AppSleuth: a Tool for Database Tuning at the Application Level

ABSTRACT Excellent work ([1]-[6]) has shown that memory management and transaction concurrency levels can often be tuned automatically by the database management systems. Other excellent work ([7]]

Priprema, identifikacija i antioksidacijska svojstva kelatnog kompleksa željeza i oligopeptida izoliranog iz mesa japanske svilaste crne kokoši (Gallus galllus domesticus Brisson)

Black-bone silky fowl iron(II)-oligopeptide chelate was synthesized from iron(II) solution and the black-bone silky fowl oligopeptide, which was extracted from the muscle protein of black-bone silky fowl (Gallus gallus domesticus Brisson). Orthogonal array analysis was used to determine the optimal conditions for the iron(II)-oligopeptide chelate preparation. Ultraviolet-visible (UV-Vis) spectroscopy, electron microscopy, and Fourier transform infrared (FTIR) spectroscopy were used to identify the structure of iron(II)-oligopeptide chelate. 2-Diphenyl-1-picrylhydrazyl (DPPH) and superoxide radical scavenging assays were performed to compare the antioxidant abilities of the black-bone silky fowl oligopeptide and iron(II)-oligopeptide chelate. The optimal conditions for iron(II) oligopeptide chelate preparation were 4 % of the black-bone silky fowl oligopeptide and a ratio of the black-bone silky fowl oligopeptide to FeCl2·4H2O of 5:1 at pH=4. Under these conditions, the chelation rate was (84.9±0.2) % (p<0.05), and the chelation yield was (40.3±0.1) % (p<0.05). The structures detected with UV-Vis spectroscopy, electron microscopy and FTIR spectra changed significantly after chelation, suggesting that Fe(II) ions formed coordinate bonds with carboxylate (-RCOO¯) and amino (-NH2) groups in the oligopeptides, confirming that this is a new oligopeptide-iron chelate. The iron(II)-oligopeptide chelate had stronger scavenging activity towards DPPH and superoxide radicals than did the black-bone silky fowl oligopeptide.Kelatni kompleks željeza i oligopeptida sintetiziran je dodatkom praha proteina izoliranog iz mesa japanske svilaste crne kokoši (Gallus galllus domesticus Brisson) otopini iona Fe2+. Optimalni uvjeti keliranja određeni su pomoću ortogonalnog plana. Struktura kelata ispitana je pomoću UV-Vis spektroskopije, elektronskog mikroskopa i FTIR spektroskopije. Uspoređena je antioksidacijska aktivnost oligopeptida i kelata, i to ispitivanjem sposobnosti uklanjanja DPPH i superoksidnih radikala. Optimalni uvjeti keliranja bili su: omjer mase oligopeptida i volumena otopine od 4 %, maseni omjer oligopeptida i otopine željezovog(II) klorida od 5:1 i pH-vrijednost od 4. Pri tim je uvjetima uspješnost keliranja bila (84,9±0,2) % (p˂0,05), a prinos kelata (40,3±0,1) % (p˂0,05). Isptivanjem spojeva pomoću UV-Vis spektroskopije, elektronskog mikroskopa i FTIR spektroskopije utvrđeno je da se struktura kelata bitno promijenila, te da je nastao novi spoj, najvjerojatnije vezivanjem iona Fe2+ s karboksilnom i amino skupinom oligopeptida. Kelatni kompleks imao je izraženiju sposobnost uklanjanja DPPH i superoksidnih radikala od oligopeptida

Direct imaging of a zero-field target skyrmion and its polarity switch in a chiral magnetic nanodisk

A target skyrmion is a flux-closed spin texture that has two-fold degeneracy and is promising as a binary state in next generation universal memories. Although its formation in nanopatterned chiral magnets has been predicted, its observation has remained challenging. Here, we use off-axis electron holography to record images of target skyrmions in a 160-nm-diameter nanodisk of the chiral magnet FeGe. We compare experimental measurements with numerical simulations, demonstrate switching between two stable degenerate target skyrmion ground states that have opposite polarities and rotation senses and discuss the observed switching mechanism.Comment: 18 pages, 4 figure

LETTERS Imaging chromophores with undetectable fluorescence by stimulated emission microscopy

Fluorescence, that is, spontaneous emission, is generally more sensitive than absorption measurement, and is widely used in optical imaging 1,2 . However, many chromophores, such as haemoglobin and cytochromes, absorb but have undetectable fluorescence because the spontaneous emission is dominated by their fast non-radiative decay The phenomenon of stimulated emission was first described by Einstein in 1917 (ref. 4). An atom or molecule in its excited state can be stimulated down to the ground state by an incident light field, resulting in the creation of a new coherent photon identical to those in the original incident field. This process only occurs when the frequency of the incident field matches the transition energy. Stimulated emission was later used as a fundamental principle for light amplification in the laser 5 . The depopulation aspect of stimulated emission has been used for population dumping from excited states 6 , super-resolution fluorescence microscopy 7 , and fluorescence lifetime imaging 8 . Here we use the light-amplification aspect of stimulated emission as a contrast mechanism for highly sensitive imaging of chromophores that have undetectable fluorescence. Such chromophores have very short-lived excited states with much faster non-radiative decay rates than their spontaneous emission rates. As a result, their feeble fluorescence is overwhelmed by backgrounds, such as stray light, solvent Raman scattering, and detector dark counts. Our solution to this problem is to conduct a dual-beam experiment to interrogate the short-lived excited state by stimulated emission, which can compete with the non-radiative decay under a strong enough stimulating field Considering the optical excitation at frequency v 01 where N 0 is the number of molecules in the ground state. For a single chromophore, DI E /I E is of the order of 10 27 . Such small attenuation cannot be detected by conventional absorption microscopy. We note that single-molecule absorption was previously achieved in cryogenic temperatures using a frequency-modulation method 10 , which is, however, difficult to implement at room temperature because of the broad molecular absorption linewidth. Moreover, absorption measurement is often complicated by scattering when imaging biological specimens. Instead of detecting direct absorption, here we detect the stimulated emission followed by the excitation of the molecule. According to Einstein 4 , the molecular cross-section s stim for stimulated emission is comparable to s abs , because of microscopic reversibility. Unlike the absorption that results in attenuation, the stimulation beam will experience an intensity gain after interacting with the molecules