Self-focusing Process Research Articles

Solvent-free mechanosynthesis of Schiff bases derived from thiadiazole with potential application in sensing ionic species and NLO applications

In this work, we report the solvent-free mechanosynthesis of three Schiff bases (SBs) derived from 1,3,4-thiadiazole covalently bonded to indole (Th-In), quinoline (Th-Qn) and triphenylamine (Th-TPA) groups. This green chemistry method showed a drastic reduction in reaction time and avoidance of solvents for obtaining SBs, with good reaction yields. The molecular structures of SBs were investigated by computational chemistry calculations, with global reactivity parameters indicative of electron acceptor behavior, estimation of frontier molecular orbitals, and their theoretical band gaps of 3.49 and 3.4 eV for Th-In and Th-Qn, respectively, and the lowest of 299 eV for Th-TPA. To evaluate the possible NLO response, the hyperpolarizabilities (β) were also estimated, which are several orders of magnitude higher than the urea value used as a reference. The absorption and emission spectra were calculated using TD-DFT. These results showed a larger redshift for Th-TPA, with possible charge transfer processes more intense than those obtained for Th-In and Th-Qn. The photophysical properties of the Schiff bases were determined, with band gap values for Th-In, Th-Qn, and Th-TPA of 2.53, 2.66, and 2.39 eV in solution and 2.77, 2.26, and 2.21 eV in film, respectively. When the SBs were evaluated as potential naked-eye colorimetric chemosensors, colorimetric changes were observed in Fe2+, Fe3+, Pb2+, Cu2+, and Ag+ ions, with Ag+ being the most promising. Z-scan was used to evaluate the nonlinear response of the SBs and showed saturable absorber behavior with self-focusing processes. Cyclic voltammetry was used to determine the electrochemical band gaps, which were 2.70, 2.71, and 1.98 eV for Th-In, Th-Qn, and Th-TPA, respectively. Th-TPA exhibits superior optical and electrical properties among the three SBs investigated. In addition, it exhibits photochromism, which can be used in conjunction with its other properties in NLO and sensor applications.

Similarity to the self influences memory for social targets

ABSTRACT The construct of the self is important in the domain of memory research. Recent work has shown that person memory is influenced by similarity of social targets to the self. The current experiments investigate self-similarity as defined by traits and political ideology to better understand how memory for social targets is organised. Across three experiments, participants formed positive or negative impressions based on each target’s picture, a trait-implying behavior (Experiments 1 & 2), and/or political ideology (conservative/liberal label in Experiment 2; political-ideological belief statements in Experiment 3) followed by a memory test. Results showed a self-similarity effect dependent on valence in Experiment 1, but not in Experiments 2 or 3 when participants processed ideological information associated with targets. These results suggest that self-similarity has an effect on memory for social targets, but that ideological information disrupts self-focused processing of others, suggesting that ideological information also has a powerful influence on what people remember about others (i.e. social targets).

Effect of transmission characteristics of femtosecond laser focusing on micro-/nanostructure morphology of titanium alloy

Various types of micro-/nanostructures can be fabricated by femtosecond laser irradiation on metal surfaces. It has received extensive attention and research because of its potential application value. In this paper, the effect of laser focusing position on the micro-/nanostructure formation on the surface of a titanium alloy (TC4) was systematically researched. The experimental results show that, in the process of femtosecond laser focusing, a spatial distribution of laser energy with a narrower beam center and a ring around the beam is formed in front of the geometric focus and the distribution of laser energy changes along the laser transmission direction. This property can affect the morphology of the micro-/nanostructure on the surface of irradiated materials. It is believed that the new spatial distribution of laser fluence caused by focusing is due to the nonlinear process of plasma defocus and laser self-focusing caused by multi-photon or tunnel ionization in front of the target by focusing the femtosecond laser. The discovery of the nonlinear characteristics of the focused femtosecond laser and the application of the unique energy spatial distribution to the surface morphology of the fabricated surface put forward a new idea for the direct fabrication of micro-/nanostructures via femtosecond laser, which has certain significance for the development of micro-/nanofabrication technology of femtosecond lasers.

