A rigid trans-spanning dinitrile ligand.

A rigid dinitrile ligand was synthesized from two xanthene units condensed to a naphthalene-1,4,5,8-diimide spacer. The rigidity and C shape of the ligand gave exclusively trans complexes with Pd(II), Ag(I), and Au(I). Evidence for complexation, coordination geometry, and stoichiometry was provided by a combination of 1H NMR, 19F NMR, and IR spectroscopy. The AuBF4 and PdCl2 complexes were shown to have a 1:1 (metal-to-ligand) stoichiometry and the AgBF4 complex was shown to have a 1:2 stoichiometry in solution. The preorganization of the dinitrile ligand resulted in complexes much more stable than their monodentate counterparts.

N2 fixation in marine heterotrophic bacteria: dynamics of environmental and molecular regulation.

Molecular and immunological techniques were used to examine N2 fixation in a ubiquitous heterotrophic marine bacterium, the facultative anaerobic Vibrio natriegens. When batch cultures were shifted from aerobic N-replete to anaerobic N-deplete conditions, transcriptional and post-translational regulation of N2 fixation was observed. Levels of nifHDK mRNA encoding the nitrogenase enzyme were highest at 140 min postshift and undetectable between 6 and 9 h later. Immunologically determined levels of nitrogenase enzyme (Fe protein) were highest between 6 and 15 h postshift, and nitrogenase activity peaked between 6 and 9 h postshift, declining by a factor of 2 after 12-15 h. Unlike their regulation in cyanobacteria, Fe protein and nitrogenase activity were present when nifHDK mRNA was absent in V. natriegens, indicating that nitrogenase is stored and stable under anaerobic conditions. Both nifHDK mRNA and Fe protein disappeared within 40 min after cultures were shifted from N2-fixing conditions (anaerobic, N-deplete) to non- N2-fixing conditions (aerobic, N-enriched) but reappeared when shifted to conditions favoring N2 fixation. Thus, unlike other N2-fixing heterotrophic bacteria, nitrogenase must be resynthesized after aerobic exposure in V. natriegens. Immunological detection based on immunoblot (Western) analysis and immunogold labeling correlated positively with nitrogenase activity; no localization of nitrogenase was observed. Because V. natriegens continues to fix N2 for many hours after anaerobic induction, this species may play an important role in providing "new" nitrogen in marine ecosystems.

Azotobacter vinelandii NIFL is a flavoprotein that modulates transcriptional activation of nitrogen-fixation genes via a redox-sensitive switch.

The NIFL regulatory protein controls transcriptional activation of nitrogen fixation (nif) genes in Azotobacter vinelandii by direct interaction with the enhancer binding protein NIFA. Modulation of NIFA activity by NIFL, in vivo occurs in response to external oxygen concentration or the level of fixed nitrogen. Spectral features of purified NIFL and chromatographic analysis indicate that it is a flavoprotein with FAD as the prosthetic group, which undergoes reduction in the presence of sodium dithionite. Under anaerobic conditions, the oxidized form of NIFL inhibits transcriptional activation by NIFA in vitro, and this inhibition is reversed when NIFL is in the reduced form. Hence NIFL is a redox-sensitive regulatory protein and may represent a type of flavoprotein in which electron transfer is not coupled to an obvious catalytic activity. In addition to its ability to act as a redox sensor, the activity of NIFL is also responsive to adenosine nucleotides, particularly ADP. This response overrides the influence of redox status on NIFL and is also observed with refolded NIFL apoprotein, which lacks the flavin moiety. These observations suggest that both energy and redox status are important determinants of nif gene regulation in vivo.

Oxygen as a key developmental regulator of Rhizobium meliloti N2-fixation gene expression within the alfalfa root nodule.

The symbiotic pattern of expression of Rhizobium meliloti N2-fixation genes is tightly coupled with the histological organization of the alfalfa root nodule and thus is under developmental control. N2-fixation gene expression is induced very sharply at a particular zone of the nodule called interzone II-III that precedes the zone where N2 fixation takes place. We show here that this coupling can be disrupted, hereby resulting in ectopic expression of N2-fixation genes in the prefixing zone II of the nodule. Uncoupling was obtained either by using a R. meliloti strain in which a mutation rendered N2-fixation gene expression constitutive with respect to oxygen in free-living bacterial cultures or by placing nodules induced by a wild-type R. meliloti strain in a microoxic environment. These results implicate oxygen as a key determinant of the symbiotic pattern of N2-fixation gene expression.

