keV
Differential cross sections for pion charge exchange on the proton at 27.5 MeV
We have measured pion single charge exchange differential cross sections on
the proton at 27.5 MeV incident kinetic energy in the center of
momentum angular range between and . The extracted cross
sections are compared with predictions of the standard pion-nucleon partial
wave analysis and found to be in excellent agreement.Comment: ReVTeX v3.0 with aps.sty, 23 pages in e-print format, 7 PostScript
Figures and 4 Tables, also available via anonymous ftp at
ftp://helena.phys.virginia.edu/pub/preprints/scx.p
The Equation of State and the Hugoniot of Laser Shock-Compressed Deuterium
The equation of state and the shock Hugoniot of deuterium are calculated
using a first-principles approach, for the conditions of the recent shock
experiments. We use density functional theory within a classical mapping of the
quantum fluids [ Phys. Rev. Letters, {\bf 84}, 959 (2000) ]. The calculated
Hugoniot is close to the Path-Integral Monte Carlo (PIMC) result. We also
consider the {\it quasi-equilibrium} two-temperature case where the Deuterons
are hotter than the electrons; the resulting quasi-equilibrium Hugoniot mimics
the laser-shock data. The increased compressibility arises from hot
pairs occuring close to the zero of the electron chemical potential.Comment: Four pages; One Revtex manuscript, two postscipt figures; submitted
to PR
Hydrogen-Helium Mixtures at High Pressure
The properties of hydrogen-helium mixtures at high pressure are crucial to
address important questions about the interior of Giant planets e.g. whether
Jupiter has a rocky core and did it emerge via core accretion? Using path
integral Monte Carlo simulations, we study the properties of these mixtures as
a function of temperature, density and composition. The equation of state is
calculated and compared to chemical models. We probe the accuracy of the ideal
mixing approximation commonly used in such models. Finally, we discuss the
structure of the liquid in terms of pair correlation functions.Comment: Proceedings article of the 5th Conference on Cryocrystals and Quantum
Crystals in Wroclaw, Poland, submitted to J. Low. Temp. Phys. (2004
Parity Violation in Neutron Resonances in 107,109Ag
Parity nonconservation (PNC) was studied in p-wave resonances in Ag by measuring the helicity dependence of the neutron total cross section. Transmission measurements on natural Ag were performed in the energy range 32 to 422 eV with the time-of-flight method at the Manuel Lujan Neutron Scattering Center at Los Alamos National Laboratory. A total of 15 p-wave neutron resonances were studied in 107Ag and ninep-wave resonances in 109Ag. Statistically significant asymmetries were observed for eight resonances in 107Ag and for four resonances in109Ag. An analysis treating the PNC matrix elements as random variables yields a weak spreading width of Îw=(2.67-1.21+2.65)Ă10-7âeV for107Ag and Îw=(1.30-0.74+2.49)Ă10-7âeV for 109Ag
The (p,n) Reaction at Intermediate Energies with the Isotopes of Oxygen (16-O, 17-O, 18-O) and 9-Be as Part of a Unified Approach to the Study of These Nuclei
This work was supported by National Science Foundation Grants PHY 76-84033A01, PHY 78-22774, and Indiana Universit
The (p,n) Reaction at Intermediate Energies With the Isotopes of Oxygen (16-O, 17-O, 18-O) and 9-Be as Part of a Unified Approach to the Study of These Nuclei
This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit
Parity Violation in Neutron Resonances in 115In
Parity nonconservation (PNC) was studied in p-wave resonances in indium by measuring the helicity dependence of the neutron total cross section in the neutron energy range 6.0â316 eV with the time-of-flight method at LANSCE. A total of 36 p-wave neutron resonances were studied in 115In, and statistically significant asymmetries were observed for nine cases. An analysis treating the PNC matrix elements as random variables yields a weak matrix element of M=(0.67-0.12+0.16)âmeV and a weak spreading width of Îw=(1.30-0.43+0.76)Ă10-7âeV
Detection of chromosome aberrations in metaphase and interphase tumor cells by in situ hybridization using chromosome-specific library probes
Chromosome aberrations in two glioma cell lines were analyzed using biotinylated DNA library probes that specifically decorate chromosomes 1, 4, 7, 18 and 22 from pter to qter. Numerical changes, deletions and rearrangements of these chromosomes were radily visualized in metaphase spreads, as well as in early prophase and interphase nuclei. Complete chromosomes, deleted chromosomes and segments of translocated chromosomes were rapidly delineated in very complex karyotypes. Simultaneous hybridizations with additional subregional probes were used to further define aberrant chromosomes. Digital image analysis was used to quantitate the total complement of specific chromosomal DNAs in individual metaphase and interphase cells of each cell line. In spite of the fact that both glioma lines have been passaged in vitro for many years, an under-representation of chromosome 22 and an over-representation of chromosome 7 (specifically 7p) were observed. These observations agree with previous studies on gliomas. In addition, sequences of chromosome 4 were also found to be under-represented, especially in TC 593. These analyses indicate the power of these methods for pinpointing chromosome segments that are altered in specific types of tumors
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