Entanglement of internal and external angular momenta of a single atom

We consider the exchange of spin and orbital angular momenta between a circularly polarized Laguerre-Gaussian beam of light and a single atom trapped in a two-dimensional harmonic potential. The radiation field is treated classically but the atomic center-of-mass motion is quantized. The spin and orbital angular momenta of the field are individually conserved upon absorption, and this results in the entanglement of the internal and external degrees of freedom of the atom. We suggest applications of this entanglement in quantum information processing.Comment: 4 pages, 2 figure

Locally Optimal Load Balancing

This work studies distributed algorithms for locally optimal load-balancing: We are given a graph of maximum degree $\Delta$, and each node has up to $L$ units of load. The task is to distribute the load more evenly so that the loads of adjacent nodes differ by at most $1$. If the graph is a path ($\Delta = 2$), it is easy to solve the fractional version of the problem in $O(L)$ communication rounds, independently of the number of nodes. We show that this is tight, and we show that it is possible to solve also the discrete version of the problem in $O(L)$ rounds in paths. For the general case ($\Delta > 2$), we show that fractional load balancing can be solved in $\operatorname{poly}(L,\Delta)$ rounds and discrete load balancing in $f(L,\Delta)$ rounds for some function $f$, independently of the number of nodes.Comment: 19 pages, 11 figure

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Theory of the optical absorption of light carrying orbital angular momentum by semiconductors

We develop a free-carrier theory of the optical absorption of light carrying orbital angular momentum (twisted light) by bulk semiconductors. We obtain the optical transition matrix elements for Bessel-mode twisted light and use them to calculate the wave function of photo-excited electrons to first-order in the vector potential of the laser. The associated net electric currents of first and second-order on the field are obtained. It is shown that the magnetic field produced at the center of the beam for the $\ell=1$ mode is of the order of a millitesla, and could therefore be detected experimentally using, for example, the technique of time-resolved Faraday rotation.Comment: Submitted to Phys. Rev. Lett. (23 Jan 2008

Cross-Document Pattern Matching

We study a new variant of the string matching problem called cross-document string matching, which is the problem of indexing a collection of documents to support an efficient search for a pattern in a selected document, where the pattern itself is a substring of another document. Several variants of this problem are considered, and efficient linear-space solutions are proposed with query time bounds that either do not depend at all on the pattern size or depend on it in a very limited way (doubly logarithmic). As a side result, we propose an improved solution to the weighted level ancestor problem

The Tree Inclusion Problem: In Linear Space and Faster

Given two rooted, ordered, and labeled trees $P$ and $T$ the tree inclusion problem is to determine if $P$ can be obtained from $T$ by deleting nodes in $T$. This problem has recently been recognized as an important query primitive in XML databases. Kilpel\"ainen and Mannila [\emph{SIAM J. Comput. 1995}] presented the first polynomial time algorithm using quadratic time and space. Since then several improved results have been obtained for special cases when $P$ and $T$ have a small number of leaves or small depth. However, in the worst case these algorithms still use quadratic time and space. Let $n_S$, $l_S$, and $d_S$ denote the number of nodes, the number of leaves, and the %maximum depth of a tree $S \in \{P, T\}$. In this paper we show that the tree inclusion problem can be solved in space $O(n_T)$ and time: O(\min(l_Pn_T, l_Pl_T\log \log n_T + n_T, \frac{n_Pn_T}{\log n_T} + n_{T}\log n_{T})). This improves or matches the best known time complexities while using only linear space instead of quadratic. This is particularly important in practical applications, such as XML databases, where the space is likely to be a bottleneck.Comment: Minor updates from last tim

Photon wave mechanics and position eigenvectors

One and two photon wave functions are derived by projecting the quantum state vector onto simultaneous eigenvectors of the number operator and a recently constructed photon position operator [Phys. Rev A 59, 954 (1999)] that couples spin and orbital angular momentum. While only the Landau-Peierls wave function defines a positive definite photon density, a similarity transformation to a biorthogonal field-potential pair of positive frequency solutions of Maxwell's equations preserves eigenvalues and expectation values. We show that this real space description of photons is compatible with all of the usual rules of quantum mechanics and provides a framework for understanding the relationships amongst different forms of the photon wave function in the literature. It also gives a quantum picture of the optical angular momentum of beams that applies to both one photon and coherent states. According to the rules of qunatum mechanics, this wave function gives the probability to count a photon at any position in space.Comment: 14 pages, to be published in Phys. Rev.

