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Automatic recognition of unique characteristics of an object can provide a powerful solution to verify its authenticity and safety. It can mitigate the growth of one of the largest underground industries—that of counterfeit goods–flowing through the global supply chain. In this article, we propose the novel concept of material biometrics, in which the intrinsic chemical properties of structural materials are used to generate unique identifiers for authenticating individual products. For this purpose, the objects to be protected are modified via programmable additive manufacturing of built-in chemical "tags" that generate signatures depending on their chemical composition, quantity, and location. We report a material biometrics-enabled manufacturing flow in which plastic objects are protected using spatially-distributed tags that are optically invisible and difficult to clone. The resulting multi-bit signatures have high entropy and can be non-invasively detected for product authentication using 35 Cl nuclear quadrupole resonance (NQR) spectroscopy. [ABSTRACT FROM AUTHOR]

The electric field gradient (EFG) at the gold nucleus is calculated using a finite field approach, to make the extraction of the nuclear quadrupole moment Q from experimental nuclear quadrupole coupling constants possible. The four-component Dirac-Coulomb Hamiltonian serves as the framework, 51 of the 79 electrons are correlated by the relativistic Fock-space coupled cluster method with single and double excitations, and the contribution of the Gaunt term, the main part of the Breit interaction, is evaluated. Large basis sets (up to 26s22p18d12f8g5h uncontracted Gaussians) are employed. Energy splittings of the 2D5/2 and 2D3/2 levels, rather than level shifts, are used to extract the EFG constants, as the former remain linear with Q up to 10-5 a.u., whereas the latter display significant nonlinearity even at Q=10-8 a.u. Larger Q values lead to larger energy changes and better precision. Excellent agreement (0.1%) is obtained between Q values derived from 2D5/2 and 2D3/2 data. Systematic errors connected with neglecting triple and higher excitations, truncating the basis and orbital active space, and approximating the Gaunt contribution are evaluated. The final value of Q(197Au) is 521(7) mb. It is lower than the muonic 547(16) mb and agrees within error bounds with the recent value of 510(15) mb obtained from molecular calculations. [ABSTRACT FROM AUTHOR]

The molybdenum angular sputtering distribution is measured during xenon ion bombardment from a plasma, with incident ion energy EXe ranging between 75 and 225 eV. A quadrupole mass spectrometer (QMS) is used to detect the fraction of sputtered neutrals that is ionized in the plasma and to obtain the angular distribution by changing the angle θ between the target normal and the QMS aperture. The results obtained in these experiments are relative and normalized to the existing data in the literature. The angular sputtering distribution for molybdenum has a maximum at θ=60°, and this maximum becomes less pronounced as the incident ion energy increases. The dependence of the total sputtering yield on incident ion energy is in good agreement with previous experiments. There is an order of magnitude increase in the sputtering yield as EXe is increased from 75 to 125 eV, and a more moderate increase for higher energies. The results of a simulation of the angular distribution of molybdenum atoms sputtered by xenon bombardment using a Monte Carlo code are also presented. They are in agreement with the experiments showing an “under-cosine” distribution (peaked at θ=45°–60°) for the lower energies which evolves towards a cosine distribution as the incident ion energy increases. [ABSTRACT FROM AUTHOR]

Highlights • This paper introduces a two-channel echo-train (TE) data acquisition system used in NQR signal detection and discovers/proves the beamforming characteristics of the TE system. • A novel beamforming approach based on this TE system is proposed which can nicely cancel interference within NQR resonance spectrum. • The proposed algorithm has excellent performance on detecting NQR signal polluted by interference and is superior to previously proposed algorithms, including the classical beamforming algorithms/detectors constructed on the TE system. Abstract Interference can be a huge challenge for Nuclear Quadrupole Resonance (NQR) signal detection in real life settings. The problem is particularly challenging when interference is strong around the resonant frequency band of the targeted NQR signal (to which we refer as the NQR band). This paper first proves the beamforming characteristics of a designed two-channel echo-train (TE) data acquisition system, and then presents a novel beamforming approach which is based on the TE system and is able to cancel interference effectively within the NQR band. After interference cancellation, NQR signal detection can be done successfully by applying an "echo train" approximate maximum likelihood (ETAML) algorithm to the residual data. The proposed algorithm is shown to be superior to previously proposed algorithms, including the classical beamforming algorithms/detectors constructed on the TE system, for detecting NQR signal polluted by interference. [ABSTRACT FROM AUTHOR]

