9,526 research outputs found
Experimental investigations on sodium-filled heat pipes
The possibilities of producing heat pipes and, especially, the necessary capillary structures are discussed. Several types of heat pipes were made from stainless steel and tested at temperatures between 400 and 1055 deg C. The thermal power was determined by a calorimeter. Results indicate: bubble-free evaporation of sodium from rectangular open chennels is possible with a heat flux of more than 1,940 W/sq cm at 1055 C. The temperature drop along the tube could be measured only at low temperatures. A subdivided heat pipe worked against the gravitational field. A heat pipe with a capillary structure made of a rolled screen was supported by rings and bars operated at 250 W/sq cm heat flux in the evaporating region
Osmotic force resisting chain insertion in a colloidal suspension
We consider the problem of inserting a stiff chain into a colloidal
suspension of particles that interact with it through excluded volume forces.
The free energy of insertion is associated with the work of creating a cavity
devoid of colloid and sufficiently large to accomodate the chain. The
corresponding work per unit length is the force that resists the entry of the
chain into the colloidal suspension. In the case of a hard sphere fluid, this
work can be calculated straightforwardly within the scaled particle theory; for
solutions of flexible polymers, on the other hand, we employ simple scaling
arguments. The forces computed in these ways are shown, for nanometer chain and
colloid diameters, to be of the order of tens of pN for solution volume
fraction for biophysical processes such as the ejection of DNA from viral
capsids into the cell cytoplasm.Comment: 16 pages,3 figures. Accepted for publication in European Physical
Journal
Morphological Thermodynamics of Fluids: Shape Dependence of Free Energies
We examine the dependence of a thermodynamic potential of a fluid on the
geometry of its container. If motion invariance, continuity, and additivity of
the potential are fulfilled, only four morphometric measures are needed to
describe fully the influence of an arbitrarily shaped container on the fluid.
These three constraints can be understood as a more precise definition for the
conventional term "extensive" and have as a consequence that the surface
tension and other thermodynamic quantities contain, beside a constant term,
only contributions linear in the mean and Gaussian curvature of the container
and not an infinite number of curvatures as generally assumed before. We verify
this numerically in the entropic system of hard spheres bounded by a curved
wall.Comment: 4 pages, 3 figures, accepted for publication in PR
The final frontier: what is distinctive about the bioethics of space missions? The cases of human enhancement and human reproduction
We examine the bioethical issues that arise from long-duration space missions, asking what there is that is distinctive about such issues. We pay particular attention to the possibility that such space missions, certainly if they lead to self-sustaining space settlements, may require human enhancement, and examine the significance of reproduction in space for bioethics. We conclude that while space bioethics raises important issues to do with human survival and reproduction in very hazardous environments, it raises no issues that are distinct from those in terrestrial bioethics. Rather, space bioethics raises extreme versions of bioethical issues that are already found in the military, when working in extreme environments (such as Antarctica), or when living in circumstances (such as in prison) where one’s autonomy is severely curtailed
Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers
This work reports on the magnetic interlayer coupling between two amorphous
CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic
coupling which oscillates as a function of the Ru thickness x, with the second
antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the
switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found
that the coercivity depends on the net magnetic moment, i.e. the thickness
difference of the two CoFeB layers. The antiferromagnetic coupling is almost
independent on the annealing temperatures up to 300 degree C while an annealing
at 350 degree C reduces the coupling and increases the coercivity, indicating
the onset of crystallization. Used as a soft electrode in a magnetic tunnel
junction, a high tunneling magnetoresistance of about 50%, a well defined
plateau and a rectangular switching behavior is achieved.Comment: 3 pages, 3 figure
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