9,292 research outputs found
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
Time-reversible Born-Oppenheimer molecular dynamics
We present a time-reversible Born-Oppenheimer molecular dynamics scheme,
based on self-consistent Hartree-Fock or density functional theory, where both
the nuclear and the electronic degrees of freedom are propagated in time. We
show how a time-reversible adiabatic propagation of the electronic degrees of
freedom is possible despite the non-linearity and incompleteness of the
self-consistent field procedure. Time-reversal symmetry excludes a systematic
long-term energy drift for a microcanonical ensemble and the number of
self-consistency cycles can be kept low (often only 2-4 cycles per nuclear time
step) thanks to a good initial guess given by the adiabatic propagation of the
electronic degrees of freedom. The time-reversible Born-Oppenheimer molecular
dynamics scheme therefore combines a low computational cost with a physically
correct time-reversible representation of the dynamics, which preserves a
detailed balance between propagation forwards and backwards in time.Comment: 4 pages, 4 figure
Manajemen Program Siaran Dialog Interaktif Di Kantor Rri Manado
Ruth Debora Massie, 090815001, mahasiswi (S1) Ilmu Komunikasi, Fakultas Ilmu Sosial dan Ilmu Politik Universitas Sam Ratulangi. Penelitian ini berjudul “Manajemen Program Siaran Dialog Interaktif di Kantor RRI Manado”. Dibawah bimbingan dari Drs. Philep. Morse. Regar, MS sebagai dosen pembimbing pertama (1) dan Dra. N. N. Mewengkang, MSi sebagai dosen pembimbing kedua.Sebuah proses manajemen dibutuhkan untuk dapat mengatur/mengontrol jalannya siaran, mulai dari merencanakan kegiatan siaran, mengorganisasikan orang-orang yang handal dalam bidangnya sesuai kebutuhan, menggerakkan sumber daya yang dimiliki, dan mengawasi segala aktivitas proses pelaksanaan siaran.Tujuan penelitian ini untu kmengetahui tentang penerapan fungsi-fungsi manajemen pada program siaran Dialog Interaktif di kantor RRI Manado.Penelitian ini menggunakan metode kualitatif deskriptif.Metode ini dipilih dengan tujuan untuk dapat lebih menggambarkan mengenai fungsi-fungsi manajemen yang diterapkan dalam program siaran radio. Yang menjadi informan kunci dalam penelitian ini adalah kepala RRI Manado, bidang pemberitaan, siaran, dan teknik studio RRI, dan 2 orang pendengar sebagai informan pendukung. Data dikumpulkan melalui wawancara, studi pustaka, dan internet searching, selanjutnya menganalisa hasil penelitian dilakukan untuk dapat memperoleh jawaban atas penelitian yang dilakukan dan berusaha untuk membuahkan suatu kerangka pikir.Hasil penelitian menunjukkan bahwaManajemen Program Siaran Dialog Interaktif di Kantor RRI Manado sudah berjalan dengan baik, dari segi fungsi manajemen, yaitu Perencanaan (Planning), Pengorganisasian (Organizing), Penggerakkan (Actuating) dan Pengawasan (Controlling). Dari segi Tools of Managemen tatau Sarana Manajemen yang ada juga dimanfaatkan sesuai dengan porsinya masing - masing
A change in temperature modulates defence to yellow (stripe) rust in wheat line UC1041 independently of resistance gene Yr36
Background Rust diseases are of major importance in wheat production worldwide. With the constant evolution of new rust strains and their adaptation to higher temperatures, consistent and durable disease resistance is a key challenge. Environmental conditions affect resistance gene performance, but the basis for this is poorly understood. Results Here we show that a change in day temperature affects wheat resistance to Puccinia striiformis f. sp tritici (Pst), the causal agent of yellow (or stripe) rust. Using adult plants of near-isogenic lines UC1041 +/- Yr36, there was no significant difference between Pst percentage uredia coverage in plants grown at day temperatures of 18°C or 25°C in adult UC1041 + Yr36 plants. However, when plants were transferred to the lower day temperature at the time of Pst inoculation, infection increased up to two fold. Interestingly, this response was independent of Yr36, which has previously been reported as a temperature-responsive resistance gene as Pst development in adult UC1041 -Yr36 plants was similarly affected by the plants experiencing a temperature reduction. In addition, UC1041 -Yr36 plants grown at the lower temperature then transferred to the higher temperature were effectively resistant and a temperature change in either direction was shown to affect Pst development up to 8 days prior to inoculation. Results for seedlings were similar, but more variable compared to adult plants. Enhanced resistance to Pst was observed in seedlings of UC1041 and the cultivar Shamrock when transferred to the higher temperature. Resistance was not affected in seedlings of cultivar Solstice by a temperature change in either direction. Conclusions Yr36 is effective at 18°C, refining the lower range of temperature at which resistance against Pst is conferred compared to previous studies. Results reveal previously uncharacterised defence temperature sensitivity in the UC1041 background which is caused by a change in temperature and independently of Yr36. This novel phenotype is present in some cultivars but absent in others, suggesting that Pst defence may be more stable in some cultivars than others when plants are exposed to varying temperatures
Dividing population genetic distance data with the software Partitioning Optimization with Restricted Growth Strings (PORGS): an application for Chinook salmon (Oncorhynchus tshawytscha), Vancouver Island, British Columbia
A new method of finding the optimal group membership and number of groupings to partition population genetic distance data is presented. The software program Partitioning Optimization with Restricted Growth Strings (PORGS), visits all possible set partitions and deems
acceptable partitions to be those that reduce mean intracluster distance. The optimal number of groups is determined with the gap statistic which compares PORGS results with a reference distribution. The PORGS method was validated by a simulated data set with a known distribution.
