Irradiation-mediated tailoring of carbon nanotubes

The ever-increasing demand for faster computers in various areas, ranging from entertaining electronics to computational science, is pushing the semiconductor industry towards its limits on decreasing the sizes of electronic devices based on conventional materials. According to the famous law by Gordon E. Moore, a co-founder of the world s largest semiconductor company Intel, the transistor sizes should decrease to the atomic level during the next few decades to maintain the present rate of increase in the computational power. As leakage currents become a problem for traditional silicon-based devices already at sizes in the nanometer scale, an approach other than further miniaturization is needed to accomplish the needs of the future electronics. A relatively recently proposed possibility for further progress in electronics is to replace silicon with carbon, another element from the same group in the periodic table. Carbon is an especially interesting material for nanometer-sized devices because it forms naturally different nanostructures. Furthermore, some of these structures have unique properties. The most widely suggested allotrope of carbon to be used for electronics is a tubular molecule having an atomic structure resembling that of graphite. These carbon nanotubes are popular both among scientists and in industry because of a wide list of exciting properties. For example, carbon nanotubes are electronically unique and have uncommonly high strength versus mass ratio, which have resulted in a multitude of proposed applications in several fields. In fact, due to some remaining difficulties regarding large-scale production of nanotube-based electronic devices, fields other than electronics have been faster to develop profitable nanotube applications. In this thesis, the possibility of using low-energy ion irradiation to ease the route towards nanotube applications is studied through atomistic simulations on different levels of theory. Specifically, molecular dynamic simulations with analytical interaction models are used to follow the irradiation process of nanotubes to introduce different impurity atoms into these structures, in order to gain control on their electronic character. Ion irradiation is shown to be a very efficient method to replace carbon atoms with boron or nitrogen impurities in single-walled nanotubes. Furthermore, potassium irradiation of multi-walled and fullerene-filled nanotubes is demonstrated to result in small potassium clusters in the hollow parts of these structures. Molecular dynamic simulations are further used to give an example on using irradiation to improve contacts between a nanotube and a silicon substrate. Methods based on the density-functional theory are used to gain insight on the defect structures inevitably created during the irradiation. Finally, a new simulation code utilizing the kinetic Monte Carlo method is introduced to follow the time evolution of irradiation-induced defects on carbon nanotubes on macroscopic time scales. Overall, the molecular dynamic simulations presented in this thesis show that ion irradiation is a promisingmethod for tailoring the nanotube properties in a controlled manner. The calculations made with density-functional-theory based methods indicate that it is energetically favorable for even relatively large defects to transform to keep the atomic configuration as close to the pristine nanotube as possible. The kinetic Monte Carlo studies reveal that elevated temperatures during the processing enhance the self-healing of nanotubes significantly, ensuring low defect concentrations after the treatment with energetic ions. Thereby, nanotubes can retain their desired properties also after the irradiation. Throughout the thesis, atomistic simulations combining different levels of theory are demonstrated to be an important tool for determining the optimal conditions for irradiation experiments, because the atomic-scale processes at short time scales are extremely difficult to study by any other means.

Kriitkko Einari J. Vehmas ja moderni taide

The doctoral dissertation Critic Einari J. Vehmas and Modern Art deals with one of the central figures of the Finnish art scene and his work as an art critic, art museum curator and cultural critic. The main body of research material consists of the writings of Einari J. Vehmas (1902 1980) from 1937 to the late 1960s. Vehmas wrote art reviews for magazines, and from the year 1945 he was a regular art critic for one of the major newspapers in Finland. Vehmas was heavily inclined towards French literature and visual arts. Marcel Proust and Charles Baudelaire influenced his views on the nature of art from the late 1920s onwards. Vehmas is commonly regarded as the most influential art critic of post-war Finland. His writings have been referred to and cited in numerous research papers on Finnish 20th-century art. A lesser known aspect of his work is his position as the deputy director of the Ateneum Art Museum, the Finnish national gallery. Through his art museum work, his opinions also shaped the canon of modern art considered particularly Finnish following the second world war. The main emphasis of the dissertation is on studying Vehmas s writings, but it also illustrates the diversity of his involvement in Finnish cultural life through biographical documents. The long chronological span of the dissertation emphasises how certain central themes accumulate in Vehmas s writings. The aim of the dissertation is also to show how strongly certain philosophical and theoretical concepts from the early 20th century, specifically Wassily Kandinsky s principle of inner necessity and Henri Bergson s epistemology highlighting intuition and instinct, continued to influence the Finnish art discourse even in the early 1960s, in part thanks to the writings of Vehmas. Throughout his production, Vehmas contemplated the state and future of modern art and humanity. Vehmas used a colourful, vitalistic rhetoric to emphasise the role of modern art as a building block of culture and humanity. At the same time, however, he was a cultural pessimist whose art views became infused with anxiety, a sense of loss, and a desire to turn his back on the world.

