The Giant Impact Simulations with Density Independent Smoothed Particle Hydrodynamics

At present, the giant impact (GI) is the most widely accepted model for the origin of the Moon. Most of the numerical simulations of GI have been carried out with the smoothed particle hydrodynamics (SPH) method. Recently, however, it has been pointed out that standard formulation of SPH (SSPH) has difficulties in the treatment of a contact discontinuity such as a core-mantle boundary and a free surface such as a planetary surface. This difficulty comes from the assumption of differentiability of density in SSPH. We have developed an alternative formulation of SPH, density independent SPH (DISPH), which is based on differentiability of pressure instead of density to solve the problem of a contact discontinuity. In this paper, we report the results of the GI simulations with DISPH and compare them with those obtained with SSPH. We found that the disk properties, such as mass and angular momentum produced by DISPH is different from that of SSPH. In general, the disks formed by DISPH are more compact: while formation of a smaller mass moon for low-oblique impacts is expected with DISPH, inhibition of ejection would promote formation of a larger mass moon for high-oblique impacts. Since only the improvement of core-mantle boundary significantly affects the properties of circumplanetary disks generated by GI and DISPH has not been significantly improved from SSPH for a free surface, we should be very careful when some conclusions are drawn from the numerical simulations for GI. And it is necessary to develop the numerical hydrodynamical scheme for GI that can properly treat the free surface as well as the contact discontinuity.Comment: Accepted for publication in Icaru

Optical control of magnetization of micron-size domains in antiferromagnetic NiO single crystals

We propose Raman-induced collinear difference-frequency generation (DFG) as a method to manipulate dynamical magnetization. When a fundamental beam propagates along a threefold rotational axis, this coherent second-order optical process is permitted by angular momentum conservation through the rotational analogue of the Umklapp process. As a demonstration, we experimentally obtained polarization properties of collinear magnetic DFG along a [111] axis of a single crystal of antiferromagnetic NiO with micro multidomain structure, which excellently agreed with the theoretical prediction.Comment: 11 pages, 3 figures, submitted to Physical Review Letter

Slow-roll inflation in (R+R*4) gravity

We reconsider the toy-model of topological inflation, based on the R*4-modified gravity. By using its equivalence to the certain scalar-tensor gravity model in four space-time dimensions, we compute the inflaton scalar potential and investigate a possibility of inflation. We confirm the existence of the slow-roll inflation with an exit. However, the model suffers from the eta-problem that gives rise to the unacceptable value of the spectral index n_s of scalar perturbations.Comment: 12 pages, 3 figures, LaTeX, misprints corrected and references update