Self-focusing and self-splitting properties of partially coherent temporal pulses propagating in dispersive media.

Based on the coherence theory for non-stationary optical fields, we introduce a new class of partially coherent pulse sources with multi-cosine-Gaussian correlated Schell-model (MCGCSM) and derive the analytic expression for the temporally mutual coherence function (TMCF) of an MCGCSM pulse beam when it propagates through dispersive media. The temporally average intensity (TAI) and the temporal degree of coherence (TDOC) of the MCGCSM pulse beams spreading in dispersive media are investigated numerically, respectively. Our results show that over propagation distance, the evolution of pulse beams is from the primary single beam into multiple subpulses or form flat-topped TAI distributions by controlling source parameters. Moreover, when the chirp coefficient s < 0, the MCGCSM pulse beams through dispersive media will show the characteristics of two self-focusing processes. The reason why there are two self-focusing processes is explained from the perspective of physical meaning. The results in this paper can open the applications of pulse beams in multiple pulse shaping and laser micromachining and material processing.

Random pulse source with the temporal multi-complex degree of coherence

Based on the coherence theory, the non-stationary optical fields with the complex degree of coherence (CDOC) are expanded from stationary fields, and random pulse sources with temporal multi-complex degree of coherence (TMCDOC) is introduced. Theoretical model for the random pulse sources with TMCDOC is established. The analytical transmission formulas for the temporally spectral density and TMCDOC of the pulse beam spreading through dispersive media are derived and its propagation properties in dispersive media are explored. One can find from the numerical results that the TMCDOC pulse beam will evolve from a single pulse at the source plane into N subpulses in the far field or produce far field spectral density with flat-topped profiles. The variation of the non-trivial phase of the CDOC can regulate the propagation angle of the TMCDOC pulse beam. Moreover, in case of the propagation in dispersive media with chirp coefficient s < 0, the TMCDOC pulse beam will exhibit self-focusing process, and its coherence curves will be reversed from the clockwise rotation in the near field to anticlockwise rotation in the far field.

ALTERATIONS IN FUNCTIONAL CONNECTIVITY: BEING WATCHED AS AN INDICATOR OF STATE ANXIETY

Anxiety increases self-focused attention and rumination. Individuals with anxiety are sensitive to being watched by others, as being watched provokes self-referential processing and induces thoughts regarding others perceptions of oneself. However, whether the neural sensitivity to being watched depends on the level of anxiety remains unclear.We investigated the relationship between anxiety and the neural sensitivity to being watched by others.The anxiety of 25 healthy participants (mean age standard deviation, 23.08 1.71 years; 12 men and 13 women) was evaluated using the Spielberger StateTrait Anxiety Inventory. Resting state electroencephalography data was collected under the alone condition and the condition of being watched by another person. By subtracting the phase lag value between the two conditions, we determined the alterations in participants functional networks when they were being watched. We then found the correlation between the Spielberger StateTrait Anxiety Inventory scores and reactivity of functional connectivity when being watched.The score of state anxiety was significantly correlated with increased phase lag values in the left precuneus, bilateral caudal anterior cingulate cortex, and right rostral middle frontal cortex in the beta band (p&lt; 0.05). We found no significant correlation between the trait anxiety scores and altered phase lag values.Functional connectivity may be involved in the default mode network relevant to self-referential processing and the dorsal attentional network. Our results suggest that self-focused mental processing and sensitivity to being watched by others could be common in people with anxiety, thus expanding the current understanding of the cognitive mechanisms behind anxiety.

