RGB generation by four-wave mixing in small-core holey fibers

We report the generation of white light comprising red, green, and blue spectral bands from a frequency-doubled fiber laser by an efficient four-wave mixing process in submicron-sized cores of microstructured holey fibers. A master-oscillator power amplifier (MOPA) source based on Yb-doped fiber is employed to generate 80 ps pulses at 1060 nm wavelength with 32 MHz repetition rate, which are then frequency-doubled in an LBO crystal to generate up to 2 W average power of green light. The green pump is then carefully launched into secondary cores of the cladding of photonic bandgap fibers. These secondary cores with diameters of about 400 to 800 nm act as highly nonlinear waveguides. At the output, we observe strong red and blue sidebands which, together with the remaining green pump light, form a visible white light source of about 360 mW. The generating process is identified as four-wave mixing where phase matching is achieved by birefringence in the secondary cores which arises from non-symmetric deformation during the fiber fabrication. Numerical models of the fiber structure and of the nonlinear processes confirm our interpretation. Finally, we discuss power scaling and limitations of the white light source due to the damage threshold of silica fibers

Steering Bose-Einstein condensates despite time symmetry

A Bose-Einstein condensate in an oscillating spatially asymmetric potential is shown to exhibit a directed current for unbiased initial conditions despite time symmetry. This phenomenon occurs only if the interaction between atoms, treated in mean-field approximation, exceeds a critical value. Our findings can be described with a three-mode model (TMM). These TMM results corroborate well with a many-body study over a time scale which increases with increasing atom number. The duration of this time scale probes the validity of the used mean-field approximation.Comment: 4 pages, 5 figure

Comment on "Coherent Ratchets in Driven Bose-Einstein Condensates"

C. E. Creffield and F. Sols (Phys. Rev. Lett. 103, 200601 (2009)) recently reported finite, directed time-averaged ratchet current, for a noninteracting quantum particle in a periodic potential even when time-reversal symmetry holds. As we explain in this Comment, this result is incorrect, that is, time-reversal symmetry implies a vanishing current.Comment: revised versio

Current behavior of a quantum Hamiltonian ratchet in resonance

We investigate the ratchet current that appears in a kicked Hamiltonian system when the period of the kicks corresponds to the regime of quantum resonance. In the classical analogue, a spatial-temporal symmetry should be broken to obtain a net directed current. It was recently discovered that in quantum resonance the temporal symmetry can be kept, and we prove that breaking the spatial symmetry is a necessary condition to find this effect. Moreover, we show numerically and analytically how the direction of the motion is dramatically influenced by the strength of the kicking potential and the value of the period. By increasing the strength of the interaction this direction changes periodically, providing us with a non-expected source of current reversals in this quantum model. These reversals depend on the kicking period also, though this behavior is theoretically more difficult to analyze. Finally, we generalize the discussion to the case of a non-uniform initial condition.Comment: 6 pages, 4 figure

Novel applications of fibre tapers

In this talk we will discuss new applications for fibre tapers ranging from femtosecond pulse manipulation to optical clock generation in micro-coil resonators. Fundamental to these interactions is the enhanced nonlinearity arising from the smaller cores making compact optical devices possible

Multichannel wavelength conversion of 40 Gbit/s NRZ DPSK signals in a highly nonlinear dispersion flattened lead silicate fibre

We experimentally demonstrate the wavelength conversion of three wavelength multiplexed 40 Gbit/s Differential Phase Shift Keyed (DPSK) signals in a 2.2m length of highly nonlinear, dispersion tailored W-type lead-silicate optical fibre

Bleeding Meckel's diverticulum diagnosis: an unusual indication for computed tomography

Despite the wide use of modern investigation techniques, the diagnosis of complications related to Meckel's diverticulum (MD) remains difficult. Arteriography is commonly indicated for acute bleeding, and radionuclide scans may help in identifying the site of intestinal hemorrhage. In contrast, computed tomography (CT) is usually considered little use in the diagnosis of bleeding MD. We present the case of a young patient with massive gastrointestinal hemorrhage, in whom the diagnosis of MD bleeding was preoperatively made with contrast-enhanced CT after two negatives arteriographie

Do naked singularities generically occur in generalized theories of gravity?

A new mechanism for causing naked singularities is found in an effective superstring theory. We investigate the gravitational collapse in a spherically symmetric Einstein-Maxwell-dilaton system in the presence of a pure cosmological constant "potential", where the system has no static black hole solution. We show that once gravitational collapse occurs in the system, naked singularities necessarily appear in the sense that the field equations break down in the domain of outer communications. This suggests that in generalized theories of gravity, the non-minimally coupled fields generically cause naked singularities in the process of gravitational collapse if the system has no static or stationary black hole solution.Comment: 4 pages including 2 eps figures, to be published in Physical Review Letter

BIAYA KECELAKAAN LALU LINTAS DI KOTA BANDA ACEH

ABSTRAK Judul : Biaya Kecelakaan Lalu Lintas di Kota Banda Aceh Nama : RIA OCHTAVIA NIM : 1301101010128 Fakultas./Jurusan : Ekonomi dan Bisnis / Ekonomi Pembangunan Dosen Pembimbing : Dra. Fikriah, M.SiPenelitian ini bertujan untuk menganalisis hubungan antara jumlah pendudukdengan jumlah kendaraan, jumlah kendaraan dengan jumlah kecelakaan, danjumlah kecelakaan dengan biaya kecelakaan lalu lintas di Kota Banda Aceh. Datayang digunakan dalam penelitian ini adalah data sekunder dari tahun 2007 sampaidengan tahun 2016. Data tersebut diperoleh dari Badan Pusat Statistik (BPS) danwebsite lainnya. Data diolah menggunakan metode analisis regres linear bergandanamun dilakukan secara berjenjang (stepwise regression). Dari hasil uji OLS danmenggunakan nilai probabilitas 5% bahwa jumlah penduduk dengan jumlahkendaraan berpengaruh positif dan signifikan dengan nilai probabilitas 0.0001,jumlah kendaraan dengan jumlah kecelakaan berpengaruh positif dan signifikandengan nilai probabilitas 0.0036, jumlah kecelakaan dengan biaya kecelakaan lalulintas berpengaruh positif dan signifikan dengan nilai probabilitas 0.006. Kata Kunci : Jumlah Penduduk, Jumlah Kendaraan, Jumlah Kecelakaan,Biaya Kecelakaan Lalu Lintas, OLS.Banda Ace