Highlights • The proposed method is a novel wavelets algorithm which effectively cancels strong and time-varying (nonstationary) interference, despite of a possible strong overlap between the interference and signal of interest, facilitating a valid detection of signal of interest. • The proposed method uses an extended Gabor-Morlet wavelets basis to approximate interference with complicated time-varying properties. The proposed method utilizes our well designed cost function to strategically extract the interference components out from NQR data precisely without distorting the signal of interest, which is beyond normal wavelets methods such as standard wavelets denoising methods. • The proposed method outperforms general Fourier analysis and the related frequency selective methods and general adaptive filtering methods on interference cancellation. Abstract Interference cancelation is a very important aspect of Nuclear Quadrupole Resonance (NQR) signal detection, and can become really difficult when the interference is considerably time-varying. We propose a novel wavelets method to effectively remove (or reduce) time-varying interference in the data and facilitate a valid detection of the NQR signal. The proposed algorithm uses an extended Gabor-Morlet wavelets basis to approximate interference with complicated time-varying properties. The proposed algorithm utilizes our well designed cost function to extract the interference components out from NQR data strategically. Mathematical derivations and numerical results from both simulated and measured data demonstrate that the proposed algorithm can precisely cancel strong time-varying interference without distorting signal of interest improving NQR detection, even when interference and signal of interest are severely overlapped. The proposed algorithm is beyond normal wavelets methods such as standard wavelets denoising methods, and exhibits better performance than normal Fourier analysis and related frequency selective methods, and general adaptive filtering methods. [ABSTRACT FROM AUTHOR]

The investigation of materials under extreme pressure conditions requires high-performance cells whose design invariably involves trade-offs between the maximum achievable pressure, the allowed sample volume, and the possibility of real-time pressure monitoring. With a newly conceived hybrid piston-clamped anvil cell, we offer a relatively simple and versatile system, suitable for nuclear magnetic resonance experiments up to 4.4 GPa. Finite-element models, taking into account mechanical and thermal conditions, were used to optimize and validate the design prior to the realization of the device. Cell body and gaskets were made of beryllium-copper alloy and the pistons and pusher were made of tungsten carbide, while the anvils consist of zirconium dioxide. The low-temperature pressure cell performance was tested by monitoring in situ the pressure-dependent 63Cu nuclear-quadrupole-resonance signal of Cu2O. [ABSTRACT FROM AUTHOR]

Summary: As the industry grows, adulteration of many products by mislabelling, re‐branding and false advertising is becoming prevalent practice. Existing solutions for analysis often require extensive sample preparation or are limited in terms of detecting different types of integrity issues. We describe a novel authentication method based on Nuclear Quadrupole Resonance (NQR) spectroscopy which is quantitative, non‐invasive and non‐destructive. It is sensitive to small deviation in the solid‐state chemical structure of a product, which changes the NQR signal properties. These characteristics are unique for different manufacturers, resulting in manufacturer‐specific watermarks. We show that nominally identical dietary supplements from different manufacturers can be accurately classified based on features from NQR spectra. Specifically, we use a machine learning‐based classification called support vector machines (SVMs) to verify the authenticity of products under test. This approach has been evaluated on three products using semi‐custom hardware and shows promising results, with typical classification accuracy of over 95%. Classification of different brands of L‐Histidine using SVM classification. [ABSTRACT FROM AUTHOR]

The cm-wave rotational spectrum of 4-cyanopyridine was studied on a pulsed supersonic jet-expansion Fourier-transform microwave spectrometer. The ground state rotational parameters for the parent and four 13C and two 15N isotopologues were determined with high accuracy in natural abundance including all quartic centrifugal distortion constants and nuclear quadrupole coupling parameters of the two nitrogen nuclei. With the study of both singly substituted 15N species, the nuclear origins of the hyperfine structures could be differentiated and the respective constants identified unambiguously. Different approaches have been used to determine the structure: empirical (rs), ab initio and semi-experimental () methods. The semi-experimental approach improves the accuracy significantly, whereas the Kraitchman's method fails again. [ABSTRACT FROM AUTHOR]

Examines the nutation nuclear quadrupole resonance spectroscopy to determine the asymmetry parameter of powder samples. Characteristic of the anisotropic nutation frequency distribution; Comparison between phase-modulated nutation spectroscopy and amplitude-modulated method; Details on each dimension underlying the phase-modulated method.

The ground state rotational spectra of eight isotopic species of a weakly bound dimer N(1)N(2) ··· HCN(3) formed between molecular nitrogen and hydrogen cyanide have been detected and measured by the technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. Rotational constants B0, centrifugal distortion constants DJ, and, where appropriate, nuclear quadrupole coupling constants χn(14N) and χ(D) have been determined. For the five isotopic species containing 14N nuclei the results are: An analysis of the B0 values shows that the equilibrium geometry is linear, or nearly so, with the nuclei in the order shown. The DJ values lead to kσ=2.39 N m-1 for the intermolecular stretching force constant while the difference χ1(14N)–χ2(14N) is interpreted in terms of a transfer of 0.016 e from N(1) to N(2) when the complex is formed in the zero-point state. [ABSTRACT FROM AUTHOR]

