Coherent spin rotation in the presence of a phonon-bottleneck effect

A characteristic of spin reversal in the presence of phonon-bottleneck is the deviation of the magnetization cycle from a reversible function into an opened hysterezis cycle. In recent experiments on molecular magnets (e.g. V$_{15}$ and Ru$_2$), the zero-field level repulsion was sufficiently large to ensure an otherwise adiabatic passage through zero-field and the magnetization curves can be described by using only a phonon-bottleneck model. Here, we generalize the phonon-bottleneck model into a model able to blend the non-adiabatic dynamics of spins with the presence of a non-equilibrium phonon bath. In this simple phenomenological model, Bloch equations are written in the eigenbasis of the effective spin Hamiltonian, considered to be a two-level system at low temperatures. The relaxation term is given by the phonon-bottleneck mechanism. To the expense of calculus time, the method can be generalized to multi-level systems, where the notion of Bloch sphere does not apply but the density matrix formalism is still applicable.Comment: as published in EuroPhys Letter

Trading-Off Reproductive Technology and Adoption: Does Subsidizing in Vitro Fertilization Decrease Adoption Rates and Should It Matter?

For those facing infertility, using assisted reproductive technology to have genetically related children is a very expensive proposition. In particular, to produce a live birth through in vitro fertilization (IVF) will cost an individual (on average) between $66,667 and$114,286 in the U.S. If forced to pay these prices out of pocket, many would be unable to afford this technology. Given this reality, a number of states have attempted to improve access to reproductive technology through state-level insurance mandates that cover IVF. Several scholars, however, have worried that increasing access in this way will cause a diminution in adoptions and have argued against enactment of state mandates for that reason. In this paper, which was selected for presentation at the 2010 Stanford-Yale Junior Faculty Forum, we push against that conclusion on two fronts. First, we interrogate the normative premises of the argument and expose its contestable implicit assumptions about how the state should balance the interests of existing children waiting for adoption and those seeking access to reproductive technology in order to have genetically related children. Second, we investigate the unexamined empirical question behind the conclusion: does state subsidization of reproductive technologies through insurance mandates actually reduce adoption; that is, is there a trade-off between helping individuals conceive and helping children waiting to be adopted? We call the claim that there is such an effect the “substitution theory.” Using the differential timing of introduction of state-level insurance mandates relating to IVF in some states and differences in the forms these mandates take, we employ several different econometric techniques (differences-in-differences, ordinary least squares, two-stage least squares) to examine the effect of these mandates on IVF utilization and adoption. Contrary to the assumption of the substitution theory, we find no strong evidence that state support of IVF through these mandates crowds out either domestic or international adoption. Appendix A re-analyses our results using the insurance mandate categorization of other studies in the literature

Minimum Altitude-Loss Soaring in a Specified Vertical Wind Distribution

Minimum altitude-loss flight of a sailplane through a given vertical wind distribution is discussed. The problem is posed as an optimal control problem, and several numerical solutions are obtained for a sinusoidal wind distribution

Adaptation to climate change on arable farms in the Dutch province of Flevoland. An inventory for the AgriAdapt project

In Flevoland, arable farming is the most dominant land use. Adaptation options related to water, pests and diseases have been studied using a literature review. The green-blue zone Oostvaarderswold in Flevoland contributes to water storage, to nature conservation and to recreation. Compensation costs for structural wetting that are associated with various frequencies of flooding have been calculated. At inundation frequencies greater than once in 5 years, buying the agricultural land might be a better option than compensating for inundation damage or income loss. Various policies will have an effect on future agriculture in the province. A literature survey of spatial policy plans shows that urbanisation will increase and that some cities, like Almere, Lelystad, Dronten and Emmeloord, will continue to grow and expand. As a consequence, more inhabitants will require more space for nature and recreational activities, which in turn will lead to agricultural land being required

Equation-free dynamic renormalization in a glassy compaction model

Combining dynamic renormalization with equation-free computational tools, we study the apparently self-similar evolution of void distribution dynamics in the diffusion-deposition problem proposed by Stinchcombe and Depken [Phys. Rev. Lett. 88, 125701 (2002)]. We illustrate fixed point and dynamic approaches, forward as well as backward in time.Comment: 4 pages, 4 figures (Minor Modifications; Submitted Version

Why is the bulk resistivity of topological insulators so small?

As-grown topological insulators (TIs) are typically heavily-doped $n$-type crystals. Compensation by acceptors is used to move the Fermi level to the middle of the band gap, but even then TIs have a frustratingly small bulk resistivity. We show that this small resistivity is the result of band bending by poorly screened fluctuations in the random Coulomb potential. Using numerical simulations of a completely compensated TI, we find that the bulk resistivity has an activation energy of just 0.15 times the band gap, in good agreement with experimental data. At lower temperatures activated transport crosses over to variable range hopping with a relatively large localization length.Comment: 4+ pages, 3 figures; published versio

Efficiency at maximum power output of an irreversible Carnot-like cycle with internally dissipative friction

We investigate the efficiency at maximum power of an irreversible Carnot engine performing finite-time cycles between two reservoirs at temperatures $T_h$ and $T_c$ $(T_c<T_h)$, taking into account of internally dissipative friction in two "adiabatic" processes. In the frictionless case, the efficiencies at maximum power output are retrieved to be situated between $\eta_{_C}/$ and $\eta_{_C}/(2-\eta_{_C})$, with $\eta_{_C}=1-T_c/{T_h}$ being the Carnot efficiency. The strong limits of the dissipations in the hot and cold isothermal processes lead to the result that the efficiency at maximum power output approaches the values of $\eta_{_C}/$ and $\eta_{_C}/(2-\eta_{_C})$, respectively. When dissipations of two isothermal and two adiabatic processes are symmetric, respectively, the efficiency at maximum power output is founded to be bounded between 0 and the Curzon-Ahlborn (CA) efficiency $1-\sqrt{1-\eta{_C}}$, and the the CA efficiency is achieved in the absence of internally dissipative friction