cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
t_k-moves on links
Creators: name: Przytycki, Jozef H.
Publisher: name: arXiv
Year: 2006
Subjects: subject: Geometric Topology (math.GT)
subject: FOS: Mathematics
subject: 57M27 (primary)

description: It is a natural question to ask whether two links are equivalent by the following moves -- parallel parts of a link are changed to k-times half-twisted parts and if they are, how many moves are needed to go from one link to the other. In particular if k=2 and the second link is a trivial link it is the question about the unknotting number. The new polynomial invariants of links often allow us to answer the above questions. Also the first homology groups of cyclic branch covers over links provide some interesting information. In the first part of the paper we apply the Jones-Conway (Homflypt) and Kauffman polynomials to find whether two links are not t_k equivalent and if they are, to gain some information how many moves are needed to go from one link to the other. In the second part we describe the Fox congruence classes and their relations with t_k moves. We use the Fox method to analyze relations between t_k moves and the first homology groups of branched cyclic covers of links.In the third part we consider the influence of t_k moves on the Goeritz and Seifert matrices and analyze Lickorish-Millett and Murakami formulas from the point of view of t_k moves and illustrate them by various examples. At the end of the paper we outline some relations with signatures of links and non-cyclic coverings of link spaces.
description: 50 pages, 44 figures; e-print prepared by Dr Makiko Ishiwata and Dr Krzysztof Wargan
Efficient transfer and storage of image data for distributed development of biomedical imaging tools
Creators: name: Tam, Roger C. L.
Publisher: name: University of British Columbia
Year: 2009

description: The central idea behind a medical informatics testbed is the sharing of geographically distributed health information resources. Medical image data is one of the most important resources that can be shared between clinical and research sites. In this thesis, we build an infrastructure for the efficient transfer and storage of medical image data to support distributed development of biomedical imaging applications. The Digital Imaging and Communications in Medicine (DICOM) standard provides interoperability in our testbed. In addition, properties of DICOM are used to help the biomedical imaging tool developer process the images. Performance analyses are done to measure the efficiency of various layers of our implementation.
Letter from the Manager of the Royal Bank of Canada in Vernon, B.C., to [Frank] A. Hewer, February 4, 1909
Creators: name: Canada, Royal Bank Of
Publisher: name: The University of British Columbia
Year: 2017

description: Letter to Frank Hewer from the manager of the Royal Bank of Canada in Vernon, B.C., dated February 4, 1909, regarding Crowne Grants for Rainbow Ranche,with reference to Mr. Hankey and Mr. Hallett.
Entanglement Enhances Security in Secret Sharing
Creators: name: Demkowicz-Dobrzanski, Rafal
name: De, Aditi Sen
name: Sen, Ujjwal
name: Lewenstein, Maciej
Publisher: name: arXiv
Year: 2008
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: We analyze tolerable quantum bit error rates in secret sharing protocols, and show that using entangled encoding states is advantageous in the case when the eavesdropping attacks are local. We also provide a criterion for security in secret sharing -- a parallel of the Csiszar-Korner criterion in single-receiver cryptography.
description: 5 pages, 1 figure, RevTeX4
Quantum dots based on parabolic quantum wells: importance of electronic correlations
Creators: name: Ihn, T.
name: Ellenberger, C.
name: Yannouleas, C.
name: Landman, U.
name: Ensslin, K.
name: Driscoll, D.
name: Gossard, A. C.
Publisher: name: arXiv
Year: 2006
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: We present measurements and theoretical interpretation of the magnetic field dependent excitation spectra of a two-electron quantum dot. The quantum dot is based on an Al$_x$Ga$_{1-x}$As parabolic quantum well with effective $g^\star$-factor close to zero. Results of tunneling spectroscopy of the four lowest states are compared to exact diagonalization calculations and a generalized Heitler--London approximation and good agreement is found. Electronic correlations, associated with the formation of an H$_2$-type Wigner molecule, turn out to be very important in this system.
Remote sensing of vegetation structure using computer vision
Creators: name: Dandois, Jonathan Philip
Publisher: name: Maryland Shared Open Access Repository
Year: 2014
Subjects: canopy structure
computer vision
ecosynth
phenology
structure from motion
UAS

