1,947 research outputs found
Comparison of 125l-labeling of polypeptides using chloramine-T and 1,3,4,6-tetrachloro-3a, 6a-diphenyl-glycoluril (Indogen R) with subsequent separation of iodide and labelled protein on cation-exchange dextran
Experiences using Chloramine-T and 1,3,4,6-Terachloro-3a, 6a-diphenylglycoluril (Iodogen R) for Radioiodination of Materials for Radioaminoassay
Desert locust populations, rainfall and climate change: insights from phenomenological models using gridded monthly data
Using autocorrelation analysis and autoregressive integrated moving average (ARIMA)modelling, we analysed a time series of the monthly number of 1° grid squares infested with desert locust Schistocerca gregaria swarms throughout the geographical range of the species from 1930â1987. Statistically significant first- and higher-order autocorrelations were found in the series. Although endogenous components captured much of the variance, adding rainfall data improved endogenous ARIMA models and resulted in more realistic forecasts. Using a square-root transformation for the locust data improved the fit. The models were only partially successful when accounting for the dramatic changes in abundance which may occur during locust upsurges and declines, in some cases successfully predicting these phenomena but underestimating their severity. Better fitting models were also produced when rainfall data were added to models of an equivalent series for desert locust hoppers (nymphs) that incorporated lagged data for locust swarms as independent variables, representing parent generations. The results are discussed in relation to predicting likely changes in desert locust dynamics with reference to potential effects of climate change
Frequency comparisons and absolute frequency measurements of 171Yb+ single-ion optical frequency standards
We describe experiments with an optical frequency standard based on a laser
cooled Yb ion confined in a radiofrequency Paul trap. The
electric-quadrupole transition from the ground state to the
state at the wavelength of 436 nm is used as the reference
transition. In order to compare two Yb standards, separate
frequency servo systems are employed to stabilize two probe laser frequencies
to the reference transition line centers of two independently stored ions. The
experimental results indicate a relative instability (Allan standard deviation)
of the optical frequency difference between the two systems of only, so that shifts in the sub-hertz range can be
resolved. Shifts of several hertz are observed if a stationary electric field
gradient is superimposed on the radiofrequency trap field. The absolute optical
transition frequency of Yb at 688 THz was measured with a cesium atomic
clock at two times separated by 2.8 years. A temporal variation of this
frequency can be excluded within a relative uncertainty of yr. Combined with recently published values for the constancy
of other transition frequencies this measurement provides a limit on the
present variability of the fine structure constant at the level of
yr.Comment: 12 pages, 5 figures, Proceedings of MPLP'04, Novosibirsk, August
22.-27., 200
Adaptable Value-Set Analysis for Low-Level Code
This paper presents a framework for binary code analysis that uses only SAT-based algorithms. Within the framework, incremental SAT solving is used to perform a form of weakly relational value-set analysis in a novel way, connecting the expressiveness of the value sets to computational complexity. Another key feature of our framework is that it translates the semantics of binary code into an intermediate representation. This allows for a straightforward translation of the program semantics into Boolean logic and eases the implementation efforts, too. We show that leveraging the efficiency of contemporary SAT solvers allows us to prove interesting properties
about medium-sized microcontroller programs
Elastic properties of grafted microtubules
We use single-particle tracking to study the elastic properties of single
microtubules grafted to a substrate. Thermal fluctuations of the free
microtubule's end are recorded, in order to measure position distribution
functions from which we calculate the persistence length of microtubules with
contour lengths between 2.6 and 48 micrometers. We find the persistence length
to vary by more than a factor of 20 over the total range of contour lengths.
Our results support the hypothesis that shearing between protofilaments
contributes significantly to the mechanics of microtubules.Comment: 9 pages, 3 figure
Magnetic behavior of Fe x Sn 1 â x amorphous alloys near the critical composition
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