Bipolar-Driven Large Magnetoresistance in Silicon

Large linear magnetoresistance (MR) in electron-injected p-type silicon at very low magnetic field is observed experimentally at room temperature. The large linear MR is induced in electron-dominated space-charge transport regime, where the magnetic field modulation of electron-to-hole density ratio controls the MR, as indicated by the magnetic field dependence of Hall coefficient in the silicon device. Contrary to the space-charge-induced MR effect in unipolar silicon device, where the large linear MR is inhomogeneity-induced, our results provide a different insight into the mechanism of large linear MR in non-magnetic semiconductors that is not based on the inhomogeneity model. This approach enables homogeneous semiconductors to exhibit large linear MR at low magnetic fields that until now has only been appearing in semiconductors with strong inhomogeneities.Comment: 23 pages, 4 figures (main text), 6 figures (supplemental material

Dehydration and ionic conductance quantization in nanopores

There has been tremendous experimental progress in the last decade in identifying the structure and function of biological pores (ion channels) and fabricating synthetic pores. Despite this progress, many questions still remain about the mechanisms and universal features of ionic transport in these systems. In this paper, we examine the use of nanopores to probe ion transport and to construct functional nanoscale devices. Specifically, we focus on the newly predicted phenomenon of quantized ionic conductance in nanopores as a function of the effective pore radius - a prediction that yields a particularly transparent way to probe the contribution of dehydration to ionic transport. We study the role of ionic species in the formation of hydration layers inside and outside of pores. We find that the ion type plays only a minor role in the radial positions of the predicted steps in the ion conductance. However, ions with higher valency form stronger hydration shells, and thus, provide even more pronounced, and therefore, more easily detected, drops in the ionic current. Measuring this phenomenon directly, or from the resulting noise, with synthetic nanopores would provide evidence of the deviation from macroscopic (continuum) dielectric behavior due to microscopic features at the nanoscale and may shed light on the behavior of ions in more complex biological channels.Comment: 13 pages, 10 figure

Thermoelectric effects in a strongly correlated model for Nax_xCoO2_2

Thermal response functions of strongly correlated electron systems are of appreciable interest to the larger scientific community both theoretically and technologically. Here we focus on the infinitely correlated t-J model on a geometrically frustrated two-dimensional triangular lattice. Using exact diagonalization on a finite sized system we calculate the dynamical thermal response functions in order to determine the thermopower, Lorenz number, and dimensionless figure of merit. The dynamical thermal response functions is compared to the infinite frequency limit and shown to be very weak functions of frequency, hence, establishing the validity of the high frequency formalism recently proposed by Shastry for the thermopower, Lorenz number, and the dimensionless figure of merit. Further, the thermopower is demonstrated to have a low to mid temperature enhancement when the sign of the hopping parameter $t$ is switched from positive to negative for the geometrically frustrated lattice considered.Comment: 16 pages, 10 figures, color version available at http://physics.ucsc.edu/~peterson/mrpeterson-condmat-NCO.pdf. V.2 has fixed minor typos in Eq. 11, 19, 25, and 26. V.3 is a color versio

Magnetic Dipole Absorption of Radiation in Small Conducting Particles

We give a theoretical treatment of magnetic dipole absorption of electromagnetic radiation in small conducting particles, at photon energies which are large compared to the single particle level spacing, and small compared to the plasma frequency. We discuss both diffusive and ballistic electron dynamics for particles of arbitrary shape. The conductivity becomes non-local when the frequency is smaller than the frequency \omega_c characterising the transit of electrons from one side of the particle to the other, but in the diffusive case \omega_c plays no role in determining the absorption coefficient. In the ballistic case, the absorption coefficient is proportional to \omega^2 for \omega << \omega_c, but is a decreasing function of \omega for \omega >> \omega_c.Comment: 25 pages of plain TeX, 2 postscipt figure

The Zel'dovich effect and evolution of atomic Rydberg spectra along the Periodic Table

In 1959 Ya. B. Zel'dovich predicted that the bound-state spectrum of the non-relativistic Coulomb problem distorted at small distances by a short-range potential undergoes a peculiar reconstruction whenever this potential alone supports a low-energy scattering resonance. However documented experimental evidence of this effect has been lacking. Previous theoretical studies of this phenomenon were confined to the regime where the range of the short-ranged potential is much smaller than Bohr's radius of the Coulomb field. We go beyond this limitation by restricting ourselves to highly-excited s states. This allows us to demonstrate that along the Periodic Table of elements the Zel'dovich effect manifests itself as systematic periodic variation of the Rydberg spectra with a period proportional to the cubic root of the atomic number. This dependence, which is supported by analysis of experimental and numerical data, has its origin in the binding properties of the ionic core of the atom.Comment: 17 pages, 12 figure

