Pseudonondiffracting slitlike beam and its analogy to the pseudonondispersing pulse

A new nonspreading beam is proposed for the case in which diffraction occurs only in one transverse coordinate. The beam has the shape of a pulse in one dimension and is constant in the other (slitlike shape). The intensity of the pulse's peak remains almost constant along a finite interval on the propagation axis. The proposed beam is analyzed and demonstrated experimentally. The analogy between this beam and the temporal pulse in a dispersive medium is discussed.

Synthesis of (V2/3Sc1/3)2AlC i-MAX phase and V2-xC MXene scrolls

We report the synthesis and characterization of a new laminated i-MAX phase, (V2/3Sc1/3)2AlC, with in-plane chemical ordering between the M-elements. We also present evidence for the solid solution (V2-xScx)2AlC, where x ≤ 0.05. Chemical etching of the Al and Sc results in a two-dimensional (2D) MXene counterpart: V2-xC from the latter phase. Furthermore, etching with HF yields single-sheet MXene of flat morphology, while LiF + HCl gives MXene scrolls. We also show a 4× reduction in etching time for (V2-xScx)2AlC compared to V2AlC, suggesting that traces of Sc changes the phase stability, and make the material more susceptible to etching. The results show a path for improved control of MXene synthesis and morphology, which may be applicable also for other MAX/MXene systems.

Scale invariant pattern recognition with logarithmic radial harmonic filters

A generalized approach leads to spatial filters that accept changes of scale by a factor of 4. The procedure employs phase filters with reduced tolerance requirements and achieves high discrimination capability and efficient light throughput. Computer simulations and laboratory experiments show the advantages of this novel approach.

Drug discovery using receptors that modulate gene expression

Cytokines and non-peptidyl small molecules, such as steroid hormones, exert many of their effects on cells through rapid regulation of gene expression. This is achieved by the activation of different families of latent transcription factors, which bind to specific sequences in the promoters of regulated genes. High throughput assay systems have been developed based on a detailed molecular understanding of these transcriptional regulation processes, and are being used as screens for both agonists and antagonists of specific cytokines and hormones. The opportunities for the discovery of novel and selective compounds using these systems is discussed.

Anergy compromises screening for tuberculosis in high-risk populations

Anergy may occur in groups at high risk for tuberculosis, compromising tuberculin skin testing. Within New York City's correctional system, anergy prevalence was 25% among opiate users referred to detoxification programs and 3% in the general population. Correlates of anergy were recent weight loss and needle sharing. The high prevalence of anergy among opiate users compromises the utility of tuberculosis screening and suggests the need for routine chest x-rays to detect pulmonary tuberculosis in some high-risk-populations.

Lithium-induced delirium with therapeutic serum lithium levels: a case report

Lithium-induced delirium occurring in geriatric patients with serum lithium levels that are within the "therapeutic" range (less than 1.5 mEq/L) has been described in the literature. We present a case that illustrates three major issues regarding this syndrome: (1) differentiating lithium-induced delirium from a recurrence of a chronic psychiatric disorder; (2) the use of the electroencephalogram in supporting this diagnosis; and (3) factors that may increase a patient's vulnerability to delirium while on lithium. A brief review of the most relevant literature is then presented. We conclude that lithium-induced neurotoxicity should be suspected in any patient receiving lithium who develops delirium, regardless of the serum level, and that immediate discontinuation of the medication be considered.

As-needed dosing of antipsychotic drugs: limitations and guidelines for use in the elderly agitated patient

OBJECTIVE

To review the as-needed dosing of antipsychotic drugs. Because insufficient data are available to evaluate this therapy, alternative strategies in managing acute agitation in elderly patients are suggested.

DATA SOURCES

A MEDLINE search of English-language articles published between 1966 and June 1992 was used to identify studies and reviews of antipsychotic drugs administered in single doses or intermittently.

STUDY SELECTION

Because of the paucity of data, all studies obtained were reviewed. Those addressing the use of drug holidays (chronic dosing with days without drug) were excluded.

