Polyphase alternating codes

This work introduces a method for constructing polyphase alternating codes in which the length of a code transmission cycle can be $p^m$ or $p-1$, where $p$ is a prime number and $m$ is a positive integer. The relevant properties leading to the construction alternating codes and the algorithm for generating alternating codes is described. Examples of all practical and some not that practical polyphase code lengths are given.Comment: Submitted to Annales Geophysica

Renormalisation group improvement in the stochastic formalism

We investigate compatibility between the stochastic infrared (IR) resummation of light test fields on inflationary spacetimes and renormalisation group running of the ultra-violet (UV) physics. Using the Wilsonian approach, we derive improved stochastic Langevin and Fokker-Planck equations which consistently include the renormalisation group effects. With the exception of stationary solutions, these differ from the naive approach of simply replacing the classical potential in the standard stochastic equations with the renormalisation group improved potential. Using this new formalism, we exemplify the IR dynamics with the Yukawa theory during inflation, illustrating the differences between the consistent implementation of the UV running and the naive approach.Comment: 18 pages, 1 figure, 1 appendix, matches accepted version in JCA

Computational study of NMR chemical shifts in periodic graphane-based systems

Tiivistelmä. Grafeeni on tasomainen heksagonaalisen hilan omaava hiilen allotrooppi, jolla on erikoislaatuisia ominaisuuksia. Se on noin kaksisataa kertaa terästä vahvempi. Se omaa parhaan sähkön- ja lämmönjohtokyvyn. Lisäksi se on taipuisa sekä läpinäkyvä materiaali. Ei ole yllätys, että sillä on useita eri sovelluskohteita, kuten komposiittimateriaalit, elektroniikka ja kvanttipisteet. Grafeenin ominaisuuksia voidaan muokata funktionalisaatiolla. Sitä voidaan esimerkiksi hydrogenoida, jolloin sen hiiliatomeihin liittyy vetyatomeja. Hydrogenoitua grafeenia kutsutaan grafaaniksi ja sen ominaisuudet ovat luonnollisesti erilaiset kuin grafeenin. Grafaanin sähköisiä ominaisuksia voidaan muokata vetyatomien määrällä, mikä on hyödyllinen ominaisuus esimerkiksi elektroniikassa. Lisäksi grafaania voidaan käyttää hyödyksi muun muassa vedyn varastoinnissa ja akuissa. Vishnyakova et al. valmisti grafaania suoraan grafiitista. Synteesituotetta analysoitiin käyttäen NMR-spektroskopiaa. He päättelivät, että tuote sisälsi grafaanin lisäksi grafeenisaarekkeita. Kuitenkin tuotteen NMR-spektrin tulkintaa vaikeutti laskennallisten NMR-tulosten vajaavaisuus. Tämän tutkimuksen tavoitteena oli siten tuottaa laskennallisia arvoja grafeenipohjaisten hiilinanosysteemien kemiallisille siirtymille. Laskennassa käytettiin niin sanottua GIPAW-menetelmää (Picard et al.), jolla voidaan määrittää jaksollisten systeemien NMR-parametreja hyödyntäen tiheysfunktionaaliteoriaa. Tutkimuksessa NMR-parametrejä määriteltiin ensimmäistä kertaa kaikille puhtaan grafaanin kuudelle eri konformaatiolle: chair, boat-1, boat-2, stirrup, twistboat ja tricycle. Puhtaita konformaatioita tutkittiin yhdessä, kahdessa ja kolmessa tasossa sekä niin sanotussa bulk-tilanteessa, jossa tasoja ajatellaan olevan päällekkäin ääretön määrä. Myös erikokoisia ja -muotoisia grafeenisaarekkeita sisältäviä grafaani-systeemejä tutkittiin kaikilla kuudella konformaatiolla. Tutkimuksessa havaittiin, että eri konformaatioiden välillä on huomattavia eroja kemiallisessa siirtymässä. Puhtaille grafaani-systeemeille havaittiin myös, että tasojen määrä vaikutti tuloksiin. Kun tuloksia verrattiin kvalitatiivisesti Vishnyakova et al. kokeellisesti määritettyihin NMR-spektreihin, niissä havaittiin paljon yhtäläisyyksiä. Laskettujen arvojen pohjalta voitiin spekuloida, että kokeellisesti tuotetussa grafeenissa oli grafeenisaarekkeita, joita ympäröi grafaania eri konformaatioissa. Tutkimus mahdollistaa siten grafaanin kokeellisten NMR-spektrien paremman analysoinnin tulevaisuudessa. Tässä tutkimuksessa keskityttiin ainoastaan NMR-varjostuksen aiheuttaman kemiallisen siirtymän määrittämiseen. Tulevaisuudessa voitaisiin myös laskea epäsuoran spin-spin-vuorovaikutuksen kytkentävakiot kaikille grafaani-konformaatioille. Toinen mahdollinen jatkotutkimuskohde voisi olla fluorografeeni, jossa grafeenilevyyn onkin vedyn sijasta liittynyt fluoria

Dynamics of small particles in electromagnetic radiation fields : A numerical solution

