疫情中的大学物理实验线上教学探索

针对新冠肺炎疫情中“停课不停学”的要求,采用先虚后实、先理论模拟再动手实践的思路,制定了“慕课资源+仿真实验+设计研究+趣味演示”的居家实验方案.在该模式下的教学形式和教学内容体现了线上线下混合、先学后教翻转、设计研究创新等实验教学改革方向.     

新型冠状病毒肺炎的流行病学参数与模型

一种新型冠状病毒感染导致的肺炎自2019年12月至今在我国以及200多个国家和地区传播.本文旨在介绍近期关于新型冠状病毒肺炎的几个重要流行病学参数的研究进展和估计方法,包括基本再生数、潜伏期和代间隔,同时还介绍两个动力学模型及其结果.这些参数刻画了新型冠状病毒肺炎的传播特点,影响控制策略的制定和有效性.简要来说,新型冠状病毒肺炎的基本再生数R0的中位数为2.6,潜伏期均值约为5.0 d,代间隔均值约为5.5 d.这表明新型冠状病毒肺炎传播速度快.诸如对确诊病人的隔离治疗、对疑似病例的隔离、对密切接触者的追踪、对疾病信息的宣传和采取自我防护等防控措施能有效降低疾病暴发的风险和规模.     

基于格兰杰因果网络的中美贸易战对上证行业冲击的研究

中美贸易战对行业冲击是普遍关注的问题,本文选取2016年8月—2019年10月的上证行业指数,构建了格兰杰因果关系网络,然后结合事件分析法对风险传播模型的参数进行估计,最后利用蒙特卡罗算法模拟行业受到贸易战冲击后金融风险传播情况,并计算贸易战发生前后的上证股市金融网络风险传播的基本再生数.研究发现:第一,贸易战明显改变了上证行业关系结构,行业指数之间联系变得更为紧密;第二,贸易战发生初期,受美国加征关税影响,上证股市感染节点数量迅速增加,并且感染规模会在第10—15个交易日内达到峰值,感染节点数量大约在第25个交易日后开始趋于平缓,市场逐渐恢复;第三,基本再生数计算结果表明,上证股市在贸易战发生初期金融风险传播较快,上证股市容易产生“同涨同跌”的现象.     

甘蔗清糖浆锤度近红外光谱分析的模型优化

采用偏最小二乘法(PLS)和光谱Savitzky-Golay(SG)平滑方法,建立甘蔗清糖浆锤度近红外光谱分析的优化模型。基于最优单波长模型预测效果划分定标集和预测集。全谱(400—2500nm)经过SG平滑处理后用PLS方法建模。建立计算机算法平台,把483种SG平滑模式和1—40的PLS因子数任意组合分别建立PLS模型,根据预测效果选出最优模型,最优模型的SG平滑模式为二阶导数平滑、4、5次多项式类型、43平滑点数,PLS因子数为13,预测均方根偏差(RMSEP)、相对预测均方根偏差(RRMSEP)和预测相关系数(rP)分别为0.433%、0.69%和0.978。预测精度很高,并且大幅度优于未做SG平滑处理直接PLS建模的预测效果。从而表明,SG平滑模式和PLS因子数的联合大范围筛选能够有效地应用于近红外光谱分析的模型优选。     

稀薄空气中圆柱腔体内系统电磁脉冲的混合模拟

系统电磁脉冲广泛存在于强电离辐射环境中,且难以有效屏蔽.为了评估稀薄空气对系统电磁脉冲的影响,本文基于粒子-流体混合模拟方法,建立了三维非稳态模型,计算并分析了稀薄空气等离子体的特性以及其与电磁场响应的相互作用.结果表明,压力越高,光电子发射面附近的次级电子数密度越高,轴向分布的梯度越大,腔体中部的电子数密度在20 Torr(1 Torr=133 Pa)下出现峰值,而电子温度随压力升高单调递减.腔体内的稀薄空气等离子体阻碍了空间电荷层的产生,电场响应峰值比真空条件下的低了一个数量级,电场脉冲宽度也显著降低.光电子运动特性决定了电流响应的峰值,压力升高,到达腔体末端的电流先增加再减小.而等离子体电流会抑制总电流的上升速率,并使电流响应出现拖尾.最后,将数值模拟结果与电子束模拟系统电磁脉冲的实验结果进行比较,验证了本文混合模拟模型的可靠性.本研究所采用的混合模拟方法相比于粒子云网格-蒙特卡罗碰撞方法,大幅减小了计算消耗.     