Nuclear Quadrupole Resonance (NQR) spectroscopy has been known for 70 years. It is suitable for the study of measured (poly)crystalline chemical compounds containing quadrupole nuclei (nuclei with spin I ≥ 1) where the characteristic NQR frequencies represent the fingerprints of these compounds. In several cases, 14N NQR can distinguish between the polymorphic crystalline phases of active pharmaceutical ingredients (APIs). In order to further stimulate 14N NQR studies, we review here several results of API polymorphism studies obtained in Ljubljana laboratories: (a) In sulfanilamide, a clear distinction between three known polymorphs (α, β, γ) was demonstrated. (b) In famotidine, the full spectra of all seven different nitrogen positions were measured; two polymorphs were distinguished. (c) In piroxicam, the 14N NQR data helped in confirming the new polymorphic form V. (d) The compaction pressure in the tablet production of paracetamol, which is connected with linewidth change, can be used to distinguish between producers of paracetamol. We established that paracetamol in the tablets of six different manufacturers can be identified by 14N NQR linewidth. (e) Finally, in order to get an extremely sensitive 14N NQR spectrometer, the optical detection of the 14N NQR signal is mentioned.

An automated instrument for improving the sensitivity of nuclear quadrupole resonance (NQR) spectroscopy is presented. The device is capable of pre-polarizing samples within a custom Halbach-type permanent magnet and then moving them into an external probe for zero-field NQR detection. Polarization transfer between protons and nitrogen (14N) nuclei in the sample occurs during demagnetization, thus increasing the amplitude of the detected NQR signals. The sample motion profile is completely programmable, thus providing a high level of control over the sample position and velocity for optimizing the polarization transfer process for various samples. Moreover, the magnet and motion controller are combined with a shielded sample probe and ultra-broadband front-end electronics (both designed in-house) to realize a complete scientific instrument for 14N NQR experiments. Compared with previous work in the field, the system is designed to be programmable, robust, and easy to use. Experimental results from several samples are also presented. [ABSTRACT FROM AUTHOR]

Based on the previous identification of metastable polymorphs in crystalline triphenylbismuth by nuclear quadrupole resonance spectroscopy (NQRS), the potential formation of similar phases was studied in Tris(2-Methoxyphenyl)Bismuthine. To this end, commercial samples with known NQRS properties were molten and re-crystallized at different speeds (shock freezing in different coolants versus slow cooling inside of a heater). In all recrystallization products we have identified a new crystal phase which has not been observed after synthesis from a solution. The new crystallographic structure has been confirmed by X-ray diffraction (XRD). The newly isolated polymorph crystallizes in the monoclinic space group P2(1)/c with only one molecule in the asymmetric unit and consequently only one 5/2-7/2 transition is observed at 88.75 MHz at 310 K. In contrast, the two transitions at 89.38 and 89.29 MHz for the well-known trigonal polymorph originate from two crystallographically distinct molecules of Tris(2-methoxy-Phenyl)Bismuthine in the asymmetric unit. Additional relaxometric NQRS shows distinctly different T2 relaxation times for the new polymorph when compared to the original samples. Additional phase transitions could not be observed during temperature sweeps between 153 K and 323 K.

The paper proposes a new method for quantitative assessment of the constant exchange of magnetization between different states without registration of cross peaks on the T 2 -T 2 topogram which significantly reduced both the experimental time and the time of computer processing of the results. [ABSTRACT FROM AUTHOR]

Nuclear quadrupole resonance (NQR) spectroscopy is proven to be a very sensitive technique for measuring distribution of electric charge around quadrupolar nuclei. Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. The electronic structure of magnesium alanate, Mg(AlH4)2, as promising hydrogen storage materials for hydrogen fuel cell-powered automobile applications, has been studied in detail by ab initio calculated NQR parameters. Furthermore, using calculated nuclear quadrupole coupling constants (NQCCs) of hydrogen atoms (²H-NQCC), the electronic structure of α-Mg(AlH4)2 with its high-pressure forms, β- and γ- Mg(AlH4)², was compared. The electric field gradient (EFG) at the site of 2H atoms was calculated to obtain NQCC parameters. The results show that in the γ-Mg(AlH4)2, 2H-NQCCs are smaller than that of other considered phases. In other words, Al-H bonds in γ-Mg(AlH4)2 nanocrystal is weaker than others and the charge transfer from Al to hydrogen atom is less than the others and therefore these hydrogens have weaker bonds with Al and easier condition for dehydrogenation is expected in γ-Mg(AlH4)². Comparison of calculated dehydrogenation enthalpies of various Mg(AlH4)2 phases verifies this prediction. All calculations performed using Gaussian 03 at the HF/3-21G level of theory. The selected level and basis set give the rather acceptable qualitative NQCCs of hydrogen atoms. [ABSTRACT FROM AUTHOR]

Using nuclear quadrupole resonance spectroscopy, it has been found that chloroform and dichloroethane absorbed by microporous hypercrosslinked polystyrene retain the capacity of the crystalline structure formation in small free spaces of the network on cooling, whereas p-dichlorobenzene demonstrates the complete loss of the capacity of crystallization. [ABSTRACT FROM AUTHOR]

