Effects of radiation damage on the charge density wave transitions in NbSe3

We have measured the electrical resistivity of NbSe₃ samples which have been radiation damaged with 2.5 MeV protons up to a defect concentration of 0.5%. We find that, unlike substitutional impurities, the defects do not destroy the charge density wave (CDW) transitions and the samples do not go superconducting. The defects become more effective scatterers below the CDW transitions so that the defect resistivity is temperature dependent. The defects pin the CDWs randomly so that carriers in the unnested regions can be scattered by the CDW. This leads to an enhancement of the defect resistivity. The resistivity of the highly damaged samples is still increasing with decreasing temperatures to below 1 K.     

Rheo-optical studies of concentrated polystyrene solutions subjected to transient simple shear flow

Concentrated polystyrene solutions were investigated on the inception and cessation of simple shear flow by means of the technique of two-color flow birefringence. Both monodisperse solutions of various molecular weights and bimodal mixtures were studied. The molecular weight affected both the amount of overshoot in the birefringence and the response time on the inception of shear flow. Large overshoots in birefringence, up to 250%, and undershoot in the orientation angle were observed. The shear stress and the first normal stress difference were calculated by using the stress–optical rule. The amount of strain at the peaks in the stress growth curves are presented along with the steady-state viscosity and primary normal stress coefficient. The experimental results are compared qualitatively with theoretical predictions of various molecular models.     

Neutrino-induced fission of neutron-rich nuclei

We calculate neutrino-induced fission cross sections for selected nuclei with Z=84-92. We show that these reactions populate the daughter nucleus at excitation energies where shell effects are significantly washed out, effectively reducing the fission barrier. If the r process occurs in the presence of a strong neutrino fluence, and electron neutrino average energies are sufficiently high, perhaps as a result of matter-enhanced neutrino flavor transformation, then neutrino-induced fission could lead to significant alteration in the r-process flow in slow outflow scenarios.     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Effects of hypothermia on ischaemic depolarisation in brain : a comparison of responses in rat and gerbil

The latency of development of ischaemic depolarization (LID) has been used to compare the relative effects of different levels of hypothermia on ischaemic responses in brains of rat and gerbil, using a model with imposed complete cessation of cerebral blood flow (CBF=0). At temperatures reducing from 37 degrees C to 20 degrees C, the LIDs were consistently shorter in the gerbil than in the rat. For example, at 37 degrees C the LID in the gerbil was 0.71+/- 01.2 min, and in the rat, 1.37 +/- 0.02 min respectively (P<0.01), whilst at 20 degrees C, the values were 5.48 +/- 0.25 min and 7.30 +/- 0.76 min (P<0.01). However, the relative effects of hypothermia on each species were similar (by linear regression with slopes of -0.29 and -0.35 min/degree C in the two species). There may be underlying differences in brain biophysics or structure between species, but in spite of this, applied hypothermia still imposes a similar depression on the development of ischaemic damage. Both models may thus be used in studies of brain hypothermia as long as the intrinsic differences are appreciated.     

Coalescence of particle-laden fluid interfaces

Colloidal particles are capable of stabilizing emulsions and, thus, slowing or preventing their complete breakdown into phase-separated systems. Direct observations of the dynamics of such particles on both water and oil droplets are reported as two colloid-laden interfaces are brought into contact with each other. As coalescence proceeds, the complementary systems, representing oil-in-water and water-in-oil emulsions, exhibit contrasting mechanisms for the formation of ring and disk structures by the particles as they serve to temporarily stabilize the approaching surfaces. An explanation of such behavior leads to a better understanding of the stabilization and breaking mechanisms of so-called Pickering emulsions.     

Gene expression in response to low temperatures in mammalian cells: a review of current ideas

This review was undertaken to identify responses of mammalian cells to cold temperatures, such as might be encountered in therapeutic procedures where body temperatures are lowered, in preservation of cells and organs, and in cryopreservation. In general, cold elicits a range of stress responses through identified signaling pathways, which may determine the survival or otherwise of the cells. Under conditions of mild hypothermia, there is evidence for responses which reflect an ordered acclimation to the new environment, whilst deep cooling invokes a more generalised stress response.     

Time scaling regimes in aggregation of magnetic dipolar particles: scattering dichroism results

We report experimental results on the aggregation kinetics in magnetorheological fluids subject to a constant uniaxial magnetic field using the technique of scattering dichroism. We show that the number of aggregated particles displays a long-time power-law dependence with exponents that correspond to two different aggregation regimes. These regimes coincide with 3D and 1D-like aggregation. We also derive the values of both time exponents for the number of aggregated particles.     

The pattern of freezing of grapevine shoots during early bud growth

The pattern of freezing of two varieties of grapevine during spring bud burst was characterised using infrared thermography. All plants studied showed endogenous freezing of the stems and subsequent rapid ice spread (0.47 cm/s) analogous to ice spread in bulk water suggesting ice travel in the xylem. Barriers to ice spread were observed between stembranches and more importantly between the stem and buds. Buds froze after the stem and freezing appeared to be initiated from the stem. The lack of a fully functional xylem system is proposed as the barrier to ice spread. All buds which froze suffered complete frost kill whilst frozen stem recovered unharmed. Only 58% of the buds froze and those that did not freeze survived completely.