Are certain dividend increases predictable? The effect of repeated dividend increases on market returns

Positive abnormal returns around dividend increase announcements are well documented. The conventional explanation for these abnormal returns is that a dividend increase conveys favorable information about a firms prospects causing the stock price to increase in response to the announcement. This study offers a new perspective by studying a special group of firms that consistently increase their dividends each year. Abnormal returns around each dividend increase announcement are investigated based on the number of consecutive annual increases. In light of survey results that indicate firms endeavor to maintain steady dividend payments, one hypothesis is that after a certain number of dividend increases, a firm may develop a reputation as a dividend-increasing firm and consequently the market will learn to anticipate future dividend increases. Consistent with this hypothesis, we find that abnormal returns are significantly positive for the first and second dividend increase. Returns are not significant for all other increases, with the exception of the ninth consecutive increase. Our results suggest that, by the third consecutive increase, the market has learned to expect further increases. Our findings are robust and provide further evidence that, consistent with other types of corporate announcements, the stock market reacts differently depending on the frequency of an action

Structure of matter in strong magnetic fields

We give a detailed presentation of Hartree-Fock calculations of atoms and molecular chains in 10^12 G magnetic fields, as are supposed to exist on the surface of neutron stars. These calculations are the first self-consistent ones treating exchange properly for atoms heavier than helium in high fields. We find that the isolated atom is energetically favored over molecular chains for Z>2 at fields greater than 1×10^12G and for Z>4 at fields greater than 5×10^12 G. These results indicate that matter on the surface of neutron stars is bound very weakly, if at all

First optical images of circumstellar dust surrounding the debris disk candidate HD 32297

Near-infrared imaging with the Hubble Space Telescope recently revealed a circumstellar dust disk around the A star HD 32297. Dust scattered light is detected as far as 400 AU radius and the linear morphology is consistent with a disk ~10 degrees away from an edge-on orientation. Here we present the first optical images that show the dust scattered light morphology from 560 to 1680 AU radius. The position angle of the putative disk midplane diverges by 31 degrees and the color of dust scattering is most likely blue. We associate HD 32297 with a wall of interstellar gas and the enigmatic region south of the Taurus molecular cloud. We propose that the extreme asymmetries and blue disk color originate from a collision with a clump of interstellar material as HD 32297 moves southward, and discuss evidence consistent with an age of 30 Myr or younger.Comment: 5 pages; Accepted for publication in ApJ Letter

A Simplified Approach to Optimally Controlled Quantum Dynamics

A new formalism for the optimal control of quantum mechanical physical observables is presented. This approach is based on an analogous classical control technique reported previously[J. Botina, H. Rabitz and N. Rahman, J. chem. Phys. Vol. 102, pag. 226 (1995)]. Quantum Lagrange multiplier functions are used to preserve a chosen subset of the observable dynamics of interest. As a result, a corresponding small set of Lagrange multipliers needs to be calculated and they are only a function of time. This is a considerable simplification over traditional quantum optimal control theory[S. shi and H. Rabitz, comp. Phys. Comm. Vol. 63, pag. 71 (1991)]. The success of the new approach is based on taking advantage of the multiplicity of solutions to virtually any problem of quantum control to meet a physical objective. A family of such simplified formulations is introduced and numerically tested. Results are presented for these algorithms and compared with previous reported work on a model problem for selective unimolecular reaction induced by an external optical electric field.Comment: Revtex, 29 pages (incl. figures

Error-resistant Single Qubit Gates with Trapped Ions

Coherent operations constitutive for the implementation of single and multi-qubit quantum gates with trapped ions are demonstrated that are robust against variations in experimental parameters and intrinsically indeterministic system parameters. In particular, pulses developed using optimal control theory are demonstrated for the first time with trapped ions. Their performance as a function of error parameters is systematically investigated and compared to composite pulses.Comment: 5 pages 5 figure

ROSAT X-ray Spectral Properties of Nearby Young Associations: TW Hydrae, Tucana-Horologium, and the beta Pic Moving Group

We present archival ROSAT data for three recently identified, nearby (D<70 pc), young (~10-40 Myr) stellar associations: the TW Hydrae Association, the Tucana-Horologium Association, and the beta Pic Moving Group. The distributions of ROSAT X-ray hardness ratios (HR1, HR2) for these three groups, whose membership is dominated by low-mass, weak-lined T Tauri stars, are tightly clustered and very similar to one another. The value of HR1 for TW Hya itself -- the only bona fide classical T Tauri star in any of the nearby groups -- is clearly anomalous among these nearby young stars. We compare the hardness ratio distributions of stars in the three nearby groups with those of T Tauri stars, the Hyades, and main sequence dwarfs in the field. This comparison demonstrates that the X-ray spectra of F through M stars soften with age, and that F and G stars evolve more rapidly in X-ray spectral hardness than do K and M stars. It is as yet unclear whether this trend can be attributed to age-dependent changes in the intrinsic X-ray spectra of stars of type F and later, to a decrease in the column density of circumstellar gas (e.g., in residual protoplanetary disks), or to the diminishing contributions of star-disk interactions to X-ray emission. Regardless, these results demonstrate that analysis of archival ROSAT X-ray spectral data can help both to identify nearby, young associations and to ascertain the X-ray emission properties of members of known associations.Comment: 17 pages, 4 figures; accepted by the Astrophysical Journa

