700 research outputs found
Fast optimal transition between two equilibrium states
We demonstrate a technique based on invariants of motion for a time-dependent
Hamiltonian, allowing a fast transition to a final state identical in theory to
that obtained through a perfectly adiabatic transformation. This method is
experimentally applied to the fast decompression of an ultracold cloud of
Rubidium 87 atoms held in a harmonic magnetic trap, in the presence of gravity.
We are able to decompress the trap by a factor of 15 within 35 ms with a strong
suppression of the sloshing and breathing modes induced by the large vertical
displacement and curvature reduction of the trap. When compared to a standard
linear decompression, we achieve a gain of a factor of 37 on the transition
time.Comment: 5 pages, 4 figures, an error in Eq. (2) has been correcte
Origin of the n-type conductivity of InN: the role of positively charged dislocations
As-grown InN is known to exhibit high unintentional n-type conductivity. Hall measurements from a range of high-quality single-crystalline epitaxially grown InN films reveal a dramatic reduction in the electron density (from low 1019 to low 1017 cm–3) with increasing film thickness (from 50 to 12 000 nm). The combination of background donors from impurities and the extreme electron accumulation at InN surfaces is shown to be insufficient to reproduce the measured film thickness dependence of the free-electron density. When positively charged nitrogen vacancies (VN+) along dislocations are also included, agreement is obtained between the calculated and experimental thickness dependence of the free-electron concentration
Optimally robust shortcuts to population inversion in two-level quantum systems
We examine the stability versus different types of perturbations of recently
proposed shortcuts-to-adiabaticity to speed up the population inversion of a
two-level quantum system. We find optimally robust processes using invariant
based engineering of the Hamiltonian. Amplitude noise and systematic errors
require different optimal protocols.Comment: 17 pages, 7 figure
Zero-minimum tillage seeding and fertilizer placement techniques for zero-tillage
Non-Peer ReviewedPreliminary results from the field evaluation of zero and minimum tillage seeding machines, as well as fertilizer placement techniques for zero-tillage are presented. Narrow hoe opener (Noble 2000), conventional double-disc (Haybuster 1206), as well as two modified double-disc press drills have been compared for their seeding performance and effects on crop yields in a continuous zero-till wheat test. Further, an air-seeder, a discer and a conventional hoe press-drill have been field evaluated both on cultivated fallow and stubble situations. Deep banding and side banding (approximately 2.5 cm from seed) of fertilizer using both disc and hoe press-drills have been compared to seed-placed fertilizer application
Valence band offset of InN/AlN heterojunctions measured by X-ray photoelectron spectroscopy
The valence band offset of wurtzite-InN/AlN (0001) heterojunctions is determined by x-ray photoelectron spectroscopy to be 1.52±0.17 eV. Together with the resulting conduction band offset of 4.0±0.2 eV, a type-I heterojunction forms between InN and AlN in the straddling arrangement
Gravity-Assist Mechanical Simulator for Outreach
There is no convenient way to demonstrate mechanically, as an outreach (or inreach) topic, the angular momentum trade-offs and the conservation of angular momentum associated with gravityassist interplanetary trajectories. The mechanical concepts that underlie gravity assist are often misunderstood or confused, possibly because there is no mechanical analog to it in everyday experience. The Gravity Assist Mech - anical Simulator is a hands-on solution to this longstanding technical communications challenge. Users intuitively grasp the concepts, meeting specific educational objectives. A manually spun wheel with high angular mass and low-friction bearings supplies momentum to an attached spherical neodymium magnet that represents a planet orbiting the Sun. A steel bearing ball following a trajectory across a glass plate above the wheel and magnet undergoes an elastic collision with the revolving magnet, illustrating the gravitational elastic collision between spacecraft and planet on a gravity-assist interplanetary trajectory. Manually supplying the angular momentum for the elastic collision, rather than observing an animation, intuitively conveys the concepts, meeting nine specific educational objectives. Many NASA and JPL interplanetary missions are enabled by the gravity-assist technique
Surface electronic properties of undoped InAlN alloys
The variation in surface electronic properties of undoped c-plane InxAl1−xN alloys has been investigated across the composition range using a combination of high-resolution x-ray photoemission spectroscopy and single-field Hall effect measurements. For the In-rich alloys, electron accumulation layers, accompanied by a downward band bending, are present at the surface, with a decrease to approximately flatband conditions with increasing Al composition. However, for the Al-rich alloys, the undoped samples were found to be insulating with approximate midgap pinning of the surface Fermi level observed
Radiography of a normal fault system by 64,000 high-precision earthquake locations: The 2009 L’Aquila (central Italy) case study
We studied the anatomy of the fault system where the 2009 L’Aquila earthquake
(MW 6.1) nucleated by means of ~64 k high-precision earthquake locations spanning
1 year. Data were analyzed by combining an automatic picking procedure for P and S
waves, together with cross-correlation and double-difference location methods reaching a
completeness magnitude for the catalogue equal to 0.7 including 425 clusters of similar
earthquakes. The fault system is composed by two major faults: the high-angle L’Aquila
fault and the listric Campotosto fault, both located in the first 10 km of the upper crust. We
detect an extraordinary degree of detail in the anatomy of the single fault segments
resembling the degree of complexity observed by field geologists on fault outcrops. We
observe multiple antithetic and synthetic fault segments tens of meters long in both the
hanging wall and footwall along with bends and cross fault intersections along the main
fault and fault splays. The width of the L’Aquila fault zone varies along strike from 0.3 km
where the fault exhibits the simplest geometry and experienced peaks in the slip
distribution, up to 1.5 km at the fault tips with an increase in the geometrical complexity.
These characteristics, similar to damage zone properties of natural faults, underline the key
role of aftershocks in fault growth and co-seismic rupture propagation processes.
Additionally, we interpret the persistent nucleation of similar events at the seismicity cutoff depth as the presence of a rheological (i.e., creeping) discontinuity explaining how normal faults detach at depth
Universality of electron accumulation at wurtzite c- and a-plane and zinc-blende InN surfaces
Electron accumulation is found to occur at the surface of wurtzite (112¯0), (0001), and (0001¯) and zinc-blende (001) InN using x-ray photoemission spectroscopy. The accumulation is shown to be a universal feature of InN surfaces. This is due to the low Г-point conduction band minimum lying
significantly below the charge neutrality level
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