Associations between self-absorption and working memory capacity: A preliminary examination of a transdiagnostic process spanning across emotional disorders

Considered a transdiagnostic process spanning across emotional disorders, self-absorption reflects self-focused processing that is excessive, sustained, and inflexible. Working memory capacity is critical for self-regulation, inclusive of mitigating perseverative thinking. Providing the first known examination of associations between self-absorption and working memory capacity, a negative association was expected. A sample of adults (N = 63; 70 % experiencing an anxiety or depressive disorder) completed the study protocol, which included completing a structured diagnostic interview, self-report measures, and a working memory capacity task. Self-absorption, as predicted, negatively correlated with working memory capacity, with an association found for the private, but not public, aspect of self-absorption. The association between private self-absorption and working memory capacity was not attributable to shared variance with public self-absorption or negative affectivity. Diagnostic status (anxiety disorder, depressive disorder, or either disorder) did not moderate the association. The results provide evidence that self-absorption relates to impairments in working memory capacity. Implications and future directions for how these results advance our understanding and treatment efforts of self-absorption are discussed.

The intergenerational transmission of emotion socialization.

We examined the extent to which new mothers' recollections of their mothers' emotion socialization practices during childhood predict sensitive/supportive responses to their own toddlers in distressing situations both directly and indirectly via effects on mothers' social information processing about infant cry signals. Mothers' adult attachment was tested as a possible moderator and we tested model invariance across racial groups. These questions were assessed using a 3-wave longitudinal study of first-time mothers (131 African American, 128 European American) followed from pregnancy until children were 14 months old. Expectant mothers were administered the Adult Attachment Interview and self-report measures of remembered childhood emotion socialization. When infants were 6 months old, mothers' cry processing was assessed using a video-recall method in which they watched videos of their interactions with their infants during distress tasks and reported on their emotions and cognitions during the interaction. Maternal sensitivity to distress at 14 months was assessed via observed maternal sensitivity during distress tasks and mothers' self-reported responses to child distress. Consistent with prediction, mothers who recalled their own mothers as high on nonsupportive responses to their distress in childhood engaged in more self-focused and negative cry processing at 6 months, which in turn predicted less supportive responding to their toddlers in distressing situations. This indirect effect was statistically significant. These effects were not moderated by adult attachment coherence. The full model was invariant across racial groups. Thus, remembered childhood emotion socialization experiences have longstanding consequences for subsequent social behavior, including parenting the next generation. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Direct and Inverse Problems of Investigating the Process of Self-Focusing of X-Ray Pulses in Plasma

Methods for solving direct and inverse problems for investigating the process of self-focusing of plane X-ray pulses in plasma are proposed and described. The mathematical model takes into account the dynamics of the electron plasma component in quasi-hydrodynamic approximation; this model is a nonlinear system of four second-order partial differential equations subject to corresponding initial and boundary value conditions. To solve the direct problem, a second-order conservative difference scheme is constructed and an iteration-free algorithm for the computations using this scheme is developed. For solving the inverse problem of determining the initial plasma and pulse parameters given the measured (or desired) characteristics of the X-ray pulse after its self-focusing, it is proposed to use the method of equivalence set designed for solving multiobjective problems in a pseudo-metric space of criteria. An algorithm for applying this method for solving the problem of interest is described.

Strong self-focusing of a chirped pulse laser in thermal quantum plasma under density transition

In the present manuscript, an analysis has been done on strong self-focusing of a chirped pulse laser in thermal quantum plasma under exponential plasma density transition. It is observed that the beam width parameter reduces up to great extent which in turns enhances the process of self-focusing. It is observed that in the embellishment of self-focusing of laser beam, thermal quantum plasma contributes significantly. Further, it is seen that with change in different parameters like intensity of the laser beam, chirped parameter value and plasma frequency, self-focusing is sensitive and becomes stronger at higher values of these parameters. The present work may have important applications in field of laser interaction with the quantum plasma, laser driven particle accelerators etc.