We establish a theoretical framework for solving the equations of motion for an arbitrarily shaped, inhomogeneous dust particle in the presence of radiation pressure. The repeated scattering problem involved is solved using a state-of-the-art volume integral equation-based T-matrix method. A Fortran implementation of the framework is used to solve the explicit time evolution of a homogeneous irregular sample geometry. The results are shown to be consistent with rigid body dynamics, between integrators, and comparable with predictions from an alignment efficiency potential map. Also, we demonstrate the explicit effect of single-particle dynamics to observed polarization using the obtained orientational results.Peer reviewe

Fast superposition T-matrix solution for clusters with arbitrarily-shaped constituent particles

A fast superposition T-matrix solution is formulated for electromagnetic scattering by a collection of arbitrarily-shaped inhomogeneous particles. The T-matrices for individual constituents are computed by expanding the Green's dyadic in the spherical vector wave functions and formulating a volume integral equation, where the equivalent electric current is the unknown and the spherical vector wave functions are treated as excitations. Furthermore, the volume integral equation and the superposition T-matrix are accelerated by the precorrected-FFT algorithm and the fast multipole algorithm, respectively. The approach allows for an efficient scattering analysis of the clusters and aggregates consisting of a large number of arbitrarily-shaped inhomogeneous particles. (C) 2016 Elsevier Ltd. All rights reserved.Peer reviewe

Evaluating two soil carbon models within the global land surface model JSBACH using surface and spaceborne observations of atmospheric CO₂

The trajectories of soil carbon (C) in the changing climate are of utmost importance, as soil carbon is a substantial carbon storage with a large potential to impact the atmospheric carbon dioxide (CO2) burden. Atmospheric CO2 observations integrate all processes affecting C exchange between the surface and the atmosphere. Therefore they provide a benchmark for carbon cycle models. We evaluated two distinct soil carbon models (CBALANCE and YASSO) that were implemented to a global land surface model (JSBACH) against atmospheric CO2 observations. We transported the biospheric carbon fluxes obtained by JSBACH using the atmospheric transport model TM5 to obtain atmospheric CO2. We then compared these results with surface observations from Global Atmosphere Watch (GAW) stations as well as with column XCO2 retrievals from the GOSAT satellite. The seasonal cycles of atmospheric CO2 estimated by the two different soil models differed. The estimates from the CBALANCE soil model were more in line with the surface observations at low latitudes (0 N–45 N) with only 1 % bias in the seasonal cycle amplitude (SCA), whereas YASSO was underestimating the SCA in this region by 32 %. YASSO gave more realistic seasonal cycle amplitudes of CO2 at northern boreal sites (north of 45 N) with underestimation of 15 % compared to 30 % overestimation by CBALANCE. Generally, the estimates from CBALANCE were more successful in capturing the seasonal patterns and seasonal cycle amplitudes of atmospheric CO2 even though it overestimated soil carbon stocks by 225 % (compared to underestimation of 36 % by YASSO) and its predictions of the global distribution of soil carbon stocks was unrealistic. The reasons for these differences in the results are related to the different environmental drivers and their functional dependencies of these two soil carbon models. In the tropical region the YASSO model showed earlier increase in season of the heterotophic respiration since it is driven by precipitation instead of soil moisture as CBALANCE. In the temperate and boreal region the role of temperature is more dominant. There the heterotophic respiration from the YASSO model had larger annual variability, driven by air temperature, compared to the CBALANCE which is driven by soil temperature. The results underline the importance of using sub-yearly data in the development of soil carbon models when they are used in shorter than annual time scales

Numerical Validation of a Boundary Element Method With E and E/N as the Boundary Unknowns

We recently developed a surface integral equation method where the electric field and its normal derivative are chosen as the boundary unknowns. After reviewing this formulation, we present preliminary numerical calculations that show good agreement with the known results. These calculations are encouraging and invite the further development of the numerical solution.Peer reviewe

Application of Tomographic Inversion in Studying Airglow in the Mesopause Region

It is pointed out that observations of periodic nightglow structures give excellent information on atmospheric gravity waves in the mesosphere and lower thermosphere. The periods, the horizontal wavelengths and the phase speeds of the waves can be determined from airglow images and, using several cameras, the approximate altitude of the luminous layer can also be determined by triangulation. In this paper the possibility of applying tomographic methods for reconstructing the airglow structures is investigated using numerical simulations. A ground-based chain of cameras is assumed, two-dimensional airglow models in the vertical plane above the chain are constructed, and simulated data are calculated by integrating the models along a great number of rays with different elevation angles for each camera. After addition of random noise, these data are then inverted to obtain reconstructions of the models. A tomographic analysis package originally designed for satellite radiotomography is used in the inversion. The package is based on a formulation of stochastic inversion which allows the input of a priori information to the solver in terms of regularization variances. The reconstruction is carried out in two stages. In the first inversion, constant regularization variances are used within a wide altitude range. The results are used in determining the approximate altitude range of the airglow structures. Then, in the second inversion, constant non-zero regularization variances are used inside this region and zero variances outside it. With this method reliable reconstructions of the models are obtained. The number of cameras as well as their separations are varied in order to find out the limitations of the method