Ultrafast Enhancement of Ferromagnetism via Photoexcited Holes in GaMnAs

We report on the observation of ultrafast photo-enhanced ferromagnetism in GaMnAs. It is manifested as a transient magnetization increase on a 100-ps time scale, after an initial sub-ps demagnetization. The dynamic magnetization enhancement exhibits a maximum below the Curie temperature Tc and dominates the demagnetization component when approaching Tc. We attribute the observed ultrafast collective ordering to the p-d exchange interaction between photoexcited holes and Mn spins, leading to a correlation-induced peak around 20K and a transient increase in Tc.Comment: 4 page

Strong Electronic Correlation Effects in Coherent Multidimensional Nonlinear Optical Spectroscopy

We discuss a many−body theory of the coherent ultrafast nonlinear optical response of systems with a strongly correlated electronic ground state that responds unadiabatically to photoexcitation. We introduce a truncation of quantum kinetic density matrix equations of motion that does not rely on an expansion in terms of the interactions and thus applies to strongly correlated systems. For this we expand in terms of the optical field, separate out contributions to the time−evolved many−body state due to correlated and uncorrelated multiple optical transitions, and use “Hubbard operator” density matrices to describe the exact dynamics of the individual contributions within a subspace of strongly coupled states, including “pure dephasing”. Our purpose is to develop a quantum mechanical tool capable of exploring how, by coherently photoexciting selected modes, one can trigger nonlinear dynamics of strongly coupled degrees of freedom. Such dynamics could lead to photoinduced phase transitions. We apply our theory to the nonlinear response of a two−dimensional electron gas (2DEG) in a magnetic field. We coherently photoexcite the two lowest Landau level (LL) excitations using three time−delayed optical pulses. We identify some striking temporal and spectral features due to dynamical coupling of the two LLs facilitated by inter−Landau−level magnetoplasmon and magnetoroton excitations and compare to three−pulse four−wave−mixing (FWM) experiments. We show that these features depend sensitively on the dynamics of four−particle correlations between an electron−hole pair and a magnetoplasmon/magnetoroton, reminiscent of exciton−exciton correlations in undoped semiconductors. Our results shed light into unexplored coherent dynamics and relaxation of the quantum Hall system (QHS) and can provide new insight into non−equilibrium co−operative phenomena in strongly correlated systems

Anionic Complexes of Nickel(II)

80-8

Rolling and Annealing Effects on Microstructure and Hardness of Commercial 405 Stainless Steel

The "cold-rolling" experiments for several values of true strain namely 5 percent, 10 percent, and 15 percent respectively have been carried out on commercial SS-405 steel samples at 350oC; the as-rolled samples were cut into several pieces in size of 10 x 10 x 5 mm3, and some pieces were annealed to 550oC for 24 hours. All samples were then mounted and polished before etching in order to observe the grain boundaries. The microstructure observation on all samples was carried out by using optical microscope (MO), meanwhile X-ray diffraction technique was employed in order to support the identification of the existing phases and to verify changes with respect to crystal orientation; the hardness tests were carried out by using Vickers micro hardness tester. The microstructure observation supported by X-ray diffraction results shows that the phase grains of rolled sample tends to take the oblong-shape, accompanied by a preferred orientation predominantly inclined toward the (110) plane. The microhardness testing results show that there has been an increase in the hardness of the as-rolled samples; Mainly because of the nearly negligible thickness of the original sample (being only 5 mm in size), the 15 percent as-rolled samples exhibits only a slight reduction in hardness compared to the 10 percent as-rolled samples; The main cause of this effect is the movement of some dislocations infiltrating the surface resulting in the reduction of the inner-stress in the bulk of the samples. In the rolled-annealed samples there is a very significant reduction in hardness compared to the as-rolled samples. Here the main cause is the recrystallization process taking place during annealing, which tends to significantly reduce the dislocations

Produktivitas Ayam Buras Hasil Seleksi Berdasarkan Pengetahuan Lokal Peternak

Penggalian potensi ayam buras (kampung) menjadi semakin penting pada kondisikrisis ekonomi seperti sekarang. Hal tersebut menyebabkan kita perlu menengokpotensi yang secara sosial diterima, secara ekonomi terjangkau dan secarateknologis mulai dikembangkan dan mudah diterapkan. Namun di pihak laintingkat produktivitasnya masih rendah karena sistem pemeliharaan danseleksinya yang kurang berkembang. Sistem pengetahuan lokal cara seleksi padamasyarakat pedesaan sebenarnya ada hanya kurang mendapat perhatian danminat para akademisi seperti pengetahuan Catur Rangga yang belum banyakdielaborasi. Tujuan dari penelitian ini adalah: a) Untuk menganalisis produktivitasayam buras hasil seleksi; b) Untuk menganalisis pengetahuan lokal peternakmengenai ayam buras; c) Untuk menganalisis hubungan antara produktivitasayam buras hasil seleksi dengan pengetahuan lokal peternak. Metode yangdigunakan dalam penelitian ini studi kasus dengan teknik PRA (Praticipation RuralAppraisal) partisipasi anggota kelompok melalui pola FGD (Focus GroupDiscussion). Data yang diambil untuk pengembangan sistem pengetahuan lokalberdasarkan variabel-variabel: (1) Sistem pengetahuan lokal, dengan parameter:a) Tulang; b) Bulu; c) Jengger; d) Kaki; e) Mata; f) Kloaka; g) Tulang dubur; h)Jari kaki; i) Kepala; Punggung. (2) Produktivitas, dengan parameter data produksitelur per bulan. Metode analisis yang digunakan adalah Uji Rank Spearman(Siegel, 1997) dan interprestasi dengan Guilford (Rakhmat, 1986). Kesimpulandari hasil penelitian ini adalah: a) Produktivitas ayam buras hasil seleksiditunjukkan oleh nilai rata-rata produksi telur 20,45/butir/bulan; b) Pengetahuanlokal peternak mengenai ayam buras sebagian besar searah dengan ilmupengetahuan modern, yang pada mulanya dikonsepsikan dengan Catur Ranggauntuk ayam adu kemudian juga digunakan untuk ayam produksi; c) Hubunganantara produktivitas ayam buras dengan pengetahuan lokal: untuk produksi ratarataproduksi telur/bulan menunjukkan hubungan yang sangat tinggi. Saran yangdiajukan bahwa parameter dari pengetahuan lokal dapat dijadikan salah satumetode untuk mengetahui produktivitas ayam buras di tingkat peternak; perludilakukan penelitian lanjutan yang lebih mendalam mengenai pengetahuan lokaluntuk variabel lain