稀薄空气中圆柱腔体内系统电磁脉冲的混合模拟

系统电磁脉冲广泛存在于强电离辐射环境中,且难以有效屏蔽.为了评估稀薄空气对系统电磁脉冲的影响,本文基于粒子-流体混合模拟方法,建立了三维非稳态模型,计算并分析了稀薄空气等离子体的特性以及其与电磁场响应的相互作用.结果表明,压力越高,光电子发射面附近的次级电子数密度越高,轴向分布的梯度越大,腔体中部的电子数密度在20 Torr(1 Torr=133 Pa)下出现峰值,而电子温度随压力升高单调递减.腔体内的稀薄空气等离子体阻碍了空间电荷层的产生,电场响应峰值比真空条件下的低了一个数量级,电场脉冲宽度也显著降低.光电子运动特性决定了电流响应的峰值,压力升高,到达腔体末端的电流先增加再减小.而等离子体电流会抑制总电流的上升速率,并使电流响应出现拖尾.最后,将数值模拟结果与电子束模拟系统电磁脉冲的实验结果进行比较,验证了本文混合模拟模型的可靠性.本研究所采用的混合模拟方法相比于粒子云网格-蒙特卡罗碰撞方法,大幅减小了计算消耗.     

新冠疫情常态化背景下大学物理实验教学实践

在新冠肺炎从突发应急状态进入常态化防控模式的背景下,针对大学物理实验课程提出"相近整合、线上线下结合"的教学方案,并以数字示波器和傅立叶级数两个实验为例予以实践。新课程重新审定课程目标,以此方案为指导,引入科学教学方法,并以调查问卷形式对课程效果进行调研和评价。实践结果表明,新教学方案在保证实验课程系统性、课程目标达成和学生满意度等方面都有较好的效果,具有较高的可推广性和借鉴价值。     

非胶结含水合物沉积物修正等效介质速度模型及其地震波场特征研究

通过数值分析,发现对应于悬浮模式、颗粒接触模式的等效介质模型A,B预测的含水合物沉积物纵波速度、横波速度及泊松比存在物理认识上的缺陷,单独考虑水合物微观模式为悬浮模式或颗粒接触模式并不合理.认为非胶结水合物的微观模式与其饱和度存在关联,并运用拉格朗日插值方法建立了新的非胶结含水合物沉积物修正等效介质速度模型.该模型体现了水合物饱和度对于水合物微观模式的影响,数值分析结果表明新模型预测结果更合理.基于新模型对非胶结含水合物沉积物的地震波场进行了数值模拟,探讨了似海底反射及空白带的形成机理,对实际水合物地震勘 关键词： 水合物 等效介质模型 似海底反射 空白带     

维数正规化和NJL模型π介子性质

利用定义于Grassmann扩展空间的Dirac代数算符表象的维数正规化方案,研究Nambu-Jona-Lasinio(NJL)模型中的π介子模式的性质.说明维数正规化方法可以给出NJL模型中强子模式的解析形式和相应的符合实验的数值结果.     

一些四齿型冠硫醚和配合物的红外光谱

四齿型冠硫醚及其配合物的红外光谱尚未见文献作系统的报道。我们研究了1,4,8,11-14-冠硫醚-4(TTP)、苯并-1,4,9,12-14-冠硫醚-4(TTX)、1,4,8,11-四硫杂间环(艹反))tetrathiameta cyclophane,TTmX)、1,4,7,10-13-冠硫醚-4(TTE)、1,5-苯并-9-冠硫醚-2(BDT)、1,5;10,14-二苯并-18-冠硫醚-4(DBTT)以及TTmX与Ru、Rh、Pd、Pt氯化物的配合物的红外光谱。工作内容及试验结果如下: 1.对上述冠硫醚及络合物的红外光谱初步作了归属。对属于C_2h点群的TTP进行了正则振动分析,用群论方法求出其振动光谱基频选律为: Г=26Ag+22Bg+23Au+25Bu 振动光谱共有96种正则振动方式,其中拉曼光谱和红外光谱各为48条。键伸缩和弯曲振动分布可表示为: Г伸缩=10Ag+7Bg+8Au+9Bu Г弯曲=16Ag+15Bg+15Au+16Bu 2.虽然前述几种四齿型冠硫醚的结构不同,但它们的红外光谱却十分相似,CH_2、苯环和C—S—C等基团振动的特征非常明显。这些冠硫醚的对称和非对称振动应分别在690cm~(-1)及730cm~(-1)附近。在冠硫醚中有苯环取代时,它们稍稍向高波数,导致同—CH_2CH_2—骨骼振动和苯环的C—H面外变形振动相重叠。     

Some effects of signal bandwidth and spectral density on the acoustic-reflex threshold in the elderly

