A novel green chemistry method for nonaqueous extraction and high-performance liquid chromatography detection of first-, second-, and third-generation tetracyclines, 4-epitetracycline, and tylosin in animal feeds

Although tetracyclines and macrolides are common additives for animal nutrition, methods for their simultaneous determination in animal feeds are nonexistent. By coupling an organic extraction and solid-phase extraction cleanup to a high-performance liquid chromatography separation and a nonaqueous postcolumn derivatization, we succeeded in detecting from 0.2 to 24.0 μg kg(-1) of tetracycline, oxytetracycline, chlortetracycline, doxycycline, tigecycline, and 4-epitetracycline in this complex and heterogeneous matrix. Minocycline and tylosin could also be detected with our procedure, but using UV spectrophotometry (1.5 ≤ LOD ≤ 1.9 mg kg(-1)). Linear responses with correlation coefficients between 0.996 and 0.999 were obtained for all analytes in the 0.5-10 mg kg(-1) concentration range. Average recoveries between 59 and 97% and between 98 and 102% were obtained for the tetracyclines and tylosin, respectively. Replicate standard deviations were typically below 5%. When this method was applied to 20 feeds marketed in Costa Rica, we detected labeling inconsistencies, banned mixtures of tetracyclines, and tetracycline concentrations that contravene international regulation.     

Bioaccessibility of tocopherols, carotenoids, and ascorbic acid from milk- and soy-based fruit beverages: influence of food matrix and processing

A study was made of the effect of high-pressure processing (HPP) and thermal treatment (TT) on plant bioactive compounds (tocopherols, carotenoids, and ascorbic acid) in 12 fruit juice-milk beverages and of how the food matrix [whole milk (JW), skimmed milk (JS), and soy milk (JSy)] modulates their bioaccessibility (%). HPP (400 MPa/40 °C/5 min) produced a significant decrease in carotenoid and ascorbic acid bioaccessibility in all three beverages and maintained the bioaccessibility of tocopherols in JW and JS while decreasing it in JSy. TT (90 °C/30 s) produced a significant decrease in tocopherol and carotenoid bioaccessibility in all three beverages and increased the bioaccessibility of ascorbic acid. With regard to the food matrix, α-tocopherol and ascorbic acid bioaccessibility was greatest in JW beverages and lowest in JSy beverages, whereas no significant differences were found among the three beverages in terms of carotenoid bioaccessibility. HPP-treated samples showed higher tocopherol and carotenoid bioaccessibility than TT-treated samples, thus indicating that HPP combined with a milk matrix positively modulates the bioaccessibility of certain types of bioactive components of food, mainly those of a lipophilic nature.     

A superconducting reversible rectifier that controls the motion of magnetic flux quanta

We fabricated a device that controls the motion of flux quanta in a niobium superconducting film grown on an array of nanoscale triangular pinning potentials. The controllable rectification of the vortex motion is due to the asymmetry of the fabricated magnetic pinning centers. The reversal in the direction of the vortex flow is explained by the interaction between the vortices trapped on the magnetic nanostructures and the interstitial vortices. The applied magnetic field and input current strength can tune both the polarity and magnitude of the rectified vortex flow. Our ratchet system is explained and modeled theoretically, taking the interactions between particles into consideration.     

镁及镁与芸苔素内酯配合对香蕉幼苗生长的影响

镁和芸苔素内酯是植物生长发育的重要营养与调节物质。通过对威廉斯香蕉苗期施用镁肥和芸苔素内酯进行研究,结果表明:镁肥和芸苔素内酯均能提高叶片抽生速度,促使假茎伸长、增粗和叶片增厚,并能提高单株干物质积累量;二者配施效果更明显。     

Study and application of non destructive methods used to determine quality of fruit and vegetables

在分析水果和蔬菜品质评估和控制的常规方法的基础上 ,分析研究了水果蔬菜的无损品质检测的新技术和方法 ,主要的技术有碰撞试验法、音频和声波振动法、X射线法、核磁共振法、图像分析法及激光技术等 研究了采用这些方法进行水果和蔬菜多种品质指标的无损检测新方法 ,为水果蔬菜的快速无损检测提供了方法和依据     

The structure of Mercury's magnetic field from MESSENGER's first flyby

During its first flyby of Mercury, the MESSENGER spacecraft measured the planet's near-equatorial magnetic field. The field strength is consistent to within an estimated uncertainty of 10% with that observed near the equator by Mariner 10. Centered dipole solutions yield a southward planetary moment of 230 to 290 nanotesla RM3 (where RM is Mercury's mean radius) tilted between 5 degrees and 12 degrees from the rotation axis. Multipole solutions yield non-dipolar contributions of 22% to 52% of the dipole field magnitude. Magnetopause and tail currents account for part of the high-order field, and plasma pressure effects may explain the remainder, so that a pure centered dipole cannot be ruled out.     

Learning in normal and mutant Drosophila larvae

Adult Drosophila melanogaster have previously been conditioned with shock to avoid various odors. In these experiments, larvae also sensed airborne odorants, responded to electric shock, and learned. Larval behavior paralleled adult behavior for (i) a mutant, smellblind, which failed to respond to odorants; (ii) three mutants, dunce, turnip, and cabbage, which were deficient in olfactory learning ability; and (iii) a mutant heterozygote, turnip/+, which learned but also forgot rapidly.     

Kepler-16: a transiting circumbinary planet

We report the detection of a planet whose orbit surrounds a pair of low-mass stars. Data from the Kepler spacecraft reveal transits of the planet across both stars, in addition to the mutual eclipses of the stars, giving precise constraints on the absolute dimensions of all three bodies. The planet is comparable to Saturn in mass and size and is on a nearly circular 229-day orbit around its two parent stars. The eclipsing stars are 20 and 69% as massive as the Sun and have an eccentric 41-day orbit. The motions of all three bodies are confined to within 0.5° of a single plane, suggesting that the planet formed within a circumbinary disk.