description: High-spatial resolution measurements of vegetation structure are needed for improving understanding of ecosystem carbon, water and nutrient dynamics, the response of ecosystems to a changing climate, and for biodiversity mapping and conservation, among many research areas.   Our ability to make such measurements has been greatly enhanced by continuing developments in remote sensing technology - allowing researchers the ability to measure numerous forest traits at varying spatial and temporal scales and over large spatial extents with minimal to no field work, which is costly for large spatial areas or logistically difficult in some locations.  Despite these advances, there remain several research challenges related to the methods by which three-dimensional (3D) and spectral datasets are joined (remote sensing fusion) and the availability and portability of systems for frequent data collections at small scale sampling locations.  Recent advances in the areas of computer vision structure from motion (SFM) and consumer unmanned aerial systems (UAS) offer the potential to address these challenges by enabling repeatable measurements of vegetation structural and spectral traits at the scale of individual trees.   However, the potential advances offered by computer vision remote sensing also present unique challenges and questions that need to be addressed before this approach can be used to improve understanding of forest ecosystems.  For computer vision remote sensing to be a valuable tool for studying forests, bounding information about the characteristics of the data produced by the system will help researchers understand and interpret results in the context of the forest being studied and of other remote sensing techniques.  This research advances understanding of how forest canopy and tree 3D structure and color are accurately measured by a relatively low-cost and portable computer vision personal remote sensing system: 'Ecosynth'.   Recommendations are made for optimal conditions under which forest structure measurements should be obtained with UAS-SFM remote sensing.  Ultimately remote sensing of vegetation by computer vision offers the potential to provide an 'ecologist's eye view', capturing not only canopy 3D and spectral properties, but also seeing the trees in the forest and the leaves on the trees.
"Did you really mean what you said?" : Sarcasm Detection in Hindi-English Code-Mixed Data using Bilingual Word Embeddings
Creators: name: Aggarwal, Akshita
name: Wadhawan, Anshul
name: Chaudhary, Anshima
name: Maurya, Kavita
Publisher: name: arXiv
Year: 2020
Subjects: subject: Computation and Language (cs.CL)
subject: FOS: Computer and information sciences

description: With the increased use of social media platforms by people across the world, many new interesting NLP problems have come into existence. One such being the detection of sarcasm in the social media texts. We present a corpus of tweets for training custom word embeddings and a Hinglish dataset labelled for sarcasm detection. We propose a deep learning based approach to address the issue of sarcasm detection in Hindi-English code mixed tweets using bilingual word embeddings derived from FastText and Word2Vec approaches. We experimented with various deep learning models, including CNNs, LSTMs, Bi-directional LSTMs (with and without attention). We were able to outperform all state-of-the-art performances with our deep learning models, with attention based Bi-directional LSTMs giving the best performance exhibiting an accuracy of 78.49%.
Cripples and Bastards and Broken Things: Masculinity, Violence, and Abjection in A Song of Ice and Fire and Game of Thrones
Creators: name: Evans, Tania
Publisher: name: The Australian National University
Year: 2019

description: Normative models of masculinity that are based upon violence, domination, and invulnerability are recognised by scholars as damaging for the individuals who enact them and for the societies in which they are enacted. In both the "real" world and the cultural texts that reflect and shape it, this narrow definition of masculinity is debated, reinforced, and/or critiqued. Challenges to normative masculinity are often identified in literary representations; but fantasy fiction seldom features in these analyses, despite the genre's ongoing engagement with masculine characters, themes, and images. The genre's long history of subversive content and ability to (re)imagine the world without the constraints of realism also suggest its capacity to expand conceptions of masculinity. Using a theoretical framework based primarily on Judith Butler's work on gender performativity and subversion, Julia Kristeva's theory of abjection, and Barbara Creed's notion of the monstrous feminine, I argue that, in George R. R. Martin's A Song of Ice and Fire (1996-) and its television adaptation Game of Thrones (2011-), when masculine characters use violence to gain power at others' expense, they are positioned as monstrous and are shown to be part of a destructive cycle, whereas when these characters use violence in ways that makes the world a more liveable place, they are able to maintain their constitutive borders and proliferate their ideas and practices through queer kinship. Illegal and excessive forms of violence used by normatively masculine characters, such as torture and rape, are critiqued through the same textual devices as legal and legitimate sovereign violence when they are individualistic and reproduce existing power structures. In contrast, female, disabled, and queer masculine characters make violence a visibly masculine act and use it in ways that are coded it as heroic or horrifying, depending on whether it empowers or disempowers others. The relationship between masculinity and violence is negotiated in the Martinverse in complex ways, and I demonstrate that the fantasy genre and its conventions have unique potential for presenting alternative masculine discourses and queer kinships that interrogate, refuse, or work the weaknesses in patriarchal logics of reproduction and repetition that maintain a lack of opportunity for certain subjects unable to access these privileged power dynamics.
Visual Marks for Functional Magnetic Resonance Imaging Visualization: A Ranking Study--Thesis and Supplement
Creators: name: Zhang, Guohao
Publisher: name: Maryland Shared Open Access Repository
Year: 2014
Subjects: Brain Connection
Functional MRI
Ranking
User Study
Visual Encoding
Visualization

