Comment on breakup densities of hot nuclei

In [V.E. Viola et al., Phys. Rev. Lett. 93 (2004) 132701, D.S. Bracken et al., Phys. Rev. C 69 (2004) 034612] the observed decrease in spectral peak energies of IMFs emitted from hot nuclei was interpreted in terms of a breakup density that decreased with increasing excitation energy. Subsequently, Raduta et al. [Ad. Raduta et al., Phys. Lett. B 623 (2005) 43] performed MMM simulations that showed decreasing spectral peaks could be obtained at constant density. In this Letter we point out that this apparent inconsistency is due to a selective comparison of theory and data that overlooks the evolution of the fragment multiplicities as a function of excitation energy.     

Molecular constants for the ã 3A2 state of formaldehyde

The 0⁺–0 and 1⁺–0 bands of the ā ³A₂X? ¹A₁ transition of formaldehyde have been reinvestigated using higher resolving power than was available in the earlier work of Raynes. The rotational analyses have been considerably extended, and improved molecular constants for the ā ³A₂ state have been obtained with the aid of a new triplet—singlet computer programme.^sSR branches of the K′ = 7K″ = 5 and K′ = 5K″ = 3 subbands have been observed in the 0⁺–0 band using 7m atm of absorbing gas. These results provide the first example of the observation of ΔK = ±2 transitions in triplet—singlet bands of a polyatomic molecule. The “perpendicular” transition moment is found to be about 10% of the “parallel” transition moment.     

On the empirical validity of koopmans’ theorem

The application of Koopmans' theorem is investigated within the context of the LCAO interpretation of a general SCF formalism. An empirical criterion for the validity of the assumption of identity of corresponding orbitals in the ion and parent system is discussed. Calculations on He, Li, Be and pyridine are reported.

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Zusammenfassung Die Gültigkeit von Koopmans' Theorem läßt sich mittels eines verallgemeinerten SCF-Formalismus prüfen. Ein Kriterium für das Zutreffen der Annahme, einander entsprechende Einteilchenzustände in Atom und Tochter-Ion seien identisch, wird in diesem Zusammenhang diskutiert. Die Rechnungen sind am Helium, Lithium, Beryllium und Pyridin durchgeführt worden.

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Résumé La validité du théorème de Koopmans dans un formalisme SCF général est étudiée au cadre d'une interprétation LCAO. Un critère empirique pour l'identité des orbitales de l'ion et du système père correspondant est discuté. Nous rapportons des calculs sur He, Li, Be et pyridine.

     

Motor-protein "roundabouts": microtubules moving on kinesin-coated tracks through engineered networks

Nanotechnology promises to enhance the functionality and sensitivity of miniaturized analytical systems. For example, nanoscale transport systems, which are driven by molecular motors, permit the controlled movement of select cargo along predetermined paths. Such shuttle systems may enhance the detection efficiency of an analytical system or facilitate the controlled assembly of sophisticated nanostructures if transport can be coordinated through complex track networks. This study determines the feasibility of complex track networks using kinesin motor proteins to actively transport microtubule shuttles along micropatterned surfaces. In particular, we describe the performance of three basic structural motifs: (1) crossing junctions, (2) directional sorters, and (3) concentrators. We also designed track networks that successfully sort and collect microtubule shuttles, pointing the way towards lab-on-a-chip devices powered by active transport instead of pressure-driven or electroosmotic flow.     