Ohutlevytuotteen välivarastoinnin ja identifioinnin menetelmäkehitystyö

Työssä tutkittiin ohutlevytuotteiden identifioimisen ja välivarastoinnin automatisointia Stofix Montage Teamin toimeksiannosta. Työn tavoitteena oli kehittää menetelmäratkaisut pakattujen ohutlevytuotteiden identifioimiseen ja niiden kuljettamiseen välivarastoon. Stofixilla ohutlevytuotteet identifioidaan ja välivarastoidaan manuaalisesti, mikä sitoo työntekijän samanaikaisesti kahteen eri työvaiheeseen. Tuotteet identifioidaan käyttäen tussikynää ja teippiä ja se on havaittu yrityksessä hitaaksi identifiointimenetelmäksi. Välivarastoidessa pakatut tuotteet nostetaan seinään vasten varastointitilaan, mikä altistaa tuotteet virumiselle ja vaurioitumiselle. Lisäksi tuotteen painon ylittäessä työturvallisuusmääräyksen salliman maksimipainon joutuu työvaiheeseen sitomaan kaksi työntekijää. Ongelmanratkaisuun ja kehitystyöhön käytettiin aikaisempien vuosien robotiikkaa käsitteleviä insinööritöitä sekä automatisoinnin suunnitteluohjekirjoja. Välivarastoinnin ja identifioinnin nykyinen prosessi analysoitiin lähtötilanne-, prosessi- ja kappaleanalyysin pohjalta, jonka kautta menetelmille valittiin komponentteja vertailua varten. Projektin läpiviemiseen käytettiin projektihallinnan aikataulu- ja projekti-suunnitelmapohjia sekä budjettilaskelman muodostavia hintavertailuja tarjouspyynnöistä. Analyysin perusteella menetelmän toteuttamiseen valittiin kattoon sijoitettava lineaarijohteella paikoittava kuusiakselinen robottikäsivarsi ja automaattisesti tulostava tarroituskone. Työn lopputulokseksi tuli robotiikalla ja alipainetarttujalla tehtävä tuotteiden välivarastointi sekä automaattisella tarroituskoneella tapahtuva identifiointi. Työ onnistui odotetusti, ja se tuotti yritykselle robottikäsivarren, alipainetarttujan ja tarroituskoneen komponenttivalinnat budjetoinnin lisäksi. Yritys voi hyödyntää työn tuloksia, kun tuotantoprosessia aletaan automatisoida. Työn jatkokehityskohteena voidaan tehdä robottisolun turvallisuussuunnitelma ja ohjelmointi, lineaarijohteen kompo-nenttivalinnat ja robotin kiinnitysrakenteen mekaniikkasuunnittelu

Observations of the Prompt Gamma-Ray Emission of GRB 070125

The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-WIND, RHESSI, Suzaku-WAM, and \textit{Swift}-BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multi-peaked emission over a period of about one minute. The total burst fluence as observed by Konus is $1.79 \times 10^{-4}$ erg/cm$^2$ (20 keV--10 MeV). Using the spectroscopic redshift $z=1.548$, we find that the burst is consistent with the ``Amati'' $E_{peak,i}-E_{iso}$ correlation. Assuming a jet opening angle derived from broadband modeling of the burst afterglow, GRB 070125 is a significant outlier to the ``Ghirlanda'' $E_{peak,i}-E_\gamma$ correlation. Its collimation-corrected energy release $E_\gamma = 2.5 \times 10^{52}$ ergs is the largest yet observed.Comment: 25 pages, 6 figures; accepted for publication in ApJ. Improved spectral fits and energetics estimate

A molecular structural mechanics model applied to the static behavior of single-walled carbon nanotubes: New general formulation

A new general formulation for the mechanical behavior of Single-Walled Carbon Nanotubes is presented. Carbon atoms are located at the nodes of an hexagonal honeycomb lattice wrapped into a cylinder. They are linked by covalent C C bonds represented by a truss or spring element, and the three-body interaction among two neighboring covalent bonds is reproduced by a rotational spring. The main advantage of our approach is to allow general load conditions (and any chirality) with no need of specific formulation for each load case, in contrast with previous works [26], [27] and [31]. Four load configurations are adopted: tension, compression, bending and torsion of cantivelered SWCNTs. Calculations with our own codes for both AMBER and Morse potential functions have been carried out, aimed to compare their final results. Initial positions of the atoms (nodes) into nanotube cylindrical geometry has been reproduced in great detail by means of a conformal mapping from the planar graphene sheet. Therefore, the effect of initial SWCNTs curvature has been introduced explicitly through a system of initial stresses (prestressed state) which contribute to maintain their circular cross-section. Numerical results and deformed shapes for nanotubes with several diameters and chiralities under each load case are used to obtain their mechanical parameters with the only objective of checking the present formulation with previous works [28], [30], [20] and [24]. Also, the significance of the atomistic discrete simulations at the nano-scale size against other continuum models is underlined.Merli Gisbert, R.; Lazaro, C.; Monleón Cremades, S.; Domingo Cabo, A. (2013). A molecular structural mechanics model applied to the static behavior of single-walled carbon nanotubes: New general formulation. Computers and Structures. 127:68-87. doi:10.1016/j.compstruc.2012.11.023S688712