We describe hardware, pulse sequences, and algorithms for nuclear quadrupole resonance (NQR) spectroscopy of medicines and dietary supplements. Medicine and food safety is a pressing problem that has drawn more and more attention. NQR is an ideal technique for authenticating these substances because it is a non-invasive method for chemical identification. We have recently developed a broadband NQR front-end that can excite and detect 14 N NQR signals over a wide frequency range; its operating frequency can be rapidly set by software, while sensitivity is comparable to conventional narrowband front-ends over the entire range. This front-end improves the accuracy of authentication by enabling multiple-frequency experiments. We have also developed calibration and signal processing techniques to convert measured NQR signal amplitudes into nuclear spin densities, thus enabling its use as a quantitative technique. Experimental results from several samples are used to illustrate the proposed methods. [ABSTRACT FROM AUTHOR]

Presents a study that reported preliminary results of structural studies in oxygen-annealed La[sub2]CuO[sub4+8] using lanthanum (La) nuclear quadrupole resonance (NQR) spectroscopy. Analysis of the La NQR spectra; Origins of the anomalies on the structural configuration; Connection of the anomalies to superconductivity.

Nuclear quadrupole resonance spectroscopy is an analytical method which allows to characterize materials which contain quadrupolar nuclei, i.e. nuclei with spin ⩾1. The measurement technology is similar to that of NMR except that no static magnetic field is necessary. In contrast to NMR, however, it is frequently necessary to scan spectra with a very large bandwidth with a span of several tens of % of the central frequency so as to localize unknown peaks. Standard NMR probeheads which are typically constructed as resonators must be tuned and matched to comparatively narrow bands and must thus be re-tuned and re-matched very frequently when scanning over a whole NQR spectrum. At low frequencies up to few MHz dedicated circuits without the need for tuning and matching have been developed, but many quadrupole nuclei have transitions in the VHF range between several tens of MHz up to several hundreds of MHz. Currently available commercial NQR probeheads employ stepper motors for setting mechanically tuneable capacitors in standard NMR resonators. These yield high quality factors (Q) and thus high SNR but are relatively large and clumsy and do not allow for fast frequency sweeps. This article presents a new concept for a NQR probehead which combines a previously published no-tune no-match wideband concept for the transmit (TX) pulse with an electronically tuneable receive (RX) part employing varactor diodes. The prototype coil provides a TX frequency range of 57 MHz with a center frequency of 97.5 MHz with a return loss of ⩽−15 dB. During RX the resonator is tuned and matched automatically to the right frequency via control voltages which are read out from a previously generated lookup table, thus providing high SNR. The control voltages which bias the varactors settle very fast and allow for hopping to the next frequency point in the spectrum within less than 100 μs. Experiments with a test sample of ZnBr 2 proved the feasibility of the method. [ABSTRACT FROM AUTHOR]

Allowed transition energies and eigenstate expansions have been calculated and tabulated in numerical form as functions of the electric field gradient asymmetry parameter for the zero field Hamiltonian of quadrupolar nuclides with I = 3 / 2 , 5 / 2 , 7 / 2 , and 9 / 2 . These results are essential to interpret nuclear quadrupole resonance (NQR) spectra and extract accurate values of the electric field gradient tensors. Applications of NQR methods to studies of electronic structure in heavy element systems are proposed. [ABSTRACT FROM AUTHOR]

We present the results from an experiment dedicated to search for quadrupole-collective isovector valence-shell excitations, states with so-called mixed proton-neutron symmetry (MSS), of 212Po. This nucleus was studied in an α-transfer reaction. The lifetimes of two short-lived excited states, candidates for the one-phonon MSS, were determined by utilizing the Doppler shift attenuation method. The experimental results are in qualitative agreement with a simple single-j shell model calculation, which, together with the observed lack of quadrupole collectivity, indicates that the isovector nature of low-lying states is a property of the leading single-particle valence shell configuration. [ABSTRACT FROM AUTHOR]

In this paper, we report on the identification of batches of analgesic paracetamol (acetaminophen) tablets using nitrogen-14 nuclear quadrupole resonance spectroscopy (14N NQR). The high sensitivity of NQR to the electron charge distribution surrounding the quadrupolar nucleus enables the unique characterization of the crystal structure of the material. Two hypothesis were tested on batches of the same brand: the within the same batch variability and the difference between batches that varied in terms of their batch number and expiry date. The multivariate analysis of variance (MANOVA) did not provide any within-batches variations, indicating the natural deviation of a medicine manufactured under the same conditions. Alternatively, the statistical analysis revealed a significant discrimination between the different batches of paracetamol tablets. Therefore, the NQR signal is an indicator of factors that influence the physical and chemical integrity of the material. Those factors might be the aging of the medicine, the manufacturing, or storage conditions. The results of this study illustrate the potential of NQR as promising technique in applications such as detection and authentication of counterfeit medicines. [ABSTRACT FROM AUTHOR]

