T. T. Chen

Persistence of psychotic symptoms as an indicator of cognitive impairment in methamphetamine users

BACKGROUND Prolonged exposure to methamphetamine (meth) has neurotoxic effects and impairs neurocognitive functions. This study aims to ascertain whether meth users who experience persistent psychosis suffer more severe cognitive impairment than those not experiencing persistent psychosis. METHODS This cross-sectional study includes 252 participants: 25 meth users without psychosis (METH-P), 50 with brief psychosis (METH+BP), and 56 with persistent psychosis (METH+PP), as well as 54 patients with schizophrenia and 67 healthy controls. The neurocognitive function and clinical psychopathology of each patient were evaluated with the Brief Assessment of Cognition in Schizophrenia (BACS) and the Brief Psychiatric Rating Scale (BPRS), respectively. RESULTS All cognitive domains evaluated with BACS (verbal memory, working memory, motor speed, verbal fluency, attention and processing speed, executive function, and composite scores) in METH+PP patients were similar to those in the schizophrenia patients and were worse than those in METH-P, METH+BP, and the healthy control subjects. Furthermore, cognitive functioning in meth users that did not experience persistent psychosis showed no statistically significant difference compared with the healthy control subjects. Among the meth users in this study, the negative symptom scores in the BPRS correlated to cognitive performance on the BACS, with the exception of motor speed. CONCLUSIONS Meth users display heterogeneity in their psychotic symptoms and cognitive profiles. Therefore, persistent psychotic symptoms may denote a risk for cognitive decline among meth users. Further longitudinal studies should be performed in the future to clarify the causal relationship between cognitive deficits and the development of persistent psychosis.

Size-dependent photoelastic effect in ZnO nanorods

Manipulation of internal strain by an external light beam called photoelastic effect has been firmly established in ZnO nanorods. The underlying mechanism of this interesting phenomenon arises from the combination of the screening of internal electric field and converse piezoelectric effect. We demonstrate that the photoelastic effect is more pronounced in thinner nanorods due to a larger surface to volume ratio. In addition to giving a good evidence for the existence of photoelastic effect in semiconductor nanorods, our finding also provides an excellent possibility for the development of nanoscale optical modulators.

Random lasing in the composites consisting of photonic crystals and semiconductor nanowires

A well designed material composed of photonic crystals (PCs) and semiconductor nanowires was proposed. To illustrate our working principle, the nanocomposites consisting of SnO2 nanowires and PCs based on Tb(OH)3/SiO2 core/shell nanospheres have been synthesized and characterized. It is found that lasing behavior can be easily achieved using this composite material. The light confined inside the PCs due to the formation of stop band can be extracted along SnO2 nanowires. The observation of random lasing behavior indicates that the composites developed here open a route for the creation of optoelectronic devices.

Electroluminescence enhancement in InGaN light-emitting diode during the electrical stressing process.

This study of the optoelectronic properties of blue light-emitting diodes under direct current stress. It is found that the electroluminescence intensity increases with duration of stress, and the efficiency droop curves illustrated that the peak-efficiency and the peak-efficiency-current increases and decreases, respectively. We hypothesize that these behaviors mainly result from the increased internal quantum efficiency.

Built-in surface electric field, piezoelectricity and photoelastic effect in GaN nanorods for nanophotonic devices.

Novel behaviors arising from the coupling between the built-in surface electric field, piezoelectricity, electron-hole pairs and external light beam were observed in GaN nanorods. An increase in the optical excitation density resulted in a blueshift in the photoluminescence spectra and a redshift in the frequency of the GaN A(1)(LO) phonon. The underlying mechanism was attributed to the screening of the built-in surface electric field by photoexcited carriers and, through the converse piezoelectric effect, a reduction in the internal strain. The existence of the built-in surface electric field in GaN nanorods was confirmed by scanning Kelvin probe microscopy. Our results firmly establish the existence of the photoelastic effect in GaN nanorods. In addition to underpinning the principle for applications in nanophotonic devices, this discovery also draws attention to the novel effects arising from the inherent large surface-to-volume ratio of nanostructures, which is possibly applicable to many other nanomaterials.

