3,966 research outputs found
Tunable subpicosecond electron bunch train generation using a transverse-to-longitudinal phase space exchange technique
We report on the experimental generation of a train of subpicosecond electron
bunches. The bunch train generation is accomplished using a beamline capable of
exchanging the coordinates between the horizontal and longitudinal degrees of
freedom. An initial beam consisting of a set of horizontally-separated beamlets
is converted into a train of bunches temporally separated with tunable bunch
duration and separation. The experiment reported in this Letter unambiguously
demonstrates the conversion process and its versatility.Comment: 4 pages, 5 figures, 1 table; accepted for publication in PR
Formation and Acceleration of Uniformly-Filled Ellipsoidal Electron Bunches Obtained via Space-Charge-Driven Expansion from a Cesium-Telluride Photocathode
We report the experimental generation, acceleration and characterization of a
uniformly-filled electron bunch obtained via space-charge-driven expansion
(often referred to as "blow-out regime") in an L-band (1.3-GHz) radiofrequency
photoinjector. The beam is photoemitted from a Cesium-Telluride semiconductor
photocathode using a short ( fs) ultraviolet laser pulse. The produced
electron bunches are characterized with conventional diagnostics and the
signatures of their ellipsoidal character is observed. We especially
demonstrate the production of ellipsoidal bunches with charges up to
nC corresponding to a -fold increase compared to previous experiments
with metallic photocathodes.Comment: 9, pages, 13 figure
Experiment and modelling of birefringent flows using commercial CFD code
It is well-known that certain fluids are birefringent and when flows are viewed in polarised light interference fringes are observed. The fringes are caused by a phase shift in the light passing through the fluid and are proportional to the integral of the maximum shear strains in the fluid. In order to understand what is happening within the three dimensional flow and overcome the difficulties due to this integration, additional computational or experimental information is needed. In this work, a commercially available computer code (Fluent) is used for the first time to model the flows. The flow data are then exported to a spreadsheet where the shear rates are integrated across the field and then banded for graphical output. The results from this are then compared to results generated from birefringent flow experiments and the agreement is found to be good since the modelled fringes show the same patterns as those in the experiment. This novel use of computational and experimental techniques together will allow quantitative analysis of three-dimensional flows in the future. Currently, there are still a lot of empirical variables involved in fitting the computational fringes to the experiment, but the results of this preliminary study show that this is a promising approach to this type of problem
A Data Flow Perspective for Business Process Integration
Business process integration has become prevalent as business is increasingly crossing organizational boundaries. While workflow technology is a standard solution for business process management, it is imperative for workflow management systems to provide effective and efficient support for collaboration. To address the issue of protecting organizations’ competitive knowledge and private information while also enabling business-to-business (B2B) collaboration, past research has focused on customized public and private process design and structure correctness of the integrated workflow. However, data flow is important for business process integration because data is always sensitive when conducting inter-organizational business and data errors could still happen even given syntactically correct activity dependence. This paper presents a data flow perspective. It gives an approach to define a “public data set” for each involved organization exemplifying the integrated workflow that is needed in order to be free from data anomalies e.g., missing data and redundant data errors
Generalized Continuous and Discrete Stick Fragmentation and Benford's Law
Inspired by the basic stick fragmentation model proposed by Becker et al. in
arXiv:1309.5603v4, we consider three new versions of such fragmentation models,
namely, continuous with random number of parts, continuous with probabilistic
stopping, and discrete with congruence stopping conditions. In all of these
situations, we state and prove precise conditions for the ending stick lengths
to obey Benford's law when taking the appropriate limits. We introduce the
aggregated limit, necessary to guarantee convergence to Benford's law in the
latter two models. We also show that resulting stick lengths are non-Benford
when our conditions are not met. Moreover, we give a sufficient condition for a
distribution to satisfy the Mellin transform condition introduced in
arXiv:0805.4226v2, yielding a large family of examples.Comment: 43 pages, 2 figure
Improved bounds for embedding certain configurations in subsets of vector spaces over finite fields
The fourth listed author and Hans Parshall (\cite{IosevichParshall}) proved
that if , , and is a connected graph on
vertices such that the largest degree of any vertex is , then if , for any , there exist points in such that if the 'th vertex is
connected to the 'th vertex by an edge in . In this paper, we give
several indications that the maximum degree is not always the right notion of
complexity and prove several concrete results to obtain better exponents than
the Iosevich-Parshall result affords. This can be viewed as a step towards
understanding the right notion of complexity for graph embeddings in subsets of
vector spaces over finite fields
Environmental Entrepreneurship and ECO-Innovation Outputs : A Pathway to Sustainable Development
Ensuring sustainability in the long-run necessitates devoting strategic solutions to the rising environmental problems. Unless nations move to a sustainable growth path characterized by economic development and human development that conserve natural resources better, the increased environmental pollution will have negative effects on population well-being. Sustainability has been seen as an entrepreneurial imperative and policy goal (Washington, 2015). However, some building blocks of theory development regarding this process of structural change remain elusive (Savona and Ciarli, 2019). The substantive for sustainable development in which transition pathways are still lacking (Dosi et al., 2017)
Observation of Coherently-Enhanced Tunable Narrow-Band Terahertz Transition Radiation from a Relativistic Sub-Picosecond Electron Bunch Train
We experimentally demonstrate the production of narrow-band (% at THz) THz transition radiation with tunable
frequency over [0.37, 0.86] THz. The radiation is produced as a train of
sub-picosecond relativistic electron bunches transits at the vacuum-aluminum
interface of an aluminum converter screen. We also show a possible application
of modulated beams to extend the dynamical range of a popular bunch length
diagnostic technique based on the spectral analysis of coherent radiation.Comment: 3 pages, 6 figure
Spontaneous Symmetry Breaking of Population between Two Dynamic Attractors in a Driven Atomic Trap: Ising-class Phase Transition
We have observed spontaneous symmetry breaking of atomic populations in the
dynamic phase-space double-potential system, which is produced in the
parametrically driven magneto-optical trap of atoms. We find that the system
exhibits similar characteristics of the Ising-class phase transition and the
critical value of the control parameter, which is the total atomic number, can
be calculated. In particular, the collective effect of the laser shadow becomes
dominant at large atomic number, which is responsible for the population
asymmetry of the dynamic two-state system. This study may be useful for
investigation of dynamic phase transition and temporal behaviour of critical
phenomena.Comment: 4 pages, 4 figure
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