Listeners' sensitivity to "onset/offset" and "ongoing" interaural delays in high-frequency, sinusoidally amplitude-modulated tones

The relative potency of onset/offset and envelope-based ongoing interaural time delays (ITDs) was assessed using high-frequency stimuli. A two-cue, two-alternative, forced-choice adaptive task was employed to measure threshold ITDs with 100% sinusoidally amplitude-modulated tones centered at 4 kHz. Modulation rates of 125, 250, and 350 Hz were tested with durations of 32, 90, or 240 ms. In the first experiment, ITDs to be detected were imposed only at the onset/offset, only within the ongoing portion, or within both the onset/offset and ongoing portions of the stimuli. Results indicated that ongoing ITDs dominated onset/offset ITDs. The relative potency of ongoing ITDs was directly proportional to duration and inversely proportional to modulation rate. Quantitative analysis suggested that listeners effectively combine onset/offset and ongoing ITDs. Furthermore, the data could be largely accounted for by assuming that listeners attend to the interaural decorrelation of the stimulus resulting from onset/offset and/or ongoing ITDs. A second experiment showed that, (1) overall, an ongoing ITD of one-half period of the envelope had little impact on listeners' sensitivity to delays of the onset/offset and (2) sensitivity to delays within the onset/offset portion of the waveform was reduced by roving the delay within the ongoing portion of the waveform.     

指南针从"理"到"文"——从物理学出发进行"文理综合"的探索

编者按:目前在我国掀起了新的基础教育改革浪潮,提出了新的教育理念,制定了课程标准,新编写的教材已在少数地方试用.面临这种形势制约改革成败的重要问题之一--新的评价体系,亟待改革完善.此文既涉及课程的构建,也涉及评价和测量.发表此文意在引起广大读者对这些问题的关注,并积极参加讨论.     

最具潜力的新型"奇迹材料"——石墨烯

2009年4月29日据物理世界网报道,意大利的科研人员成功地用石墨烯制造了首枚包含两个晶体管的集成电路(见封面主图),它拥有简单的计算能力,标制着碳基电子学时代的到来.这枚只有两个晶体管的集成电路虽然很小,却是向制造碳基高性能电子器件迈出的重要一步.     

Pressure-driven "molecular metal" to "atomic metal" transition in crystalline Ga

We present the ultrasonic study of gallium (Ga I) under high pressure up to 1.7 GPa, including the measurements of the density and elastic properties during phase transitions to Ga II and to a liquid state. The observed large drop of both bulk and shear moduli (by 30% and 55%, correspondingly) during the phase transition to Ga II, as well as the increase of the Poisson's ratio from typically "covalent" ( approximately 0.22) to "metallic" ( approximately 0.32) values, experimentally testifies to the coexistence of a molecular and metallic behavior in Ga I and to the disappearance of the "covalency" during the transition to Ga II. A high value of the pressure derivative of the bulk modulus for Ga I and the increase in the Poisson's ratio can be associated with the weakening of the covalency in compressed Ga I and considered as a precursor of the transition to normal metal.     

对《物理与文化》一文的反响

本刊2004年开辟“物理与文化”专栏以来，得到读者、作者的关怀与支持；大家希望“物理与文化”栏目为科学文化与人文文化的沟通与融合多作贡献；同时，也为物理教学改革，实现“三维教学”目标提供参考素材．为此决定拓展“物理与文化”专栏的内容及形式，设想如下．1．继续办好“物理与艺术”、“物理与体育”……文化技术层面的专题．2．内容扩展(1)精神层面：物理学工作者(不仅包括物理学家，也包括一般物理学工作者，还包括有志于物理学的青年学子)的人生追求，思想风貌，情感、态度、价值观、信仰……(2)教育层面：物理教学中的文化视角，“以人为本”、“面向全体学生”、“尊重个性、爱护人才”的文化气氛，学派、名校与校园文化，在物理教学中科学与人文的沟通与融合等．(3)理论层面：有关物理文化或物理与文化关系的理论研究、阐述、学术争论等．3．形式可多种多样，包括论文、散文、杂文、诗词、通信、格言、对话、书评……作为“拓展”的开端，本期发表了郭雅生等同志呈陈佳洱院士的信和著名物理学家彭桓武先生的诗选．