The acoustic-reflex thresholds (ART) for multicomponent tonal complexes of varying bandwidth and spectral density were obtained from 20 normal-hearing (air-conduction thresholds less than or equal to 20 dB HL at 250-8000 Hz) young adults ranging in age from 20-30 years and 20 normal-hearing, old subjects ranging in age from 60-71 years. The results revealed that the ART decreased with spectral density, plateauing after seven components in the young group and after five components in the old group; the decrease in the acoustic-reflex threshold as a result of the increase in spectral density was less in the old than in the young group. The bandwidth effect (when bandwidth was plotted in hertz or octaves) on the acoustic-reflex threshold was present in the young adults, but substantially reduced in the elderly, as evidenced by the statistically significant interaction between subject group and signal bandwidth. The spectral density results are discussed in terms of their theoretic implications for the energy summation capacity and frequency resolution of the auditory system. The bandwidth results are discussed in terms of their theoretic implications for the frequency-resolving power of the auditory system.     

Upward spread of masking, hearing loss, and speech recognition in young and elderly listeners

Upward spreading of masking, measured in terms of absolute masked threshold, is greater in hearing-impaired listeners than in listeners with normal hearing. The purpose of this study was to make further observations on upward-masked thresholds and speech recognition in noise in elderly listeners. Two age groups were used: One group consisted of listeners who were more than 60 years old, and the second group consisted of listeners who were less than 36 years old. Both groups had listeners with normal hearing as well as listeners with mild to moderate sensorineural loss. The masking paradigm consisted of a continuous low-pass-filtered (1000-Hz) noise, which was mixed with the output of a self-tracking, sweep-frequency Bekesy audiometer. Thresholds were measured in quiet and with maskers at 70 and 90 dB SPL. The upward-masked thresholds were similar for young and elderly hearing-impaired listeners. A few elderly listeners had lower upward-masked thresholds compared with the young control group; however, their on-frequency masked thresholds were nearly identical to the control group. A significant correlation was found between upward-masked thresholds and the Speech Perception in Noise (SPIN) test in elderly listeners.     

COVID-19 associated perimyocarditis

Perimyocarditis is a well-known acute inflammation of the pericardium and the underlying myocardium. Most commonly perimyocarditis is of viral aetiology, specifically the coxsackie B virus. However, nowadays SARS-CoV-2 associated with COVID-19 infections has emerged as a potential rare cause of perimyocarditis. This case report will demonstrate a case of a young female with perimyocarditis as diagnosed by magnetic resonance imaging (MRI) accompanied by antigens indicating a past COVID-19 infection. Clinical status as well as Findings at MRI, echocardiography and lab results will be reviewed.     

Vocal Intensity Characteristics inNormal and Elderly Speakers

The relationship of lung pressure, fundamental frequency, peak airflow, open quotient, and maximal flow declination rate to vocal intensity for a normal speaking, young male control group and an elderly male group was investigated. The control group consisted of 17 healthy male subjects with a mean age of 30 years and the elderly group consisted of 11 healthy male subjects with a mean age of 77 years. Data were collected at three levels of vocal intensity: soft, comfortable, and loud, corresponding to 25%, 50%, and 75% of dynamic range, respectively. Phonational threshold pressure and lung pressure were obtained using the intraoral technique. The oral airflow waveform was inverse filtered to provide an approximation to the glottal airflow waveform from which measures of fundamental frequency, peak airflow, open quotient, and maximal flow declination rate were determined. Excess lung pressure was calculated as lung pressure minus estimated phonational threshold pressure. The results show for both groups an increase in sound pressure level across the conditions, with corresponding increases in lung pressure, excess lung pressure, fundamental frequency, peak airflow, and maximal flow declination rate. Open quotient decreased with increasing vocal intensity. Lung pressure, sound pressure level, and peak airflow were all found to be significantly greater for the control group than for the elderly group at each condition. Open quotient was found to be significantly lower in the control group than in the elderly group at each condition. No significant difference was observed for excess lung pressure, phonational threshold pressure, fundamental frequency, or maximal flow declination rate between the two groups. These results show that a difference in vocal intensity does exist between young and elderly voices and that this difference is the result of differences in lung pressure, peak airflow, and open quotient.     

Age differences for stop-consonant and vowel perception in adults

The purpose of this study was to determine the role of static, dynamic, and integrated cues for perception in three adult age groups, and to determine whether age has an effect on both consonant and vowel perception, as predicted by the "age-related deficit hypothesis." Eight adult subjects in each of the age ranges of young (ages 20-26), middle aged (ages 52-59), and old (ages 70-76) listened to synthesized syllables composed of combinations of [b d g] and [i u a]. The synthesis parameters included manipulations of the following stimulus variables: formant transition (moving or straight), noise burst (present or absent), and voicing duration (10, 30, or 46 ms). Vowel perception was high across all conditions and there were no significant differences among age groups. Consonant identification showed a definite effect of age. Young and middle-aged adults were significantly better than older adults at identifying consonants from secondary cues only. Older adults relied on the integration of static and dynamic cues to a greater extent than younger and middle-aged listeners for identification of place of articulation of stop consonants. Duration facilitated correct stop-consonant identification in the young and middle-aged groups for the no-burst conditions, but not in the old group. These findings for the duration of stop-consonant transitions indicate reductions in processing speed with age. In general, the results did not support the age-related deficit hypothesis for adult identification of vowels and consonants from dynamic spectral cues.     