description: We report results from two experiments ranking visual encoding methods and three node positioning techniques for visualizing brain connection derived from functional magnetic resonance imaging. Brain visualization designers face many design choices to depict the brain network. Inspired by the previous studies by Mackinlay and Cleveland et al., we re-think the rank of their effectiveness in complex brain network. In the first experiment, the effectiveness of nine visual marks in this experiment was tested through four selected brain network analysis tasks. The second experiment tested three node positioning techniques through two tasks. Results indicate our Ring visualization, a circular layout of the nodes, was found to be best suited for tasks involving neighbor identification and comparison. Showing adjacent matrix directly as grid was better for tasks comparing connection strength in lobe level. For the varied encoding methods compared, lightness and slope encoding were least accurate for interpreting encoded values. Length, size and angle encoding showed consistently good performance. Based on the results, suggestions for developing brain connection visualization are provided.
CL FDM, UB Hildesheim (Sommersemester 2021, mittwochs um 12:30 Uhr) - Poster der Veranstaltungsreihe
Creators: name: Strauch, Annette
Publisher: name: Zenodo
Year: 2021
Subjects: UB Hildesheim
Forschungsnahe Dienste
FDM-Training
FDM-Support
Aktives FDM
Open Science

description: Forscherinnen und Forscher sollten „den kompletten Forschungsprozess dokumentieren“. Der Umgang mit Forschungsdaten ist essentiell für die wissenschaftliche Tätigkeit.  In den „Coffee Lectures“ kommen Studierende, Forscherinnen und Forscher mit Expertinnen und Experten aus der Fachcommunity und anderen Vertretern der Universitäten und externen Fachleuten zusammen. Die „Coffee Lectures“ (Dauer etwa 40 Minuten) und Workshops finden mehrmals im Semester statt. Eine Anmeldung ist nicht erforderlich. Alle Veranstaltungen werden aufgrund der aktuellen Corona-Infektionslage DIGITAL übertragen.
 Wo? Über das Tool BBB, siehe Veranstaltungskalender der SUH: www.uni-hildesheim.de/veranstaltungen/veranstaltungskalender/
Strain control of the competition between metallic and semiconducting states in single-layers of TaSe$_3$
Creators: name: Silva-Guillén, Jose Angel
name: Canadell, Enric
Publisher: name: arXiv
Year: 2020
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: TaSe$_3$ is a metallic layered material whose structure is built from TaSe$_3$ trigonal prismatic chains. In this work we report a first-principles density functional theory study of TaSe$_3$ single-layers and we find that, despite the existence of non negligible Se...Se interlayer interactions, TaSe$_3$ single layers are found to be metallic. However, an interesting competition between metallic and semiconducting states is found under the effect of strain. The single-layers keep the metallic behaviour under biaxial strain although the nature of the hole carriers changes. In contrast, uniaxial strain along the chains direction induces the stabilization of a semiconducting state. Potential electronic instabilities due to Fermi surface nesting are found for single-layers under either biaxial strain or uniaxial strain along the long (inter-chain) axis of the layers. Bilayers and trilayers have also been considered. The structural and electronic features behind these unexpected observations are analyzed.
The Source Locations of Major Flares and CMEs in the Emerging Active Regions
Creators: name: Liu, Lijuan
name: Wang, Yuming
name: Zhou, Zhenjun
name: Cui, Jun
Publisher: name: arXiv
Year: 2021
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: Space Physics (physics.space-ph)
subject: FOS: Physical sciences

description: Major flares and coronal mass ejections (CMEs) tend to originate from the compact polarity inversion lines (PILs) in the solar active regions (ARs). Recently, a scenario named as "collisional shearing" is proposed by \citet{Chintzoglou_2019} to explain the phenomenon, which suggests that the collision between different emerging bipoles is able to form the compact PIL, driving the shearing and flux cancellation that are responsible to the subsequent large activities. In this work, through tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs, we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of "collisional shearing". We find that none of the active PILs is the self PIL (sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional PILs (cPILs) formed due to the collision between different bipoles, 6 from the conjoined systems of sPIL and cPIL, and 2 from the conjoined systems of sPIL and ePIL (external PIL between the AR and the nearby preexisting polarities). Collision accompanied by shearing and flux cancellation is found developing at all PILs prior to the eruptions, with $84\%$ (16/19) cases having collisional length longer than 18~Mm. Moreover, we find that the magnitude of the flares is positively correlated with the collisional length of the active PILs, indicating that the intenser activities tend to originate from the PILs with severer collision. The results suggest that the "collisional shearing", i.e., bipole-bipole interaction during the flux emergence is a common process in driving the major activities in emerging ARs.
description: 33 pages, 19 figurs, accepted for publication in ApJ
Design and implementation of a content-based video retrieval system
Creators: name: Shi, Yaping
Publisher: name: University of British Columbia
Year: 2009

