3,617 research outputs found
Bott periodicity for symmetric ground states of gapped free-fermion systems
Building on the symmetry classification of disordered fermions, we give a
proof of the proposal by Kitaev, and others, for a "Bott clock" topological
classification of free-fermion ground states of gapped systems with symmetries.
Our approach differs from previous ones in that (i) we work in the standard
framework of Hermitian quantum mechanics over the complex numbers, (ii) we
directly formulate a mathematical model for ground states rather than
spectrally flattened Hamiltonians, and (iii) we use homotopy-theoretic tools
rather than K-theory. Key to our proof is a natural transformation that squares
to the standard Bott map and relates the ground state of a d-dimensional system
in symmetry class s to the ground state of a (d+1)-dimensional system in
symmetry class s+1. This relation gives a new vantage point on topological
insulators and superconductors.Comment: 55 pages; one figure added; corrections in Section 8; proofs in
Section 6 expande
Qubit-Initialisation and Readout with Finite Coherent Amplitudes in Cavity QED
We consider a unitary transfer of an arbitrary state of a two-level atomic
qubit in a cavity to the finite amplitude coherent state cavity field. Such
transfer can be used to either provide an effective readout measurement on the
atom by a subsequent measurement on the light field or as a method for
initializing a fixed atomic state - a so-called "attractor state", studied
previously for the case of an infinitely strong cavity field. We show that with
a suitable adjustment of the coherent amplitude and evolution time the qubit
transfers all its information to the field, attaining a selected state of high
purity irrespectively of the initial state.Comment: 6 pages, 4 figure
Homotopy Theory of Topological Insulators
We transfer the classification results for disordered free fermions to the setting of translation-invariant ground states and complete the framework developed by Kitaev in which true symmetries are encoded as pseudo-symmetries satisfying Clifford algebra relations. In this mathematical setting, we give a homotopy theoretic proof of the Periodic Table for topological insulators and superconductors in its generalized form allowing for the presence of a defect. Permitting arbitrary numbers of valence and conduction bands, we extend the homotopy classification to include the Hopf insulator and a newly identified topological phase we call the Hopf superconductor. In this general setting, we show that the distinction between strong and weak topological phases needs to be altered in order to prevent strong phases from being realized by stacking lower dimensional phases
Homotopy Theory of Strong and Weak Topological Insulators
We use homotopy theory to extend the notion of strong and weak topological
insulators to the non-stable regime (low numbers of occupied/empty energy
bands). We show that for strong topological insulators in d spatial dimensions
to be "truly d-dimensional", i.e. not realizable by stacking lower-dimensional
insulators, a more restrictive definition of "strong" is required. However,
this does not exclude weak topological insulators from being "truly
d-dimensional", which we demonstrate by an example. Additionally, we prove some
useful technical results, including the homotopy theoretic derivation of the
factorization of invariants over the torus into invariants over spheres in the
stable regime, as well as the rigorous justification of replacing by
and by as is common in the current
literature.Comment: 11 pages, 3 figure
Betacoronavirus genomes: How genomic information has been used to deal with past outbreaks and the COVID-19 pandemic
In the 21st century, three highly pathogenic betacoronaviruses have emerged, with an alarming rate of human morbidity and case fatality. Genomic information has been widely used to understand the pathogenesis, animal origin and mode of transmission of betacoronaviruses in the aftermath of the 2002-03 severe acute respiratory syndrome (SARS) and 2012 Middle East respiratory syndrome (MERS) outbreaks. Furthermore, genome sequencing and bioinformatic analysis have had an unprecedented relevance in the battle against the 2019-20 coronavirus disease 2019 (COVID-19) pandemic, the newest and most devastating outbreak caused by a coronavirus in the history of mankind, allowing the follow up of disease spread and transmission dynamics in near real time. Here, we review how genomic information has been used to tackle outbreaks caused by emerging, highly pathogenic, betacoronavirus strains, emphasizing on SARS-CoV, MERS-CoV and SARS-CoV-2.In the 21st century, three highly pathogenic betacoronaviruses have emerged, with an alarming rate of human morbidity and case fatality. Genomic information has been widely used to understand the pathogenesis, animal origin and mode of transmission of betacoronaviruses in the aftermath of the 2002-03 severe acute respiratory syndrome (SARS) and 2012 Middle East respiratory syndrome (MERS) outbreaks. Furthermore, genome sequencing and bioinformatic analysis have had an unprecedented relevance in the battle against the 2019-20 coronavirus disease 2019 (COVID-19) pandemic, the newest and most devastating outbreak caused by a coronavirus in the history of mankind, allowing the follow up of disease spread and transmission dynamics in near real time. Here, we review how genomic information has been used to tackle outbreaks caused by emerging, highly pathogenic, betacoronavirus strains, emphasizing on SARS-CoV, MERS-CoV and SARS-CoV-2