Vocal Tract Resonance Analysis of Aging Voice Using Long-Term Average Spectra

This study is the first to use long-term average spectra (LTAS) to investigate resonance characteristics of dynamic speech in young adulthood and old age. A total of 80 speakers participated, divided equally by age group and gender. All elderly speakers were healthy, active members of the community. Measurement of the first three spectral peaks in LTAS from the first paragraph of the Rainbow Passage revealed significant lowering of peak 1 from young adulthood to old age in both men and women. Peaks 2 and 3 also lowered significantly across the adult lifespan in women and showed a tendency to lower in men. These acoustic findings are consistent with anatomic data suggesting that aging results in lengthening of the supraglottic vocal tract. Findings that women demonstrate more substantial lowering of spectral peaks with aging than men suggest that women may undergo more pronounced age-related lengthening of the supraglottic vocal tract. Alternatively, it is possible that elderly men systematically alter tongue position during vowel articulation while elderly women are less inclined to do so. Taken in conjunction with previous research, these findings suggest a "mixed model" of vocal tract resonance changes with aging in which an interaction exists between gender, the resonance effects of laryngeal lowering, and vowel articulatory patterns.     

Temporal processing deficits in the pre-senescent auditory system

This study tested the hypothesis that temporal processing deficits are evident in the pre-senescent (middle-aged) auditory system for listening tasks that involve brief stimuli, across-frequency-channel processing, and/or significant processing loads. A gap duration discrimination (GDD) task was employed that used either fixed-duration gap markers (experiment 1) or random-duration markers (experiment 2). Independent variables included standard gap duration (0, 35, and 250 ms), marker frequency (within- and across-frequency), and task complexity. A total of 18 young and 23 middle-aged listeners with normal hearing participated in the GDD experiments. Middle age was defined operationally as 40-55 years of age. The results indicated that middle-aged listeners performed more poorly than the young listeners in general, and that this deficit was sometimes, but not always, exacerbated by increases in task complexity. A third experiment employed a categorical perception task that measured the gap duration associated with a perceptual boundary. The results from 12 young and 12 middle-aged listeners with normal hearing indicated that the categorical boundary was associated with shorter gaps in the young listeners. The results of these experiments indicate that temporal processing deficits can be observed relatively early in the aging process, and are evident in middle age.     

Modeling the COVID-19 epidemic and awareness diffusion on multiplex networks

The coronavirus disease 2019(COVID-19)has been widely spread around the world,and the control and behavior dynamics are still one of the important research directions in the world.Based on the characteristics of COVID-19’s spread,a coupled disease-awareness model on multiplex networks is proposed in this paper to study and simulate the interaction between the spreading behavior of COVID-19 and related information.In the layer of epidemic spreading,the nodes can be divided into five categories,where the topology of the network represents the physical contact relationship of the population.The topological structure of the upper network shows the information interaction among the nodes,which can be divided into aware and unaware states.Awareness will make people play a positive role in preventing the epidemic diffusion,influencing the spread of the disease.Based on the above model,we have established the state transition equation,through the microscopic Markov chain approach(MMCA),and proposed the propagation threshold calculation method under the epidemic model.Furthermore,MMCA iteration and the Monte Carlo method are simulated on the static network and dynamic network,respectively.The current results will be beneficial to the study of COVID-19,and propose a more rational and effective model for future research on epidemics.     

Harmonics-to-Noise Ratio: An Index of Vocal Aging

Distinguishing between vocal changes that occur with normal aging and those that are associated with disease is an important goal of research in voice. Several acoustic measures have been used in an attempt to illuminate the integrity of the vocal mechanism, including harmonics-to-noise ratio (HNR), jitter, and fundamental frequency (F₀). HNR is a measure that quantifies the amount of additive noise in the voice signal; jitter reflects the periodicity of vocal fold vibration. In this study, measures of HNR, jitter and F₀ were used to compare vocal function in three groups of normally speaking women: young adults, middle-aged adults, and elderly adults. Significant differences in HNR emerged between the elderly women and the other two groups. F₀ differences were also apparent between the elderly group and the two younger groups; there were no significant differences in jitter between the three groups. HNR was found to be a more sensitive index of vocal function than jitter. The significant lowering of HNR evident in the elderly speakers may be attributable in part to medications taken by the majority of these elderly subjects.