description: As computer application enters a multimedia era, video data is becoming an information source. In this thesis, we investigate various video indexing and retrieval techniques and describe an implementation of a prototype video retrieval system that supports queries based on either visual or semantic content of video data. In our system the basic unit for video indexing and retrieval is the shot. Several shot boundary detection techniques have been implemented and evaluated. Each shot is represented by one or more key frames. The image feature vector of each key frame usually has very high dimensionality. So first we reduce the dimensionality of the feature space using the Principal Component Analysis (PCA) technique because most existing multi-dimensional indexing structure grows exponentially in size as the number of dimension increases. We've successfully reduced the dimension of the data sets obtained from our test video sequences from 256 to less than 10 while preserving more than 90 percent of the distance information between data points. Then we choose adaptive bucket k-d tree to index the PCA-transformed data points. For the semantic annotation of video data, we propose a predicate-based annotation which has several advantage over the existing key word based annotation, including expressiveness and the ability to support inference. We also introduce a knowledge base which contains some common facts and rules that can be shared by different videos. Some of the annotations are derivable from other annotations using the rules in the knowledge base, so they need not to be explicitly added. In this way we can save a human annotator's work as well as storage space.
PublishInCovid19 at WNUT 2020 Shared Task-1: Entity Recognition in Wet Lab Protocols using Structured Learning Ensemble and Contextualised Embeddings
Creators: name: Singh, Janvijay
name: Wadhawan, Anshul
Publisher: name: arXiv
Year: 2020
Subjects: subject: Computation and Language (cs.CL)
subject: FOS: Computer and information sciences

description: In this paper, we describe the approach that we employed to address the task of Entity Recognition over Wet Lab Protocols -- a shared task in EMNLP WNUT-2020 Workshop. Our approach is composed of two phases. In the first phase, we experiment with various contextualised word embeddings (like Flair, BERT-based) and a BiLSTM-CRF model to arrive at the best-performing architecture. In the second phase, we create an ensemble composed of eleven BiLSTM-CRF models. The individual models are trained on random train-validation splits of the complete dataset. Here, we also experiment with different output merging schemes, including Majority Voting and Structured Learning Ensembling (SLE). Our final submission achieved a micro F1-score of 0.8175 and 0.7757 for the partial and exact match of the entity spans, respectively. We were ranked first and second, in terms of partial and exact match, respectively.
Visualising potential space : articulating the connections between self and nature through textile and drawing practice
Creators: name: Blake, Sally Jane
Publisher: name: The Australian National University
Year: 2018

description: This practice-led thesis explores the relationship between the inner world of the researcher and the outer world of nature, and developed from concern about human-led ecological crises such as climate change and flora and fauna extinctions. A methodology based on Donald Winnicott's theory of potential space is used to explore this relationship. Potential space is a state of mind that allows for inner and outer reality to be negotiated with an attitude of openness and playfulness. These connections have been explored using textile and drawing-based works that articulate and record the patterns and transformations that emerged between self and nature in potential space. Through experiences and collaborations with nature the visual research takes a number of forms including weaving, piecing, plant dyeing, drawings made with rain and burns, stitching and piercing paper. This research extends Winnicott's psychodynamic concept by exploring its relevance for understanding the relationship between self and nature. A number of art-making methodologies are presented as ways to understand and investigate the synergies, connections and tensions between humans and nature.
Computer-mediated communication in a software engineering project course
Creators: name: Page, Steven
Publisher: name: University of British Columbia
Year: 2009

description: Independent tools and fully integrated systems are currently being applied to educational settings, delivering educational content and activities to students. Asynchronous, computer-mediated communications enable students to reflect upon what they are learning, share their thoughts, and read those of others. Such communication tools facilitate active and collaborative learning. Two integrated systems, the Virtual University and the World Wide Web Course Tools, are examined, and compared to one another. Both are Web-based systems that deliver course content and activities to students, across a variety of hardware platforms and without geographical restriction. They are systems that integrate features for a full learning environment, combining instructor preparation facilities, on-line course content, student activities, assessment facilities, and communication tools into a single application. Comparisons are drawn between these systems based on their feature sets, and in the context of CPSC 319, an undergraduate software engineering team project course. I have observed the course, as a teaching assistant, for two years. It appeared to be a good fit for on-line tools, particularly because teamwork is a central emphasis of the course, and the students are familiar with computers. The intensity of the group work, however, and the unique grading structure, makes the course less compatible with these tools than it first appeared. A study of the course newsgroup and other on-line conference systems showed that, as expected, most students participated in the optional on-line discussion groups. The shape of this participation changed, however, between 1995-96 and 1996-97. There was a significant increase in the number of messages posted by each participant, while fewer students actually posted messages. The students rejected the VGroups conferencing system overwhelmingly, because it was perceived to duplicate tools they already had, and failed to reach a critical mass of participants.
On the Steinberg property of the Contou-Carrere symbol
Creators: name: Romo, Fernando Pablos
Publisher: name: arXiv
Year: 2006
Subjects: subject: Commutative Algebra (math.AC)
subject: K-Theory and Homology (math.KT)
subject: Number Theory (math.NT)
subject: FOS: Mathematics
subject: 19F15, 19C20