Acceleration of electrons in the interaction of a subterawatt laser pulse with a nonuniform plasma

We consider the effect of nonlinear self-focusing and self-modulation processes on the acceleration of electrons in the interaction of a subterawatt femtosecond laser pulse with a gas jet plasma. A three-dimensional particle-in-cell (3D PIC) simulation of the interaction of laser radiation with a low-density nonuniform plasma shows that laser pulse self-focusing that arises when the critical power of relativistic self-focusing determined by the local concentration of plasma electrons exceeds the pulse power results in efficient generation of a plasma wave. Due to a decrease in the phase velocity of the wake plasma wave generated via self-modulation of the laser pulse, electrons are trapped into the accelerating phase of the plasma wave and are accelerated to energies of ∼10 MeV. It is demonstrated that under the conditions for limiting the electrons’ acceleration region by the length of their dephasing, quasi-monoenergetic electron bunches with a characteristic energy of ∼9 MeV can be produced. The effective temperature of the accelerated electrons and their angular distribution, obtained by 3D PIC simulation, are in good agreement with those determined in the experiment.

Self-focused processing after severe traumatic brain injury: Relationship to neurocognitive functioning and mood symptoms.

To investigate the impact of neurocognitive functioning on the self-focused processing styles of rumination and reflection, and the relationship to mood symptoms after severe traumatic brain injury (TBI). A cross-sectional design with a between-group component comparing self-focused processing styles and mood symptoms of adults with TBI and age- and gender-matched controls. Fifty-two participants with severe TBI (75% male, M age=36.56, SD=12.39) completed cognitive tests of attention, memory, executive functioning and the Awareness Questionnaire, Reflection and Rumination Questionnaire (RRQ), and Depression, Anxiety, and Stress Scales (DASS - 21). Fifty age- and gender-matched controls completed the RRQ and DASS-21. TBI participants reported significantly greater mood symptoms than controls (p<.05); however, levels of rumination and reflection did not significantly differ. TBI participants high on both reflection and rumination had significantly greater mood symptoms than those with high reflection and low rumination (p<.001). Higher levels of rumination and reflection were associated with better working memory and immediate and delayed verbal memory (r=.36-.43, p<.01). Higher levels of rumination were also associated with greater verbal fluency, self-awareness, and mood symptoms (r=.36-.70, p<.01). Individuals with better memory functioning may be more likely to engage in self-focused processing after severe TBI. Reflection without ruminative tendencies is more adaptive for mental health than reflection with rumination. Individuals with severe TBI report more mood symptoms than non-injured controls but do not differ on self-focused processing. Poorer memory function is related to lower levels of rumination and reflection. Reflection without ruminative tendencies is adaptive for mental health after severe TBI. Individuals with greater self-awareness and ruminative tendencies are at increased risk of mental health problems following severe TBI. Rumination and reflection were assessed using a self-report measure which assumes that people with severe TBI are able to reliably report on self-focused processing styles. The direction of associations between self-focused processing, self-awareness, and mood symptoms could not be determined due to the cross-sectional design.

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas with linear density and temperature ramps

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas are investigated in the presence of various laser intensities and linear density and temperature ramps. Considering the ponderomotive force and using the momentum transfer and energy equations, the nonlinear electron density is derived. Taking into account the paraxial approximation and nonlinear electron density, a nonlinear differential equation, governing the focusing and defocusing of the laser beam, is obtained. Results show that in the absence of ramps the laser beam is focused between a minimum and a maximum value of laser intensity. For a certain value of laser intensity and initial electron density, the self-focusing process occurs in a temperature range which reaches its maximum at turning point temperature. However, the laser beam is converged in a narrow range for various amounts of initial electron density. It is indicated that the σ2 parameter and its sign can affect the self-focusing process for different values of laser intensity, initial temperature, and initial density. Finally, it is found that although the electron density ramp-down diverges the laser beam, electron density ramp-up improves the self-focusing process.

Are experiences of psychosis associated with unhelpful metacognitive coping strategies? A systematic review of the evidence.

