7,771 research outputs found
Formation of dynamical Schr\"odinger cats in low-dimensional ultracold attractive Bose gases
Dynamical Schr\"odinger cats can be formed when a one-dimensional attractive
Bose-gas cloud is scattered off a potential barrier. Once formed, these objects
are stable in time. The phenomenon and its mechanism -- transformation of
kinetic energy to internal energy of the scattered atomic cloud -- are obtained
by solving the time-dependent many-boson Schr\"odinger equation. Implications
are discussed.Comment: 11 pages, 3 figure
Ground state fragmentation of repulsive BEC in double-trap potentials
The fragmentation of the ground state of a repulsive condensate immersed into
a double-trap potential is found to be a general and critical phenomenon. It
takes place for a given number of bosons if their scattering length is larger
than some critical value or for a given value of the scattering length if the
number of bosons is above some critical number. We demonstrate that the
geometry of the inner trap determines these critical parameters while the
number of the fragments and the fraction of bosons in the various fragments can
be manipulated by the outer trap. There is also a maximal number of bosons for
which the ground state is fragmented. If this number is exceeded, the
fragmented state becomes a very low-lying excited state of the condensate. This
maximal number of bosons can be substantially manipulated by varying the inner
and outer traps. To study three-fold fragmentation we have chosen a potential
well with two barriers as the inner trap and embedded by two types of outer
ones. A many-fold fragmentation is also addressed.Comment: 18 pages + 9 figure
Characterization of InGaN and InAlN epilayers by microdiffraction X-Ray reciprocal space mapping
We report a study of InGaN and InAlN epilayers grown on GaN/Sapphire substrates by microfocused three-dimensional X-ray Reciprocal Space Mapping (RSM). The analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused X-ray beam, allows us to gain uniquely valuable information about the microstructure of III-N alloy epilayers. It is found that “seed” InGaN mosaic nanocrystallites are twisted with respect to the ensemble average and strain free. This indicates that the growth of InGaN epilayers follows the Volmer-Weber mechanism with nucleation of “seeds” on strain fields generated by the a-type dislocations which are responsible for the twist of underlying GaN mosaic blocks. In the case of InAlN epilayer formation of composition gradient was observed at the beginning of the epitaxial growth
Environment assisted electron capture
Electron capture by {\it isolated} atoms and ions proceeds by
photorecombination. In this process a species captures a free electron by
emitting a photon which carries away the excess energy. It is shown here that
in the presence of an {\it environment} a competing non-radiative electron
capture process can take place due to long range electron correlation. In this
interatomic (intermolecular) process the excess energy is transferred to
neighboring species. The asymptotic expression for the cross section of this
process is derived. We demonstrate by explicit examples that under realizable
conditions the cross section of this interatomic process can clearly dominate
that of photorecombination
On interacting fermions and bosons with definite total momentum
Any {\it exact} eigenstate with a definite momentum of a many-body
Hamiltonian can be written as an integral over a {\it symmetry-broken} function
. For two particles, we solve the problem {\it exactly} for all energy
levels and any inter-particle interaction. Especially for the ground-state,
is given by the simple Hartree-Fock/Hartree ansatz for fermions/bosons.