Experimental culture of black tiger shrimp Penaeus monodon Fabricius, 1798 in open sea floating cage

An experiment was designed and conducted to assess the feasibility for culture of Penaeus monodon in 6 m dia HDPE circular floating cage, installed at 10-12 m depth off Visakhapatnam in the Bay of Bengal. The cage was fixed with three cylindrical nets; inner net of 2 mm mesh (6 m dia×5.5 m height) to rear post-larvae from stock to 80th day; middle net of 10 mm mesh (6 m×5.5 m) to rear juveniles from day 81 onwards and an outer net of 40 mm mesh (8 m dia×4.5 m height) to prevent entry of predators. Post-larvae (PL23) of P. monodon (mean total length 16.1±3.8 mm), were stocked in the cage at a density of 1179 PL m-3). Bottom water parameters viz., salinity, temperature, dissolved oxygen, pH and ammonia (NH3-N) recorded in the cage site during the culture period were 34-35 ppt, 26-32°C, 3.9-4.6 ml l-1, 8.1-8.3 and 0.05-0.07 mg l-1, respectively. Shrimp feed varying in size suitable to different growth stages, was used during the trial. Feed was given twice during the first 20 days and thrice during 21-99 days. Feeding rate per day ranged from 133.3% of the biomass of shrimp at stocking time to 3.1% of the biomass of shrimp at preharvest. P. monodon registered a growth rate of 0.87 mm (TL)/0.018 g (wt) per day during first 30 days; 0.89 mm/0.069 g per day during 31-60 days and 0.37 mm/0.051 g per day during 61-90 days. On day 100, about 207 kg of shrimp (production rate, 1.62 kg m-3) was harvested and the mean size of harvested shrimp was 81.54±15.20 mm TL/4.50±2.80 g wt. Survival recorded was 31.4% and the feed conversion ratio (FCR) was 3.97. Present study demonstrated the possibility for culture of P. monodon in open sea floating cage. The possible causes for low survival and high FCR are discussed

Regulation of Heme Biosynthesis in Neurospora crassa

The mold Neurospora crassa does not accumulate porphyrins in iron deficiency but instead accumulates the sideramine desferricoprogen. In iron deficiency there is an accumulation of δ-aminolevulinic acid and the δ-aminolevulinic acid dehydratase level is very low. A similar situation exists in cobalt toxicity and zinc deficiency. The δ-aminolevulinic acid synthetase and ferroprotoporphyrin chelatase comparatively show only marginal changes under these conditions. Addition of iron and zinc to the respective metal-deficient cultures results in an induction of δ-aminolevulinic acid dehydratase. The induction of δ-aminolevulinic acid dehydratase is repressed by protoporphyrin and less effectively by hemin and hemoglobin. Iron deficiency, zinc deficiency, and cobalt toxicity have been found to interfere with the conversion of protoporphyrin into heme, thus rendering protoporphyrin available to repress the enzyme. This repression can be counteracted by iron and much more effectively by coprogen. A model has been proposed in which protoporphyrin has been visualized as the corepressor for the enzyme δ-aminolevulinic acid dehydratase. It is held that iron in the form of coprogen converts protoporphyrin to heme, the latter having a lesser affinity for the aporepressor. Coprogen can inhibit heme binding to the aporepressor and thus render the repressor nonfunctional. This will lead to a derepression of the enzyme δ-aminolevulinic acid dehydratase

Morphometric Characters and Meristic Counts of Mastacembelus armatus (Lacebede, 1800) from Maruthur Anicut, Tirunelveli District, India

The present study highlights about morphometric measurement and meristic count of Mastacembelus armatus (Lacebede, 1800) collected from the Maruthur wetland ecosystem have been investigated with 23 specimens to observe the relationship between morphometric characters. Identification of species is an initial step in any research work and plays a vital role in the behavioural study. Morphometric character analysis and meristic counts are considered as simplest and authentic methods for fish species identification which is termed as morphological systematics. Fourteen different morphometric characters in percentage of total fish length (9 characters), head length (5 characters), and five different meristic counts (branched and unbranched rays) have been studied. The obtained result reveals that morphometric characters vary depending on the growth and size of the fish. However, the meristic counts were comparatively similar. All the characters show a positive correlation both in the percentage of total length and head length. The different morphometric and meristic counts of M. armatus have been analyzed for the population dynamics which includes taxonomy study and proper identification of fishes. The fin formula was calculated for some hard rays and soft rays. Therefore, this study supplement additional data for the identification of the fish species