Observation of Umklapp processes in non-crystalline materials

Umklapp processes are known to exist in cristalline materials, where they control important properties such as thermal conductivity, heat capacity and electrical conductivity. In this work we report the provocative observation of Umklapp processes in a non-periodical system, namely liquid Lithium. The lack of a well defined periodicity seems then not to prevent the existence of these scattering processes mechanisms provided that the local order of the systems i.e. the maxima of the static structure factor supply the equivalent of a reciprocal lattice vector in the case of cristalline materials.Comment: 13 pages P

Spin Tunneling and Phonon-assisted Relaxation in Mn12-acetate

We present a comprehensive theory of the magnetization relaxation in a Mn12-acetate crystal in the high-temperature regime (T>1 K), which is based on phonon-assisted spin tunneling induced by quartic magnetic anisotropy and weak transverse magnetic fields. The overall relaxation rate as function of the longitudinal magnetic field is calculated and shown to agree well with experimental data including all resonance peaks measured so far. The Lorentzian shape of the resonances, which we obtain via a generalized master equation that includes spin tunneling, is also in good agreement with recent data. We derive a general formula for the tunnel splitting energy of these resonances. We show that fourth-order diagonal terms in the Hamiltonian lead to satellite peaks. A derivation of the effective linewidth of a resonance peak is given and shown to agree well with experimental data. In addition, previously unknown spin-phonon coupling constants are calculated explicitly. The values obtained for these constants and for the sound velocity are also in good agreement with recent data. We show that the spin relaxation in Mn12-acetate takes place via several transition paths of comparable weight. These transition paths are expressed in terms of intermediate relaxation times, which are calculated and which can be tested experimentally.Comment: 18 pages, 22 EPS figures, REVTe

Therapeutic effect of hyperbaric oxygen in psoriasis vulgaris: two case reports and a review of the literature

<p>Abstract</p> <p>Introduction</p> <p>Psoriasis is an inflammatory and immunological cutaneous disease. The high morbidity in patients with psoriasis results from severe clinical manifestations and/or adverse effects of treatment. The Undersea and Hyperbaric Medical Society and Federal Medicare and Medicaid Services have approved the use of hyperbaric oxygen (HBO₂) for more than 15 indications, including wound healing, infections and late effects of radiation, which are largely unresponsive to conventional treatments. Accumulated data show that HBO₂ has anti-inflammatory effects and other positive influences on the immune system, making it a rational treatment in the management of psoriasis plaques and arthritis.</p> <p>Case presentation</p> <p>We present the cases of two patients with long histories of psoriasis vulgarus who exhibited marked improvement with use of HBO_2. The first patient was 40 years old and had pustular psoriasis and psoriatic arthritis. He was treated with six sessions of HBO₂ (at 2.8 atmospheres of pressure for 60 minutes), which successfully controlled his symptoms. At the 18-month post-treatment follow up, the patient exhibited complete remission of psoriasis and marked improvement in psoriatic arthritis without medication. The second patient was 55 years old with extensive psoriatic lesions, and exhibited marked improvement within 15 sessions of HBO₂. No adverse effects of HBO₂ were identified.</p> <p>Conclusions</p> <p>HBO₂ may possess potential therapeutic efficacy in the management of psoriasis. We outline the pathogenesis of psoriasis and the selective anti-inflammatory and immunosuppressive effects of HBO₂. We hope that this will provide a basis for elucidating the mechanisms of action and consequently pave the way for further controlled studies.</p

Forest microclimates and climate change: importance, drivers and future research agenda

Forest microclimates contrast strongly with the climate outside forests. To fully understand and better predict how forests' biodiversity and functions relate to climate and climate change, microclimates need to be integrated into ecological research. Despite the potentially broad impact of microclimates on the response of forest ecosystems to global change, our understanding of how microclimates within and below tree canopies modulate biotic responses to global change at the species, community and ecosystem level is still limited. Here, we review how spatial and temporal variation in forest microclimates result from an interplay of forest features, local water balance, topography and landscape composition. We first stress and exemplify the importance of considering forest microclimates to understand variation in biodiversity and ecosystem functions across forest landscapes. Next, we explain how macroclimate warming (of the free atmosphere) can affect microclimates, and vice versa, via interactions with land-use changes across different biomes. Finally, we perform a priority ranking of future research avenues at the interface of microclimate ecology and global change biology, with a specific focus on three key themes: (1) disentangling the abiotic and biotic drivers and feedbacks of forest microclimates; (2) global and regional mapping and predictions of forest microclimates; and (3) the impacts of microclimate on forest biodiversity and ecosystem functioning in the face of climate change. The availability of microclimatic data will significantly increase in the coming decades, characterizing climate variability at unprecedented spatial and temporal scales relevant to biological processes in forests. This will revolutionize our understanding of the dynamics, drivers and implications of forest microclimates on biodiversity and ecological functions, and the impacts of global changes. In order to support the sustainable use of forests and to secure their biodiversity and ecosystem services for future generations, microclimates cannot be ignored.Peer reviewe