Implications for several and many particles as well as a numerical example are
provided
On-top fragmentation stabilizes atom-rich attractive Bose-Einstein condensates
It is well known that attractive condensates do not posses a stable ground
state in three dimensions. The widely used Gross-Pitaevskii theory predicts the
existence of metastable states up to some critical number
of atoms. It is demonstrated here that
fragmented metastable states exist for atom numbers well above
. The fragments are strongly overlapping in
space. The results are obtained and analyzed analytically as well as
numerically. The implications are discussed.Comment: 12 pages, 4 figure
Josephson Junctions defined by a Nano-Plough
We define superconducting constrictions by ploughing a deposited Aluminum
film with a scanning probe microscope. The microscope tip is modified by
electron beam deposition to form a nano-plough of diamond-like hardness, what
allows the definition of highly transparent Josephson junctions. Additionally a
dc-SQUID is fabricated to verify appropriate functioning of the junctions. The
devices are easily integrated in mesoscopic devices as local radiation sources
and can be used as tunable on-chip millimeter wave sources
Quantitative Physicochemical Analysis of Acid-Base Balance and Clinical Utility of Anion Gap and Strong Ion Gap in 806 Neonatal Calves with Diarrhea
BackgroundAcid-base abnormalities in neonatal diarrheic calves can be assessed by using the Henderson-Hasselbalch equation or the simplified strong ion approach which use the anion gap (AG) or the strong ion gap (SIG) to quantify the concentration of unmeasured strong anions such as d-lactate. Hypothesis/ObjectivesTo determine and compare the clinical utility of AG and SIG in quantifying the unmeasured strong anion charge in neonatal diarrheic calves, and to examine the associations between biochemical findings and acid-base variables by using the simplified strong ion approach. We hypothesized that the SIG provides a more accurate prediction of unmeasured strong anions than the AG. AnimalsEight hundred and six neonatal diarrheic calves admitted to a veterinary teaching hospital. MethodsRetrospective study utilizing clinicopathologic findings extracted from medical records. ResultsHyperphosphatemia was an important predictor of venous blood pH. Serum inorganic phosphorus and plasma d-lactate concentrations accounted for 58% of the variation in venous blood pH and 77% of the variation in AG and SIG. Plasma d- and total lactate concentrations were slightly better correlated with SIG (r(s)=-0.69;-0.78) than to AG (r(s)=0.63;0.74). Conclusions and Clinical ImportanceStrong ion gap is slightly better at quantifying the unmeasured strong anion concentration in neonatal diarrheic calves than AG. Phosphorus concentrations should be included as part of the calculation of A(tot) when applying the simplified strong ion approach to acid-base balance to critically ill animals with hyperphosphatemia
Quantitative Physicochemical Analysis of Acid-Base Balance and Clinical Utility of Anion Gap and Strong Ion Gap in 806 Neonatal Calves with Diarrhea
BackgroundAcid-base abnormalities in neonatal diarrheic calves can be assessed by using the Henderson-Hasselbalch equation or the simplified strong ion approach which use the anion gap (AG) or the strong ion gap (SIG) to quantify the concentration of unmeasured strong anions such as d-lactate. Hypothesis/ObjectivesTo determine and compare the clinical utility of AG and SIG in quantifying the unmeasured strong anion charge in neonatal diarrheic calves, and to examine the associations between biochemical findings and acid-base variables by using the simplified strong ion approach. We hypothesized that the SIG provides a more accurate prediction of unmeasured strong anions than the AG. AnimalsEight hundred and six neonatal diarrheic calves admitted to a veterinary teaching hospital. MethodsRetrospective study utilizing clinicopathologic findings extracted from medical records. ResultsHyperphosphatemia was an important predictor of venous blood pH. Serum inorganic phosphorus and plasma d-lactate concentrations accounted for 58% of the variation in venous blood pH and 77% of the variation in AG and SIG. Plasma d- and total lactate concentrations were slightly better correlated with SIG (r(s)=-0.69;-0.78) than to AG (r(s)=0.63;0.74). Conclusions and Clinical ImportanceStrong ion gap is slightly better at quantifying the unmeasured strong anion concentration in neonatal diarrheic calves than AG. Phosphorus concentrations should be included as part of the calculation of A(tot) when applying the simplified strong ion approach to acid-base balance to critically ill animals with hyperphosphatemia
General variational many-body theory with complete self-consistency for trapped bosonic systems
In this work we develop a complete variational many-body theory for a system
of trapped bosons interacting via a general two-body potential. In this
theory both the many-body basis functions {\em and} the respective expansion
coefficients are treated as variational parameters. The optimal variational
parameters are obtained {\em self-consistently} by solving a coupled system of
non-eigenvalue -- generally integro-differential -- equations to get the
one-particle functions and by diagonalizing the secular matrix problem to find
the expansion coefficients. We call this theory multi-configurational Hartree
for bosons or MCHB(M), where M specifies explicitly the number of one-particle
functions used to construct the configurations. General rules for evaluating
the matrix elements of one- and two-particle operators are derived and applied
to construct the secular Hamiltonian matrix. We discuss properties of the
derived equations. It is demonstrated that for any practical computation where
the configurational space is restricted, the description of trapped bosonic
systems strongly depends on the choice of the many-body basis set used, i.e.,
self-consistency is of great relevance. As illustrative examples we consider
bosonic systems trapped in one- and two-dimensional symmetric and asymmetric
double-well potentials. We demonstrate that self-consistency has great impact
on the predicted physical properties of the ground and excited states and show
that the lack of self-consistency may lead to physically wrong predictions. The
convergence of the general MCHB(M) scheme with a growing number M is validated
in a specific case of two bosons trapped in a symmetric double-well.Comment: 53 pages, 8 figure
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