Performance implications of the thermal-induced frequency drift infast wavelength switched systems with heterodyne detection

The frequency modulation response and tuning dynamics of a two-section DFB laser are determined by carrier and thermal modulation of the active layer refractive index. In response to a step change in the injection current for switching between channels in a wavelength division multiplexed system, the optical frequency changes rapidly due to the carrier effect, and then slowly drifts toward a steady state value due to the thermal effect. For wavelength switched applications with heterodyne detection, the drifting of the optical frequency broadens the spectrum of the IF signal and may impose a limit on the time that the signal remains within the IF passband (residency time). The IF spectral broadening and residency time are investigated theoretically and experimentally. Based upon a minimum mean square error fit between experimental and theoretical FM responses, the dependence of the spectral broadening and residency time on the bias condition of the laser and the optical frequency switching interval is characterized     

Traveling wave method for calculation of linewidth, frequencytuning, and stability of semiconductor lasers

The authors present a new traveling wave method for calculating the linewidth, the frequency tuning efficiency, and a mode stability parameter for a general class of laser-diode structures. The method leads to simple semianalytic expressions which allow an easy numerical determination of the three parameters     

Sequential emission of neutrons in the reaction16O+64Ni at 7.5–12 MeV per nucleon

Neutron energy and angular distributions have been studied in coincidence with projectilelike fragments (PF) for quasielastic and deeply inelastic collisions of¹⁶O on⁶⁴Ni at 7.5–12 MeV/u bombarding energy. The neutron yield can be explained assuming only two isotropically emitting sources:i) sequential emission from fully accelerated PF andii) evaporation from fully accelerated targetlike fragments (TF). ForZ=6 andZ=8 ejectiles known excited states in¹³C and¹⁷O could be identified. For oxygen, this suggests a direct excitation process,n pickup from the target. No significant evidence for preequilibrium neutron emission was found even at the highest bombarding energy. The TF temperatures and neutron multiplicities are consistent with the assumption that thermal equilibrium was reached during the binary reaction.     

Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

改进光电晶体管线性运行的反馈电路

当设计者用光电晶体管将一个调制后的光信号转换成电信号时,如果有高亮度的背光使光电晶体管饱和,就会遇到麻烦.当光电晶体管基极端悬浮时,其集电极/射极电压只取决于信号与背光重叠而产生的光电流.光电晶体管增益及其作用区范围由R1阻值(见图1)确定.R1阻值较高时,电路的增益增加,但光电晶体管会很快饱和.图1中没有背光照射时,晶体管工作在其线性区的偏置点φ2,Q1的集电极电压围绕VCE作线性变化.其输出VOUT准确地重复使调制光信号产生幅度波动.当施加外部稳定的背光照明时,电路的工作点移至偏置点φ3,输出电压被压缩并出现失真.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.