Order-disorder at Fe sites in SrFe2/3B″1/3O3 (B″=Mo, W, Te, U) tetragonal double perovskites

We have prepared SrFe_2/3B″_1/3O₃ (B″=Mo, U, Te, and W) double perovskites in polycrystalline form by ceramic methods. Phases with B″=U, Te and W have been studied by X-ray powder diffraction and the results have been compared with neutron diffraction data available for B″=Mo. At room temperature, the stoichiometric samples crystallize in the tetragonal crystal system (space group I4/m, Z=4). Cell parameters when B″=U, Te and W are a=5.6936(1) Å, c=8.0637(1)Å; a=5.5776(1) Å, c=7.9144(3) Å and a=5.5707(3) Å, c=7.9081(5) Å, respectively.The Mössbauer spectra at room temperature for all compounds show hyperfine parameters belonging to two Fe³⁺ sites located at lattice positions with different degrees of distortion. This is in agreement with diffraction data that indicate that the series of compounds display different degrees of Fe-site disorder, which increases in the following sequence: Mo<U<Te<W.     

Crystal Structure of LiRh-type IrZn Determined by Powder X-ray and Selected Area Electron Diffraction

The LiRh-type crystal structure of the equiatomic intermetallic compound IrZn turns out to be a competitor to the otherwise energetically favored CsCl-type structures of congeneric transition metal zinc phases, thus enlightening the structural impact of element-specific factors beyond the Hume-Rothery concept.     

High speed coding for velocity by archerfish retinal ganglion cells

ABSTRACT: BACKGROUND: Archerfish show very short behavioural latencies in response to falling prey. This raises the question, which response parameters of retinal ganglion cells to moving stimuli are best suited for fast coding of stimulus speed and direction. RESULTS: We compared stimulus reconstruction quality based on the ganglion cell response parameters latency, first interspike interval, and rate. For stimulus reconstruction of moving stimuli using latency was superior to using the other stimulus parameters. This was true for absolute latency, with respect to stimulus onset, as well as for relative latency, with respect to population response onset. Iteratively increasing the number of cells used for reconstruction decreased the calculated error close to zero. CONCLUSIONS: Latency is the fastest response parameter available to the brain. Therefore, latency coding is best suited for high speed coding of moving objects. The quantitative data of this study are in good accordance with previously published behavioural response latencies.     

Highly sensitive determination of 68 psychoactive pharmaceuticals,illicit drugs,and related human metabolites in wastewater by liquid chromatography–tandem mass spectrometry

The present work describes the development and validation of a highly sensitive analytical method for the simultaneous determination of 68 compounds, including illicit drugs (opiates, opioids, cocaine compounds, amphetamines, and hallucinogens), psychiatric drugs (benzodiazepines, barbiturates, anesthetics, antiepileptics, antipsychotics, antidepressants, and sympathomimetics), and selected human metabolites in influent and effluent wastewater (IWW and EWW) by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The method involves a pre-concentration and cleanup step, carried out by solid-phase extraction (SPE) using the adsorbent Strata-XC, followed by the instrumental analysis performed by LC–MS/MS, using a Kinetex pentafluorophenyl (PFP) reversed-phase fused-core column and electrospray ionization (ESI) in both positive and negative modes. A systematic optimization of mobile phases was performed to cope with the wide range of physicochemical properties of the analytes. The PFP column was also compared with two reversed-phase columns: fused-core C18 and XB-C18 (with a cross-butyl C18 ligand). SPE optimization and critical aspects associated with the trace level determination of the target compounds (e.g., matrix effects) have been also considered and discussed. Fragmentation patterns for all the classes were proposed. The validated method provides absolute recoveries between 75 and 120 % for most compounds in IWW and EWW. Low method limits of detection were achieved (between 0.04 and 10.0 ng/L for 87 % of the compounds), allowing a reliable and accurate quantification of the analytes at trace level. The method was successfully applied to the analysis of these compounds in five wastewater treatment plants in Santorini, a touristic island of the Aegean Sea, Greece. Thirty-two out of 68 compounds were detected in all IWW samples in the range between 0.6 ng/L (for nordiazepam) and 6,822 ng/L (for carbamazepine) and 22 out of 68 in all EWW samples, with values between 0.4 ng/L (for 9-OH risperidone) and 2,200 ng/L (for carbamazepine). The novel methodology described herein maximizes the information on the environmental analysis of these substances and also provides a first profile of 68 drugs in a Greek touristic area.