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN.

Ring-Opening-Induced Toughening of a Low-Permittivity Polymer-Metal Interface

Integrating low dielectric permittivity (low-k) polymers to metals is an exacting fundamental challenge because poor bonding between low-polarizability moieties and metals precludes good interfacial adhesion. Conventional adhesion-enhancing methods such as using intermediary layers are unsuitable for engineering polymer/metal interfaces for many applications because of the collateral increase in dielectric permittivity. Here, we demonstrate a completely new approach without surface treatments or intermediary layers to obtain an excellent interfacial fracture toughness of > 13 J/m(2) in a model system comprising copper. and a cross-linked polycarbosilane with k similar to 2.7 obtained by curing a cyclolinear polycarbosilane in air.Our results suggest that interfacial oxygen catalyzed molecularring-opening and anchoring of the opened ring moieties of the polymer to copper is the main toughening mechanism. This novel approach of realizing adherent low-k polymer/metal structures without intermediary layers by activating metal-anchoring polymer moieties at the interface could be adapted for applications such as device wiring and packaging, and laminates and composites.

Ordering near the percolation threshold in models of two-dimensional interacting bosons with quenched dilution

Randomly diluted quantum boson and spin models in two dimensions combine the physics of classical percolation with the well-known dimensionality dependence of ordering in quantum lattice models. This combination is rather subtle for models that order in two dimensions but have no true order in one dimension, as the percolation cluster near threshold is a fractal of dimension between 1 and 2: two experimentally relevant examples are the O(2) quantum rotor and the Heisenberg antiferromagnet. We study two analytic descriptions of the O(2) quantum rotor near the percolation threshold. First a spin-wave expansion is shown to predict long-ranged order, but there are statistically rare points on the cluster that violate the standard assumptions of spin-wave theory. A real-space renormalization group (RSRG) approach is then used to understand how these rare points modify ordering of the O(2) rotor. A new class of fixed points of the RSRG equations for disordered one-dimensional bosons is identified and shown to support the existence of long-range order on the percolation backbone in two dimensions. These results are relevant to experiments on bosons in optical lattices and superconducting arrays, and also (qualitatively) for the diluted Heisenberg antiferromagnet La-2(Zn,Mg)(x)Cu1-xO4.

Aikapankki - Tutkimus lahjaperustaiseen vaihtoon perustuvasta yhteisöllisyyden rakentamisesta Helsingissä

