9,747 research outputs found
Force to Debond Brackets from High-fusing and Low-fusing Porcelain Systems
The purpose of this study was to test the hypothesis that porcelain surface finishing, ie, low- and high-fusing porcelain, has an effect on the amount of force required to debond orthodontic brackets. A total of 20 high-fusing and 20 low-fusing porcelain specimens were prepared, polished, and bonded with standard edgewise brackets using a suggested porcelain bonding protocol. The brackets were debonded with a universal testing machine at shear mode. Resin removal was performed using two methods: a multifluted carbide bur with and without the use of Sof-Lex polishing discs. Representative specimens were studied under a scanning electron microscope before and after debonding to assess the surface morphology and potential surface damage. Statistical analysis with a t-test revealed that there was no difference between the two porcelain treatments on the force to debond values and no qualitative differences were observed on the porcelain surface between the two resin clean-up methods. From a clinical perspective, the practitioner can bond ceramic restorations without previous knowledge of the porcelain type used
Interplay of disorder and geometrical frustration in doped Gadolinium Gallium Garnet
The geometrically-frustrated, triangular antiferromagnet GGG exhibits a rich
mix of short-range order and isolated quantum states. We investigate the
effects of up to 1% Neodymium substitution for Gallium on the ac magnetic
response at temperatures below 1 K in both the linear and nonlinear regimes.
Substitutional disorder actually drives the system towards a more perfectly
frustrated state, apparently compensating for the effect of imperfect
Gadolinium/Gallium stoichiometry, while at the same time more closely
demarcating the boundaries of isolated, coherent clusters composed of hundreds
of spins. Optical measurements of the local Nd environment substantiate the
picture of an increased frustration index with doping.Comment: 5 pages, 5 figure
Penerapan Standar Akuntansi Pemerintah, Sistem Pengendalian Intern Pemerintah dan Kompetensi Sumber Daya Manusia Terhadap Kualitas Laporan Keuangan dengan Komitmen Organisasi Sebagai Variabel Pemoderasi di Kabupaten Tanjung Jabung Barat
Penelitian ini bertujuan untuk mengetahui pengaruh penerapan standar akuntansi pemerintah, sistem pengendalian intern pemerintah dan kompetensi sumber daya manusia terhadap kualitas laporan keuangan dengan komitmen organisasi sebagai variabel pemoderasi di Kabupaten Tanjung Jabung Barat. Sampel dalam penelitian yaitu Kepala OPD, Bendahara OPD dan Pejabat Penatausahaan Keuangan (PPK) OPD dilingkungan pemerintah Kabupaten Tanjung Jabung Barat yang berjumlah 93 responden. Data dalam penelitian adalah data primer. Pengujian hipotesis menggunakan analisis regresi linear berganda dan MRA dengan bantuan program SPSS. Hasil penelitian menunjukkan penerapan standar akuntansi pemerintah, sistem pengendalian intern pemerintah dan kompetensi sumber daya manusia berpengaruh baik secara simultan maupun parsial terhadap kualitas laporan keuangan. Komitmen organisasi sebagai variabel moderasi berhasil memoderasi hubungan penerapan standar akuntansi pemerintah, dan sistem pengendalian intern pemerintah terhadap kualitas laporan keuangan, sedangkan komitmen organisasi tidak berhasil memoderasi hubungan antara kompetensi sumber daya manusia terhadap kualitas laporan keuangan
A non self-referential expression of Tsallis' probability distribution function
The canonical probability distribution function (pdf) obtained by optimizing
the Tsallis entropy under the linear mean energy constraint (first formalism)
or the escort mean energy constraint (third formalism) suffer
self-referentiality. In a recent paper [Phys. Lett. A {\bf335} (2005) 351-362]
the authors have shown that the pdfs obtained in the two formalisms are
equivalent to the pdf in non self-referential form. Based on this result we
derive an alternative expression, which is non self-referential, for the
Tsallis distributions in both first and third formalisms.Comment: 3 page
Enhancement of laser-driven ion acceleration in non-periodic nanostructured targets
Using particle-in-cell simulations, we demonstrate an improvement of the
target normal sheath acceleration (TNSA) of protons in non-periodically
nanostructured targets with micron-scale thickness. Compared to standard flat
foils, an increase in the proton cutoff energy by up to a factor of two is
observed in foils coated with nanocones or perforated with nanoholes. The
latter nano-perforated foils yield the highest enhancement, which we show to be
robust over a broad range of foil thicknesses and hole diameters. The
improvement of TNSA performance results from more efficient hot-electron
generation, caused by a more complex laser-electron interaction geometry and
increased effective interaction area and duration. We show that TNSA is
optimized for a nanohole distribution of relatively low areal density and that
is not required to be periodic, thus relaxing the manufacturing constraints.Comment: 11 pages, 8 figure
Generation of attosecond electron bunches and x-ray pulses from few-cycle femtosecond laser pulses
Laser-plasma electron accelerators can be used to produce high-intensity x-rays, as electrons accelerated in wakefields emit radiation due to betatron oscillations. Such x-ray sources inherit the features of the electron beam; sub-femtosecond electron bunches produce betatron sources of the same duration, which in turn allow probing matter on ultrashort time scales. In this paper we show, via Particle-in-Cell simulations, that attosecond electron bunches can be obtained using low-energy, ultra-short laser beams both in the self-injection and the controlled injection regimes at low plasma densities. However, only in the controlled regime does the electron injection lead to a stable, isolated attosecond electron bunch. Such ultrashort electron bunches are shown to emit attosecond x-ray bursts with high brilliance
Slow and fast micro-field components in warm and dense hydrogen plasmas
The aim of this work is the investigation of the statistical properties of
local electric fields in an ion-electron two component plasmas for coupled
conditions. The stochastic fields at a charged or at a neutral point in plasmas
involve both slow and fast fluctuation characteristics. The statistical study
of these local fields based on a direct time average is done for the first
time. For warm and dense plasma conditions, typically , , well controlled molecular dynamics (MD)
simulations of neutral hydrogen, protons and electrons have been carried out.
Relying on these \textit{ab initio} MD calculations this work focuses on an
analysis of the concepts of statistically independent slow and fast local field
components, based on the consideration of a time averaged electric field. Large
differences are found between the results of these MD simulations and
corresponding standard results based on static screened fields. The effects
discussed are of importance for physical phenomena connected with stochastic
electric field fluctuations, e.g., for spectral line broadening in dense
plasmas.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
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