Mechanism of thermally activated c-axis dissipation in layered High-Tc_c superconductors at high fields

We propose a simple model which explains experimental behavior of $c$-axis resistivity in layered High-T$_c$ superconductors at high fields in a limited temperature range. It is generally accepted that the in-plane dissipation at low temperatures is caused by small concentration of mobile pancake vortices whose diffusive motion is thermally activated. We demonstrate that in such situation a finite conductivity appears also in $c$-direction due to the phase slips between the planes caused by the mobile pancakes. The model gives universal relation between the components of conductivity which is in good agreement with experimental data.Comment: RevTeX, 4 pages, 2 Postscript figure

Full Bulk Spin Polarization and Intrinsic Tunnel Barriers at the Surface of Layered Manganites

Transmission of information using the spin of the electron as well as its charge requires a high degree of spin polarization at surfaces. At surfaces however this degree of polarization can be quenched by competing interactions. Using a combination of surface sensitive x-ray and tunneling probes, we show for the quasi-two-dimensional bilayer manganites that the outermost Mn-O bilayer, alone, is affected: it is a 1-nm thick insulator that exhibits no long-range ferromagnetic order while the next bilayer displays the full spin polarization of the bulk. Such an abrupt localization of the surface effects is due to the two-dimensional nature of the layered manganite while the loss of ferromagnetism is attributed to weakened double exchange in the reconstructed surface bilayer and a resultant antiferromagnetic phase. The creation of a well-defined surface insulator demonstrates the ability to naturally self-assemble two of the most demanding components of an ideal magnetic tunnel junction.Comment: 19 pages, 5 figure

Tilt-modulus enhancement of the vortex lattice in the layered superconductor 2H-NbSe2

Quantum Matter and Optic

De prevalentie en determinanten van bezoek van partners, kinderen, familie en vrienden aan Nederlandse gedetineerden: de rol van sociale netwerkkenmerken en criminele geschiedenis

Scholarship has shown that visitation is an especially important experience for inmates and can have a beneficial impact on life after release. Receiving visits in prison, however, is not self-evident.This study uses data from a nationally representative sample of adults incarcerated in the Netherlands (N=4.376) to estimate the prevalence of, and identify determinants for, visits from partner, child(ren), family and friends. Consistent with expectations from social support theory, results indicate that having a strong social network is associated with visitation. Inmates who are older, have a non-Western background and have short prison stays are less likely to be visited. Unexpectedly, the type of offense and incarceration history were less predictive of prison visits, although results differed across visitor types. Implications of these findings for prison administrators and research are discussed.Criminal Justice: Legitimacy, accountability, and effectivit

Absence of the Transition into Abrikosov Vortex State of Two-Dimensional Type-II Superconductor with Weak Pinning

The resistive properties of thin amorphous NbO_{x} films with weak pinning were investigated experimentally above and below the second critical field H_{c2}. As opposed to bulk type II superconductors with weak pinning where a sharp change of resistive properties at the transition into the Abrikosov state is observed at H_{c4}, some percent below H_{c2} (V.A.Marchenko and A.V.Nikulov, 1981), no qualitative change of resistive properties is observed down to a very low magnetic field, H_{c4} < 0.006 H_{c2}, in thin films with weak pinning. The smooth dependencies of the resistivity observed in these films can be described by paraconductivity theory both above and below H_{c2}. This means that the fluctuation superconducting state without phase coherence remains appreciably below H_{c2} in the two-dimensional superconductor with weak pinning. The difference the H_{c4}/H_{c2} values, i.e. position of the transition into the Abrikosov state, in three- and two-dimensional superconductors conforms to the Maki-Takayama result 1971 year according to which the Abrikosov solution 1957 year is valid only for a superconductor with finite dimensions. Because of the fluctuation this solution obtained in the mean field approximation is not valid in a relatively narrow region below H_{c2} for bulk superconductors with real dimensions and much below H_{c2} for thin films with real dimensions. The superconducting state without phase coherence should not be identified with the mythical vortex liquid because the vortex, as a singularity in superconducting state with phase coherence, can not exist without phase coherence.Comment: 4 pages, 4 figure

Existence of the Abrikosov vortex state in two-dimensional type-II superconductors without pinning

Theory alternative to the vortex lattice melting theories is advertised. The vortex lattice melting theories are science fiction cond-mat/9811051 because the Abrikosov state is not the vortex lattice with crystalline long-range order. Since the fluctuation correction to the Abrikosov solution is infinite in the thermodynamic limit (K.Maki and H.Takayama, 1972) any fluctuation theory of the mixed state should consider a superconductor with finite sizes. Such nonperturbative theory for the easiest case of two-dimensional superconductor in the lowest Landau level approximation is presented in this work. The thermodynamic averages of the spatial average order parameter and of the Abrikosov parameter $\beta_{a}$ are calculated. It is shown that the position H_{c4} of the transition into the Abrikosov state (i.e. in the mixed state with long-range phase coherence) depends strongly on sizes of two-dimensional superconductor. Fluctuations eliminate the Abrikosov vortex state in a wide region of the mixed state of thin films with real sizes and without pinning disorders, i.e. H_{c4} << H_{c2}. The latter has experimental corroboration in Phys.Rev.Lett. 75, 2586 (1995).Comment: 4 pages, 0 figure

Visitation Enablers and Barriers: Evaluating the Influences of Practical, Relational, and Experiential Factors on Visitation in Dutch Prisons

This paper aims to advance theory and knowledge about prison visitation by organizing prior studies within a framework of visitation enablers and barriers and examining how practical, relational, and experiential factors explain variation in prison visiting among 773 adult males across eight Dutch prisons. Findings suggest that all three domains play out at once to influence visitation. Whether visitors come to visit seems to depend on their relationship with the incarcerated individual, whereas traveling distance is more predictive of how often they visit. Policies that introduce practical barriers can differentially affect visits from specific relationships. Finally, results indicate that incarcerated individuals make decisions about visits based on their in-prison experiences. Policy and research implications are discussed.Criminal Justice: Legitimacy, accountability, and effectivit

Receiving visits in prison and aggressive and contraband misconduct among Dutch prisoners

Criminal Justice: Legitimacy, accountability, and effectivit

Receiving Visits and the Relative Timing of Inmates’ Infractions: Investigations into how Inmates’ Behavior Change Before and After Visits in Dutch Prisons

ObjectivesThis study tests the relative timing of inmate infractions in the weeks before and after a visit.MethodOur sample is a cohort of 823 male inmates who participated in the Dutch Prison Visitation Study (DPVS) (2017) and had visitation and misconduct data. Using two-level random effects logistic regression models, we examined week-to-week associations between infractions and prison visits, including visits from partners, family, friends, and official visitors.ResultsThe probability of an infraction is comparable to average levels in anticipation of visits, increases up to 18 percent in the weeks immediately following visits, and then returns to baseline levels. This pattern is found for contraband infractions, but no effects were found for aggressive infractions. Strongest effects were found for family and official visits. When inmates are visited frequently, the risk of infractions postvisit is similar to average levels.ConclusionsThe findings show that visits can have harmful effects on inmate infractions. These effects seem to stem from increases in contraband infractions. More research is needed to further understand the mechanism behind visits’ effects.Criminal Justice: Legitimacy, accountability, and effectivit