description: The aim of this work is to show that the Contou-Carrère symbol satisfies the property of Steinberg symbols: $_{A((t))^\times} = 1$ for all elements $f,1-f \in A((t))^\times$. Moreover, we offer a cohomological characterization of the Contou-Carrère symbol from the commutator of a central extension of groups.
description: 9 pages; a part on Witt parameters added; Lemma 3.2 modified
Letter from O. Davidson (per the T. Eaton Company) to [Frank] Hewer, February 8, 1909
Creators: name: Davidson, O.
Publisher: name: The University of British Columbia
Year: 2017

description: Letter to Frank Hewer from O. Davidson of the T. Eaton Company, dated February 8, 1909. regarding balance owing on recent order due to shipping costs and advice about furniture shipping strategies.
Phonemer at WNUT-2020 Task 2: Sequence Classification Using COVID Twitter BERT and Bagging Ensemble Technique based on Plurality Voting
Creators: name: Wadhawan, Anshul
Publisher: name: arXiv
Year: 2020
Subjects: subject: Computation and Language (cs.CL)
subject: FOS: Computer and information sciences

description: This paper presents the approach that we employed to tackle the EMNLP WNUT-2020 Shared Task 2 : Identification of informative COVID-19 English Tweets. The task is to develop a system that automatically identifies whether an English Tweet related to the novel coronavirus (COVID-19) is informative or not. We solve the task in three stages. The first stage involves pre-processing the dataset by filtering only relevant information. This is followed by experimenting with multiple deep learning models like CNNs, RNNs and Transformer based models. In the last stage, we propose an ensemble of the best model trained on different subsets of the provided dataset. Our final approach achieved an F1-score of 0.9037 and we were ranked sixth overall with F1-score as the evaluation criteria.
Conditions for stability and instability of retrial queueing systems with general retrial times
Creators: name: Kernane, Tewfik
Publisher: name: arXiv
Year: 2008
Subjects: subject: Probability (math.PR)
subject: FOS: Mathematics
subject: 60K25, 90B22

description: We study the stability of single server retrial queues under general distribution for retrial times and stationary ergodic service times, for three main retrial policies studied in the literature: classical linear, constant and control policies. The approach used is the renovating events approach to obtain sufficient stability conditions by strong coupling convergence of the process modeling the dynamics of the system to a unique stationary ergodic regime. We also obtain instability conditions by convergence in distribution to improper limiting sequences.
Spectral Weights, d-wave Pairing Amplitudes, and Particle-hole Tunneling Asymmetry of a Strongly Correlated Superconductor
Creators: name: Chou, Chung-Pin
name: Lee, T. K.
name: Ho, Chang-Ming
Publisher: name: arXiv
Year: 2006
Subjects: subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: The spectral weights (SW's) for adding and removing an electron of the Gutzwiller projected d-wave superconducting (SC) state of the t-J-type models are studied numerically on finite lattices. Restrict to the uniform system but treat exactly the strong correlation between electrons, we show that the product of weights is equal to the pairing amplitude squared, same as in the weakly coupled case. In addition, we derive a rigorous relation of SW with doping in the electron doped system and obtain particle-hole asymmetry of the conductance-proportional quantity within the SC gap energy and, also, the anti-correlation between gap sizes and peak heights observed in tunneling spectroscopy on high Tc cuprates.
description: 4 Revtex pages and 4 .eps figures. Published version
The effects of driving time scales on heating in a coronal arcade
Creators: name: Howson, Thomas
name: De Moortel, Ineke
name: Fyfe, Lianne
Publisher: name: arXiv
Year: 2020
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: Context. The relative importance of AC and DC heating in maintaining the temperature of the corona is not well constrained. Aims. Investigate the effects of the characteristic time scales of photospheric driving on the injection and dissipation of energy within a coronal arcade. Methods. We have conducted three dimensional MHD simulations of foot point driving imposed on an arcade. We modified the typical driving time scales to understand the efficiency of heating obtained using AC and DC drivers. We considered the implications for the injected Poynting flux and the nature of the energy release in dissipative regimes. Results. For the same driver amplitude and complexity, long time scale motions are able to inject a much greater Poynting flux into the corona. Consequently, in non-ideal regimes, slow stressing motions result in a greater increase in plasma temperature than for wave-like driving. In dissipative simulations, Ohmic heating is found to be much more significant than viscous heating. For all drivers in our parameter space, energy dissipation is greatest close to the base of the arcade where the magnetic field strength is strongest and at separatrix surfaces, where the field connectivity changes. Across all simulations, the background field is stressed with random foot point motions (in a manner typical of DC heating studies) and even for short time scale driving, the injected Poynting flux is large given the small amplitude flows considered. For long time scale driving, the rate of energy injection was comparable to the expected requirements in active regions. The heating rates were found to scale with the perturbed magnetic field strength and not the total field strength. Conclusions. Alongside recent studies which show power within the corona is dominated by low frequency motions, our results suggest that in the closed corona, DC heating is more significant than AC heating.
description: 14 pages, 16 figures
Low-loss integrated nanophotonic circuits with layered semiconductor materials
Creators: name: Liu, Tianyi
name: Paradisanos, Ioannis
name: He, Jijun
name: Cadore, Alisson R.
name: Liu, Junqiu
name: Churaev, Mikhail
name: Wang, Rui Ning
name: Raja, Arslan S.
name: Javerzac-Galy, Clément
name: Rölli, Philippe
name: De Fazio, Domenico
name: Rosa, Barbara L. T.
name: Tongay, Sefaattin
name: Soavi, Giancarlo
name: Ferrari, Andrea C.
name: Kippenberg, Tobias J.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Optics (physics.optics)
subject: Applied Physics (physics.app-ph)
subject: FOS: Physical sciences

