16,979 research outputs found
Proof of a generalized Geroch conjecture for the hyperbolic Ernst equation
We enunciate and prove here a generalization of Geroch's famous conjecture
concerning analytic solutions of the elliptic Ernst equation. Our
generalization is stated for solutions of the hyperbolic Ernst equation that
are not necessarily analytic, although it can be formulated also for solutions
of the elliptic Ernst equation that are nowhere axis-accessible.Comment: 75 pages (plus optional table of contents). Sign errors in elliptic
case equations (1A.13), (1A.15) and (1A.25) are corrected. Not relevant to
proof contained in pape
Carbon nanotubes immersed in superfluid helium: the Impact of quantum confinement on wetting and capillary action
7 págs.; 5 figs.; 1 tab. ; Associated content mp4 video: http://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.6b02414A recent experimental study [Ohba, Sci. Rep. 2016,
6, 28992] of gas adsorption on single-walled carbon nanotubes at
temperatures between 2 and 5 K reported a quenched propagation
of helium through carbon nanotubes with diameters below 7 Å
despite the small kinetic diameter of helium atoms. After assessing
the performance of a potential model for the He−nanotube
interaction via ab initio calculations with density functional theorybased
symmetry adapted perturbation theory, we apply orbital-free
helium density functional theory to show that the counterintuitive
experimental result is a consequence of the exceptionally high zeropoint
energy of helium and its tendency to form spatially separated
layers of helium upon adsorption at the lowest temperatures.
Helium filling factors are derived for a series of carbon nanotubes
and compared to the available experimental data. © 2016 American Chemical SocietyThis work has been supported by the COST Action CM1405
“Molecules in Motion (MOLIM)”. M.P.d.L.-C. gratefully
acknowledges support from MINECO (Spain) under Grant
MAT2016-75354-P and thanks the CTI (CSIC) and CESGA
supercomputer facilities (Spain) for the resources provided.Peer reviewe
Monodromy-data parameterization of spaces of local solutions of integrable reductions of Einstein's field equations
For the fields depending on two of the four space-time coordinates only, the
spaces of local solutions of various integrable reductions of Einstein's field
equations are shown to be the subspaces of the spaces of local solutions of the
``null-curvature'' equations constricted by a requirement of a universal (i.e.
solution independent) structures of the canonical Jordan forms of the unknown
matrix variables. These spaces of solutions of the ``null-curvature'' equations
can be parametrized by a finite sets of free functional parameters -- arbitrary
holomorphic (in some local domains) functions of the spectral parameter which
can be interpreted as the monodromy data on the spectral plane of the
fundamental solutions of associated linear systems. Direct and inverse problems
of such mapping (``monodromy transform''), i.e. the problem of finding of the
monodromy data for any local solution of the ``null-curvature'' equations with
given canonical forms, as well as the existence and uniqueness of such solution
for arbitrarily chosen monodromy data are shown to be solvable unambiguously.
The linear singular integral equations solving the inverse problems and the
explicit forms of the monodromy data corresponding to the spaces of solutions
of the symmetry reduced Einstein's field equations are derived.Comment: LaTeX, 33 pages, 1 figure. Typos, language and reference correction
Studies on the market milk of Iowa
A study of market milk conditions in Iowa by the market milk laboratory of the dairy department at Iowa State College reveals the fact that the state has a real milk problem to deal with.
In the cities and towns in which the investigation was carried on, the results indicate these facts:
The milk and cream, whether raw or pasteurized, commonly contains excessive numbers of bacteria, altho samples without excessive numbers were sometimes found.
The presence of large numbers of bacteria in pasteurized milk and cream indicates that the heat exposure used in some plants is too low, altho improper handling after pasteurization is also partly responsible for this condition
Fermented Milk
The consumption of various types of fermented milk is common in all countries in which milk is available. The food value of such products is unquestioned and their desirability, especially in the case of certain intestinal disorders, is insisted on by many persons. The recent necessity for food conservation has emphasized the possibility of preparing nourishing beverages as well as liquids to be used in cookery from skim milk, buttermilk and whey, which would otherwise be discarded or used for animal feeding
The pasteurization of milk in the final package
In the work reported in this bulletin an effort was made to determine the most favorable vat temperature and time of exposure for final package pasteurization. The only type of cap used was the Dacro cap, although; probably in a general way the results would be applicable also to other packages used for pasteurizing. The points considered in the determination were bacterial efficiency, creaming ability and the heated flavor produced.
