Nanophotonics with the scanning electron microscope

Physical size and power consumption are both increasingly important issues in increasing the data throughput of future optical interconnects, switches and ultimately even optical memory elements. In this respect, phase-change memories have proven to be strong candidates, with data recording done by switching the material between amorphous and crystalline phases, much in line with today's DVD/DVR technology. However, polymorphic systems exist in which crystalline-to-crystalline transitions can provide for higher-base logics as well. In particular, by coding each distinct optical characteristic by a unique label, the different optical cross-sections of absorption and scattering of the crystalline phases of a single nanoparticle can be used as a logical element

On the heavy-tailedness of Student's tt-statistic

Let $\{X_i\}_{i\geq1}$ be an i.i.d. sequence of random variables and define, for $n\geq2$, T_n=\cases{n^{-1/2}\hat{\sigma}_n^{-1}S_n,\quad \hat{\sigma}_n>0,\cr 0,\quad \hat{\sigma}_n=0,}with S_n=\sum_{i=1}^nX_i, \hat{\sigma}^2_n=\frac{1}{n-1}\sum_{i=1}^n(X_i-n^{-1}S_n)^2. We investigate the connection between the distribution of an observation $X_i$ and finiteness of $\mathrm{E}|T_n|^r$ for $(n,r)\in \mathbb{N}_{\geq2}\times\mathbb{R}^+$. Moreover, assuming $T_n\stackrel{d}{\longrightarrow}T$, we prove that for any $r>0$, $\lim_{n\to\infty}\mathrm{E}|T_n|^r=\mathrm{E}|T|^r<\infty$, provided there is an integer $n_0$ such that $\mathrm {E}|T_{n_0}|^r$ is finite.Comment: Published in at http://dx.doi.org/10.3150/10-BEJ262 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Optical size control in growth of gallium nanoparticles

We report that a low level of optical excitation provides a substantial influence on the size distribution of gallium nanoparticles grown from the atomic beam on a cryogenic substrate, thus providing a new way of achieving tailored films of nanoparticles with given characteristics. The growth experiments, performed in situ in the vacuum chamber of a scanning electron microscope (SEM) equipped with an inverted effusion cell, revealed that the median diameter of the nanoparticles decreases with increasing irradiating optical power, with 0.1, 0.2 and 0.4 mW average power resulting in 70, 50 and 45 nm particles, respectively

Phase-change memory functionality in gallium nanoparticles

We report that the structural phase of gallium nanoparticles can be switched by optical excitation and read via their cathodoluminescence (CL) when excited by a scanning electron beam. This opens a new paradigm in developing high-density phase change optical memory elements. A film of gallium nanoparticles was sputtered at the end face of an optical fiber, through which the reflectivity at 195 K was monitored by a 1.31 µm laser. By launching a single pulse from a 1.55 µm laser (17 mW, 1 µs) to the sample, a solid-to-liquid phase transition was observed as an immediate change of reflectivity from 10.0 to 10.5 %. CL spectra were measured immediately before and after the phase transition. The spectra show that gallium nanoparticles luminesce in the range of 400-650 nm, in which there at 520 nm is a 10 % difference of emission before and after the phase transition, due to a difference in optical properties. In future continuation of this first demonstration of electron beam read-out of the phase of nanoparticles, it is likely that the electron beam itself can change the phase of individual nanoparticles in the film, and that this phase furthermore can be read out at lower power by its cathode luminescence response with the same electron beam

Generation of surface plasmons by electron beam excitation

We report on the first demonstration of excitation of propagating surface plasmon polaritons (SPPs) by injection of a beam of free electrons on an unstructured metal interface, providing a highly localized and intense source of plasmon waves. The plasmons were detected by a grating-assisted decoupling into light at a set of distances from the excitation point. This technique allows the high-resolution mapping of plasmon and photon emission from metal nanostructures

Visual Servoing for Floppy Robots Using LWPR

We have combined inverse kinematics learned by LWPR with visual servoing to correct for inaccuracies in a low cost robotic arm. By low cost we mean weak inaccurate servos and no available joint-feedback. We show that from the trained LWPR model the Jacobian can be estimated. The Jacobian maps wanted changes in position to corresponding changes in control signals. Estimating the Jacobian for the first iteration of visual servoing is straightforward and we propose an approximative updating scheme for the following iterations when the Jacobian can not be estimated exactly. This results in a sufficient accuracy to be used in a shape sorting puzzle.

