Collimated-hole structures as efficient differential pumping barrier, one-way valve and tool for aligning Penning traps

A collimated-hole structure consists of a very large number of parallel channels which have each a very small diameter and are closely packed together. Such devices, installed in vacuum systems allow one to separate regions of very different gas pressures. A collimated-hole structure has high transmission for a directed ion beam with low emittance but a very low conductance for rest gas atoms or molecules exhibiting random walk. Therefore it is proposed to use such a structure as one-way valve and/or efficient differential pumping barrier in set-ups using Penning traps. Furthermore, these devices might be very useful to align the axis of a Penning trap with the direction of the magnetic field lines which is essential to avoid systematic uncertainties in high-accuracy mass spectroscopy.     

Numerical and experimental investigation on multibody systems with revolute clearance joints

A comprehensive combined numerical and experimental study on the dynamic response of a slider-crank mechanism with revolute clearance joints is presented and discussed in this paper to provide an experimental verification and validation of the predictive capabilities of the multibody clearance joint models. This study is supported in an experimental work in a test rig, which consists of a slider-crank mechanism with an adjustable radial clearance at the revolute joint between the slider and the connecting rod. The motion of the slider is measured with a linear transducer and an accelerometer. Dynamic tests at different operating crank speeds and with several clearance sizes are performed. The maximum slider acceleration, associated with the impact acceleration, is used as a measure of the impact severity. The obtained results demonstrate the dynamical behavior of a multibody mechanical system with a clearance joint. Finally, the correlation between the numerical and experimental results is presented and discussed leading to validated models of clearance revolute joints.     

Smooth driving of M?ssbauer electromechanical transducers

Quality of Mössbauer spectra is strongly related to the performance of source velocity modulator. Traditional electromechanical driving techniques demand hard-edged square or triangular velocity waveforms that introduce long settling times and demand careful driver tuning. For this work, the behavior of commercial velocity transducers and drive units was studied under different working conditions. Different velocity reference waveforms in constant-acceleration, constant-velocity and programmable-velocity techniques were tested. Significant improvement in spectrometer efficiency and accuracy was achieved by replacing triangular and square hard edges with continuous smooth-shaped transitions. A criterion for best waveform selection and synchronization is presented and attainable enhancements are evaluated. In order to fully exploit this driving technique, a compact microprocessor-based architecture is proposed and a suitable data acquisition system implementation is presented. System linearity and efficiency characterization are also shown.     

HPLC�CDAD Analysis of Hydrochlorothiazide and Irbesartan in Hypertensive Patients on Fixed-Dose Combination Therapy

Hydrochlorothiazide (HCTZ) and the angiotensin II type 1 receptor antagonist (ARB) irbesartan (IRBE) are well-known antihypertensive drugs, frequently administered as a low-dose combination in a single pill. In this work, a simple, sensitive, and selective high-performance liquid chromatographic (HPLC) method with diode-array detection was developed for simultaneous determination of HCTZ and IRBE levels in the plasma of hypertensive patients given a fixed combination of 12.5 mg HCTZ and 300 mg IRBE. Compounds were extracted from acidified plasma samples with 3 mL ethyl acetate, and eluted at 6 and 19 min from a C₄ column by elution with an acetonitrile?Cphosphate buffer (pH 3.6) mobile-phase gradient at a flow rate of 1 mL min^?1. The assay was linear over the ranges 2.5?C500 and 20?C4,000 ng mL^?1 for HCTZ and IRBE, respectively. Overall intra-assay and inter-assay variation were within acceptance limits. Limits of quantification were 2.5 and 20 ng mL^?1 for HCTZ and IRBE, respectively. Plasma samples remained stable for 12 h at room temperature, through three thaw?Cfreeze cycles, and for 2 and 7 months at ?20 °C. In hypertensive patients, residual concentrations were 22.3 ± 6.0 and 241.8 ± 39.0 ng mL^?1 for HCTZ and IRBE, respectively. There was no interference from other co-administered drugs. Despite the different physicochemical properties of HCTZ and IRBE, our method enables accurate measurement of both drugs for assessment of compliance by patients treated by fixed-dose combination therapy with HCTZ?CIRBE.     

Formation of copper(I)-templated [2]rotaxanes using ��click�� methodology: influence of the base, the thread and the catalyst

Three new copper(I)-assembled [2]rotaxanes incorporating the same macrocycle and different axes containing a bipy, a phen or a terpy have been synthesized thanks to CuAAC reaction for attaching the stoppers. The influence of the nature of the base used for the stoppering reaction was investigated on the formation of the bipy-containing rotaxane. The yield of the [2]rotaxane synthesis was increased when using a phen as a coordinating unit in the thread with [Cu(CH₃CN)₄](PF₆) as catalyst. The strong influence of the nature of the catalyst was clearly evidenced for the formation of the terpy rotaxane, increasing the yield of the stoppering reaction from 0 to 95% by just substituting the Cu(I) catalyst. Finally, the best conditions found for our systems are the use of Na₂CO₃ as a base and Cu(tren??)Br as a catalyst.     

Indirect Study of the 2H(d,p)3H and 2H(d,n)3He Reactions at Astrophysical Energies via the Trojan Horse Method

The ²H(d,p)³H and ²H(d,n)³He reactions have been indirectly studied by means of the Trojan Horse Method applied to the quasi-free ²H(³He, p³H)¹H?²H(³He, n³He)¹H reaction at 18?MeV of beam energy. This is the first experiment where the spectator (here ¹H) has been detected in coincidence with the charged participant, avoiding the limitations of standard neutron detectors. The d ? d relative energy has been measured from 1.5?MeV down to 2?keV, at center of mass angles from 40° to 170°. Indirect angular distributions are compared with the direct behaviour in the overlapping regions.     

Aromaticity and electronic delocalization in all-metal clusters with single, double, and triple aromatic character

A series of monocyclic planar inorganic compounds with single, double, and triple (anti)aromatic character has been studied. The electron delocalization and aromaticity of these compounds have been assessed by means of two-center and multicenter electronic delocalization indices and their ??-, ??-, and ??-components. Results show that these indices are excellent predictors of the ??-, ??-, and ??-aromatic character of all-metal and semimetal clusters.     

Ochres from rituals of prehistoric human funerals at the Toca do Enoque site, Piau��, Brazil

The archaeological site known as Toca do Enoque (geographical coordinates, 09° 14?? 65.3?? S 43° 55?? 62.5?? W) is a rock shelter located in the Serra das Andorinhas (Serra das Confusões National Park), rural area of the city of Guaribas, state of Piauí, Brazil. Several rupestrian paintings (anthropomorphic and zoomorphic motifs along with some pure graphisms), predominantly in red, are found on the sandstone walls. Charcoals, lithic materials, necklaces with teeth, animal bones, gastropod shells, ochres and human skeletons (dated from 6,220 ± 40 to 6,610 ± 40 years before present, BP) were identified in recent excavations in this shelter. Red and yellow ochre samples were collected from prehistoric funeral structures and analyzed with powder X-ray diffractometry, Fourier-transform infrared spectroscopy and ⁵⁷Fe transmission Mössbauer spectroscopy at 298 K and 80 K. Mössbauer data indicate that the red ochre do contain predominantly hematite (??-Fe₂O₃) whereas goethite (??-FeOOH) is the major mineral in the yellow ochre.