Pro gradu -tutkielmassani tutkin aikapankkijärjestelmässä tapahtuvaa palveluiden vaihtoa vertaamalla sitä lahjanvaihtoon. Tutkielmassa kuvaan kuinka Kumpulan Vaihtopiirinä toimintansa aloittaneen Stadin Aikapankin aktiiviset jäsenet kokevat toiminnan, kun se on laajennut oman asuinalueen ulkopuolelle. Aikapankin voi mieltää uudenlaiseksi vapaaehtoistyön muodoksi. Aikapankin jäsenet tuottavat toisilleen palveluita ja mittaavat näihin käytettyä aikaa aikapisteillä, jotka toimivat vaihdon välineenä. Aikapankissa kaikkien työ arvotetaan saman arvoiseksi. Tutkielman pääaineistona on kymmenen käyttäjän avohaastattelut. Näitä täydennetään vaihtotilastolla ja osallistuvan havainnoinnin menetelmällä. Tutkimusta varten on kerätty tausta-aineistoa kahdella sähköpostihaastattelulla kahdelta Ruotsissa ja Englannissa toimivien aikapankkien työntekijältä. Merkittävin tutkimusongelma liittyy aikapankin tasa-arvoisen työnarvottamiseen. Kysyn miten ja millä ehdoin aikapankin kaltainen sosiaalinen innovaatio toimii? Lisäksi kysyn, mitä ehtojen täyttymisestä seuraa? Lähestyn kysymystä Emil Durkheimin modernisaatioteoriaan ja Marcel Maussin lahjanvaihtoa käsittelevään teoreettiseen ajatteluun nojaten. Teoreettisessa keskustelussa viitataan myös Karl Polanyin Maussia tukevaan näkemykseen esimodernien vaihtokäytäntöjen ilmenemisestä markkinatalouden rakenteistamassa maailmassa. Lisäksi pohdin tutkielmassani sitä, mitä aikapankissa vaihdettavat aikapisteet tekisivät, mitä oikea raha ei tekisi paremmin. Vastaus on se, että tutkittavani eivät saisi rahalla sitä, mitä he tavoittelevat – yhteisöä. Tutkielman lopussa keskustelen myös sitä, mikä on aikapankin luomien epämarkkinataloussuhteiden taloudellinen konteksti. Kontekstiin liittyen voidaan todeta, että tutkittavat eivät pakene rahataloutta. He solmivat perinteisen yhteisöllisen siteen (perheen) mukaista (lahjaperustaista) vaihtoa lähellä asuviin ihmisiin. Tutkielmassa päädytään siihen tulokseen, että aikapankin haasteeksi ei muodostu niinkään markkinoille vieras tasapuolinen työn hinnoittelu, vaan sellaisten yhteisöllisten siteiden heikkous, joiden varaan vaihto leviäisi. Tästä syystä aikapankkia perustettaessa ratkaisevaksi muodostuu se, minkä yhteisöllisen siteen varaan vaihtosuhteet muodostuvat. Tästä syystä tutkielmassa tullaan siihen tulokseen, että aikapankkitoiminta olisi hyvä pitää paikallisena. Sosiaalipoliittisesta näkökulmasta katsottuna tutkimusaihe on merkittävä ja tuore. Aihetta tutkittu jo sosiaalipolitiikan alalla, muttei aikaisemmin Suomessa. Aikaisemman muualla tehdyn tutkimuksen tulokset ovat lähestyneet aihetta muun muassa sosiaalisen pääomaan käsitteen avulla. Tutkittavani vaihtavat myös sellaisia palveluita, joita julkinen sektori tuottaa suomessa, kuten lastenhoitoa. Taustoitan tutkimusta aikaisemmalla tutkimuskirjallisuudella ja kuvaan Suomessakin yleistynyttä vertaistuotantokeskustelua. Vertaistuotanto avaa uuden näkökulman palvelutuotantoon 1990-luvulla jalansijaa saaneiden tilaaja-tuottaja–mallien rinnalle. Tutkielman tarkoitus on tuottaa käytännönläheistä tietoa aikapankkitoiminnasta kiinnostuneille yhteisöille ja organisaatioille. Tämän lisäksi tutkimus täydentää aiempien aikapankkeja käsitelleiden tutkimusten tuloksia tarkastelemalla toiminnan ehtoja, ei ainoastaan sen seurauksia.

Conformational Variability in Modified Nucleosides. Crystal and Molecular Structure of 2',3'-O-Isopropylidene Inosine

The crystal structure of 2',3'-O-isopropylidene inosine shows a number of interesting features. The four independent molecules in the asymmetric unit exhibit significant conformational variations. Ribose puckers fall in the O(4')-exo region, unfavourable in unsubstituted nucleosides. Hypoxanthine bases show base-pairing (I.I) in a manner analogous to the guanine self pairs (G.G) in 2',3'-O-isopropylidene guanosine but with a C(2)-H…O(6) hydrogen bond instead of N(2)-H…O(6).

Crystal Structure of Sodium Deoxyinosine Monophosphate

The crystal and molecular structure of sodium deoxyinosine monophosphate (5'-dIMP) has been determined by x-ray crystallographic methods. The crystals belong to orthorhombic space group P212121, with a = 21.079(5) Aring, b = 9.206(3) Aring and c = 12.770(6) Aring. This deoxynucleotide shows common nucleotide features namely anti conformation about the glycosyl bond, C2' endo pucker for the deoxyribose sugar and gauche-gauche orientation for the phosphate group. The sodium ion is directly coordinated to the O3' atom, a feature observed in many crystal structures of sodium salts of nucleotides.

Tuning the electronic effective mass in double-doped SrTiO3

We elucidate the relationship between effective mass and carrier concentration in an oxide semiconductor controlled by a double-doping mechanism. In this model oxide system, Sr1-xLaxTiO3-delta, we can tune the effective mass ranging from 6 to 20m(e) as a function of filling (carrier concentration) and the scattering mechanism, which are dependent on the chosen lanthanum-and oxygen-vacancy concentrations. The effective mass values were calculated from the Boltzmann transport equation using the measured transport properties of thin films of Sr1-xLaxTiO3-delta. We show that the effective mass decreases with carrier concentration in this large-band-gap, low-mobility oxide, and this behavior is contrary to the traditional high-mobility, small-effective-mass semiconductors.

