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Is the Hygiene Hypothesis an Example of Hormesis?
The “hygiene hypothesis” has been suggested to explain the rising incidence of allergic disorders in developed countries. The postulated mechanism is that infectious and/or microbial agents stimulate the immune system toward Th1 (allergy fighting) rather than Th2 (allergy promoting) response. This paper reviews the evidence related to early life infectious/microbial exposures and subsequent atopic disorders and evaluates whether these data suggest a hormetic effect. Our review indicates an insufficient and contradictory association for bacterial/viral infections, with protective effects being either absent or specific to certain infections and/or populations. Chronic, heavy parasitic burdens appear to confer protection against atopic disorders, but are associated with considerable pathology. Moreover, light parasitic burden may increase allergic responses (i.e., no “low dose” beneficial effect). In contrast, there is consistent evidence that general microbial exposures, particularly gut commensals, may be protective against allergy development, which is consistent with a hormetic effect (i.e., potentially beneficial effects at low doses and detrimental effects at high levels). Conclusion: General microbial exposures in relation to the “hygiene hypothesis” may represent a hormetic effect, although further research with more rigorous study methods (i.e., prospective designs and measurement of exposure timing, dose, route, etc.) are needed
Multi-band superconductivity in LaFeAsO_{0.9}F_{0.1} single crystals probed by high-field vortex torque magnetometry
To probe manifestations of multiband superconductivity in oxypnictides, we
measured the angular dependence of the magnetic torque in the
mixed state of LaOFFeAs single crystals as a function of
temperature and magnetic fields up to 18 T. The paramagnetic
contribution of the Fe ions is properly treated in order to extract the
effective mass anisotropy parameter from
. We show that depends strongly on both and ,
reaching a maximum value of 10 followed by a decrease towards values
close to 1 as is lowered. The observed field dependencies of the London
penetration depth and suggest the onset of suppression
of a superconducing gap at .Comment: 7 pages, 7 figure
Muon-spin rotation measurements of the penetration depth of the Mo_3Sb_7 superconductor
Measurements of the magnetic field penetration depth \lambda in
superconductor Mo_3Sb_7 (T_c~2.1 K) were carried out by means of
muon-spin-rotation. The absolute values of \lambda, the Ginzburg-Landau
parameter \kappa, the first H_{c1} and the second H_{c2} critical fields at T=0
are \lambda(0)=720(100)nm, \kappa(0)=55(9), \mu_0H_{c1}(0)=1.8(3)mT, and
\mu_0H_{c2}(0)=1.9(2)T. The zero temperature value of the superconducting
energy gap \Delta(0) was found to be 0.35(1)meV corresponding to the ratio
2\Delta(0)/k_BT_c=3.83(10). At low temperatures \lambda^{-2}(T) saturates and
becomes constant below T~0.3T_c, in agreement with what is expected for s-wave
BCS superconductors. Our results suggest that Mo_3Sb_7 is a BCS superconductor
with the isotropic energy gapComment: 5 pages, 4 figure
3D-xy critical properties of YBa2Cu4O8 and magnetic field induced 3D to 1D crossover
We present reversible magnetization data of a YBa2Cu4O8 single crystal and
analyze the evidence for 3D-xy critical behavior and a magnetic field induced
3D to 1D crossover. Remarkable consistency with these phenomena is observed in
agreement with a magnetic field induced finite size effect, whereupon the
correlation length transverse to the applied magnetic field cannot grow beyond
the limiting magnetic length scale L_H. By applying the appropriate scaling
form we obtain the zero-field critical temperature, the 3D to 1D crossover, the
vortex melting line and the universal ratios of the related scaling variables.
Accordingly there is no continuous phase transition in the (H,T)-plane along
the H_c2-lines as predicted by the mean-field treatment.Comment: 8 pages, 4 figure
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