How does leafless undergrowth affect quality and logging costs in thinning?

Gallring är en beståndsvårdande utglesning där gagnvirke tillvaratas. Syftet med gallring är att styra över produktionen på ett lägre antal stammar och på sikt skapa ett bestånd med en högre medelstamsvolym än om gallring inte genomförts. Gallring kan utföras enligt olika former, vilket påverkar produktiviteten i drivningsarbetet och beståndets karaktär efter utförd åtgärd. I vissa bestånd kan det finnas ett undre skikt av löv eller gran som försvårar gallringen, så kallad försvårande underväxt. Den här studien syftade till att undersöka om underväxtröjning är en åtgärd som kan leda till att minska kostnaderna i gallring i bestånd med underväxt. En tidsstudie utfördes i två talldominerade bestånd med lövdominerad underväxt i 2-3 meters höjd. Inom varje bestånd lades sex parceller ut, där hälften av parcellerna genom lottens hjälp valdes ut för underväxtröjning innan gallring. Skördarstudien utfördes som en frekvensstudie, vilket gav fördelningen mellan arbetsmomenten och tidsåtgången. Röjarens tidsåtgång i röjningsarbetet och skotarens tidsåtgång i lastning och förflyttning mellan uppställningsplatser tidsstuderades och resterande arbetsmoment för skotaren modellerades för att kunna beräkna produktiviteten. Lövunderväxten hade en signifikant påverkan på skördarens produktivitet i gallring. I underväxtröjda bestånd ökade produktiviteten med 12,3 % vid en skördad medelstamsvolym på 0,06 m³fub och 8,2 % vid en skördad medelstamsvolym på 0,10 m³fub. Skördarens kostnader minskade med 8,8 kr/m³fub vid en skördad medelstam på 0,06 m³fub och 3,8 kr/m³fub vid en skördad medelstam på 0,10 m³fub. Skotarens arbete påverkades inte signifikant av underväxten varpå reduktionen i drivningskostnad motsvarade skördarens minskning. Vid en röjningskostnad på 1300 kr/ha, vilket motsvarar en kostnad på 32,5 kr/m³fub vid ett volymsuttag på 40 m³fub/ha, blir nettot 21,3 % lägre vid en skördad medelstamsvolym på 0,06 m3fub och 34,04 % lägre vid en skördad medelstamsvolym på 0,10 m3fub om man utför en underväxtröjning. Underväxtröjningen bedömdes därför inte vara en ekonomisk åtgärd i bestånd där gallring utfördes under perioder med avlövad underväxt.Thinning is a stand developing treatment during which merchantable wood is harvested. Thinning is done to redirect the production on a lower number of stems and in a longer term get a stand with a higher mean stem volume. Thinning can be done under different forms, which affects the productivity in felling and the character of the stand after performed treatment. In some stands undergrowth of deciduous tree species or spruce may be present which complicates the machine work in thinning. This study aimed to investigate if undergrowth clearing is a treatment method that can be used to decrease the costs of thinning in stands with undergrowth. Time studies were performed in two pine dominated stands with deciduous undergrowth in 2-3 meters height. Within each stand 6 study units were established and half of them were undergrowth cleared before thinning. The harvester study was performed as a frequency study, which gave the distribution between work elements and time consumption. The brush-cutter´s time consumption in undergrowth clearing and the forwarder´s time consumption in loading and moving between loading positions were studied and the rest of the forwarder´s work elements was modelled to be able to calculate the productivity. The deciduous undergrowth had a significant impact on the harvester’s productivity in thinning. In undergrowth cleared stands the productivity increased by 12.3 % at a harvested mean stem volume of 0.06 m³fub and by 8.2 % at a harvested mean stem volume of 0.10 m³fub. The harvesting costs decreased by 8.8 SEK/m³fub at a harvested mean stem volume of 0.06 m³fub and by 3.8 SEK/m³fub at a harvested mean stem volume of 0.10 m³fub. The forwarder´s work was not significantly affected by undergrowth whereupon the reduction in logging costs corresponded to the harvester´s decrease. At a undergrowth clearing cost of 1300 SEK/ha, which correspond to a cost of 32.5 SEK/m3fub at a harvested volume of 40 m3fub/ha, become the net income 21.3 % less at a harvested mean stem volume of 0.06 m3fub and 34.04 % less at a harvested mean stem volume of 0.10 m3fub. Undergrowth clearance was not estimated to be an economic method in stands where thinning was performed under conditions with leafless undergrowth