6,543 research outputs found
Experimental observation of the optical spin transfer torque
The spin transfer torque is a phenomenon in which angular momentum of a spin
polarized electrical current entering a ferromagnet is transferred to the
magnetization. The effect has opened a new research field of electrically
driven magnetization dynamics in magnetic nanostructures and plays an important
role in the development of a new generation of memory devices and tunable
oscillators. Optical excitations of magnetic systems by laser pulses have been
a separate research field whose aim is to explore magnetization dynamics at
short time scales and enable ultrafast spintronic devices. We report the
experimental observation of the optical spin transfer torque, predicted
theoretically several years ago building the bridge between these two fields of
spintronics research. In a pump-and-probe optical experiment we measure
coherent spin precession in a (Ga,Mn)As ferromagnetic semiconductor excited by
circularly polarized laser pulses. During the pump pulse, the spin angular
momentum of photo-carriers generated by the absorbed light is transferred to
the collective magnetization of the ferromagnet. We interpret the observed
optical spin transfer torque and the magnetization precession it triggers on a
quantitative microscopic level. Bringing the spin transfer physics into optics
introduces a fundamentally distinct mechanism from the previously reported
thermal and non-thermal laser excitations of magnets. Bringing optics into the
field of spin transfer torques decreases by several orders of magnitude the
timescales at which these phenomena are explored and utilized.Comment: 11 pages, 4 figure
Lithographically and electrically controlled strain effects on anisotropic magnetoresistance in (Ga,Mn)As
It has been demonstrated that magnetocrystalline anisotropies in (Ga,Mn)As
are sensitive to lattice strains as small as 10^-4 and that strain can be
controlled by lattice parameter engineering during growth, through post growth
lithography, and electrically by bonding the (Ga,Mn)As sample to a
piezoelectric transducer. In this work we show that analogous effects are
observed in crystalline components of the anisotropic magnetoresistance (AMR).
Lithographically or electrically induced strain variations can produce
crystalline AMR components which are larger than the crystalline AMR and a
significant fraction of the total AMR of the unprocessed (Ga,Mn)As material. In
these experiments we also observe new higher order terms in the
phenomenological AMR expressions and find that strain variation effects can
play important role in the micromagnetic and magnetotransport characteristics
of (Ga,Mn)As lateral nanoconstrictions.Comment: 11 pages, 4 figures, references fixe
Self-Reported Route Familiarity and Road Safety Negative Outcomes: First Results from a Transnational Survey-Based Study
Previous research has shown the influence of drivers' route familiarity on road safety. The drivers' familiarity was possibly related to some negative safety outcomes such as speeding, violations, inattention. On the other hand, drivers unfamiliar with the route (especially if foreigners) were related to over-involvement in specific types or at-fault crashes. Drivers' route familiarity is mainly identifiable from frequency-based self-reported scales and distance from residence scales. In this study, another perspective was used, by relying on surveys. The familiarity with given routes and the behavioral differences with respect to generic routes was self-reported by drivers, who have answered to a specifically designed survey. Other questions were related to other safety issues and negative outcomes, such as accidents and sanctions/violations. The survey was submitted to both Italian and Norwegian young drivers, to explore also possible cultural/geographic differences of the phenomenon. The first results from the study are presented here, by focusing on the relevant aspects emerged from both the Italian and Norwegian surveys. In particular, the representation of the habitual routes is different between Italy and Norway. Some stated behavioral differences emerge from the comparison between answers related to the generic routes travelled and those specifically related to the habitual routes. Most accidents occur on routes frequently traveled, while there is a relevant part of fines which occur on roads rarely/never travelled. Those tendencies should be confirmed and other possible relationships should be explored after having enlarged the sample of respondents
Voltage control of magnetocrystalline anisotropy in ferromagnetic - semiconductor/piezoelectric hybrid structures
We demonstrate dynamic voltage control of the magnetic anisotropy of a
(Ga,Mn)As device bonded to a piezoelectric transducer. The application of a
uniaxial strain leads to a large reorientation of the magnetic easy axis which
is detected by measuring longitudinal and transverse anisotropic
magnetoresistance coefficients. Calculations based on the mean-field
kinetic-exchange model of (Ga,Mn)As provide microscopic understanding of the
measured effect. Electrically induced magnetization switching and detection of
unconventional crystalline components of the anisotropic magnetoresistance are
presented, illustrating the generic utility of the piezo voltage control to
provide new device functionalities and in the research of micromagnetic and
magnetotransport phenomena in diluted magnetic semiconductors.Comment: Submitted to Physical Review Letters. Updates version 1 to include a
more detailed discussion of the effect of strain on the anisotropic
magnetoresistanc
Finite dimensional corrections to mean field in a short-range p-spin glassy model
In this work we discuss a short range version of the -spin model. The
model is provided with a parameter that allows to control the crossover with
the mean field behaviour. We detect a discrepancy between the perturbative
approach and numerical simulation. We attribute it to non-perturbative effects
due to the finite probability that each particular realization of the disorder
allows for the formation of regions where the system is less frustrated and
locally freezes at a higher temperature.Comment: 18 pages, 5 figures, submitted to Phys Rev
Oxidative stress biomarkers and hormonal profile in human patients undergoing varicocelectomy