Nuclear quadrupole resonant spectroscopy is method similar to nuclear magnetic resonant spectroscopy also called zero field NMR [1, 2]. The response signal magnitude is very low and it is immersed in to the noise. There can be used some methods to harvest signal from noise it can be matched receiver [3] or averaging. This authors describe detector for Nuclear quadrupole resonant spectroscopy based on statistic methods and probability of distribution, that allow to measure repetitive signals below noise level. The paper presents the mathematical model and practical solution of the detector, and problems such as the dynamic range and signal distortion based on the signal-to-noise ratio are also analyzed in the given context. If the time of signal occurrence is known, the repetitive signal below the noise level can be harvested out of noise by averaging because of the wanted signal is correlated therefor highlighted by averaging contrast to the noise which is not correlated so it is supressed by averaging. The same principle we can use in domain of digital signal. So the input signal can be converted to the digital representation. There is an comparator with a triggering level immersed in the noise so the comparator is flipping continuously and the probability of output values is affected by input signal. The output digital signal can be processed by FPGA. [ABSTRACT FROM AUTHOR]

Highlights: [•] Developed an ultra-broadband (“non-resonant”) MR system with un-tuned sample coil. [•] Used system to perform simple multi-frequency NQR experiments with a single coil. [•] Repeated the multi-frequency experiments to build two-dimensional (2D) NQR spectra. [•] These 2D spectra reveal coupling between 14N NQR lines arising from the same site. [•] Experimentally verified using several solid powder samples, including mixtures. [ABSTRACT FROM AUTHOR]

Asymmetry parameters of the electric field gradient tensor at 75As nuclei were determined for chalcogenide glassy semiconductors (CGS) of the Ge-As-Se system by comparing the experimental and simulated 75As nuclear quadrupole resonance nutation interferograms. The electric field gradient asymmetry in CGS was analyzed, and it is believed that a structural change in these glassy semiconductors takes place at [ABSTRACT FROM AUTHOR]

Abstract: The direct measurement and identification of solid state arsenic phases using 75As NMR is made difficult by the simultaneous conditions of large quadrupole moment and low coordination symmetry in many compounds. However, specific arsenic minerals can efficiently be detected and discriminated via nuclear quadrupolar resonance (NQR). We report on the first NMR and NQR measurements in the natural minerals enargite (Cu3AsS4), niccolite (NiAs), arsenopyrite (FeAsS) and loellingite (FeAs2). The NQR frequencies have been determined from both high-field NMR powder patterns and via zero-field frequency sweeps. Density functional theory (DFT) based ab initio calculations support the experimental results. The compounds studied here are common in terms of the known set of As-containing minerals. They are sometimes encountered in the context of base metal or gold mining. The study represents a significant addition to the list of arsenic minerals that can now be detected with NQR techniques. [Copyright &y& Elsevier]

We report the detection and analysis of a suspected counterfeit sample of the antimalarial medicine Metakelfin through developing nitrogen-14 nuclear quadrupole resonance (14N NQR) spectroscopy at a quantitative level. The sensitivity of quadrupolar parameters to the solid-state chemical environment of the molecule enables development of a technique capable of discrimination between the same pharmaceutical preparations made by different manufacturers. The 14N NQR signal returned by a tablet (or tablets) from a Metakelfin batch suspected to be counterfeit was compared with that acquired from a tablet(s) from a known-to-be-genuine batch from the same named manufacturer. Metakelfin contains two active pharmaceutical ingredients, sulfalene and pyrimethamine, and NQR analysis revealed spectral differences for the sulfalene component indicative of differences in the processing history of the two batches. Furthermore, the NQR analysis provided quantitative information that the suspected counterfeit tablets contained only 43 ± 3%, as much sulfalene as the genuine Metakelfin tablets. Conversely, conventional nondestructive analysis by Fourier transform (FT)-Raman and FT-near infrared (NIR) spectroscopies only achieved differentiation between batches but no ascription. High performance liquid chromatography (HPLC)-UV analysis of the suspect tablets revealed a sulfalene content of 42 ± 2% of the labeled claim. The degree of agreement shows the promise of NQR as a means of the nondestructive identification and content-indicating first-stage analysis of counterfeit pharmaceuticals. [ABSTRACT FROM AUTHOR]

Abstract: Unlimited solid solution Fe1−x Co x Ga3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T 1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N 2(E F ). [Copyright &y& Elsevier]

Abstract: In order to alleviate base-line distortions in nitrogen-14 NQR spectra originating from pulse breakthrough, low power radio-frequency (rf) pulses were applied. It is recalled that the required power is four times lower than that for an equivalent NMR experiment. This is easily explained by the fact that, in NMR, half the amplitude of the rf field is active. Moreover, the selectivity profile (i.e. the peak amplitude as a function of the difference between the carrier frequency and the resonance frequency) exhibits a shape which is, in most cases, more favorable in NQR than in NMR. An appropriate theory has been developed for explaining these experimental observations. It is concluded that low power NQR is perfectly feasible and should even be recommended for most applications, provided that the line-width of the NQR signal is not too large. [Copyright &y& Elsevier]