High-temperature terahertz optical diode effect without magnetic order in polar FeZnMo3_3O8_8

We present a terahertz spectroscopic study of polar ferrimagnet FeZnMo$_3$O$_8$. Our main finding is a giant high-temperature optical diode effect, or nonreciprocal directional dichroism, where the transmitted light intensity in one direction is over 100 times lower than intensity transmitted in the opposite direction. The effect takes place in the paramagnetic phase with no long-range magnetic order in the crystal, which contrasts sharply with all existing reports of the terahertz optical diode effect in other magnetoelectric materials, where the long-range magnetic ordering is a necessary prerequisite. In \fzmo, the effect occurs resonantly with a strong magnetic dipole active transition centered at 1.27 THz and assigned as electron spin resonance between the eigenstates of the single-ion anisotropy Hamiltonian. We propose that the optical diode effect in paramagnetic FeZnMo$_3$O$_8$ is driven by signle-ion terms in magnetoelectric free energy

Observation of inter-Landau-level quantum coherence in semiconductor quantum wells

Using three-pulse four-wave-mixing femtosecond spectroscopy, we excite a non-radiative coherence between the discrete Landau levels of an undoped quantum well and study its dynamics. We observe quantum beats that reflect the time evolution of the coherence between the two lowest Landau level magnetoexcitons. We interpret our observations using a many-body theory and find that the inter Landau level coherence decays with a new time constant, substantially longer than the corresponding interband magnetoexciton dephasing times. Our results indicate a new intraband excitation dynamics that cannot be described in terms of uncorrelated interband excitations.Comment: 5 pages, 5 figures, to appear in Phys. Rev. B Rapid Communication

Ultrafast dynamics of coherences in the quantum Hall system

Using three-pulse four-wave-mixing optical spectroscopy, we study the ultrafast dynamics of the quantum Hall system. We observe striking differences as compared to an undoped system, where the 2D electron gas is absent. In particular, we observe a large off-resonant signal with strong oscillations. Using a microscopic theory, we show that these are due to many-particle coherences created by interactions between photoexcited carriers and collective excitations of the 2D electron gas. We extract quantitative information about the dephasing and interference of these coherences.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let

Ultrafast dynamics and sub-wavelength periodic structure formation following irradiation of GaAs with femtosecond laser pulses

A theoretical investigation of the ultrafast processes and dynamics of the excited carriers upon irradiation of GaAs with femtosecond (fs) pulsed lasers is performed in conditions that induce material damage and eventually surface modification of the heated solid. A parametric study is followed to correlate the produced transient carrier density with the damage threshold for various pulse duration values {\tau}p (it increases as ~ at relatively small values of {\tau}p while it drops for pulse durations of the order of some picoseconds) based on the investigation of the fundamental multiscale physical processes following fs-laser irradiation. Moreover, fluence values for which the originally semiconducting material demonstrates a metallic behaviour are estimated. It is shown that a sufficient number of carriers in the conduction band are produced to excite Surface Plasmon (SP) waves that upon coupling with the incident beam and a fluid-based surface modification mechanism lead to the formation of sub-wavelength periodic structures orientated perpendicularly to the laser beam polarization. Experimental results for the damage threshold and the frequencies of induced periodic structures show a good agreement with the theoretical predictions.Comment: 11 color pages To appear in the Physical Review

Delirium, frailty and mortality: interactions in a prospective study of hospitalized older people

BACKGROUND: It is unknown if the association between delirium and mortality is consistent for individuals across the whole range of health states. A bimodal relationship has been proposed, where delirium is particularly adverse for those with underlying frailty, but may have a smaller effect (perhaps even protective) if it is an early indicator of acute illness in fitter people. We investigated the impact of delirium on mortality in a cohort simultaneously evaluated for frailty. METHODS: We undertook an exploratory analysis of a cohort of consecutive acute medical admissions aged ≥70. Delirium on admission was ascertained by psychiatrists. A Frailty Index (FI) was derived according to a standard approach. Deaths were notified from linked national mortality statistics. Cox regression was used to estimate associations between delirium, frailty and their interactions on mortality. RESULTS: The sample consisted of 710 individuals. Both delirium and frailty were independently associated with increased mortality rates (delirium: HR 2.4, 95%CI 1.8–3.3, p<0.01; frailty (per SD): HR 3.5, 95%CI 1.2–9.9, p=0.02). Estimating the effect of delirium in tertiles of FI, mortality was greatest in the lowest tertile: tertile 1 HR 3.4 (95%CI 2.1–5.6); tertile 2 HR 2.7 (95%CI 1.5–4.6); tertile 3 HR 1.9 (95% CI 1.2–3.0). CONCLUSION: While delirium and frailty contribute to mortality, the overall impact of delirium on admission appears to be greater at lower levels of frailty. In contrast to the hypothesis that there is a bimodal distribution for mortality, delirium appears to be particularly adverse when precipitated in fitter individuals