Concise row-pruning algorithm to invert a matrix

Presented here, in a vector formulation, is an O(mn2) direct concise algorithm that prunes/identifies the linearly dependent (ld) rows of an arbitrary m X n matrix A and computes its reflexive type minimum norm inverse A(mr)-, which will be the true inverse A-1 if A is nonsingular and the Moore-Penrose inverse A+ if A is full row-rank. The algorithm, without any additional computation, produces the projection operator P = (I - A(mr)- A) that provides a means to compute any of the solutions of the consistent linear equation Ax = b since the general solution may be expressed as x = A(mr)+b + Pz, where z is an arbitrary vector. The rank r of A will also be produced in the process. Some of the salient features of this algorithm are that (i) the algorithm is concise, (ii) the minimum norm least squares solution for consistent/inconsistent equations is readily computable when A is full row-rank (else, a minimum norm solution for consistent equations is obtainable), (iii) the algorithm identifies ld rows, if any, and reduces concerned computation and improves accuracy of the result, (iv) error-bounds for the inverse as well as the solution x for Ax = b are readily computable, (v) error-free computation of the inverse, solution vector, rank, and projection operator and its inherent parallel implementation are straightforward, (vi) it is suitable for vector (pipeline) machines, and (vii) the inverse produced by the algorithm can be used to solve under-/overdetermined linear systems.

Influence of acetyl and bromine substitutions on stacking. Crystal and molecular structures of 8-bromo-2',3',5'-triacetyl adenosine and 8-bromo 2',3',5'-triacetyl guanosine

The three dimensional structures of 8-bromo 2',3',5' triacetyl adenosine (8-Br Tri A) and 8-bromo 2',3',5'-triacetyl guanosine (8-Br Tri G) have been determined by single crystal X-ray diffraction methods to study the combined effect of bromine and acetyl substitutions on molecular conformation and interactions. The ribose puckers differ from those found in unbrominated Tri A and Tri G and unacetylated 8-Br A and 8-Br G analogues

Possible Neutrino-Antineutrino Oscillation Under Gravity and its Consequences

We show that under gravity the effective masses for neutrino and antineutrino are different which opens a possible window of neutrino-antineutrino oscillation even if the rest masses of the corresponding eigenstates are same. This is due to CPT violation and possible to demonstrate if the neutrino mass eigenstates are expressed as a combination of neutrino and antineutrino eigenstates, as of the neutral kaon system, with the plausible breaking of lepton number conservation. In early universe, in presence of various lepton number violating processes, this oscillation might lead to neutrino-antineutrino asymmetry which resulted baryogenesis from the B-L symmetry by electro-weak sphaleron processes. On the other hand, for Majorana neutrinos, this oscillation is expected to affect the inner edge of neutrino dominated accretion disks around a compact object by influencing the neutrino sphere which controls the accretion dynamics, and then the related type-II supernova evolution and the r-process nucleosynthesis.

Secondary Perturbation Effects in Keplerian Accretion Disks: Elliptical Instability

Origin of turbulence in cold accretion disks, particularly in 3D, which is expected to be hydrodynamic but not magnetohydrodynamic, is a big puzzle. While the flow must exhibit some turbulence in support of the transfer of mass inward and angular momentum outward, according to the linear perturbation theory it should always be stable. We demonstrate that the 3D secondary disturbance to the primarily perturbed disk which exhibits elliptical vortices into the system solves the problem. This result is essentially applicable to the outer region of accretion disks in active galactic nuclei where the gas is significantly cold and neutral in charge and the magnetic Reynolds number is smaller than 10^4.

Modeling of wheeled mobile robots using dextrous manipulation kinematics

Abstract—This document introduces a new kinematic simulation of a wheeled mobile robot operating on uneven terrain. Our modeling method borrows concepts from dextrous manipulation. This allows for an accurate simulation of the way 3-dimensional wheels roll over a smooth ground surface. The purpose of the simulation is to validate a new concept for design of off-road wheel suspensions, called Passive Variable Camber (PVC). We show that PVC eliminates kinematic slip for an outdoor robot. Both forward and inverse kinematics are discussed and simulation results are presented.