Density functional theory (DFT) calculations were performed to investigate the electronic structure properties of pristine and Si-doped aluminum nitride nanotubes as n or P-semiconductors at the B3LYP/6-31G* level of theory in order to evaluate the influence of Si-doped in the (6,0) zigzag AlNNTs. We extended the DFT calculation to predict the electronic structure properties of Si-doped aluminum nitride nanotubes, which are very important for production of solid-state devices and other applications. To this aim, pristine and Si-doped AlNNT structures in two models (Si and Si) were optimized, and then the electronic properties, the isotropic (CS) and anisotropic (CS) chemical shielding parameters for the sites of various Al and N atoms, NQR parameters for the sites of various of Al and N atoms, and quantum molecular descriptors were calculated in the optimized structures. The optimized structures, the electronic properties, NMR and NQR parameters, and quantum molecular descriptors for the Si and Si models show that the Si model is a more reactive material than the pristine or Si model. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The results of investigation of the promising thermoelectric compound CuAlO by the nuclear-quadrupole-resonance spectroscopy of the copper nuclei Cu are presented. An assumption regarding the defect structure of the crystals is made on the basis of analysis of the asymmetric shape of the resonance lines. The experiments with the nutational nuclear quadrupole resonance of Cu are indicative of the axial symmetry of the electric-field-gradient tensor on copper nuclei in the investigated samples. [ABSTRACT FROM AUTHOR]

Abstract: The experiment with phase inversion and phase-inverted echo-amplitude detected nutation (PEANUT) was introduced in the nuclear quadrupole resonance (NQR). Formulas were obtained describing the NQR (I=3/2) experiment. Exemplary experiments are provided confirming the predicted particularities of the PEANUT spectra in NQR Cl-35. It is proposed to apply the method for the purpose of determination the asymmetry parameter of the electric field gradient (EFG) tensor in powders with the help of the analysis of PEANUT interferograms. Application of two-dimensional PEANUT experiments, in which the nutation frequencies correlate with the resonance NQR frequencies, can substantially simplify the interpretation of complex spectra. [Copyright &y& Elsevier]

Abstract: Electric field gradients and chemical shielding tensors of the stable monoclinic crystal phase of ethanol are computed. The projector-augmented wave (PAW) and gauge-including projector-augmented wave (GIPAW) models in the periodic plane-wave density functional theory are used. The crystal data from X-ray measurements, as well as the structures where either all atomic, or only hydrogen atom positions are optimized in the density functional theory are analyzed. These structural models are also studied by including the semi-empirical van der Waals correction to the density functional theory. Infrared spectra of these five crystal models are calculated. [Copyright &y& Elsevier]

Abstract: While the synthetic utility and reactivity of the so-called “GaI” species is reasonably well established, its exact composition remains unknown. Using primarily multinuclear magnetic resonance techniques (and supported with powder X-ray diffraction measurements), we offer some new insights into the composition of “GaI”. Using 127I nuclear quadrupole resonance (NQR) experiments, it is clearly demonstrated that gallium diiodide (GaI2) is a significant component of this material, while GaI3 is not. This finding is in contrast with a prior literature account, which noted that Ga2I3 (i.e., one equivalent of GaI3 per equivalent of Ga metal) was present in significant amounts. Additional solid-state nuclear magnetic resonance (SSNMR) experiments using the 69/71Ga probe nuclei in multiple magnetic fields clearly establish, via its diagnostic Knight-shifted resonance, the presence of Ga0 metal, which is in agreement with prior literature. Taken together, a composition may be tentatively offered: that “GaI” is, to a large extent, two equivalents of Ga0 metal with two equivalents of GaI2, where the latter is composed of Ga+ and ions. This composition may be represented as [Ga0]2[Ga]+[GaI4]−. [Copyright &y& Elsevier]

series of dimeric molecules (ClPNAr) where Ar = CHZ, Z = H or Cl in 2-4 positions, was calculated by the RHF/6-31G* method with the full geometry optimization. A specific nature of the intramolecular steric orientation of aryl groups was revealed, therewith in the case Ar = CHCl-2 short nonvalent contacts were founf between the ortho-chlorine atom and PCl group manifested in the peculiarity of geometric parameters and NQR spectroscopy data of this compound. The correlation of the Cl NQR frequencies of P-Cl bonds with the values of the charges on the chlorine atoms obtained by quantum-chemical calculations of the molecules was analyzed. [ABSTRACT FROM AUTHOR]