Proteins in soy might have a higher role in cancer prevention than previously expected: soybean protein fractions are more effective MMP-9 inhibitors than non-protein fractions, even in cooked seeds
The search for anticancer MMP-9 inhibitors (MMPIs) in food products has become a major
goal for research. MMPIs in soy have been related only to saponins and isoflavones, but recently, low
specific protein fractions in soybeans were shown to reduce MMP-9 activity as well. The present
work aimed at comparing the MMPI potential of protein fractions (P) and non-protein fractions (NP)
isolated from soybean seeds, before and after soaking and cooking, mimicking dietary exposures.
Reverse and substrate zymography, as well as a fluoregenic DQ gelatin assay were used to evaluate
MMP-9 activities. Colon cancer cell migration and proliferation was also tested in HT29 cells.
Regarding MMP-9 inhibition, proteins in soy presented IC50 values 100 times lower than non-protein
extracts, and remained active after cooking, suggesting that proteins may be more effective MMP-9
inhibitors than non-protein compounds. Using the determined IC50 concentrations, NP fractions
were able to induce higher inhibitions of HT29 cell migration and proliferation, but not through
MMP-9 inhibition, whilst protein fractions were shown to specifically inhibit MMP-9 activity. Overall,
our results show that protein fractions in soybeans might have a higher role in soy-related cancer
prevention as MMPIs than previously expected. Being nontoxic and active at lower concentrations,
the discovery of these heat-resistant specific MMPI proteins in soy can be of significant importance for
cancer preventive diets, particularly considering the increasing use of soy proteins in food products
and the controversy around isoflavones amongst consumersinfo:eu-repo/semantics/publishedVersio
ISURF: RFID Enabled Collaborative Supply Chain Planning Environment
To be able to cope with the requirements of today’s competitive and demanding digital world of business, companies, especially SMEs, need to be more agile, and be ready to react to the changing requirements of the sector. This requires a better view and a more comprehensive analysis of the whole marketplace which can be achieved through a knowledge oriented collaborative supply chain planning initiative. The parties also need to be capable of monitoring the supply chain visibility in a real time fashion, which can be enabled through the use of RFID devices.
RFID enabled collaborative supply chain planning has been achieved by big industry players in well defined restricted business circumstances through some selected standard message schemes. However, SMEs are still far behind in this process due to their small IT budgets. In iSURF Project we address this problem by providing a set of open source tools to enable seamless collection of supply chain visibility, synchronizing this with master data, exchanging supply chain visibility and other planning data with each other through a service oriented supply chain planning environment which also handles the interoperability of the messages exchanged
Assessing distribution shifts and ecophysiological characteristics of the only Antarctic winged midge under climate change scenarios
Parts of Antarctica were amongst the most rapidly changing regions of the planet during the second half of the Twentieth Century. Even so, today, most of Antarctica remains in the grip of continental ice sheets, with only about 0.2% of its overall area being ice-free. The continent’s terrestrial fauna consists only of invertebrates, with just two native species of insects, the chironomid midges Parochlus steinenii and Belgica antarctica. We integrate ecophysiological information with the development of new high-resolution climatic layers for Antarctica, to better understand how the distribution of P. steinenii may respond to change over the next century under different IPCC climate change scenarios. We conclude that the species has the potential to expand its distribution to include parts of the west and east coasts of the Antarctic Peninsula and even coastal ice-free areas in parts of continental Antarctica. We propose P. steinenii as an effective native sentinel and indicator species of climate change in the Antarctic
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