15,553 research outputs found
The role of spinning electrons in paramagnetic phenomena
An attempt is made to explain paramagnetic phenomena without assuming the orientation of a molecule or ion in a magnetic field. Only the spin angular momentum is assumed to be responsible. A derivative of the Gurie-Langevin law and the magnetic moments of ions are given as a function of the number of electrons in an inner, incomplete shell. An explanation of Gerlach's experiments with iron and nickel vapors is attempted. An explanation of magnetomechanical experiments with ferromagne elements is given
Analysis of somatic mutations across the kinome reveals loss-of-function mutations in multiple cancer types
AbstractIn this study we use somatic cancer mutations to identify important functional residues within sets of related genes. We focus on protein kinases, a superfamily of phosphotransferases that share homologous sequences and structural motifs and have many connections to cancer. We develop several statistical tests for identifying Significantly Mutated Positions (SMPs), which are positions in an alignment with mutations that show signs of selection. We apply our methods to 21,917 mutations that map to the alignment of human kinases and identify 23 SMPs. SMPs occur throughout the alignment, with many in the important A-loop region, and others spread between the N and C lobes of the kinase domain. Since mutations are pooled across the superfamily, these positions may be important to many protein kinases. We select eleven mutations from these positions for functional validation. All eleven mutations cause a reduction or loss of function in the affected kinase. The tested mutations are from four genes, including two tumor suppressors (TGFBR1 and CHEK2) and two oncogenes (KDR and ERBB2). They also represent multiple cancer types, and include both recurrent and non-recurrent events. Many of these mutations warrant further investigation as potential cancer drivers.</jats:p
Quasilocal energy for rotating charged black hole solutions in general relativity and string theory
We explore the (non)-universality of Martinez's conjecture, originally
proposed for Kerr black holes, within and beyond general relativity. The
conjecture states that the Brown-York quasilocal energy at the outer horizon of
such a black hole reduces to twice its irreducible mass, or equivalently, to
\sqrt{A} /(2\sqrt{pi}), where `A' is its area. We first consider the charged
Kerr black hole. For such a spacetime, we calculate the quasilocal energy
within a two-surface of constant Boyer-Lindquist radius embedded in a constant
stationary-time slice. Keeping with Martinez's conjecture, at the outer horizon
this energy equals the irreducible mass. The energy is positive and
monotonically decreases to the ADM mass as the boundary-surface radius
diverges. Next we perform an analogous calculation for the quasilocal energy
for the Kerr-Sen spacetime, which corresponds to four-dimensional rotating
charged black hole solutions in heterotic string theory. The behavior of this
energy as a function of the boundary-surface radius is similar to the charged
Kerr case. However, we show that in this case it does not approach the
expression conjectured by Martinez at the horizon.Comment: 15 page
Multi-Qubit Gates in Arrays Coupled by 'Always On' Interactions
Recently there has been interest in the idea of quantum computing without
control of the physical interactions between component qubits. This is highly
appealing since the 'switching' of such interactions is a principal difficulty
in creating real devices. It has been established that one can employ 'always
on' interactions in a one-dimensional Heisenberg chain, provided that one can
tune the Zeeman energies of the individual (pseudo-)spins. It is important to
generalize this scheme to higher dimensional networks, since a real device
would probably be of that kind. Such generalisations have been proposed, but
only at the severe cost that the efficiency of qubit storage must *fall*. Here
we propose the use of multi-qubit gates within such higher-dimensional arrays,
finding a novel three-qubit gate that can in fact increase the efficiency
beyond the linear model. Thus we are able to propose higher dimensional
networks that can constitute a better embodiment of the 'always on' concept - a
substantial step toward bringing this novel concept to full fruition.Comment: 20 pages in preprint format, inc. 3 figures. This version has fixed
typos and printer-friendly figures, and is to appear in NJ
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