Differences in Clinical Features of Methamphetamine Users with Persistent Psychosis and Patients with Schizophrenia

Background: Methamphetamine exerts neurotoxic effects and elicits psychotic symptoms. This study attempted to compare clinical differences between methamphetamine users with persistent psychosis (MAP) and patients with schizophrenia. In addition, we examined the discrimination validity by using symptom clusters to differentiate between MAP and schizophrenia. Methods: We enrolled 53 MAP patients and 53 patients with schizophrenia. The psychopathology of participants was assessed using the Chinese version of the Diagnostic Interview for Genetic Studies and the 18-item Brief Psychiatric Rating Scale. Logistic regression was used to examine the predicted probability scores of different symptom combinations on discriminating between MAP and schizophrenia. The receiver operating characteristic (ROC) analyses and area under the curve (AUC) were further applied to examine the discrimination validity of the predicted probability scores on differentiating between MAP and schizophrenia. Results: We found that MAP and schizophrenia demonstrated similar patterns of delusions. Compared to patients with schizophrenia, MAP experienced significantly higher proportions of visual hallucinations and of somatic or tactile hallucinations. However, MAP exhibited significantly lower severity in conceptual disorganization, mannerism/posturing, blunted affect, emotional withdrawal, and motor retardation compared to patients with schizophrenia. The ROC analysis showed that a predicted probability score combining the aforementioned 7 items of symptoms could significantly differentiate between MAP and schizophrenia (AUC = 0.77). Conclusion: Findings in the current study suggest that nuanced differences might exist in the clinical presentation of secondary psychosis (MAP) and primary psychosis (schizophrenia). Combining the symptoms as a whole may help with differential diagnosis for MAP and schizophrenia.

Creating optical anisotropy of CdSe/ZnS quantum dots by coupling to surface plasmon polariton resonance of a metal grating

An efficient method that can be used to control the optical anisotropy of CdSe/ZnS quantum dots by coupling to the surface plasmon polariton resonance of a metal grating has been demonstrated. It is found that the unpolarized emission and Raman scattering signals arising from CdSe/ZnS quantum dots can be manipulated and exhibit a strong anisotropic behavior based upon our strategy. The optical anisotropy is interpreted in terms of the coupling between the directional surface plasmon of metal grating and the emitted light beam of quantum dots. Due to the importance of quantum dots in optoelectronic devices, our new approach should be useful for future application.

Selectively enhanced emission and suppression in Si0.5Ge0.5/Si multiple quantum wells by photonic crystals

Selective enhancement and suppression of the photoluminescence arising from Si0.5Ge0.5/Si multiple quantum wells by photonic crystals (PCs) have been demonstrated. The formation of the stop band in PCs is designed to be a filter as well as a reflector. It is found that the self-assembled PCs are able to selectively enhance the luminescence of the type-II transitions at the interface between Si and Si0.5Ge0.5/Si layers and suppress the emission from Si. Our working principle shown here can be extended to many other material systems and should be very useful for creating high power solid-state emitters.

Optically modulated internal strain in InGaN quantum dots grown on SIN x nano masks

Optically modulated internal strain has been observed in InGaN quantum dots (QDs) deposited on SiN(x) nano masks. The modulated internal strain can induce a number of intriguing effects, including the change of refractive index and the redshift of InGaN A(1)(LO) phonon. The underlying mechanism can be well accounted for in terms of the variation of internal strain through the converse piezoelectric effect arising from the screening of the internal electric field due to spatial separation of photoexcited electrons and holes. Our results point out a convenient way for the fine tuning of physical properties in nitride-based semiconductor nanostructures, which is very important for high quality optoelectronic devices.