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Coatings play a crucial role in the functionality of vacuum chambers in particle accelerators, serving a dual goal by efficiently facilitating pumping and mitigating electron cloud effects. However, their impact on the surface impedance of the chamber walls raises concerns, potentially affecting the machine performance and imposing limitations on achievable energies and currents. Therefore, an electromagnetic characterization is essential for a comprehensive study of accelerator structures, particularly in the context of the next-generation machines where the demand for extremely short particle bunches accentuates the importance of evaluating material responses in the very-high-frequency region. We present a technique for probing the sub-THz response of coating materials by measuring pulsed signals passing through a specifically designed waveguide, in which is placed a slab with the deposited material under test. The proposed methodology allows for a comprehensive exploration of the electromagnetic properties of the most used technical surfaces (substrate plus coatings) in accelerators under realistic conditions, providing valuable insights into their behavior in the sub-THz frequency range. The experimental data of three different Non-Evaporable Getter coating samples, prepared on a copper substrate at the CERN deposition facilities under different sputtering conditions, are discussed. The findings contribute to a deeper understanding of the complex interactions between coatings and accelerator structures, with the aim of optimizing performance and efficiency in the evolving landscape of particle acceleration technologies. The limitations and advantages of the technique are also reported.
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The use of a combination of three-drug regimen has improved HIV-1 infected patients' life span and quality; however the emergence of drug-resistant strains remains a main problem. Reverse transcriptase inhibitors (RTIs) consist of a main part of highly active anti-retroviral therapy (HAART) regimen. The present study aimed to investigate resistant mutations to RTI drugs in both treatment naïve and under treatment HIV patients in Mashhad city, north-eastern Iran. RNA was extracted from sera of 22 treatment naïve and 22 under treatment patients. The mean age of under treated and treatment naive groups were 38.5±6.7 and 40.8±7.9 respectively. cDNA was synthesized and amplified with Nested PCR assay targeting specific sequences of RT gene. The PCR products were sent for sequencing. Bidirectional sequencing results were analysed using HIV drug resistance database supplied by Stanford University (HIV Drug Resistance Database, https://hivdb.stanford.edu). Among under treatment patients 10 out of 22 (45%) had at least one high-level resistance mutation which was higher than high level resistance mutation rate among treatment naive cases (P<0.01). Detected resistance mutations were as follows: K101E, K103N, K103E, V106M, V108I, E138A, V179T, Y181C, M184V, Y188L, Y188H, Y188F, G190A, L210W, T215F, T215Y, K219Q, and P225H. A high level of resistance mutations to RT inhibitors was observed that causes drug resistance especially against lamivudine (3TC). Such mutations should be considered as probable responsible for therapeutic failure. Serial surveillance studies of circulating drug resistance mutations are recommended.
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We report a study on the hydrogen bonding mechanisms of three aliphatic alcohols (2-propanol, methanol, and ethanol) and one diol (ethylene glycol) in water solution using a time-domain ellipsometer in the THz region. The dielectric response of the pure liquids is nicely modeled by the generalized Debye-Lorentz equation. For binary mixtures, we analyze the data using a modified effective Debye model, which considers H-bond rupture and reformation dynamics and the motion of the alkyl chains and of the OH groups. We focus on the properties of the water-rich region, finding anomalous behavior in the absorption properties at very low solute molar concentrations. These results, first observed in the THz region, are in line with previous findings from different experiments and can be explained by taking into account the amphiphilic nature of the alcohol molecules.
Assuntos
Álcoois , Ligação de Hidrogênio , Água , Água/química , Álcoois/química , Espectroscopia Terahertz/métodos , Etanol/química , 2-Propanol/químicaRESUMO
Background: Open cranial vault reconstruction is the standard technique of craniosynostosis correction that may cause significant blood loss. Objectives: The current study aimed at comparing the effect of tranexamic acid (TXA), controlled hypotension, and their combination on perioperative blood loss and transfusion requirement in craniosynostosis surgery. Methods: The present randomized, double-blind clinical trial was conducted on 75 infants referred for craniosynostosis surgery during 2017 - 2018. Ten minutes before the start of surgery, 10 mg/kg of TXA was administered intravenously to patients in the first group (TXA group). In the second group, patients were subjected to the controlled hypotension anesthesia (CHA) using intravenous remifentanil 0.1 µ/kg (CHA group). In the third group, the patients underwent CHA similar to that of the second group, along with intravenous injection of 10 mg/kg of TXA (CHA-TXA group). Then, patients' mean arterial pressure (MAP), heart rate (HR), total blood loss, and transfusion volume were evaluated and recorded. Results: The results of the present study revealed that although the changes in MAP and HR parameters over time (three hours after surgery) were significant in all three groups, the lowest decrease was observed in the CHA-TXA group (P-value < 0.05). In addition, the total perioperative blood loss in the CHA-TXA group with the mean of 181.20 ± 82.71 cc was significantly less than the total perioperative blood loss in the CHA and TXA groups with the means of 262.00 ± 104.04 cc and 212.80 ± 80.75 cc, respectively (P-value < 0.05). Moreover, the transfusion volume in the CHA-TXA group with the mean of 112.40 ± 53.50 cc was significantly lower than the transfusion volume in the CHA and TXA groups with the means of 174.00 ± 73.93 cc and 160.63 ± 59.35 cc, respectively (P-value < 0.05). In contrast, the total blood loss and transfusion volume were not significantly different between the CHA and TXA groups (P-value > 0.05). Conclusions: According to the results of the present study, although the administration of TXA alone could effectively prevent blood loss and was associated with fewer transfusion requirements, the combination of this approach with hypotensive anesthesia resulted in more reduction in perioperative blood loss and transfusion volume as well as better hemodynamic stability.