This review investigated whether unhelpful metacognitive coping strategies, such as attentional biases, worry, rumination, and thought control, are associated with experiences of psychosis. These processes, known collectively as the Cognitive Attentional Syndrome (CAS), form a central tenet of the Self-Regulatory Executive Function model. Three research questions based on assumptions underlying the CAS were addressed. It was predicted that processes of (a) self-focused processing, (b) negative perseverative thinking (worry and rumination), and (c) counterproductive thought control would be associated with experiences of psychosis. A comprehensive search of the literature identified 51 eligible studies: 17 investigated self-focused attention, 25 investigated perseverative processing (worry: n=18; rumination: n=10), and 9 investigated thought control strategies. Findings indicated that unhelpful metacognitive coping strategies associated with the CAS are related to experiences of psychosis and appear to share important relationships with distress. Implications for future research and clinical practice are discussed.

Controlling the sing and magnitude of Kerr nonlinearity in four-level N-type EIT medium

Third-order nonlinear susceptibility in a four-level system with N-type configuration is studied by applying the electromagnetically induced transparency (EIT). The system is irradiated with a weak probe and two strong coupling fields. Behaviour of real (Kerr nonlinearity) and imaginary parts of third-order susceptibility and linear absorption spectrum of probe field is investigated with coupling field intensity and its frequency detuning. Results are shown that, the sign of both imaginary and real parts of third-order nonlinear susceptibility in one of Kerr peaks, changes from positive to negative with increasing the coupling field intensity. The EIT windows are not sensitive for intensity but extend for negative and shortened for positive detuning's. Furthermore, the magnitude of Kerr and nonlinear absorption (or gain) peaks efficiently modify with increasing the intensity. This can be important in practical applications such as lasing without inversion, subluminal and superluminal propagation and optical limiting effect based on self-focusing or self-defocusing process.

Experiential Self-Focus in Social Anxiety Disorder: Is it Beneficial?

Self-focused processing is a significant maintaining factor in cognitive models of social anxiety disorder (SAD), but it may also be analytic (detached, evaluative, maladaptive) or experiential (concrete, nonevaluative, adaptive). The current study aimed to investigate the effect of self-focus modes in a sample meeting criteria for SAD as previous studies have yielded mixed results. Individuals meeting criteria for SAD and nonanxious controls (N = 80, 77.5% female; mean age = 19.46) were randomly allocated to complete a task inducing analytic or experiential self-focused processing, followed by a social interaction task, including measurement of affective and cognitive variables. Controls demonstrated the expected benefits of experiential compared to analytic self-focus on social anxiety, negative affect, and self-beliefs. Unexpectedly, SAD participants reported no difference between self-focus conditions. Results suggest that experiential processing may have no benefit for SAD individuals proximal to a social threat. Implications of these findings are discussed.

High intensity laser beam propagation through a relativistic warm magnetoplasma

In this work, nonlinear aspects of a circularly polarized high intensity Gaussian laser beam propagating in a relativistic warm magnetized plasma are studied, taking into account the relativistic ponderomotive force. The differential equation governing the dimensionless beam width parameter is achieved and numerically solved by introducing the dielectric permittivity of such plasma and using the paraxial ray approximation. The effects of entrance laser intensity and its polarization state, external magnetic field, and electron temperature on the laser spot size evolution are studied. It is found that for both right and left-handed polarization states increasing initial laser intensity deteriorates the self-focusing mechanism while rising electron temperature improves it. It is also observed that enhancing magnetic field leads to faster and stronger self-focusing in the case of right-handed polarization and an attenuation in the self-focusing process in the case of left-handed one. In addition, the spatial distribution of normalized modified electron density as well as laser intensity profiles as a function of plasma length and beam radius is plotted and discussed for three self-focusing, self-trapping, and defocusing regimes.