A new nuclear quadrupole double resonance spectrometer based on a commercial superconducting quantum interference device (SQUID) setup (a Magnetic Property Measurement System (MPMS) from Quantum Design) is described. The experiment involves the indirect detection of pure quadrupole resonances (PQR) of a dilute spin system via the direct SQUID detected NMR of an abundant spin system. The experiment is conducted at low (3-20 K) temperatures and the magnetic field is cycled between a high (5.5 T) polarizing field, to an intermediate (0.1 T) detection field, to zero field where the sample is irradiated with a modulated search RF and back to the detection field. Loss of the NMR signal indicates the detection of a PQR. The RF circuit used for both the NMR and zero field irradiation is digitally controlled. Use of the External Device Control allows for the complete automation of the system. Test measurements on diphenyl ether are in good agreement with previously reported results. Pure 17O quadrupole resonances were detected for spin systems with concentrations as low as 120 μM. [ABSTRACT FROM AUTHOR]

Abstract: The acquisition of nuclear quadrupole resonance (NQR) spectra with wideband uniform rate and smooth truncation (WURST) pulses is investigated. 75As and 35Cl NQR spectra acquired with the WURST echo sequence are compared to those acquired with standard Hahn-echo sequences and echo sequences which employ composite refocusing pulses. The utility of WURST pulses for locating NQR resonances of unknown frequency is investigated by monitoring the integrated intensity and signal to noise of 35Cl and 75As NQR spectra acquired with transmitter offsets of several hundreds kilohertz from the resonance frequencies. The WURST echo sequence is demonstrated to possess superior excitation bandwidths in comparison to the pulse sequences which employ conventional monochromatic rectangular pulses. The superior excitation bandwidths of the WURST pulses allows for differences in the characteristic impedance of the receiving and excitation circuits of the spectrometer to be detected. Impedance mismatches have previously been reported by Marion and Desvaux [D.J.Y. Marion, H. Desvaux, J. Magn. Reson. (2008) 193(1) 153–157] and Muller et al. [M. Nausner, J. Schlagnitweit, V. Smrecki, X. Yang, A. Jerschow, N. Muller, J. Magn. Reson. (2009) 198(1) 73–79]. In this regard, WURST pulse sequences may afford an efficient new method for experimentally detecting impedance mismatches between receiving and excitation circuits, allowing for the optimization of solids and solution NMR and NQR spectrometer systems. The use of the Carr–Purcell Meiboom–Gill (CPMG) pulse sequence for signal enhancement of NQR spectra acquired with WURST pulses and conventional pulses is also investigated. Finally, the utility of WURST pulses for the acquisition of wideline NQR spectra is demonstrated by acquiring part of the 63/65Cu NQR spectrum of CuCN. [ABSTRACT FROM AUTHOR]

The N NQR frequencies of selected 1,4-benzoquinonedioximes were measured using cross relaxation double resonance. As the number of substituents increase, a significant shift in the NQR values is observed. Comparison of unsubstituted and tri-substituted 1,4-benzoquinonedioximes shows that the quadrupole coupling constant ( χ) increases by about 1000 kHz and the asymmetry parameter ( η) decreases from ≈0.7 to 0.3 respectively. Ab-initio calculations show that for the unsubstituted compound hydrogen bonding between oxime groups and pi-ring stacking is possible which cannot be accommodated for in heavily methyl substituted dioximes and this results in distinct NQR parameters. [ABSTRACT FROM AUTHOR]

Applying the quantum-chemical calculations by MP2/6-31G* method molecular structures of trichlorophosphazenes Cl3P=NCOCX3 with X = F and Cl were determined and barriers to intramolecular reorientation of PCl3 group relative to P=N bond and of CF3 and CCl3 groups relative to C-C bond were estimated. The values of potential barriers to internal rotation calculated for isolated molecules were compared with the values of the barriers obtained from the data of NQR and NMR spectroscopy of the compounds in the crystalline state. The structural and dynamic features of the studied molecules are discussed. [ABSTRACT FROM AUTHOR]

Abstract: 2-Chloro-2′-deoxyadenosine (Cladribine) chemotherapeutic drug has been studied experimentally in solid state by 35Cl NQR and NMR–NQR double resonance and theoretically by the Density Functional Theory. Fifteen resonance frequencies on 14N have been detected and assigned to particular nitrogen sites in the 2-CdA molecule. The effects of tautomerism, regioisomerism, conformations and molecular aggregations, related to intermolecular hydrogen bond formation, on the NQR parameters have been analysed within the DFT and AIM (Atoms in Molecules) formalism. The properties of the whole molecule, the so-called global reactivity descriptors, have been calculated for a comparison of both syn and anti conformations of 2-CdA molecule to check the effect of crystal packing on molecular conformation. [Copyright &y& Elsevier]