DATA EXTRACTION

No data are available regarding the efficacy of as-needed dosing of antipsychotics in elderly agitated patients; thus, data obtained from treating acutely psychotic patients are described, and differences between this population and elderly agitated patients are discussed.

DATA SYNTHESIS

Antipsychotics are used frequently to control agitated behavior in elderly patients, although double-blind studies have not consistently demonstrated the superiority of active drug over placebo.

CONCLUSIONS

Rigorous placebo-controlled trials of the safety and efficacy of as-needed dosing of antipsychotics are needed. As-needed dosing of any drug to control behavior should be reserved only for infrequent, sustained agitation that cannot be linked to an eliciting event. Orders for such dosing must include definitive, detailed directions for nursing personnel specifying target behaviors, maximum daily dosages, and monitoring parameters for assessing efficacy and adverse effects.

Phase stability of the nanolaminates V2Ga2C and (Mo1-xVx)2Ga2C from first-principles calculations

We here use first-principles calculations to investigate the phase stability of the hypothetical laminated material V₂Ga₂C and the related alloy (Mo_1–xV_x)₂Ga₂C, the latter for a potential parent material for synthesis of (Mo_1–xV_x)₂C, a new two-dimensional material in the family of so called MXenes.

We here use first-principles calculations to investigate the phase stability of the hypothetical laminated material V₂Ga₂C and the related alloy (Mo_1–xV_x)₂Ga₂C, the latter for a potential parent material for synthesis of (Mo_1–xV_x)₂C, a new two-dimensional material in the family of so called MXenes. We predict that V₂Ga₂C is thermodynamically stable with respect to all identified competing phases in the ternary V–Ga–C phase diagram. We further calculate the stability of ordered and disordered configurations of Mo and V in (Mo_1–xV_x)₂Ga₂C and predict that ordered (Mo_1–xV_x)₂Ga₂C for x ≤ 0.25 is stable, with an order–disorder transition temperature of ∼1000 K. Furthermore, (Mo_1–xV_x)₂Ga₂C for x = 0.5 and x ≥ 0.75 is suggested to be stable, but only for disordered Mo–V configurations, and only at elevated temperatures. We have also investigated the electronic and elastic properties of V₂Ga₂C; the calculated bulk, shear, and Young's modulus are 141, 94, and 230 GPa, respectively.

C-H activation of light alkanes on MXenes predicted by hydrogen affinity

C-H activation of light alkanes is one of the most important reactions for a plethora of applications but requires catalysts to operate at feasible conditions. MXenes, a new group of two-dimensional materials, have shown great promise as heterogeneous catalysts for several applications. However, the catalytic activity of MXenes depends on the type and distribution of termination groups. Theoretically, it is desired to search for a relation between the catalytic activity and the termination configuration by employing a simple descriptor in order to avoid tedious activation energy calculations. Here, we show that MXenes are promising for splitting C-H bonds of light alkanes. Furthermore, we present how a quantitative descriptor - the hydrogen affinity - can be used to characterize the termination configuration of Ti₂CT_z (T = O, OH) MXenes, as well as the catalytic activity towards dehydrogenation reactions, using propane as model system. First-principles calculations reveal that the hydrogen affinity can be considered as an intrinsic property of O and OH terminated Ti₂C MXenes, in which the mean hydrogen affinity for the terminated Ti₂C MXenes is linearly correlated to the statistical average of their OH fraction. In addition, the C-H activation energies exhibit a strong scaling relationship to the hydrogen affinity. This quantity can therefore yield quick predictions of catalytic activity of terminated Ti₂C MXenes towards C-H activations, and even predict their chemical selectivity toward scissoring different C-H bonds. We believe that the hydrogen affinity will accelerate the discovery of further applications of the broad family of MXenes in heterogeneous catalysis.