description: Monolayer transition metal dichalcogenides with direct bandgaps are emerging candidates for microelectronics, nano-photonics, and optoelectronics. Transferred onto photonic integrated circuits (PICs), these semiconductor materials have enabled new classes of light-emitting diodes, modulators and photodetectors, that could be amenable to wafer-scale manufacturing. For integrated photonic devices, the optical losses of the PICs are critical. In contrast to silicon, silicon nitride (Si3N4) has emerged as a low-loss integrated platform with a wide transparency window from ultraviolet to mid-infrared and absence of two-photon absorption at telecommunication bands. Moreover, it is suitable for nonlinear integrated photonics due to its high Kerr nonlinearity and high-power handing capability. These features of Si3N4 are intrinsically beneficial for nanophotonics and optoelectronics applications. Here we report a low-loss integrated platform incorporating monolayer molybdenum ditelluride (1L-MoTe2) with Si3N4 photonic microresonators. We show that, with the 1L-MoTe2, microresonator quality factors exceeding 3 million in the telecommunication O-band to E-band are maintained. We further investigate the change of microresonator dispersion and resonance shift due to the presence of 1L-MoTe2, and extrapolate the optical loss introduced by 1L-MoTe2 in the telecommunication bands, out of the excitonic transition region. Our work presents a key step for low-loss, hybrid PICs with layered semiconductors without using heterogeneous wafer bonding.
Taub-NUT Black Holes in Third order Lovelock Gravity
Creators: name: Hendi, S. H.
name: Dehghani, M. H.
Publisher: name: arXiv
Year: 2008
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: We consider the existence of Taub-NUT solutions in third order Lovelock gravity with cosmological constant, and obtain the general form of these solutions in eight dimensions. We find that, as in the case of Gauss-Bonnet gravity and in contrast with the Taub-NUT solutions of Einstein gravity, the metric function depends on the specific form of the base factors on which one constructs the circle fibration. Thus, one may say that the independence of the NUT solutions on the geometry of the base space is not a robust feature of all generally covariant theories of gravity and is peculiar to Einstein gravity. We find that when Einstein gravity admits non-extremal NUT solutions with no curvature singularity at $r=N$, then there exists a non-extremal NUT solution in third order Lovelock gravity. In 8-dimensional spacetime, this happens when the metric of the base space is chosen to be $\Bbb{CP}^{3}$. Indeed, third order Lovelock gravity does not admit non-extreme NUT solutions with any other base space. This is another property which is peculiar to Einstein gravity. We also find that the third order Lovelock gravity admits extremal NUT solution when the base space is $T^{2}\times T^{2}\times T^{2}$ or $S^{2}\times T^{2}\times T^{2}$. We have extended these observations to two conjectures about the existence of NUT solutions in Lovelock gravity in any even-dimensional spacetime.
description: 10 pages
Jet radio emission in Cygnus X-1 and its orbital modulation
Creators: name: Szostek, A.
name: Zdziarski, A. A.
Publisher: name: arXiv
Year: 2006
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We present results of our detailed theoretical study of the observed orbital modulation of the radio emission in Cyg X-1. The modulation occurs due to free-free absorption in the wind from the companion star varying with the orbital phase, and our results put strong constraints on the spatial distribution of the jet radio emission at the frequencies of 2-15 GHz. A crucial role in enhancing the asymmetry of the wind absorption suffered by the jet emission is played by the irradiation by X-rays emitted in the vicinity of the black hole. This increases the wind temperature by more than order of magnitude with respect to that of the wind of an isolated supergiant. The observed phase lags of the minima of the radio emission with respect to the spectroscopic zero phase strongly imply the bulk of the mass of the jet is nonrelativistic (~5 x 10^8 cm/s) within the jet core. The jet can, however, become relativistic outside the core. Also, the jet can have a two-component structure, being slow on the outside and fast inside, in which case its synchrotron-emitting part may be relativistic already in the core. We also consider the observed superorbital modulation of the radio emission (with the period of ~150 d) and find it can be explained by a jet precession both causing variable wind absorption and changing the jet Doppler factor. Finally, we consider the case of Cyg X-3, and show that its lack of observable orbital radio modulation (in spite of strong modulation of X-rays) is explained by that system being both much more compact and much more luminous than Cyg X-1.
description: Accepted for publication in MNRAS; new revised version with small changes; 13 pages, 16 figures
Associative spectra of graph algebras I. Foundations, undirected graphs, antiassociative graphs
Creators: name: Lehtonen, Erkko
name: Waldhauser, Tamás
Publisher: name: arXiv
Year: 2020
Subjects: subject: Combinatorics (math.CO)
subject: Rings and Algebras (math.RA)
subject: FOS: Mathematics