The aetiology of varicocele is multifactorial although hormonal imbalance and oxidative stress play a key role in the progression of illness. No conclusive evidence has been presented previously, describing the changes in these two factors and the evolution of patients after varicocelectomy. Semen characteristics and hormonal profile were analysed in 36 infertile men with unilateral left varicocele and 33 age-paired controls (proved to be fertile men), after careful inclusion/exclusion selection criteria. Liposoluble and hydrosoluble antioxidants, oligoelements and enzyme activities of the antioxidant defence system were also determined in plasma and erythrocyte from antecubital and spermatic veins, and in spermatozoa. Data were compared between groups at different times before and after varicocelectomy. Decreased levels of liposoluble and hydrosoluble antioxidants and increased activities of the antioxidant defence system enzymes were observed in patients compared with controls. Varicocelectomy normalized this condition at different post-surgical times. Levels of Zn and Se in seminal plasma, protein carbonyls and fragmented DNA remained elevated up to 1 month after surgery. Luteinizing and follicle stimulating hormone concentrations exhibited a biphasic behaviour while testosterone was diminished in patients but normalized soon after varicocelectomy. The results clearly demonstrate the link between the antioxidant defence system, hormonal status and semen characteristics along the post-varicocelectomy period. We suggest that oxidative biomarkers may be appropriate in controlling the evolution of post-varicocelectomy patients, and antioxidant supplementation may improve the clinical condition of infertile men with varicocele.Instituto de Investigaciones Bioquímicas de La Plat
Oxidative stress biomarkers and hormonal profile in human patients undergoing varicocelectomy
The aetiology of varicocele is multifactorial although hormonal imbalance and oxidative stress play a key role in the progression of illness. No conclusive evidence has been presented previously, describing the changes in these two factors and the evolution of patients after varicocelectomy. Semen characteristics and hormonal profile were analysed in 36 infertile men with unilateral left varicocele and 33 age-paired controls (proved to be fertile men), after careful inclusion/exclusion selection criteria. Liposoluble and hydrosoluble antioxidants, oligoelements and enzyme activities of the antioxidant defence system were also determined in plasma and erythrocyte from antecubital and spermatic veins, and in spermatozoa. Data were compared between groups at different times before and after varicocelectomy. Decreased levels of liposoluble and hydrosoluble antioxidants and increased activities of the antioxidant defence system enzymes were observed in patients compared with controls. Varicocelectomy normalized this condition at different post-surgical times. Levels of Zn and Se in seminal plasma, protein carbonyls and fragmented DNA remained elevated up to 1 month after surgery. Luteinizing and follicle stimulating hormone concentrations exhibited a biphasic behaviour while testosterone was diminished in patients but normalized soon after varicocelectomy. The results clearly demonstrate the link between the antioxidant defence system, hormonal status and semen characteristics along the post-varicocelectomy period. We suggest that oxidative biomarkers may be appropriate in controlling the evolution of post-varicocelectomy patients, and antioxidant supplementation may improve the clinical condition of infertile men with varicocele.Instituto de Investigaciones Bioquímicas de La Plat
A Numerical Study of Ultrametricity in Finite Dimensional Spin Glasses
We use a constrained Monte Carlo technique to analyze ultrametric features of
a 4 dimensional Edwards-Anderson spin glass with quenched couplings J=\pm 1. We
find that in the large volume limit an ultrametric structure emerges quite
clearly in the overlap of typical equilibrium configurations.Comment: 8 one column pages, latex, 4 figures with epsfig.st
Status of the Cylindical-GEM project for the KLOE-2 Inner Tracker
The status of the R&D on the Cylindrical-GEM (CGEM) detector foreseen as
Inner Tracker for KLOE-2, the upgrade of the KLOE experiment at the DAFNE
phi-factory, will be presented. The R&D includes several activities: i) the
construction and complete characterization of the full-size CGEM prototype,
equipped with 650 microns pitch 1-D longitudinal strips; ii) the study of the
2-D readout with XV patterned strips and operation in magnetic field (up to
1.5T), performed with small planar prototypes in a dedicated test at the H4-SPS
beam facility; iii) the characterization of the single-mask GEM technology for
the realization of large-area GEM foils.Comment: 4 pages, 10 figures, Presented at Vienna Conference on
Instrumentation (Feb 15-20, 2010, Vienna, Austria). Submitted to the
Proceeding
Inferring relationships between pairs of individuals from locus heterozygosities
BACKGROUND: The traditional exact method for inferring relationships between individuals from genetic data is not easily applicable in all situations that may be encountered in several fields of applied genetics. This study describes an approach that gives affordable results and is easily applicable; it is based on the probabilities that two individuals share 0, 1 or both alleles at a locus identical by state. RESULTS: We show that these probabilities (z(i)) depend on locus heterozygosity (H), and are scarcely affected by variation of the distribution of allele frequencies. This allows us to obtain empirical curves relating z(i)'s to H for a series of common relationships, so that the likelihood ratio of a pair of relationships between any two individuals, given their genotypes at a locus, is a function of a single parameter, H. Application to large samples of mother-child and full-sib pairs shows that the statistical power of this method to infer the correct relationship is not much lower than the exact method. Analysis of a large database of STR data proves that locus heterozygosity does not vary significantly among Caucasian populations, apart from special cases, so that the likelihood ratio of the more common relationships between pairs of individuals may be obtained by looking at tabulated z(i )values. CONCLUSIONS: A simple method is provided, which may be used by any scientist with the help of a calculator or a spreadsheet to compute the likelihood ratios of common alternative relationships between pairs of individuals
- …