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Using a customized time-domain ellipsometer operating in the THz range, the molecular dynamics of a liquid binary solution based on water and isopropyl alcohol (2-propanol) is investigated. The setup is capable of detecting small changes in the optical properties of the mixture within a single measurement. The complex dielectric response of samples with different concentrations is studied through the direct measurement of the ellipsometric parameters. The results are described using an effective Debye model, from which the relaxation parameters associated with different activation energies can be consistently extracted. Significant deviations between experimental data and the theoretical expectations at an intermediate volume percentage of 2-propanol in water are observed and interpreted as produced by competing effects: the creation/destruction of hydrogen bonding on the one hand, and the presence of cluster/aggregation between water and alcohol molecules on the other.
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Ellipsometry is extensively used in the optical regime to investigate the properties of many materials as well as to evaluate with high precision the surface roughness and thickness of thin films and multilayered systems. Due to the inherent non-coherent detection technique, data analyses in optical ellipsometry tend to be complicated and require the use of a predetermined model, therefore indirectly linking the sample properties to the measured ellipsometric parameters. The aim of this tutorial is to provide an overview of terahertz (THz) time-domain ellipsometry, which is based instead on a coherent detection approach and allows in a simple and direct way the measurement of the material response. After giving a brief description of the technology presently used to generate and detect THz radiation, we introduce the general features of an ellipsometric setup operating in the time domain, putting in evidence similarities and differences with respect to the classical optical counterpart. To back up and validate the study, results of THz ellipsometric measurements carried out on selected samples are presented.
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We report on the realisation of a customized THz time domain spectroscopic ellipsometer (THz-TDSE) based on fiber-coupled photoconductive antennas, operating in a wide range of incident angles and allowing also standard transmission spectroscopy without any optical realignment. To ensure accurate parameter extraction for a broad range of materials, we developed a fast and effective algorithm-assisted method to calibrate the setup and compensate for the nonideality in the response of the THz system. The procedure allows to minimise errors induced by imperfect response of the antennas and polarizers, imprecise setting of the impinging and receiving angles in the goniometric mechanical arms, and unavoidable mismatches in the THz beam optics. Differently from other calibration methods applied in the literature, our approach compares in time domain the ellipsometric derived electric field s- and p-polarised components at a given angle of incidence with the reconstructed ones, attained by using the complex dielectric function of a known sample. The calibrated response is determined with high precision by setting the system in transmission mode. In order to validate the technique, ellipsometric measurements have been carried out at various angle of incidences on a number of materials both in solid and liquid form, and their data compared with what obtained by conventional THz spectroscopy. Results show that THz-TDSE accompanied with an accurate calibration procedure is an effective technique for material characterization, especially in case of samples with a high absorption rate that are not easily investigated through transmission measurements.
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We report the design, fabrication and experimental validation of a THz all-dielectric multi-mode q-plate having a fixed rate of change of the optical axis. The device consists of space-variant birefringent slabs manufactured by 3D printing using melt-extruded Acrylonitrile Butadiene Styrene (ABS). The desired form birefringence is analytically evaluated and experimentally measured by the THz time domain spectroscopy technique. The manufactured q-plate design is characterized using a polarization-sensitive imaging setup. The full electric field spatial maps are acquired from the beam propagating through the q-plate. The device enables the realization of both radial and azimuthal vector beams at discrete frequency intervals by controlling the space-dependent orientation of the ordinary and extraordinary axes in the transverse plane with a multi-mode sequence.
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A novel, to the best of our knowledge, methodology based on the combination of experimental measurements and simulations of the wave transmission through a metasurface at different angles is presented, enabling us to identify the fundamental and first high-order mode of spoof surface plasmon polaritons (SSPPs) excited in the terahertz regime. The approach offers a new way, an alternative to standard near field imaging, to trace out the presence of SSPPs on a metal-dielectric interface.