Short pulse laser-induced dissociation of vibrationally cold, trapped molecular ions

An electrostatic trapping scheme for use in the study of light-induced dissociation of molecular ions is outlined. We present a detailed description of the electrostatic reflection storage device and specifically demonstrate its use in the preparation of a vibrationally cold ensemble of deuterium hydride (HD+) ions. By interacting an intense femtosecond laser with this target and detecting neutral fragmentation products, we are able to elucidate previously inaccessible dissociation dynamics for fundamental diatomics in intense laser fields. In this context, we present new results of intense field dissociation of HD+ which are interpreted in terms of recent theoretical calculations.

Double-ionization dynamics of laser-driven helium

We report a new method which allows sequential and non-sequential double-ionization rates in laser-driven helium to be distinguished and calculated separately. The method is applied to calculate such rates for two laser pulses, one of 0.236 au frequency and 8.0 × 1015 W cm-2 peak intensity, the other of 1.0 au frequency and also of 8.0 × 1015 W cm-2 peak intensity.

On the mechanism for optomechanical entanglement and its revelation

An intuitive and accurate picture of the occurrence of optomechanical entanglement in a system of great current experimental interest is provided. At the optimal working point for entanglement generation, the interaction of a light field with a micromechanical oscillator is described in terms of simple SU( 2) transformations. This allows the analysis of a recent proposal for the revelation of quantumness in the state of a massive mirror from a clear and experimentally biased viewpoint.

Noise resilience and entanglement evolution in two nonequivalent classes of quantum algorithms

The speedup provided by quantum algorithms with respect to their classical counterparts is at the origin of scientific interest in quantum computation. However, the fundamental reasons for such a speedup are not yet completely understood and deserve further attention. In this context, the classical simulation of quantum algorithms is a useful tool that can help us in gaining insight. Starting from the study of general conditions for classical simulation, we highlight several important differences between two nonequivalent classes of quantum algorithms. We investigate their performance under realistic conditions by quantitatively studying their resilience with respect to static noise. This latter refers to errors affecting the initial preparation of the register used to run an algorithm. We also compare the evolution of the entanglement involved in the different computational processes.

SRIF receptor subtype expression and involvement in positive and negative contractile effects of somatostatin-14 (SRIF-14) in ventricular cardiomyocytes.

Background/Aims: Somatostatin-14 (SRIF-14), a neuropeptide co-stored with acetylcholine in the cardiac parasympathetic innervation, exerts both positive and negative influences directly on contraction of ventricular cardiomyocytes, indicative of involvement of more than one of five known SRIF (SSTR) receptor subtypes. The aim was to characterize receptor subtype expression in adult rat ventricular cardiomyocytes and to investigate the influence of a series of SRIF (SSTR) subtype-selective agonists on contractile parameters. Methods: mRNA and protein expression of each receptor subtype were quantified by RT-PCR and immunoblotting respectively; for contraction studies, cells were stimulated at 0.5 Hz under basal conditions and in the presence of isoprenaline (ISO, 10-8M). Results: all five SRIF (SSTR) receptor subtypes were expressed in cardiomyocytes although SRIF1A (SSTR2) and SRIF2A (SSTR1) were less abundant than the other subtypes. L803087 (10-8M), a SRIF2B (SSTR4) agonist, attenuated ISO-stimulated peak contractile amplitude and prolonged relaxation time (T50). L796778 (10-7M), a SRIF1C (SSTR3) agonist, augmented basal and ISO-stimulated peak contractile amplitude; L779976 (10-8M) and L817818 (10-9M), agonists at SRIF1A (SSTR2) and SRIF1B (SSTR5) receptors, respectively, also augmented ISO-stimulated peak amplitude. Conclusion: these data support involvement of SRIF2B (SSTR4) receptors in the negative contractile effects of SRIF-14, while one or more of the three SRIF1 receptor subtypes (SSTR2, 3 or 5) may contribute to the positive contractile effects of SRIF-14.

High precision C-14 dating of Holocene peat deposits: A comparison of Bayesian calibration and wiggle-matching approaches

The chronologies of five northern European ombrotrophic peat bogs subjected to a large ANIS C-14 dating effort (32-44 dates/site) are presented here. The results of Bayesian calibration (BCal) of dates with a prior assumption of chronological ordering were compared with a Bayesian wiggle-match approach (Bpeat) which assumes constant linear accumulation over sections of the peat profile. Interpolation of BCal age estimates of dense sequences of C-14 dates showed variable patterns of peat accumulation with time, with changes in accumulation occurring at intervals ranging from 20 to 50 cm. Within these intervals, peat accumulation appeared to be relatively linear. Close analysis suggests that some of the inferred variations in accumulation rate were related to the plant macrofossil composition of the peat. The wiggle-matched age-depth models had relatively high chronological uncertainty within intervals of closely spaced 14 C dates, suggesting that the premise of constant linear accumulation over large sections of the peat profile is unrealistic. Age models based on the assumption of linear accumulation over large parts of a peat core (and therefore only effective over millennial timescales), are not compatible with studies examining environmental change during the Holocene, where variability often occurs at decadal to centennial time-scales. Ideally, future wiggle-match age models should be constrained, with boundaries between sections based on the plant macrofossil composition of the peat and physical-chemical parameters such as the degree of decomposition. Strategies for the selection of material for dating should be designed so that there should be enough C-14 dates to accurately reconstruct the peat accumulation rate of each homogeneous stratigraphic unit. (c) 2006 Elsevier Ltd. All rights reserved.

Changes in solar activity and Holocene climatic shifts derived from C-14 wiggle-match dated peat deposits

Closely spaced sequences of accelerator mass spectrometer (AMS) C-14 dates of peat deposits display century-scale wiggles which can be fitted to the radiocarbon calibration curve. By wiggle-matching such sequences, high-precision calendar age chronologies can be generated which show that changes in mire surface wetness during the Bronze Age/Iron Age transition (c. 850 cal. BC) and the 'Little Ice Age' (Wolf, Sporer, Maunder and Dalton Minima) occurred during periods of suddenly increasing atmospheric concentration of C-14. Replicate evidence from peat-based proxy climate indicators in northwest Europe suggest these changes in climate may have been driven by temporary declines of solar activity. Carbon-accumulation rates of two raised peat bogs in the UK and Denmark record low values during the 'Little Ice Age' which reflects reduced primary productivity of the peat-forming vegetation during these periods of climatic deterioration.