Abstract: Thermal stability of 4-chloro-3,5-dimethyl-phenol (chloroxylenol) in solid state has been studied by 35Cl-NQR spectroscopy. Two NQR resonance lines at the frequencies 34.348 and 34.415MHz at 77K have been assigned to chlorine atoms from two crystallographically inequivalent molecules on the basis of the B3LYP/6-311++G∗∗ results. The temperature dependence of the resonance frequency and full width at half maximum suggest the occurrence of small-angle torsional oscillations of the mean activation energy of 3.83kJ/mol and rotation of both methyl groups around their symmetry axis C3 with the activation energies 12.49 and 11.27kJ/mol for CH3 in molecule A and B, respectively. B3LYP/6-311++G∗∗ method reproduced very well the activation energies of both motions. [Copyright &y& Elsevier]

Abstract: In spite of a renewed interest in Nuclear Quadrupole Resonance (NQR), especially of nitrogen-14 (for instance, for the detection and characterization of explosives), a full NQR instrument, ready to use in the laboratory, is not commercially available. We describe here an entirely homemade spectrometer, reasonably transportable, including the transmit-receive system, frequency generation, data acquisition, probes and a specialized software for driving the instrument and for data processing. [Copyright &y& Elsevier]

Recent work on the nuclear quadrupole resonance (NQR) investigation of molecular dynamics in the solid state has relied on 2D methods. We report our studies of dynamic processes by 1D shaped pulse NQR spectroscopy. Significant advantages include considerably shorter experimental duration, clear definition of the exchange time window, and avoidance of off-resonance effects. The reorientation of the Cl3C˜ group in polycrystalline chloral hydrate [Cl3C-CH(OH)2] is considered as a test case. This may be modelled as a three-site exchange process. An analysis of the generalised Bloch-McConnell equation is performed to formulate the kinetic matrix. The present approach involves simultaneous excitation of the sites that undergo chemical exchange by employing a suitably modulated shaped RF pulse, followed by a mixing time, and finally a suitable read pulse for signal detection. The experimental signal intensities are plotted against the mixing time to extract the kinetic parameters, i.e. the exchange rate and the spin-lattice relaxation rate. Variable temperature measurements are carried out to determine the activation parameters. Short experiment times are possible in our 1D mode, enabling a large number of runs to be readily performed as a function of mixing time and temperature. The kinetic and activation parameters obtained in the case of chloral hydrate are in good agreement with recent literature values. [ABSTRACT FROM AUTHOR]

Nuclear quadrupole resonance (NQR) offers an unequivocal method of detecting hidden narcotics and explosives. Unfortunately, the practical use of NQR is restricted by the low signal-to-noise ratio (SNR) and means to improve the SNR are vital to enable a rapid, reliable and convenient system. In this correspondence, we develop two multichannel detectors to counter the typically present radio frequency interference. Numerical simulations indicate that the proposed methods offers a significantly improved robustness to uncertainties in the parameters detailing the examined sample. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of dichloroisocyanuric acid derivatives was analysed by 35Cl-NQR spectroscopy and DFT calculations. Here we concentrate our attention on three different factors: type of metallic substituent (sodium and potassium), temperature of the sample (liquid nitrogen and room) and degree of hydration (an amount of water molecules attached to analysed compounds). In particular, all the variations in 35Cl-NQR frequencies upon hydration of salts containing sodium and potassium ions are explained as a consequence of H-bonds formation and accompanied effects of charge redistribution. Our studies can be useful in searching for the derivatives of dichloroisocyanuric acid revealing higher antimicrobial activity. [Copyright &y& Elsevier]

Nuclear quadrupole resonance (NQR) offers an unequivocal method of detecting and identifying both hidden explosives, such as land mines, and a variety of narcotics. Unfortunately, the practical use of NQR is restricted by a low signal-to-noise ratio (SNR), and means to improve the SNR are vital to enable a rapid, reliable, and convenient system. In this paper, we introduce a frequency-selective approximate maximum-likelihood (FSAML) detector, operating on a subset of the available frequencies, making it robust to the typically present narrow-band interference. The method exploits the inherent temperature dependency of the NQR frequencies as a way to enhance the SNR. Numerical evaluations, using both simulated and real NQR data, indicate a significant gain in probability of accurate detection as compared to a current state-of-the-art approach. [ABSTRACT FROM AUTHOR]

In this paper, ab initio calculated NQR parameters for some quinoline-containing derivatives are presented. The calculations are carried out in a search for the relationships between the charge distribution of these compounds and their ability to interact with haematin. On the basis of NQR parameters, π-electron density on the nitrogen atom of the quinoline ring plays a dominant role in determining the ability of quinolines to interact with haematin. This point was confirmed with investigation of Fe+3 cation-π quinoline ring interactions in 2- and 4-aminoquinoline. However, our results do not show any preference for those carbon atoms of the quinoline ring which previous reports have noted. In order to calculate the NQR parameters, the electric field gradient (EFG) should be evaluated at the site of a quadrupolar nucleus in each compound. EFGs are calculated by the Gaussian 98 program using the B3LYP/6-31G* level of theory. [ABSTRACT FROM AUTHOR]