77 research outputs found
Subpicosecond (320 fs) pulses from CW passively mode-locked external cavity two-section multiquantum well lasers
Pulses from a passively mode-locked two-section multi-quantum well laser coupled to an external cavity are compressed to subpicosecond pulse widths using an external grating telescope compressor. A minimum deconvolved pulse width of 0.32 ps is measured, close to the transform limit, with peak powers of 1.9 W
Flint for safer smart contracts
The Ethereum blockchain platform supports the execution of decentralised applications or smart contracts. These typically hold and transfer digital currency to other parties on the platform; however, they have been subject to numerous attacks due to the unintentional introduction of bugs. Over a billion dollars worth of currency has been stolen since its release in July 2015. As smart contracts cannot be updated after deployment, it is imperative that the programming language supports the development of robust contracts. We propose Flint, a new statically-typed programming language specifically designed for writing robust smart contracts. Flint's features enforce the writing of safe and predictable code. To encourage good practices, we introduce protection blocks. Protection blocks restrict who can run code and when (using typestate) it can be executed. To prevent vulnerabilities relating to the unintentional loss of currency, Flint Asset traits provide safe atomic operations, ensuring the state of contracts is always consistent. Writes to state are restricted, simplifying reasoning about smart contracts
The Complete Spectrum of the String
We obtain the complete physical spectrum of the string, for arbitrary
. The constraints freeze coordinates, while the remaining
coordinates appear in the currents only {\it via} their energy-momentum tensor.
The spectrum is then effectively described by a set of ordinary Virasoro-like
string theories, but with a non-critical value for the central charge and a
discrete set of non-standard values for the spin-2 intercepts. In particular,
the physical spectrum of the string includes the usual massless states of
the Virasoro string. By looking at the norms of low-lying states, we find
strong indications that all the strings are unitary.Comment: 28 page
On Sibling and Exceptional W Strings
We discuss the physical spectrum for strings based on the algebras ,
, , and . For a simply-laced string, we find a
connection with the unitary Virasoro minimal model, where is the
dual Coxeter number of the underlying Lie algebra. For the string based on
, we find a connection with the unitary super-Virasoro
minimal model.Comment: 16 page
Broad-band wavelength tunable picosecond pulses from CW passively mode-locked two-section multiple quantum-well lasers
The Interacting String
We present a procedure for computing gauge-invariant scattering amplitudes in
the string, and use it to calculate three-point and four-point functions.
We show that non-vanishing scattering amplitudes necessarily involve external
physical states with excitations of ghosts as well as matter fields. The
crossing properties of the four-point functions are studied, and it is shown
that the duality of the Virasoro string amplitudes generalises in the
string, with different sets of intermediate states being exchanged in different
channels. We also exhibit a relation between the scattering amplitudes of the
string and the fusion rules of the Ising model.Comment: (Revised version), 26 pages, Plain Tex, CTP TAMU-86/92, KUL-TF-92/4
On the spectrum and scattering of W3 strings
We present a detailed investigation of scattering processes in string
theory. We discover further physical states with continuous momentum, which
involve excitations of the ghosts as well as the matter, and use them to gain a
better understanding of the interacting theory. The scattering amplitudes
display factorisation properties, with states from the different sectors of the
theory being exchanged in the various intermediate channels. We find strong
evidence for the unitarity of the theory, despite the unusual ghost structure
of some of the physical states. Finally, we show that by performing a
transformation of the quantum fields that involves mixing the ghost fields with
one of the matter fields, the structure of the physical states is dramatically
simplified. The new formalism provides a concise framework within which to
study the string.Comment: 37 pages. CPT TAMU-4/93, Preprint-KUL-TF-93/2. (Note Added,
clarifying issues raised in preprint KCL-TH-93-2, hep-th/9302114.
Subpicosecond (320 fs) pulses from CW passively mode-locked external cavity two-section multiquantum well lasers
Graded contractions of bilinear invariant forms of Lie algebras
We introduce a new construction of bilinear invariant forms on Lie algebras,
based on the method of graded contractions. The general method is described and
the -, -, and -contractions are
found. The results can be applied to all Lie algebras and superalgebras (finite
or infinite dimensional) which admit the chosen gradings. We consider some
examples: contractions of the Killing form, toroidal contractions of ,
and we briefly discuss the limit to new WZW actions.Comment: 15 page
Defending the genome from the enemy within:mechanisms of retrotransposon suppression in the mouse germline
The viability of any species requires that the genome is kept stable as it is transmitted from generation to generation by the germ cells. One of the challenges to transgenerational genome stability is the potential mutagenic activity of transposable genetic elements, particularly retrotransposons. There are many different types of retrotransposon in mammalian genomes, and these target different points in germline development to amplify and integrate into new genomic locations. Germ cells, and their pluripotent developmental precursors, have evolved a variety of genome defence mechanisms that suppress retrotransposon activity and maintain genome stability across the generations. Here, we review recent advances in understanding how retrotransposon activity is suppressed in the mammalian germline, how genes involved in germline genome defence mechanisms are regulated, and the consequences of mutating these genome defence genes for the developing germline
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