High pasteurization temperatures are undesirable because of the reduced creaming ability and marked heated flavor of milk so treated
Iowa Educational Market Milk Contest
According to the United States Department of Agriculture, the firnt milk and cream contest In this country was held at the National Dairy Show at Chicago In 1906. Since that time such contests have been held in conjunction with various dairy shows, fairs and other meetings, such as campaigns for the improvement of city milk supplies, In which milk producers and dealers were Interested; up to February, 1915, 87 such contests had been judged by members of the Dairy division or the United States Department or Agriculture.
In general, it is believed that these contests have been of distinct service from an educational standpoint In teaching exhibitors the ad· vantages or disadvantages of various methods of handling milk, altho It Is recognized that commonly the attention given to the exhibited milk or cream is not given to the general supply.
The Dairy department of Iowa State college held its first educational market milk contest December 2.J, 1914, in connection with Its annual short course. Previous studies had shown that much of the milk (both raw and pasteurized) sold In the state was not of the quality it should be and the contest was proposed as a means of stimulating its Improvement
Studies on the clarification of milk—II
In a former publication of this station the results obtained in a study of the clarification of milk with the DeLaval clarifier are presented. The data show: first that commonly, altho by no means constantly, the plates poured from clarified milk contained a larger number of colonies than plates poured from Unclarified milk of the same lot; this was undoubtedly due to a breaking up of the clumps of organisms and should be spoken of as an \u27apparent increase since the large number of bacteria in the slime indicates that there was actually an elimination of organisms; second, that there was in every case a decrease in the number of cells during clarification; third, that the clarifier slime contained a large number of bacteria and cells in addition to a variable amount of dirt and sometimes red blood cells. The publication pointed out that, while it must \u27be admitted it would be desirable to prevent foreign material from getting into milk, this is impossible for the great bulk of our milk supply because of the increased cost of production and that accordingly clarification of milk followed by efficient pasteurization must be looked upon as a commendable substitution
Observables for spacetimes with two Killing field symmetries
The Einstein equations for spacetimes with two commuting spacelike Killing
field symmetries are studied from a Hamiltonian point of view. The complexified
Ashtekar canonical variables are used, and the symmetry reduction is performed
directly in the Hamiltonian theory. The reduced system corresponds to the field
equations of the SL(2,R) chiral model with additional constraints.
On the classical phase space, a method of obtaining an infinite number of
constants of the motion, or observables, is given. The procedure involves
writing the Hamiltonian evolution equations as a single `zero curvature'
equation, and then employing techniques used in the study of two dimensional
integrable models. Two infinite sets of observables are obtained explicitly as
functionals of the phase space variables. One set carries sl(2,R) Lie algebra
indices and forms an infinite dimensional Poisson algebra, while the other is
formed from traces of SL(2,R) holonomies that commute with one another. The
restriction of the (complex) observables to the Euclidean and Lorentzian
sectors is discussed.
It is also shown that the sl(2,R) observables can be associated with a
solution generating technique which is linked to that given by Geroch.Comment: 23 pages (LateX-RevTeX), Alberta-Thy-55-9
Growth control of GaAs nanowires using pulsed laser deposition with arsenic over pressure
Using pulsed laser ablation with arsenic over pressure, the growth conditions
for GaAs nanowires have been systematically investigated and optimized. Arsenic
over pressure with As molecules was introduced to the system by thermal
decomposition of polycrystalline GaAs to control the stoichiometry and shape of
the nanowires during growth. GaAs nanowires exhibit a variety of geometries
under varying arsenic over pressure, which can be understood by different
growth processes via vapor-liquid-solid mechanism. Single-crystal GaAs
nanowires with uniform diameter, lengths over 20 m, and thin surface oxide
layer were obtained and can potentially be used for further electronic
characterization
- …