description: Associative spectra of graph algebras are examined with the help of homomorphisms of DFS trees. Undirected graphs are classified according to the associative spectra of their graph algebras; there are only three distinct possibilities: constant 1, powers of 2, and Catalan numbers. Associative and antiassociative digraphs are described, and associative spectra are determined for certain families of digraphs, such as paths, cycles, and graphs on two vertices.
description: 21 pages
Direct observation of domain wall structures in curved permalloy wires containing an anti-notch
Creators: name: Sandweg, C. W.
name: Wiese, N.
name: McGrouther, D.
name: Hermsdoerfer, S. J.
name: Schultheiss, H.
name: Leven, B.
name: McVitie, S.
name: Hillebrands, B.
name: Chapman, J. N.
Publisher: name: arXiv
Year: 2008
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: The formation and field response of head-to-head domain walls in curved permalloy wires, fabricated to contain a single anti-notch, have been investigated using Lorentz microscopy. High spatial resolution maps of the vector induction distribution in domain walls close to the anti-notch have been derived and compared with micromagnetic simulations. In wires of 10 nm thickness the walls are typically of a modified asymmetric transverse wall type. Their response to applied fields tangential to the wire at the anti-notch location was studied. The way the wall structure changes depends on whether the field moves the wall away from or further into the notch. Higher fields are needed and much more distorted wall structures are observed in the latter case, indicating that the anti-notch acts as an energy barrier for the domain wall.
description: submitted for publication in J. Appl. Phys. (5 pages, 5 figure)
Inductance and mutual inductance of superconductor integrated circuit features with sizes down to 120 nm. Part I
Creators: name: Tolpygo, Sergey. K.
name: Golden, Evan B.
name: Weir, Terence J.
name: Bolkhovsky, Vladimir
Publisher: name: arXiv
Year: 2021
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: Data are presented on inductance of various features used in superconductor digital integrated circuits such as microstrip and stripline inductors with linewidths down to 120 nm and different combinations of ground plane layers, effect of perforations of various sizes in the ground planes and their distance to the inductors on inductance, inductance of vias of various sizes between adjacent layers and composite vias between distant superconducting layers. Effects of magnetic flux trapping in ground plane moats on coupling to nearby inductors are discussed for circuit cooling in a residual field of several configurations. Test circuits used for the measurements were fabricated in a new 150-nm node of a fully planarized process with eight niobium layers, SC2 process, developed at MIT Lincoln Laboratory for superconductor electronics and in its 250-nm node SC1, as well as in the standard fabrication process SFQ5ee. The SC2 process utilizes 193-nm photolithography in combination with plasma etching and chemical mechanical planarization of interlayer dielectrics to define inductors with linewidth down to about 100 nm on critical layers. All other processes use 248 nm photolithography. Effects of variation of process parameters on circuit inductors are discussed. The measured data are compared with the results of inductance extraction using software packages InductEx and wxLC. Part II is devoted to mutual inductance of various closely spaced features in integrated circuits, meanders, and transformers.
description: 21 pagers, 21 figures, 4 tables, 61 references. This work was presented at Applied Superconductivity Conference, ASC 2020 Virtual Conference, Oct. 24 - Nov. 7, 2020
Setting the string shoving picture in a new frame
Creators: name: Bierlich, Christian
name: Chakraborty, Smita
name: Gustafson, Gösta
name: Lönnblad, Leif
Publisher: name: arXiv
Year: 2020
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: Nuclear Theory (nucl-th)
subject: FOS: Physical sciences