Early detection of neuroleptic-induced parkinsonism in elderly patients with dementia

The recently promulgated Health Care Finance Administration guidelines regarding the use of neuroleptic medications for nursing home residents do not offer criteria for the frequency or nature of the required assessments of neuroleptic-induced parkinsonism (NIP). NIP has been poorly characterized in the elderly and empirical evidence on which to base guidelines for monitoring NIP is sparse. We examined the onset of NIP in 12 closely monitored, elderly psychiatric inpatients diagnosed with dementia being treated with perphenazine. Significant increases in the Simpson Extrapyramidal Side Effect Scale total score were detected by day 4 of treatment with perphenazine at a mean dose of 8.0 mg. This increase was highly correlated with the final NIP severity. This is the first report to demonstrate that routine screening of elderly patients can detect NIP within days of the initiation of neuroleptic treatment. Early detection of NIP may allow for effective intervention to reduce the ultimate severity and associated morbidity of NIP.

Flexible Free-Standing MoO3/Ti3C2T z MXene Composite Films with High Gravimetric and Volumetric Capacities

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, Ti3C2T z MXene is mixed with MoO3 nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive Ti3C2T z flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO3 nanobelts, in turn, prevent the restacking of the Ti3C2T z nanosheets. Benefitting from these advantages, a MoO3/Ti3C2T z film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g-1 and 1836 C cm-3 at 1 A g-1 for an ≈ 10 µm thick film; and 767 C g-1 and 1664 C cm-3 at 1 A g-1 for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO3/Ti3C2T z films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg-1 and 39.2 Wh L-1, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.

Tailored synthesis approach of (Mo2/3Y1/3)2AlC i-MAX and its two-dimensional derivative Mo1.33CTz MXene: enhancing the yield, quality, and performance in supercapacitor applications

A vacancy-ordered MXene, Mo_1.33CT_z, obtained from the selective etching of Al and Sc from the parent i-MAX phase (Mo_2/3Sc_1/3)₂AlC has previously shown excellent properties for supercapacitor applications. Attempts to synthesize the same MXene from another precursor, (Mo_2/3Y_1/3)₂AlC, have not been able to match its forerunner. Herein, we show that the use of an AlY_2.3 alloy instead of elemental Al and Y for the synthesis of (Mo_2/3Y_1/3)₂AlC i-MAX, results in a close to 70% increase in sample purity due to the suppression of the main secondary phase, Mo₃Al₂C. Furthermore, through a modified etching procedure, we obtain a Mo_1.33CT_z MXene of high structural quality and improve the yield by a factor of 6 compared to our previous efforts. Free-standing films show high volumetric (1308 F cm^-3) and gravimetric (436 F g^-1) capacitances and a high stability (98% retention) at the level of, or even beyond, those reported for the Mo_1.33CT_z MXene produced from the Sc-based i-MAX. These results are of importance for the realization of high quality MXenes through use of more abundant elements (Y vs. Sc), while also reducing waste (impurity) material and facilitating the synthesis of a high-performance material for applications.

Hidden images in halftone pictures

A method of concealing an image in a different halftone image is proposed. Continuous-tone levels of the visible images are represented by the area of the halftone dots. However, the hidden image is encoded by the dots' positions inside their cells. Only a spatial correlator with a unique filter function can reveal the hidden image from the halftone picture. The technique and its robustness to noise and distortions are demonstrated.

Pyridinic Nitrogen Modification for Selective Acetylenic Homocoupling on Au(111)

On-surface acetylenic homocoupling has been proposed to construct carbon nanostructures featuring sp hybridization. However, the efficiency of linear acetylenic coupling is far from satisfactory, often resulting in undesired enyne products or cyclotrimerization products due to the lack of strategies to enhance chemical selectivity. Herein, we inspect the acetylenic homocoupling reaction of polarized terminal alkynes (TAs) on Au(111) with bond-resolved scanning probe microscopy. The replacement of benzene with pyridine moieties significantly prohibits the cyclotrimerization pathway and facilitates the linear coupling to produce well-aligned N-doped graphdiyne nanowires. Combined with density functional theory calculations, we reveal that the pyridinic nitrogen modification substantially differentiates the coupling motifs at the initial C-C coupling stage (head-to-head vs head-to-tail), which is decisive for the preference of linear coupling over cyclotrimerization.

