Measurability of Wilson loop operators

We show that the nondemolition measurement of a spacelike Wilson loop operator W(C) is impossible in a relativistic non-Abelian gauge theory. In particular, if two spacelike-separated magnetic flux tubes both link with the loop C, then a nondemolition measurement of W(C) would cause electric charge to be transferred from one flux tube to the other, a violation of relativistic causality. A destructive measurement of W(C) is possible in a non-Abelian gauge theory with suitable matter content. In an Abelian gauge theory, many cooperating parties distributed along the loop C can perform a nondemolition measurement of the Wilson loop operator if they are equipped with a shared entangled ancilla that has been prepared in advance. We also note that Abelian electric charge (but not non-Abelian charge) can be transported superluminally, without any accompanying transmission of information.Comment: 17 pages, 7 figures, REVTe

Efficient networks for quantum factoring

We consider how to optimize memory use and computation time in operating a quantum computer. In particular, we estimate the number of memory quantum bits (qubits) and the number of operations required to perform factorization, using the algorithm suggested by Shor [in Proceedings of the 35th Annual Symposium on Foundations of Computer Science, edited by S. Goldwasser (IEEE Computer Society, Los Alamitos, CA, 1994), p. 124]. A K-bit number can be factored in time of order K3 using a machine capable of storing 5K+1 qubits. Evaluation of the modular exponential function (the bottleneck of Shor’s algorithm) could be achieved with about 72K3 elementary quantum gates; implementation using a linear ion trap would require about 396K3 laser pulses. A proof-of-principle demonstration of quantum factoring (factorization of 15) could be performed with only 6 trapped ions and 38 laser pulses. Though the ion trap may never be a useful computer, it will be a powerful device for exploring experimentally the properties of entangled quantum states

Trends for Outer Disk Profiles

The surface-brightness profiles of galaxy disks fall into three main classes, based on whether they are simple exponentials (Type I), bend down at large radii (Type II, "truncations") or bend up at large radii (Type III, "antitruncations"). Here, we discuss how the frequency of these different profiles depends on Hubble type, environment, and the presence or absence of bars; these trends may herald important new tests for disk formation models.Comment: LaTeX, 2 pages, 1 EPS figure, uses modified newpasp.sty (included). To appear in Formation and Evlution of Galaxy Disks, eds. J.G. Funes and E.M. Corsin

The PHANTOM Omni as an under-actuated robot

As haptic interactions begin leaving research areas for commercial applications, accurate user interactions with virtual objects take new precedence. A common, low-cost haptic interface device is the PHANTOM Omni. This device has six degrees of freedom for positioning, allowing the user to position and orientate the device anywhere in its workspace. One downside to the PHANTOM is that it only has motors for controlling the position of the device, meaning the orientation of the device does not affect the interactions felt by the user through the haptic code. However, it is possible to incorporate these un-actuated joints to affect the force the user experiences, giving a feeling similar to bending a rod. Two methods are explored: a simple spatial analysis technique using Bezier curves and a more general virtual manipulator synchronization method using a null-space filter to determine device movement

Tissue-specific regulation of 1,25-dihydroxyvitamin D action in the target tissues of rats

Tissue response to 1,25(OH)[subscript]2D[subscript]3 action was evaluated by examining vitamin D-dependent VDR, 24-OHase, and CaBP mRNA expressions, 24-OHase activities, and VDR concentrations in kidney and intestine. Of 4 groups of rats, 2 groups were fed an adequate vitamin D (300-600 IU/wk), 1.0-1.2% calcium (Ca) diet, designated NC, and 2 groups were fed an adequate vitamin D, 0.02% Ca diet, designated LC. One group from each diet was treated with excess vitamin D[subscript]3 (75,000 IU/wk). These groups were designated NCT and LCT, respectively;Plasma 1,25(OH)[subscript]2D[subscript]3 concentrations were quantified and used to calculate metabolic clearance rates (MCR) and production rates (PR) of 1,25(OH)[subscript]2D[subscript]3. Plasma 1,25(OH)[subscript]2D[subscript]3 concentration in NCT rats was low to normal compared with that of NC rats. An increase in plasma 1,25(OH)[subscript]2D[subscript]3 concentration was measured in LC rats (5- to 6-fold) over that of NC rats. Plasma 1,25(OH)[subscript]2D[subscript]3 concentration in LCT rats was not significantly increased. Increases in 1,25(OH)[subscript]2D[subscript]3 PR in hypercalcemic NCT rats by 3 fold and in 1,25(OH)[subscript]2D[subscript]3 MCR in hypocalcemic LCT rats by 3.8-fold, indicated induction of extrarenal 1[alpha]-hydroxylase and 24-hydroxylase, respectively;Plasma PTH concentrations were low (~45 pg/ml) in both NC and NCT rats. Dietary Ca restriction of both LC and LCT groups, however, caused a significant (P \u3c 0.01) and proportional increases in PTH concentration. In the kidney, VDR concentration and 24-OHase activity in NCT rats were increased, but these responses were decreased in LC and LCT rats. In similar fashion, the expression of renal VDR, 24-OHase, and CaBP mRNAs were increased in NCT rats and decreased in LC and LCT rats. In the intestine, VDR concentration was increased by NCT treatment, however, 24-OHase activity appeared suppressed. Thyroparathyroidectomy of NCT rats resulted in a 2-fold increase in intestinal 24-OHase activity over that of intact NCT rats, which suggested a potential role of calcitonin in the suppression of intestinal 24-OHase. Furthermore, calcitonin administration to LCT rats resulted in a significant (P \u3c 0.001) decrease in intestinal 24-OHase mRNA expression. The same calcitonin effect was not attributable to kidney;These results demonstrate tissue-specific regulation of 1,25(OH)[subscript]2D[subscript]3 action in rat kidney and intestine. The data also are suggestive of a novel role for calcitonin as a negative modulator of intestinal 24-OHase activity that would potentially block an important inactivation pathway of 1,25(OH)[subscript]2D[subscript]3