Influence of sintering time on switching of the femtosecond nonlinear optical properties of CuNb2O6

Transition of mixed phases (monoclinic and orthorhombic) to pure orthorhombic phase was achieved during the synthesis process of CuNb2O6 by varying the sintering time. The suppression of monoclinic phase and dominant formation of orthorhombic CuNb2O6 was confirmed from the XRD and FTIR data analysis. FESEM studies demonstrated that due to increase in sintering time, coarsening process initiated the grain growth and trapping of pores leading to pore-free structures. The nonlinear optical (NLO) properties of mixed and pure copper niobate were studied by the Z-scan technique using near-infrared (800 nm, ∼150 fs, 80 MHz) laser excitation. Mixed phases exhibited saturable absorption and self-defocusing behaviour while pure orthorhombic demonstrated reverse saturable absorption and self-focusing process. The switching of nonlinearity along with increase in NLO coefficient of O-CuNb2O6 was attributed to the decreased metal-oxygen bond length and pore free structure. The increase in nonlinear absorption coefficient with input irradiance suggests the occurrence of effective 3 PA (2 PA followed by ESA) process. The magnitudes of nonlinear absorption coefficient (2.14 × 10−23m3/W2) and nonlinear refractive index (6.0 × 0−17 m2/W) of O-CuNb2O6 were found to be higher than well-known NLO materials. Orthorhombic CuNb2O6 exhibited optical limiting action with low limiting threshold of 38.26 μJ/cm2 and favouring NLO properties suggesting that the material to be an entrant candidate for safety devices against ultrashort pulsed lasers.

Direct self-focusing synthesis of monodisperse [Au8(PPh3)7]2+ nanoclusters.

Direct and scalable synthesis of monodisperse gold nanoclusters is highly desired but remains a great challenge due to the complexity of chemical reactions. In this regard, a suitable precursor is important as it can simplify the synthesis processes and offer controllability in tuning the product. In this study, we found that Au(PPh3)2Cl could be used as an effective precursor for the direct synthesis of atomically monodisperse [Au8(PPh3)7]2+ nanoclusters without the need of tedious post-synthetic purification steps. The Au(PPh3)2Cl precursor could be directly reduced by NaBH4 (0.25 molar equivalent) in a dichloromethane solution; this produced Au8 clusters with a 35% reaction yield. Time-dependent mass spectrometry and in situ UV-vis absorption spectroscopy reveal that the synthesis process is initiated by the rapid formation of the Au6-Au8 mixture, followed by a slow spontaneous self-focusing process that converges the mixture into atomically monodisperse Au8. The success of this direct synthesis has been hypothesized to arise from the relatively stronger Au(i)Au(i) aurophilic attraction between Au(i)-PPh3 complexes that facilitates the aggregation of Au(i)-PPh3 on Au(0) cores.

Pathways by which mothers' physiological arousal and regulation while caregiving predict sensitivity to infant distress.

Pathways by which maternal physiological arousal (skin conductance level [SCL]) and regulation (respiratory sinus arrhythmia [RSA] withdrawal) while parenting are linked with concurrent and subsequent maternal sensitivity were examined. Mothers' (N = 259) SCL and RSA were measured during a resting baseline and while interacting with their 6-month-old infants during tasks designed to elicit infant distress. Then, mothers were interviewed about their emotional and cognitive responses to infant cues (i.e., cry processing) while caregiving using a video recall procedure. Maternal sensitivity was observed during the distressing tasks at 6 months and again when children were 1-year-old. Mothers who were well-regulated (higher RSA suppression from baseline to parenting tasks) engaged in less negative and self-focused cry processing while interacting with their infants, which in turn predicted higher maternal sensitivity at both time points. In addition, SCL arousal and RSA regulation interacted such that maternal arousal was associated with more empathic/infant focused cry processing among mothers who were simultaneously well-regulated, which in turn predicted maternal sensitivity, albeit only at 6 months. These effects were independent of a number of covariates demonstrating the unique role of mothers' physiological regulation while caregiving on sensitivity. Implications for intervention are discussed. (PsycINFO Database Record