Predictive theoretical screening of phase stability for chemical order and disorder in quaternary 312 and 413 MAX phases

In this work we systematically explore a class of atomically laminated materials, Mn+1AXn (MAX) phases upon alloying between two transition metals, M' and M'', from groups III to VI (Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W). The materials investigated focus on so called o-MAX phases with out-of-plane chemical ordering of M' and M'', and their disordered counterparts, for A = Al and X = C. Through use of predictive phase stability calculations, we confirm all experimentally known phases to date, and also suggest a range of stable ordered and disordered hypothetical elemental combinations. Ordered o-MAX is favoured when (i) M' next to the Al-layer does not form a corresponding binary rock-salt MC structure, (ii) the size difference between M' and M'' is small, and (iii) the difference in electronegativity between M' and Al is large. Preference for chemical disorder is favoured when the size and electronegativity of M' and M'' is similar, in combination with a minor difference in electronegativity of M' and Al. We also propose guidelines to use in the search for novel o-MAX; to combine M' from group 6 (Cr, Mo, W) with M'' from groups 3 to 5 (Sc only for 312, Ti, Zr, Hf, V, Nb, Ta). Correspondingly, we suggest formation of disordered MAX phases by combing M' and M'' within groups 3 to 5 (Sc, Ti, Zr, Hf, V, Nb, Ta). The addition of novel elemental combinations in MAX phases, and in turn in their potential two-dimensional MXene derivatives, allow for property tuning of functional materials.

Impact of strain, pressure, and electron correlation on magnetism and crystal structure of Mn2GaC from first-principles

The atomically laminated Mn2GaC has previously been synthesized as a heteroepitaxial thin film and found to be magnetic with structural changes linked to the magnetic anisotropy. Related theoretical studies only considered bulk conditions and thus neglected the influence from possible strain linked to the choice of substrate. Here we employ first principles calculations considering different exchange-correlation functionals (PBE, PW91, PBEsol, AM05, LDA) and effect from use of + U methods (or not) combined with a magnetic ground-state search using Heisenberg Monte Carlo simulations, to study influence from biaxial in-plane strain and external pressure on the magnetic and crystal structure of Mn2GaC. We find that PBE and PBE + U, with Ueff ≤ 0.25 eV, gives both structural and magnetic properties in quantitative agreement with available experimental data. Our results also indicate that strain related to choice of substrate or applied pressure is a route for accessing different spin configurations, including a ferromagnetic state. Moreover, the easy axis is parallel to the atomic planes and the magnetocrystalline anisotropy energy can be increased through strain engineering by expanding the in-plane lattice parameter a. Altogether, we show that a quantitative description of the structural and magnetic properties of Mn2GaC is possible using PBE, which opens the way for further computational studies of these and related materials.

Application of serial- and parallel-projection methods to correlation-filter design

We describe generalized projection procedures for the design of arbitrary filter functions for correlators. More specifically, serial and parallel implementations of projection-based algorithms are employed. The novelty of this procedure lies in its generality and its ability to handle wide varieties of constraints by the same procedure. The procedure is demonstrated by the design of filters for the 4-ƒ linear correlator, the phase-extraction correlator, and variants thereof. The filters are subject to a variety of constraints, including rotation-invariant pattern recognition and class discrimination. Examples are given to show the versatility, flexibility, and applicability of the design process to a variety of pattern-recognition tasks. Satisfactory results are also obtained because of the combination with the special nonlinear correlators proposed for pattern recognition.

Three-dimensional optical Fourier transform and correlation

Optical implementation of a three-dimensional (3-D) Fourier transform is proposed and demonstrated. A spatial 3-D object, as seen from the paraxial zone, is transformed to the 3-D spatial frequency space. Based on the new procedure, a 3-D joint transform correlator is described that is capable of recognizing targets in the 3-D space.

Reconstruction of longitudinal distributed incoherent sources

We describe measurement of the degree of coherence induced by a random light source distributed along the longitudinal z axis. If this degree of coherence is measured only between all the in-plane pairs of points placed along the radial lines it is proportional to the Fourier transform of the source's three-dimensional intensity distribution as seen from the paraxial far zone. A reconstruction of the source shape from the measured degree of coherence is also demonstrated.