1,442 research outputs found
A primary word list: a revision of the 1935 Gates primary word list,
Thesis (Ed.M.)--Boston Universit
A minichromosome of LGVI from crossing two quasi-terminal reciprocal translocations
Non-reciprocal translocations, in which one chromosome is a pure donor and another is a pure recipient, have found abundant uses in genetics, molecular biology, and cytology (Perkins 1997Advances in Genetics 36:239-398). Our original aim was to prepare a strain carrying a chromosome truncated in both arms, with the idea that such a small chromosome would be easily purified by pulsed field electrophoresis and would be a good preliminary substrate for genomic sequencing
Full Aging in Spin Glasses
The discovery of memory effects in the magnetization decays of spin glasses
in 1983 began a large effort to determine the exact nature of the decay. While
qualitative arguments have suggested that the decay functions should scale as
, the only time scale in the system, this type of scaling has not yet
been observed. In this letter we report strong evidence for the scaling of the
TRM magnetization decays as a function of . By varying the rate and the
profile that the sample is cooled through its transition temperature to the
measuring temperature, we find that the cooling plays a major role in
determining scaling. As the effective cooling time decreases, scaling improves and for we find almost perfect
scaling. We also find that subtraction of a stationary term
from the magnetization decay has a small effect on the scaling but changes the
form of the magnetization decay and improves overlap between curves produced
with different .Comment: 4 pages, 3 figure
Intense tumour-cell destruction by syngeneic mice: role of macrophages, complement activation and tumour-cell factors.
When injected i.p. and in large numbers (10(7)) into syngeneic mice, 125IUdR-labelled L1210 cells are rapidly destroyed in a small proportion of animals, while in the other animals the lysis is low. This bimodal distribution is clearly visible 24 h after cell injection. The intense lysis occurs in fewer animals when macrophage-derived lysosomal enzymes are inhibited by trypan blue and if the complement is depleted by high doses of cobra venom factor (CVF). The intense destruction occurs in more animals after adjuvant treatment, if the mice are latently contaminated, after a moderate production of C3b by low doses of CVF, or after the injection of a tumour-cell dialysate. The destruction seems to be the result of positive feedback reaction which involves at least macrophages and complement activation
Ultrafast demagnetization in the sp-d model: a theoretical study
We propose and analyze a theoretical model of ultrafast light-induced
magnetization dynamics in systems of localized spins that are coupled to
carriers' spins by sp-d exchange interaction. A prominent example of a class of
materials falling into this category are ferromagnetic (III,Mn)V
semiconductors, in which ultrafast demagnetization has been recently observed.
In the proposed model light excitation heats up the population of carriers,
taking it out of equilibrium with the localized spins. This triggers the
process of energy and angular momentum exchange between the two spin systems,
which lasts for the duration of the energy relaxation of the carriers. We
derive the Master equation for the density matrix of a localized spin
interacting with the hot carriers and couple it with a phenomenological
treatment of the carrier dynamics. We develop a general theory within the sp-d
model and we apply it to the ferromagnetic semiconductors, taking into account
the valence band structure of these materials. We show that the fast spin
relaxation of the carriers can sustain the flow of polarization between the
localized and itinerant spins leading to significant demagnetization of the
localized spin system, observed in (III,Mn)V materials.Comment: 15 pages, 8 figure
A miniprep procedure for isolating genomic DNA from Magnoporthe grisea
We have developed a simple miniprep procedure for the isolation of genomic DNA from the ascomycete Magnaporthe grisea. This pathogen of many grasses, including rice, has a moderate growth rate and produces intermediate to low numbers of conidia when grown in culture. Thus, in our previous DNA preparation procedure we inoculated swirling liquid cultures with mycelium that had been fragmented in a blender rather than with conidia. The mycelium obtained from these cultures was ground in liquid nitrogen for DNA extraction. Though the quantity and quality of DNA obtained by this method is satisfactory, the technique is too laborious for analysis of many strains. We developed the procedure described below to eliminate the need to fragment mycelium in a blender to inoculate cultures and to eliminate the need to grind mycelium in liquid nitrogen for DNA extraction. The new procedure, which relies on the enzymatic removal of cell walls and the lysis of protoplasts, should be readily adaptable to other filamentous fungi with growth characteristics similar to those of M. grisea
Anharmonic Decay of Vibrational States in Amorphous Silicon
Anharmonic decay rates are calculated for a realistic atomic model of
amorphous silicon. The results show that the vibrational states decay on
picosecond timescales and follow the two-mode density of states, similar to
crystalline silicon, but somewhat faster. Surprisingly little change occurs for
localized states. These results disagree with a recent experiment.Comment: 10 pages, 4 Postscript figure
Magnetocaloric Study of Spin Relaxation in `Frozen' Dipolar Spin Ice Dy2Ti2O7
The magnetocaloric effect of polycrystalline samples of pure and Y-doped
dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K
to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic
interest, it is proposed that the magnetocaloric effect may be used as an
appropriate tool for the qualitative study of slow relaxation processes in the
spin ice regime. In the high temperature regime the temperature change on
adiabatic demagnetization was found to be consistent with previously published
entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by
adiabatic demagnetization was followed by an irreversible rise in temperature
that persisted after the removal of the applied field. The relaxation time
derived from this temperature rise was found to increase rapidly down to 0.3 K.
The data near to 0.3 K indicated a transition into a metastable state with much
slower relaxation, supporting recent neutron scattering results. In addition,
magnetic dilution of 50 % concentration was found to significantly prolong the
dynamical response in the milikelvin temperature range, in contrast with
results reported for higher temperatures at which the spin correlations are
suppressed. These observations are discussed in terms of defects and loop
correlations in the spin ice state.Comment: 9 figures, submitted to Phys. Rev.
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