133 research outputs found
Human Skin Temperature and Biological Clocks: A Laboratory Exercise for Physiology Students
A simple laboratory experiment is described, consisting of taking the mean temperature between two fingers of human subjects. The results from comparing male and female students is presented. The change in skin temperature over four hours is documented, to demonstrate the importance of doing standardized experiments at the same time of day
Some Factors Influencing the Life Span of Golden Hamsters
The golden hamster has found increased use as a laboratory animal over the last two decades. It is of particular interest because it hibernates although its periods of dormancy are short compared to those of other hibernators (1). The complete spectrum of physiological norms should be determined for this common animal just as they were for the laboratory rat. In the list of normal values for the hamster there is little published information on life span (2). This paper will present records of life spans of 126 hamsters kept under controlled laboratory conditions. Approximately 43% of the colony were maintained with a daily light cycle in a coldroom (6 ± 2 ° C.) for about 4 months each winter. Other conditions of the experiment have been described earlier in detail (1). For the purposes of this analysis the cold-exposed group was treated as a homogenous population, in spite of the fact that some of the animals hibernated. This combining of animals was due to the fact that there was such variation in the total duration of hibernation over the winter periods. Some hamsters hibernated for one day, others were in hibernation for a total of 95 days. The systematic pattern of results justifies this approach to this analysis. To be specific, the data treated in this paper look as if cold-exposure with or without hibernation produced the same effects upon the animals, in most respects. Furthermore, the hibernators were distributed nearly equally among four groups of cold-exposed animals. Later analyses will attempt to consider the influence of hibernation as a separate factor. We will ref.er in this report only to the cold-exposed group: this means a mixed group of males and females of two strains of animals, most of which were coldexposed 4 months, but a few of which received only 3 months of cold-exposure at 6° C. and a few weeks at 16° C. About 12 of the males and 10 of the females hibernated for variable periods of time
Overlapping of Ranges of Eastern and Western Hognose Snakes in Southeastern Iowa
Overlapping of ranges of the eastern hognose snake (Heterodon platyrhinos Latreille) and the western hognose snake (Heterodon nasicus nasicus Baird and Girrard) is reported from a sand prairie in Muscatine County, Iowa
Radiative Heat Loss from Skin to Cold Glass Windows
Today institutional rooms of many types have single large glass window panes measuring as large as 3.0 meters by 2.5 meters; animal colonies are maintained near these windows in winter, office workers sit by them and thinly clad patients on littercarts are placed beside them. Even though both local air and wall temperature may be 22°C, human subjects beside the windows in winter feel cold because body heat is radiated to the glass which acts as a heat sink. An experiment was conducted during two Iowa winters with measurements of temperatures of outside air, room, wall, undraped glass window, drape-covered window and skin to determine radiated heat loss and to assess the effects of a radiation shield (drape). The glass could be as low as 2°C. Results showed greater protection to the skin by the drape as the weather became colder, although the glass temperature did not change with the weather as much as was expected. Using a standardized room for calculations, we showed that if a person moved from a back wall to a position beside the glass window, he would increase his total heat loss by 32 percent
Measurement of Standard Metabolism, Water Loss and Body Temperature of the Little Brown Bat
A complete description is given of a respirometer, suitable for unrestrained five to ten gram bats, from which the following variables were simultaneously directly measured: air and body temperatures, relative humidity, oxygen consumption, carbon dioxide production, water loss, and electrocardiograms. Temperature was measured with specially mounted bead thermistors and a wheatstone bridge. Relative humidity was measured with an adsorptive electronic sensor which was excited by a transistorized oscillator, and had the voltage output rectified and fed to an oscillograph. Electrocardiograms were taken with custom-made safety pins chronically indwelling through the dorsolateral thoracic epidermis. Electrical connection was made with common clothing snap fasteners. Various controlled humidities were produced by bubbling air through saturated salt solutions. Water vapor was converted to acetylene and collected along with respiratory gases over mercury for subsequent analysis with a gas chromatograph
Stability of a cubic fixed point in three dimensions. Critical exponents for generic N
The detailed analysis of the global structure of the renormalization-group
(RG) flow diagram for a model with isotropic and cubic interactions is carried
out in the framework of the massive field theory directly in three dimensions
(3D) within an assumption of isotropic exchange. Perturbative expansions for RG
functions are calculated for arbitrary up to the four-loop order and
resummed by means of the generalized Pad-Borel-Leroy technique.
