1,499 research outputs found
Translating programming languages for intermediate codes
Many of the important data structures used in a compiler are intermediate representations of the program being compiled. Often these representations take the form of trees, with several node types, each of which has different attributes. Tree representations can be described with grammars, just like programming languages. For each grammar rule, there is one constructor that belongs to the class for its left-hand-side symbol. I simply extend the abstract class with a concrete class for each grammar rule. Each grammar rule has right hand side components that must be represented in the data structures.compiler, lexical analysis, abstract syntax, intermediate representation, abstract machine language
Distribution of the Object Oriented Databases. A Viewpoint of the MVDB Model's Methodology and Architecture
In databases, much work has been done towards extending models with advanced tools such as view technology, schema evolution support, multiple classification, role modeling and viewpoints. Over the past years, most of the research dealing with the object multiple representation and evolution has proposed to enrich the monolithic vision of the classical object approach in which an object belongs to one hierarchy class. In particular, the integration of the viewpoint mechanism to the conventional object-oriented data model gives it flexibility and allows one to improve the modeling power of objects. The viewpoint paradigm refers to the multiple descriptions, the distribution, and the evolution of object. Also, it can be an undeniable contribution for a distributed design of complex databases. The motivation of this paper is to define an object data model integrating viewpoints in databases and to present a federated database architecture integrating multiple viewpoint sources following a local-as-extended-view data integration approach.object-oriented data model, OQL language, LAEV data integration approach, MVDB model, federated databases, Local-As-View Strategy.
Dynamic scaling of fronts in the quantum XX chain
The dynamics of the transverse magnetization in the zero-temperature XX chain
is studied with emphasis on fronts emerging from steplike initial magnetization
profiles. The fronts move with fixed velocity and display a staircase like
internal structure whose dynamic scaling is explored both analytically and
numerically. The front region is found to spread with time sub-diffusively with
the height and the width of the staircase steps scaling as t^(-1/3) and t^1/3,
respectively. The areas under the steps are independent of time, thus the
magnetization relaxes in quantized "steps" of spin-flips.Comment: 4 pages, 3 eps figures, RevTe
pairs from a nuclear transition signaling an elusive light neutral boson
Electron-positron pairs have been observed in the 10.95-MeV decay
in O. The branching ratio of the ee pairs compared to the
3.84-MeV decay of the level is deduced to be
. This magnetic monopole (M0) transition cannot proceed by
-ray decay and is, to first order, forbidden for internal pair
creation. However, the transition may also proceed by the emission of a light
neutral or boson. Indeed, we do observe a sharp peak in the
angular correlation with all the characteristics belonging to the
intermediate emission of such a boson with an invariant mass of 8.5(5)
MeV/c. It may play a role in the current quest for light dark matter in the
universe.Comment: 6 page
Observation of Anomalous Internal Pair Creation in Be: A Possible Signature of a Light, Neutral Boson
Electron-positron angular correlations were measured for the isovector
magnetic dipole 17.6 MeV state (, ) ground state
(, ) and the isoscalar magnetic dipole 18.15 MeV (,
) state ground state transitions in Be. Significant
deviation from the internal pair creation was observed at large angles in the
angular correlation for the isoscalar transition with a confidence level of . This observation might indicate that, in an intermediate step, a
neutral isoscalar particle with a mass of 16.70 (stat)
(sys) MeV and was created.Comment: 5 pages, 5 figure
Transmission resonance spectroscopy in the third minimum of 232Pa
The fission probability of 232Pa was measured as a function of the excitation
energy in order to search for hyperdeformed (HD) transmission resonances using
the (d,pf) transfer reaction on a radioactive 231Pa target. The experiment was
performed at the Tandem accelerator of the Maier-Leibnitz Laboratory (MLL) at
Garching using the 231Pa(d,pf) reaction at a bombarding energy of E=12 MeV and
with an energy resolution of dE=5.5 keV. Two groups of transmission resonances
have been observed at excitation energies of E=5.7 and 5.9 MeV. The fine
structure of the resonance group at E=5.7 MeV could be interpreted as
overlapping rotational bands with a rotational parameter characteristic to a HD
nuclear shape. The fission barrier parameters of 232Pa have been determined by
fitting TALYS 1.2 nuclear reaction code calculations to the overall structure
of the fission probability. From the average level spacing of the J=4 states,
the excitation energy of the ground state of the 3rd minimum has been deduced
to be E(III)=5.05 MeV.Comment: 6 pages, 8 figure
Multidimensional NMR identifies the conformational shift essential for catalytic competence in the 60-kDa Drosophila melanogaster dUTPase trimer
The catalytic mechanism of dUTP pyrophosphatase (dUTPase), responsible
for the prevention of uracil incorporation into DNA, involves ordering
of the flexible C terminus of the enzyme. This conformational shift is
investigated by multidimensional NMR on the Drosophila enzyme. Flexible
segments of the homotrimer give rise to sharp resonances in the
H-1-N-15 heteronuclear single-quantum coherence (HSQC) spectra, which
are clearly distinguishable from the background resonances of the well
folded protein globule. Binding of the product dUMP or the analogues
dUDP and alpha,beta-imino-dUTP to the enzyme induces a conformational
change reflected in the disappearance of eight sharp resonances. This
phenomenon is interpreted as nucleotide binding-induced ordering of
some residues upon the folded protein globule. Three-dimensional
N-15-edited H-1-N-15 HSQC total correlation spectroscopy (TOCSY) and
H-1-N-15 HSQC nuclear Overhauser effect spectroscopy measurements
allowed clear assignment of these eight specific resonance peaks. The
residues identified correspond to the conserved C-terminal sequence
motif, indicating that (i) this conformational shift is amenable to NMR
studies in solution even in the large trimeric molecule and (ii)
formation of the closed enzyme conformer in the case of the Drosophila
enzyme does not require the complete triphosphate chain of the
substrate. NMR titration of the enzyme with the nucleotide ligands as
well as kinetic data indicated significant deviation from the model of
independent active sites within the homotrimer. The results suggest
allosterism in the eukaryotic dUTPase
WO3–EDA hybrid nanoplates and nanowires: synthesis, characterization, formation mechanism and thermal decomposition
Previously the WO3–EDA hybrid material was obtained only from solvothermal reactions.</p
Low-lying GT(+) strength in Co-64 studied via the Ni-64(d,He-2)Co-64 reaction
The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios
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