885 research outputs found
Effects of carbon nanotubes/graphene nanoplatelets hybrid systems on the structure and properties of polyetherimide-based foams
Foams based on polyetherimide (PEI) with carbon nanotubes (CNT) and PEI with graphene nanoplatelets (GnP) combined with CNT were prepared by water vapor induced phase separation. Prior to foaming, variable amounts of only CNT(0.1–2.0wt%) or a combination of GnP(0.0–2.0 wt %) and CNT (0.0–2.0 wt %) for a total amount of CNT-GnP of 2.0 wt %, were dispersed in a solvent using high power sonication, added to the PEI solution, and intensively mixed. While the addition of increasingly higher amounts of only CNT led to foams with more heterogeneous cellular structures, the incorporation of GnP resulted in foams with ¿ner and more homogeneous cellular structures. GnP in combination with CNT effectively enhanced the thermal stability of foams by delaying thermal decomposition and mechanically-reinforced PEI. The addition of 1.0 wt % GnP in combination with 1.0 wt % CNT resulted in foams with extremely high electrical conductivity, which was related to the formation of an optimum conductive network by physical contact between GnP layers and CNT, enabling their use in electrostatic discharge (ESD) and electromagnetic interference (EMI) shielding applications. The experimental electrical conductivity values of foams containing only CNT ¿tted well to a percolative conduction model, with a percolation threshold of 0.06 vol % (0.1 wt %) CNTPostprint (published version
Good Gottesman-Kitaev-Preskill codes from the NTRU cryptosystem
We introduce a new class of random Gottesman-Kitaev-Preskill (GKP) codes
derived from the cryptanalysis of the so-called NTRU cryptosystem. The derived
codes are good in that they exhibit constant rate and average distance scaling
with high probability, where is the number of
bosonic modes, which is a distance scaling equivalent to that of a GKP code
obtained by concatenating single mode GKP codes into a qubit-quantum error
correcting code with linear distance. The derived class of NTRU-GKP codes has
the additional property that decoding for a stochastic displacement noise model
is equivalent to decrypting the NTRU cryptosystem, such that every random
instance of the code naturally comes with an efficient decoder. This
construction highlights how the GKP code bridges aspects of classical error
correction, quantum error correction as well as post-quantum cryptography. We
underscore this connection by discussing the computational hardness of decoding
GKP codes and propose, as a new application, a simple public key quantum
communication protocol with security inherited from the NTRU cryptosystem.Comment: 23 pages, 10 figures, comments welcome! Version 2 has minor
correction
System Development for Geolocation in Harsh Environments
Wireless sensor networks (WSN) consist of a set of distributed devices equipped with multiple sensors, which can be employed in different environments of varying characteristics. Nowadays, node localization has become one of their most basic and important requirements. Due to the nature of certain environments, typical positioning systems, such as Global Navigation Satellite System (GNSS), cannot be employed. Therefore, in recent years several alternative positioning mechanisms have risen.
ROMOVI is a project which has as its main goal the development of low cost autonomous robots capable of monitoring and perform logistic tasks on the steep slopes of the Douro river vineyards. Integrated in this project, this dissertation proposes the development of a full-custom wireless communication system for geolocation purposes in harsh environments. Using a Symmetric Double Sided Two Way Ranging (SDS-TWR) algorithm, it is possible to achieve ranging measures between nodes, thus providing accurate relative positioning.
This work focuses mainly on the study of the SDS-TWR algorithm and its major error sources, such as those due to digital clock drift, among others. A preamble based on Frank-Zadoff-Chu sequence was developed and, due to its good periodic autocorrelation properties, a system employing the transmission and reception of this preamble was implemented in hardware, through a field programmable gate array (FPGA). By employing an embedded logic processor, the Altera Nios II, control over the complete procedure of the aforementioned algorithm is possible, to perform and analyze the main advantages of the SDS-TWR algorithm.
Finally, a medium access control (MAC) layer frame format was defined, in order to enable future development of communication among multiple nodes, to enhance the original algorithm and, as such, provide the capability of trilateration
Destined or Doomed? Hungarian Dissidents and Their Western Friends, 1973-1998
Through the lens of Hungarian dissidents and their supporters in the West, the following study analyzes the motivations of intellectuals from East and West to engage in an open East-West dialogue, their efforts to change the social and political structure of the Cold War, and their contributions to the peaceful revolutions of 1989. It investigates the alliance of intellectuals from either side of the Iron Curtain, their formative experiences and mutual influences. To understand the origins, functions, and legacy of this network, the study investigates the period from the 1960s to the late 1990s, focusing on the years 1973 to 1998.
Findings suggest that the motivations that would bring intellectuals from either side of the Iron Curtain together in the 1980s originated in similarly formative experiences in the 1960s, which shattered their youthful convictions and initiated a search for a new intellectual identity that would bring Easterners and Westerners together by the late 1970s. In response to the encounter, the participants developed a distinct set of political and historical convictions that rooted in cultural liberalism, their commitment to free, open and democratic societies, and the acceptance of universal human rights.
This case study touches upon developments throughout Eastern Europe and evaluates the history of the Cold War as interplay between East and West. It indicates a retreat from authoritarian rule in the East as early as 1987, and highlights the problematic, one-sided perception of the Hungarian Democratic Opposition in the West. It discusses the achievements of the former dissidents, and their struggle to adjust to the situation in post-1989 Europe.
The project is based on archival research in six different countries; findings are based on documents found in private collections, national libraries, institutional, national and state security archives. Additionally, over forty eyewitnesses and experts shared their experiences and views in interviews conducted between 2009 and 2012
The History of Lawrence University, 1847-1925
viii, 493 pages. William Francis Raney, David G. Ormsby Professor of European History, was on the faculty at Lawrence University from 1920 to 1955. He researched and wrote this extensive history of Lawrence University between the time of his retirement in 1955 and his death in 1962. Marshall Hulbert \u2726 prepared the work for printing and a limited run was published by Lawrence University in 1984.https://lux.lawrence.edu/archives_selections/1005/thumbnail.jp
Effects of Type I Migration on Terrestrial Planet Formation
Planetary embryos embedded in a gas disc suffer a decay in semimajor axis --
type I migration -- due to the asymmetric torques produced by the interior and
exterior wakes raised by the body (Goldreich & Tremaine 1980; Ward 1986). This
presents a challenge for standard oligarchic approaches to forming the
terrestrial planets (Kokubo & Ida 1998) as the timescale to grow the progenitor
objects near 1 AU is longer than that for them to decay into the Sun. In this
paper we investigate the middle and late stages of oligarchic growth using both
semi-analytic methods (based upon Thommes et al. 2003) and N-body integrations,
and vary gas properties such as dissipation timescale in different models of
the protoplanetary disc. We conclude that even for near-nominal migration
efficiencies and gas dissipation timescales of ~1 Myr it is possible to
maintain sufficient mass in the terrestrial region to form Earth and Venus if
the disc mass is enhanced by factors of ~2-4 over the minimum mass model. The
resulting configurations differ in several ways from the initial conditions
used in previous simulations of the final stages of terrestrial accretion (e.g.
Chambers 2001), chiefly in (1) larger inter-embryo spacings, (2) larger embryo
masses, and (3) up to ~0.4 Earth masses of material left in the form of
planetesimals when the gas vanishes. The systems we produce are reasonably
stable for ~100 Myr and therefore require an external source to stir up the
embryos sufficiently to produce final systems resembling the terrestrial
planets.Comment: 49 pages, 22 figures; accepted in AJ, expected Dec '0
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