Raman cooling and heating of two trapped Ba+ ions

We study cooling of the collective vibrational motion of two 138Ba+ ions confined in an electrodynamic trap and irradiated with laser light close to the resonances S_1/2-P_1/2 (493 nm) and P_1/2-D_3/2 (650 nm). The motional state of the ions is monitored by a spatially resolving photo multiplier. Depending on detuning and intensity of the cooling lasers, macroscopically different motional states corresponding to different ion temperatures are observed. We also derive the ions' temperature from detailed analytical calculations of laser cooling taking into account the Zeeman structure of the energy levels involved. The observed motional states perfectly match the calculated temperatures. Significant heating is observed in the vicinity of the dark resonances of the Zeeman-split S_1/2-D_3/2 Raman transitions. Here two-photon processes dominate the interaction between lasers and ions. Parameter regimes of laser light are identified that imply most efficient laser cooling.Comment: 8 pages, 5 figure

Rotation periods of Post-T Tauri stars in Lindroos systems

We present a rotational study of Post-T Tauri stars (PTTSs) in Lindroos systems, defined as binaries with early type primaries on the main-sequence (MS) and late-type secondaries on the pre-main-sequence (PMS) phase. The importance of this study in comparison with previous ones is that the Lindroos sample is not X-ray selected so we avoid a possible bias towards fast rotators. In this preliminary study we have monitored eleven stars in the UBVRI bands during two campaigns of ten consecutive nights each. Eight of the observed PTTSs show periodic modulations in their lightcurves and the derived periods range from 1.9d to 8.0d. The comparison of these results with theoretical rotational tracks based on disk-star locking theory shows that star-disk decoupling times of 1-20 Myr could reproduce the rotational properties of the targets, assuming an initial rotation period of ~8d and a mass of 1 Mo. We have studied the rotation-activity relations of Lindroos PTTSs and compared them with those found in other groups of PMS and zero-age main-sequence (ZAMS) ~1 Mo stars. The Lindroos sample displays activity-rotation relations very similar to those found in TTSs. It contains a mixture of very active stars, with Lx/Lbol ratios close to the saturation level of -3, and less active (unsaturated) stars. This could be the result of different star-disk decoupling times. Future monitoring of a larger and unbiased sample of PTTS will be important to confirm the significance of these results

Hudson's Theorem for finite-dimensional quantum systems

We show that, on a Hilbert space of odd dimension, the only pure states to possess a non-negative Wigner function are stabilizer states. The Clifford group is identified as the set of unitary operations which preserve positivity. The result can be seen as a discrete version of Hudson's Theorem. Hudson established that for continuous variable systems, the Wigner function of a pure state has no negative values if and only if the state is Gaussian. Turning to mixed states, it might be surmised that only convex combinations of stabilizer states give rise to non-negative Wigner distributions. We refute this conjecture by means of a counter-example. Further, we give an axiomatic characterization which completely fixes the definition of the Wigner function and compare two approaches to stabilizer states for Hilbert spaces of prime-power dimensions. In the course of the discussion, we derive explicit formulas for the number of stabilizer codes defined on such systems.Comment: 17 pages, 3 figures; References updated. Title changed to match published version. See also quant-ph/070200

X-ray Properties of Pre--Main-Sequence Stars in the Orion Nebula Cluster with Known Rotation Periods

We re-analyze all archival Chandra/ACIS observations of the Orion Nebula Cluster (ONC) to study the X-ray properties of a large sample of pre--main-sequence (PMS) stars with optically determined rotation periods. Our goal is to elucidate the origins of X-rays in PMS stars by seeking out connections between the X-rays and the mechanisms most likely driving their production--rotation and accretion. In our sample X-ray luminosity is significantly correlated with stellar rotation, in the sense of decreasing Lx/Lbol with more rapid rotation, suggesting that these stars are in the "super-saturated" regime of the rotation-activity relationship. However, we also find that stars with optical rotation periods are significantly biased to high Lx. This is not the result of magnitude bias in the optical rotation-period sample but rather to the diminishingly small amplitude of optical variations in stars with low Lx. Evidently, there exists in the ONC a population of stars whose rotation periods are unknown and that possess lower average X-ray luminosities than those of stars with known rotation periods. These stars may sample the linear regime of the rotation-activity relationship. Accretion also manifests itself in X-rays, though in a somewhat counterintuitive fashion: While stars with spectroscopic signatures of accretion show harder X-ray spectra than non-accretors, they show lower X-ray luminosities and no enhancement of X-ray variability. We interpret these findings in terms of a common origin for the X-ray emission observed from both accreting and non-accreting stars, with the X-rays from accreting stars simply being attenuated by magnetospheric accretion columns. This suggests that X-rays from PMS stars have their origins primarily in chromospheres, not accretion.Comment: Accepted by the Astronomical Journal. 43 pages, 16 figure