For efficiency, where values of n were larger, restricted growth strings (RGS) were used to bipartition populations during a nested search (bi-PORGS). Bi-PORGS was applied to a set of genetic data from 18 Chinook salmon (Oncorhynchus
tshawytscha) populations from the west coast of Vancouver Island. The optimal grouping of these populations
corresponded to four geographic locations: 1) Quatsino Sound, 2) Nootka Sound, 3) Clayoquot +Barkley sounds,
and 4) southwest Vancouver Island. However, assignment of populations to groups did not strictly reflect the geographical divisions; fish of Barkley Sound origin that had strayed into the Gold River and close genetic similarity
between transferred and donor populations meant groupings crossed geographic boundaries. Overall, stock structure determined by this partitioning method was similar to that
determined by the unweighted pair-group method with arithmetic averages (UPGMA), an agglomerative clustering algorithm
Gravitational wave generation from bubble collisions in first-order phase transitions: an analytic approach
Gravitational wave production from bubble collisions was calculated in the
early nineties using numerical simulations. In this paper, we present an
alternative analytic estimate, relying on a different treatment of
stochasticity. In our approach, we provide a model for the bubble velocity
power spectrum, suitable for both detonations and deflagrations. From this, we
derive the anisotropic stress and analytically solve the gravitational wave
equation. We provide analytical formulae for the peak frequency and the shape
of the spectrum which we compare with numerical estimates. In contrast to the
previous analysis, we do not work in the envelope approximation. This paper
focuses on a particular source of gravitational waves from phase transitions.
In a companion article, we will add together the different sources of
gravitational wave signals from phase transitions: bubble collisions,
turbulence and magnetic fields and discuss the prospects for probing the
electroweak phase transition at LISA.Comment: 48 pages, 14 figures. v2 (PRD version): calculation refined; plots
redone starting from Fig. 4. Factor 2 in GW energy spectrum corrected. Main
conclusions unchanged. v3: Note added at the end of paper to comment on the
new results of 0901.166
Magnetic states of linear defects in graphene monolayers: effects of strain and interaction
The combined effects of defect-defect interaction and of uniaxial or biaxial
strains of up to 10\% on the development of magnetic states on the
defect-core-localized quasi-one-dimensional electronic states generated by the
so-called 558 linear extended defect in graphene monolayers are investigated by
means of {\it ab initio} calculations. Results are analyzed on the basis of the
heuristics of the Stoner criterion. We find that conditions for the emergence
of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel
strains (along the defect direction) at both limits of isolated and interacting
558 defects. Parallel strains are shown to lead to two cooperative effects that
favor the emergence of itinerant magnetism: enhancement of the DOS of the
resonant defect states in the region of the Fermi level and tuning of the Fermi
level to the maximum of the related DOS peak. A perpendicular strain is
likewise shown to enhance the DOS of the defect states, but it also effects a
detunig of the Fermi level that shifts away from the maximum of the DOS of the
defect states, which inhibts the emergence of magnetic states. As a result,
under biaxial strains the stabilization of a magnetic state depends on the
relative magnitudes of the two components of strain.Comment: 9 pages 8 figure
Magnetic Field of Relativistic Nonlinear Plasma Wave
Longitudinal and transverse behavior of magnetic field of relativistic
nonlinear three-dimensional plasma wave is investigated. It is shown that the
magnetic field of the wave is different from zero and performs higher frequency
oscillations compared to the plasma electron frequency. An increase in the
nonlinearity leads to strengthening of magnetic field. The oscillations of
magnetic field in transverse direction arise, that caused by the phase front
curving of nonlinear plasma wave. The numerical results well conform with
predictions of the analytical consideration of weakly-nonlinear case.Comment: 6 pages, 3 figure
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