The Light Curve and Internal Magnetic Field of the Mode-Switching Pulsar PSR B0943+10

A number of radio pulsars exhibit intriguing mode-switching behavior. Recent observations of PSR B0943+10 revealed correlated radio and X-ray mode switches, providing a new avenue for understanding this class of objects. The large X-ray pulse fraction observed during the radio quiet phase (Q mode) was previously interpreted as a result of changing obscuration of X-rays by dense magnetosphere plasma. We show that the large X-ray pulse fraction can be explained by including the beaming effect of a magnetic atmosphere, while remaining consistent with the dipole field geometry constrained by radio observations. We also explore a more extreme magnetic field configuration, where a magnetic dipole displaced from the center of the star produces two magnetic polar caps of different sizes and magnetic field strengths. These models are currently consistent with data in radio and X-rays and can be tested or constrained by future X-ray observations.Comment: 5 pages, 5 figures, submitted to ApJ

On the Role of Global Warming on the Statistics of Record-Breaking Temperatures

We theoretically study long-term trends in the statistics of record-breaking daily temperatures and validate these predictions using Monte Carlo simulations and data from the city of Philadelphia, for which 126 years of daily temperature data is available. Using extreme statistics, we derive the number and the magnitude of record temperature events, based on the observed Gaussian daily temperatures distribution in Philadelphia, as a function of the number of elapsed years from the start of the data. We further consider the case of global warming, where the mean temperature systematically increases with time. We argue that the current warming rate is insufficient to measurably influence the frequency of record temperature events over the time range of the observations, a conclusion that is supported by numerical simulations and the Philadelphia temperature data.Comment: 11 pages, 6 figures, 2-column revtex4 format. For submission to Journal of Climate. Revised version has some new results and some errors corrected. Reformatted for Journal of Climate. Second revision has an added reference. In the third revision one sentence that explains the simulations is reworded for clarity. New revision 10/3/06 has considerable additions and new results. Revision on 11/8/06 contains a number of minor corrections and is the version that will appear in Phys. Rev.

The use of oscillatory signals in the study of genetic networks

The structure of a genetic network is uncovered by studying its response to external stimuli (input signals). We present a theory of propagation of an input signal through a linear stochastic genetic network. It is found that there are important advantages in using oscillatory signals over step or impulse signals, and that the system may enter into a pure fluctuation resonance for a specific input frequency.Comment: 46 pages, 5 figures. Submitted to PNAS on May 27th 2004. The paper is under consideratio

Efficient generation of neural stem cell-like cells from adult human bone marrow stromal cells

Clonogenic neural stem cells (NSCs) are self-renewing cells that maintain the capacity to differentiate into brain-specific cell types, and may also replace or repair diseased brain tissue. NSCs can be directly isolated from fetal or adult nervous tissue, or derived from embryonic stem cells. Here, we describe the efficient conversion of human adult bone marrow stromal cells (hMSC) into a neural stem cell-like population (hmNSC, for human marrow-derived NSC-like cells). These cells grow in neurosphere-like structures, express high levels of early neuroectodermal markers, such as the proneural genes NeuroD1, Neurog2, MSl1 as well as otx1 and nestin, but lose the characteristics of mesodermal stromal cells. In the presence of selected growth factors, hmNSCs can be differentiated into the three main neural phenotypes: astroglia, oligodendroglia and neurons. Clonal analysis demonstrates that individual hmNSCs are multipotent and retain the capacity to generate both glia and neurons. Our cell culture system provides a powerful tool for investigating the molecular mechanisms of neural differentiation in adult human NSCs. hmNSCs may therefore ultimately help to treat acute and chronic neurodegenerative diseases

Surface flux drivers for the slowdown of the Atlantic Meridional Overturning Circulation in a high resolution global coupled climate model

This paper investigates the causation for the decline of the Atlantic Meridional Overturning Circulation (AMOC) from approximately 17 Sv to about 9 Sv, when the atmospheric resolution of the Max Planck Institute-Earth System Model is enhanced from ∼1° to ∼0.5°. The results show that the slowdown of the AMOC is caused by the cessation of deep convection. In most modeling studies, this is thought to be controlled by buoyancy fluxes in the convective regions, for example, by surface freshwater flux that is introduced locally or via enormous input from glacier or iceberg melts. While we find that freshwater is still the key to the reduction of AMOC seen in the higher-resolution run, the freshening of the North Atlantic does not need to be directly caused by local freshwater fluxes. Instead, it can be caused indirectly through winds via a reduced wind-driven gyre circulation and salinity transport associated to this circulation, as seen in the higher-resolution run. © 2019. The Authors

Response of northern North Atlantic and Atlantic meridional overturning circulation to reduced and enhanced wind stress forcing

Surface wind stress strongly influences AMOC variability on interannual time scales. On longer time scales, however, its role in AMOC variations is less clear. Here, we show a non-linear AMOC response to globally reduced and enhanced wind stress forcing, based on sensitivity experiments with MPI-ESM1.2. Under reduced wind stress forcing, the AMOC strength strongly decreases. In contrast, under enhanced wind stress forcing the AMOC strength increases only in the first decades and then decreases, stabilizing at a value similar to the reference simulation. To reveal possible mechanisms underlying this response, we assess the response of the northern North Atlantic circulation and climate to the changed wind stress forcing. Initially, the response is linear: reduced wind stress forcing weakens the gyre circulation and the associated heat and salt transport, leading to larger winter sea ice extent and a shutdown of subpolar deep convection. In the Nordic Seas, the fresher and lighter subsurface state leads to a decrease in the baroclinic pressure and the overflow strength. Under enhanced wind stress forcing, initially the opposite is happening. However, eventually subpolar surface density anomalies are determined by warmer temperature rather than increased salinity, leading to a decrease in surface density and a weakening of subpolar deep convection. The resulting AMOC weakening reduces the Atlantic inflow salinity, and subsequently the Nordic Seas baroclinic pressure and overflow strength. The quasi-equilibrium response of the northern North Atlantic circulation and climate under enhanced wind stress forcing differs from the reference simulation, even though the AMOC strength converges

Tolerance of Hyas araneus zoea I larvae to elevated seawater PCO2 despite elevated metabolic costs

Early life stages of marine crustaceans respond sensitively to elevated seawater P CO 2 . However, the underlying physiological mechanisms have not been studied well. We therefore investigated the effects of elevated seawater P CO 2 on oxygen consumption, dry weight, elemental composition, median developmental time (MDT) and mortality in zoea I larvae of the spider crab Hyas araneus (Svalbard 79°N/11°E; collection, May 2009; hatch, December 2009). At the time of moulting, oxygen consumption rate had reached a steady state level under control conditions. In contrast, elevated seawater P CO 2 caused the metabolic rate to rise continuously leading to a maximum 1.5-fold increase beyond control level a few days before moulting into the second stage (zoea II), followed by a pronounced decrease. Dry weight of larvae reared under high CO 2 conditions was lower than in control larvae at the beginning of the moult cycle, yet this difference had disappeared at the time of moulting. MDT of zoea I varied between 45 ± 1 days under control conditions and 42 ± 2 days under the highest seawater CO 2 concentration. The present study indicates that larval development under elevated seawater P CO 2 levels results in higher metabolic costs during premoulting events in zoea I. However, H. araneus zoea I larvae seem to be able to compensate for higher metabolic costs as larval MDT and survival was not affected by elevated P CO 2 leve