Coordinates and stability matrix eigenvalues for the cubic fixed point are
found under the optimal value of the transformation parameter. Critical
dimensionality of the model is proved to be equal to that
agrees well with the estimate obtained on the basis of the five-loop
\ve-expansion [H. Kleinert and V. Schulte-Frohlinde, Phys. Lett. B342, 284
(1995)] resummed by the above method. As a consequence, the cubic fixed point
should be stable in 3D for , and the critical exponents controlling
phase transitions in three-dimensional magnets should belong to the cubic
universality class. The critical behavior of the random Ising model being the
nontrivial particular case of the cubic model when N=0 is also investigated.
For all physical quantities of interest the most accurate numerical estimates
with their error bounds are obtained. The results achieved in the work are
discussed along with the predictions given by other theoretical approaches and
experimental data.Comment: 33 pages, LaTeX, 7 PostScript figures. Final version corrected and
added with an Appendix on the six-loop stud
Polymers in long-range-correlated disorder
We study the scaling properties of polymers in a d-dimensional medium with
quenched defects that have power law correlations ~r^{-a} for large separations
r. This type of disorder is known to be relevant for magnetic phase
transitions. We find strong evidence that this is true also for the polymer
case. Applying the field-theoretical renormalization group approach we perform
calculations both in a double expansion in epsilon=4-d and delta=4-a up to the
1-loop order and secondly in a fixed dimension (d=3) approach up to the 2-loop
approximation for different fixed values of the correlation parameter, 2=<a=<3.
In the latter case the numerical results need appropriate resummation. We find
that the asymptotic behavior of self-avoiding walks in three dimensions and
long-range-correlated disorder is governed by a set of separate exponents. In
particular, we give estimates for the 'nu' and 'gamma' exponents as well as for
the correction-to-scaling exponent 'omega'. The latter exponent is also
calculated for the general m-vector model with m=1,2,3.Comment: 13 pages, 5 figure
Critical behavior of certain antiferromagnets with complicated ordering: Four-loop \ve-expansion analysis
The critical behavior of a complex N-component order parameter
Ginzburg-Landau model with isotropic and cubic interactions describing
antiferromagnetic and structural phase transitions in certain crystals with
complicated ordering is studied in the framework of the four-loop
renormalization group (RG) approach in (4-\ve) dimensions. By using
dimensional regularization and the minimal subtraction scheme, the perturbative
expansions for RG functions are deduced and resummed by the Borel-Leroy
transformation combined with a conformal mapping. Investigation of the global
structure of RG flows for the physically significant cases N=2 and N=3 shows
that the model has an anisotropic stable fixed point governing the continuous
phase transitions with new critical exponents. This is supported by the
estimate of the critical dimensionality obtained from six loops
via the exact relation established for the complex and real
hypercubic models.Comment: LaTeX, 16 pages, no figures. Expands on cond-mat/0109338 and includes
detailed formula
Divergent Perturbation Series
Various perturbation series are factorially divergent. The behavior of their
high-order terms can be found by Lipatov's method, according to which they are
determined by the saddle-point configurations (instantons) of appropriate
functional integrals. When the Lipatov asymptotics is known and several lowest
order terms of the perturbation series are found by direct calculation of
diagrams, one can gain insight into the behavior of the remaining terms of the
series. Summing it, one can solve (in a certain approximation) various
strong-coupling problems. This approach is demonstrated by determining the
Gell-Mann - Low functions in \phi^4 theory, QED, and QCD for arbitrary coupling
constants. An overview of the mathematical theory of divergent series is
presented, and interpretation of perturbation series is discussed. Explicit
derivations of the Lipatov asymptotic forms are presented for some basic
problems in theoretical physics. A solution is proposed to the problem of
renormalon contributions, which hampered progress in this field in the late
1970s. Practical schemes for summation of perturbation series are described for
a coupling constant of order unity and in the strong-coupling limit. An
interpretation of the Borel integral is given for 'non-Borel-summable' series.
High-order corrections to the Lipatov asymptotics are discussed.Comment: Review article, 45 pages, PD
Critical behavior of the two-dimensional N-component Landau-Ginzburg Hamiltonian with cubic anisotropy
We study the two-dimensional N-component Landau-Ginzburg Hamiltonian with
cubic anisotropy. We compute and analyze the fixed-dimension perturbative
expansion of the renormalization-group functions to four loops. The relations
of these models with N-color Ashkin-Teller models, discrete cubic models,
planar model with fourth order anisotropy, and structural phase transition in
adsorbed monolayers are discussed. Our results for N=2 (XY model with cubic
anisotropy) are compatible with the existence of a line of fixed points joining
the Ising and the O(2) fixed points. Along this line the exponent has
the constant value 1/4, while the exponent runs in a continuous and
monotonic way from 1 to (from Ising to O(2)). For N\geq 3 we find a
cubic fixed point in the region , which is marginally stable or
unstable according to the sign of the perturbation. For the physical relevant
case of N=3 we find the exponents and at the cubic
transition.Comment: 14 pages, 9 figure
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