description: Based on the recent success of the \angantyr model in describing multiplicity distributions of the hadronic final state in high energy heavy ion collisions, we investigate how far one can go with a such a string-based scenario to describe also flow effects measured in such collisions. For this purpose we improve our previous so-called \textit{shoving} model, where strings that are close in space--time tend to repel each other in a way that could generate anisotropic flow, and we find that this model can indeed generate such flows in Å collisions. The flow generated is not quite enough to reproduce measurements, but we identify some short-comings in the presented implementation of the model that, when fixed, could plausibly give a more realistic amount of flow.
description: 42 pages, 34 figures, submission to JHEP
Damped quantum harmonic oscillator
Creators: name: Isar, A.
name: Sandulescu, A.
Publisher: name: arXiv
Year: 2006
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: In the framework of the Lindblad theory for open quantum systems the damping of the harmonic oscillator is studied. A generalization of the fundamental constraints on quantum mechanical diffusion coefficients which appear in the master equation for the damped quantum oscillator is presented; the Schrödinger and Heisenberg representations of the Lindblad equation are given explicitly. On the basis of these representations it is shown that various master equations for the damped quantum oscillator used in the literature are particular cases of the Lindblad equation and that the majority of these equations are not satisfying the constraints on quantum mechanical diffusion coefficients. Analytical expressions for the first two moments of coordinate and momentum are also obtained by using the characteristic function of the Lindblad master equation. The master equation is transformed into Fokker-Planck equations for quasiprobability distributions. A comparative study is made for the Glauber $P$ representation, the antinormal ordering $Q$ representation and the Wigner $W$ representation. It is proven that the variances for the damped harmonic oscillator found with these representations are the same. By solving the Fokker-Planck equations in the steady state, it is shown that the quasiprobability distributions are two-dimensional Gaussians with widths determined by the diffusion coefficients. The density matrix is represented via a generating function, which is obtained by solving a time-dependent linear partial differential equation derived from the master equation. Illustrative examples for specific initial conditions of the density matrix are provided.
description: 36 pages, review article
PSR B0656+14: the unified outlook from the infrared to X-rays
Creators: name: Zharikov, S.
name: Zyuzin, D.
name: Shibanov, Yu.
name: Kirichenko, A.
name: Mennickent, R. E.
name: Geier, S.
name: Cabrera-Lavers, A.
Publisher: name: arXiv
Year: 2021
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: We report detection of PSR B0656$+$14 with the Gran Telescopio Canarias in narrow optical $F657$, $F754$, $F802$, and $F902$ and near-infrared $JHK_s$ bands. The pulsar detection in the $K_s$ band extends its spectrum to 2.2 $μ$m and confirms its flux increase towards the infrared. We also present a thorough analysis of the optical spectrum obtained by us with the VLT. For a consistency check, we revised the pulsar near-infrared and narrow-band photometry obtained with the \textit{HST}. We find no narrow spectral lines in the optical spectrum. We compile available near-infrared-optical-UV and archival 0.3-20keV X-ray data and perform a self-consistent analysis of the rotation phase-integrated spectrum of the pulsar using unified spectral models. The spectrum is best fitted by the four-component model including two blackbodies, describing the thermal emission from the neutron star surface and its hot polar cap, the broken power-law, originating from the pulsar magnetosphere, and an absorption line near $\sim$0.5 keV detected previously. The fit provides better constraints on the model parameters than using only a single spectral domain. The derived surface temperature is $T_{NS}^{\infty}=7.9(3)\times10^5$K. The intrinsic radius (7.8-9.9 km) of the emitting region is smaller than a typical neutron star radius (13km) and suggests a nonuniform temperature distribution over the star surface. In contrast, the derived radius of the hot polar cap is about twice as large as the `canonical' one. The spectrum of the nonthermal emission steepens from the optical to X-rays and has a break near 0.1 keV. The X-ray data suggest the presence of another absorption line near 0.3keV.
description: 18 pages, 9 figures, Accepted for publication in MNRAS
Surface reflectance and shape from images using a collinear light source
Creators: name: Lu, Jiping
Publisher: name: University of British Columbia
Year: 2009

description: The purpose of computer vision is to extract useful information from images. Image features such as occluding contours, edges, flow, brightness, and shading provide geometric and photometric constraints on the surface shape and reflectance of physical objects in the scene. In this thesis, two novel techniques are proposed for surface reflectance extraction and surface recovery. They integrate geometric and photometric constraints in images of a rotating object illuminated under a collinear light source (where the illu- minant direction of the light source lies on or near the viewing direction of the camera). The rotation of the object can be precisely controlled. The object surface is assumed to be C2 and its surface reflectance function is uniform. The first technique, called the photogeometric technique, uses geometric and photometric constraints on surface points with surface normal perpendicular to the image plane to calculate 3D locations of surface points, then extracts the surface reflectance function by tracking these surface points in the images. Using the extracted surface reflectance function and two images of the surface, the technique recovers the depth and surface orientation of the surface simultaneously. The second technique, named the wire-frame technique, further exploits geometric and photometric constraints on the surface points with surface orientation coplanar with the viewing direction and the rotation axis to extract a set of 3D curves. The set of 3D curves comprises a wire frame on the surface. The depth and surface orientation between curves on the wire frame can be interpolation by using geometric or photometric methods. The surface reflectance function can be extracted from the points on the wire frame and used for photometric interpolation. The wire-frame technique is superior because it does not need the surface reflectance function to extract the wire frame. It also works on piecewise uniform surfaces and requires only that the light source be coplanar with the viewing direction and the rotation axis. In addition, by interpolating the depth and surface orientation from a dense wire frame, the surface recovered is more accurate. The two techniques have been tested on real images of surfaces with different reflectance properties and geometric structures. The experimental results and comprehensive analysis show that the proposed techniques are efficient and robust. As an attempt to extend our research to computer graphics, work on extracting the shading function from real images for graphics rendering shows some promising results.