用AsTray随心设置EeePC的显示屏分辨率

不论是采用7英寸还是9英寸显示屏的EeePc都存在一个不足．分辨率较低有时甚至会因为不能完整显示程序窗口造成无法操作。特别是第一代采用7英寸显示屏的EeePC．分辨率只有800×480,虽然可以通过EeePC自带的“EeePC Tray Utility”调整为800×600,但仍然不能完整显示部分程序的窗口,而且要浏览显示的全部内容还需要上下移动,非常不方便。     

Thermometry in Normal Liquid 3He Using a Quartz Tuning Fork Viscometer

We have developed the use of quartz tuning forks for thermometry in normal liquid ³He. We have used a standard 32 kHz tuning fork to measure the viscosity of liquid ³He over a wide temperature range, 6 mK<T<1.8 K, at SVP. For thermometry above 40 mK we used a calibrated ruthenium oxide resistor. At lower temperatures we used vibrating wire thermometry. Our data compare well with previous viscosity measurements, and we give a simple empirical formula which fits the viscosity data over the full temperature range. We discuss how tuning forks can be used as convenient thermometers in this range of temperatures with just a single parameter needed for calibration.     

Quartz Tuning Fork: Thermometer, Pressure- and Viscometer for Helium Liquids

Commercial quartz oscillators of the tuning-fork type with a resonant frequency of ∼ 32 kHz have been investigated in helium liquids. The oscillators are found to have at best Q values in the range 10⁵–10⁶, when measured in vacuum below 1.5 K. However, the variability is large and for very low temperature operation the sensor has to be preselected. We explore their properties in the regime of linear viscous hydrodynamic response in normal and superfluid ³He and ⁴He, by comparing measurements to the hydrodynamic model of the sensor. Dedicated to former JLTP editor Frank Pobell.     

自己架个服务器

随着个人电脑功能越来越强大以及宽带的普及,在个人电脑上架设服务器已不再是遥不可及的梦想。许多朋友都想在自己的电脑上建个Web服务器来发布自己的主页,或是建个FTP服务器和好友交流文件。架设服务器的DIY过程可以为你带来无限的乐趣和成就感,具体怎么做呢?请往下看吧。对于自建服务器来说,最重要的区别在于是否公网IP的问题,那么什么是公网IP?什么是非公网IP呢?说起来也很简单,公网IP就是用户登录互联网之后,由ISP为用户提供的一个全球惟一的IP地址,虽然它分配给了个人电脑,但它与白宫网站的IP地址没什么不同,在网上都可以直接…     

Probing Andreev Reflection in Superfluid 3He-B Using a Quartz Tuning Fork

Direct measurements of the Andreev reflection of the quasiparticles excitations in superfluid ³He-B in the ballistic regime at 0.5 bar using a quartz tuning fork are presented. Based on these measurements, we were able to determine the value of the ratio Δ(0)/kT _c to be 1.71, in reasonable agreement with previous measurements. Moreover, it seems that Andreev reflection of excitations gives a possibility to determine the value of the constant λ characterizing the velocity field profile. This value for a tuning fork was estimated to be 1.28, different from that for cylindrical wire (λ～0.95), suggesting that the anti-phase oscillatory motion and the geometry of the tuning prongs lead to an enhancement of the velocity of the superfluid flow.     

Vibrating Quartz Fork—A Tool for Cryogenic Helium Research

Oscillating objects such as discs, piles of discs, spheres, grids and wires have been widely used in cryogenic fluid dynamics and in quantum fluids research since the discovery of superfluidity. A new addition are quartz tuning forks, commercially available frequency standards. We review their use as thermometers, pressure- and viscometers as well as their potential as generators and detectors of cavitation and turbulence in viscous and superfluid He liquids.      

Plastic Properties of Solid 4He Probed by a Moving Wire: Viscoelastic and Stochastic Behavior Under High Stress

We present measurements of a thin wire moving through solid ⁴He. Measurements were made over a wide temperature range at pressures close to the melting curve. We describe the new experimental technique and present preliminary measurements at relatively high driving forces (stresses) and velocities (strain rates). The wire moves by plastic deformation of the surrounding solid facilitated by quantum tunneling of vacancies and the motion of defects. In the bcc phase we observe very pronounced viscoelastic effects with relaxation times spanning several orders of magnitude. In the hcp phase we observe stochastic step-like motion of the wire. During the step, the wire can move at extremely high velocities. On cooling, the wire ceases to move at a temperature of around 1 K. We are unable to detect any motion at lower temperatures, down to below 10 mK.     

Response of a Mechanical Oscillator in Solid 4He

We present the first measurements of the response of a mechanical oscillator in solid ⁴He. We use a lithium niobate tuning fork operating in its fundamental resonance mode at a frequency of around 30 kHz. Measurements in solid ⁴He were performed close to the melting pressure. The tuning fork resonance shows substantial frequency shifts on cooling from around 1.5 K to below 10 mK. The response shows an abrupt change at the bcc-hcp transition. At low temperatures, below around 100 mK, the resonance splits into several overlapping resonances.     

High Quality Tuning Forks in Superfluid 3He-B Below?200?��K

We have investigated the influence of the damping force acting on high quality tuning forks (Q??10⁶) of different sizes and geometries in superfluid ³He-B at temperatures below 200 ??K and a pressure of 0.1 bar. The measurements show that at low velocities, the damping of the largest fork expressed in terms of its resonance characteristic width ??f ₂ rises up as its velocity increases. This is in contradiction to the damping of the fork due to Andreev reflection and it may be caused by the interaction of this fork with excitations trapped in the Andreev bond states. We present our preliminary experimental results.     

Quantum Turbulence Generated and Detected by a Vibrating Quartz Fork

Flow due to a commercially available vibrating quartz fork is studied in gaseous helium, He I, He II and ³He–B, over a wide range of temperatures and pressures. On increasing the driving force, the flow changes in character from laminar (characterized by a linear velocity versus drive dependence) to turbulent (characterized by a square root velocity versus drive dependence). In classical fluids, we characterize this transition by a critical Reynolds number, Re _c =U _cr δ/ν, where U _cr is the critical velocity, ν stands for the kinematic viscosity, $\delta=\sqrt{2\nu/\omega}$ is the viscous penetration depth and ω is the angular frequency of oscillations. U _cr of order 10 cm/s observed in He II and 1 mm/s in ³He–B agree with those found with other vibrating objects such as spheres, wires and grids, as well as with available numerical simulations of vortex motion in an applied ac flow.