Observation of shell structure in sodium nanowires

The quantum states of a system of particles in a finite spatial domain in general consist of a set of discrete energy eigenvalues; these are usually grouped into bunches of degenerate or close-lying levels, called shells. In fermionic systems, this gives rise to a local minimum in the total energy when all the states of a given shell are occupied. In particular, the closed-shell electronic configuration of the noble gases produces their exceptional stability. Shell effects have previously been observed for protons and neutrons in nuclei and for clusters of metal atoms. Here we report the observation of shell effects in an open system - a sodium metal nanowire connecting two bulk sodium metal electrodes, which are progressively pulled apart. We measure oscillations in the statistical distribution of conductance values, for contact cross-sections containing up to a hundred atoms or more. The period follows the law expected from shell-closure effects, similar to the abundance peaks at `magic numbers' of atoms in metal clusters.Comment: The argumentation in favour of shell structure owing to the fluctuations in the free energy of the nanowires has been strengthened. Further improvements in the presentation include the plot of the radius of the wires versus shell number in Fig.

A High Power and Ultrahigh Frequency Mode-Locked Laser Monolithically Integrated with an SOA

We report 628 GHz and 1.20 THz pulse repetition frequencies with 142 mW peak powers from a passively mode-locked side-wall SGDBR laser integrated with an SOA, demonstrating high reproducibility, controllability and a wide operation range

Primordial magnetic fields at preheating

Using lattice techniques we investigate the generation of long range cosmological magnetic fields during a cold electroweak transition. We will show how magnetic fields arise, during bubble collisions, in the form of magnetic strings. We conjecture that these magnetic strings originate from the alignment of magnetic dipoles associated with EW sphaleron-like configurations. We also discuss the early thermalisation of photons and the turbulent behaviour of the scalar fields after tachyonic preheating.Comment: 7 pages. Talk presented at Lattice200

Peningkatan Hasil Belajar IPS Kelas VI dengan Model Pembelajaran Kooperatif Tipe Examples Non Examples di Sdn 007 Teratak Air Hitam Kecamatan Sentajo Raya

Social science subjects are arranged in a systematic, comrehensive, and integrated in the learning processtowards succes in the life in the community. With the approach it is expected that learners will acquire a broaderunderstanding and dept in the field of science related. This reseach method in classroom action reseach usingtwo cycle the end of each cycle is given daily test given to students in as musc as 19 persons in the class VI SDN007 Teratak Air Hitam sub-district Sentajo Raya. The reseach result obtained the result of the study preliminarydata 65,3 increase by an average of learning outcomes of IPS to 75 in cycle I. I the second cycle obtained anaverage of 90 with the learning cycle I is 14,58% and from cycle I to cycle II amounted of 37,89%. Activities theteacher looks at the cycle I the first meeting of 66,67% with enough categories, while at the second meetingincreased so that the average obtained by 75%, with good categories. In cycle II it turns out that teacherlearning has increased sothat the obtained average 83,3% with good categories, while at the second meetingcycle II obtained average to 91,67 % with very good categories. Data activity studens looks at the cycle I the firsmeeting obatined an average of 61,11 with lee categories, at the second meeting obtained an average 72,22%with enough categories. In the second cycle obtained an average of the first meeting of 80,56% with goodcategory, while in the second meeting with average to 91,67% with the cagory very well. So it can be concludedthat the applicatin of cooperative medel type example non examplescan improve learning outcomes IPS

Electron-vibration interaction in single-molecule junctions: from contact to tunneling regime

Point contact spectroscopy on a H2O molecule bridging Pt electrodes reveals a clear crossover between enhancement and reduction of the conductance due to electron-vibration interaction. As single channel models predict such a crossover at transmission probability of t=0.5, we used shot noise measurements to analyze the transmission and observed at least two channels across the junction where the dominant channel has t=0.51+/-0.01 transmission probability at the crossover conductance, which is consistent with the predictions for single-channel models.Comment: 4 pages, 1 table, 4 figure

Excess current in point contacts on two-band superconductor MgB2_2 in magnetic field

Series of $I(V)$ characteristic and bias-dependent differential resistance $dV/dI(V)$ for point-contacts on the single crystals of two-band superconductor MgB$_2$ were measured in magnetic field up to 9 T. We have obtained magnetic field dependences of the excess current on the $I(V)$ curves and analyzed them using Koshelev and Golubov (Phys. Rev. Lett. {\bf 90}, 177002 (2003)) theoretical results for the mixed state of a dirty two-band superconductor. Introducing a simple model for the excess current in the point contact in the mixed state our data can be qualitatively described utilizing theoretical magnetic filed behavior of the $\sigma$ and $\pi$-band superconducting order parameters and the corresponding averaged electronic density of states in MgB$_2$.Comment: 4 pages, 3 figs, RevTex4; V2: plain text improved, BTK fit is added to insets of Fig.

Atomic size oscillations in conductance histograms for gold nanowires and the influence of work hardening

Nanowires of different nature have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for gold wires that the balance between various metastable nanowire configurations is influenced by the microstructure of the starting materials and we discover a new set of periodic structures, which we interpret as due to the atomic discreteness of the contact size for the three principal crystal orientations.Comment: This version corrects an error in attributing the three observed periods, and includes a comparison with recent model calculation