Chloroplast gene sequence data suggest a single origin of the predisposition for symbiotic nitrogen fixation in angiosperms.

Of the approximately 380 families of angiosperms, representatives of only 10 are known to form symbiotic associations with nitrogen-fixing bacteria in root nodules. The morphologically based classification schemes proposed by taxonomists suggest that many of these 10 families of plants are only distantly related, engendering the hypothesis that the capacity to fix nitrogen evolved independently several, if not many, times. This has in turn influenced attitudes toward the likelihood of transferring genes responsible for symbiotic nitrogen fixation to crop species lacking this ability. Phylogenetic analysis of DNA sequences for the chloroplast gene rbcL indicates, however, that representatives of all 10 families with nitrogen-fixing symbioses occur together, with several families lacking this association, in a single clade. This study therefore indicates that only one lineage of closely related taxa achieved the underlying genetic architecture necessary for symbiotic nitrogen fixation in root nodules.

A note on the periodic orbits of a self excited rigid body

The aim of the present paper is to study the periodic orbits of a perturbed self excited rigid body with a fixed point. For studying these periodic orbits we shall use averaging theory of first order.

Fixation pattern analysis with microperimetry in nystagmus patients

Objective: To assess the usefulness of microperimetry (MP) as an additional objective method for characterizing the fixation pattern in nystagmus. Design: Prospective study. Participants: Fifteen eyes of 8 subjects (age, 12–80 years) with nystagmus from the Lluís Alcanyís Foundation (University of Valencia, Spain) were included. Methods: All patients had a comprehensive ophthalmologic examination including a microperimetric examination (MAIA, CenterVue, Padova, Italy). The following microperimetric parameters were evaluated: average threshold (AT), macular integrity index (MI), fixating points within a circle of 1° (P1) and 2° of radius (P2), bivariate contour ellipse area (BCEA) considering 63% and 95% of fixating points, and horizontal and vertical axes of that ellipse. Results: In monocular conditions, 6 eyes showed a fixation classified as stable, 6 eyes showed a relatively unstable fixation, and 3 eyes showed an unstable fixation. Statistically significant differences were found between the horizontal and vertical components of movement (p = 0.001), as well as in their ranges (p < 0.001). Intereye comparison showed differences between eyes in some subjects, but only statistically significant differences were found in the fixation coordinates X and Y (p < 0.001). No significant intereye differences were found between microperimetric parameters. Between monocular and binocular conditions, statistically significant differences in the X and Y coordinates were found in all eyes (p < 0.02) except one. No significant differences were found between MP parameters for monocular or binocular conditions. Strong correlations of corrected distance visual acuity (CDVA) with AT (r = 0.812, p = 0.014), MI (r = –0.812, p = 0.014), P1 (r = 0.729, p = 0.002), horizontal diameter of BCEA (r = –0.700, p = 0.004), and X range (r = –0.722, p = 0.005) were found. Conclusions: MP seems to be a useful technology for the characterization of the fixation pattern in nystagmus, which seems to be related to the level of visual acuity achieved by the patient.

3D Visual Data-Driven Spatiotemporal Deformations for Non-Rigid Object Grasping Using Robot Hands

Sensing techniques are important for solving problems of uncertainty inherent to intelligent grasping tasks. The main goal here is to present a visual sensing system based on range imaging technology for robot manipulation of non-rigid objects. Our proposal provides a suitable visual perception system of complex grasping tasks to support a robot controller when other sensor systems, such as tactile and force, are not able to obtain useful data relevant to the grasping manipulation task. In particular, a new visual approach based on RGBD data was implemented to help a robot controller carry out intelligent manipulation tasks with flexible objects. The proposed method supervises the interaction between the grasped object and the robot hand in order to avoid poor contact between the fingertips and an object when there is neither force nor pressure data. This new approach is also used to measure changes to the shape of an object’s surfaces and so allows us to find deformations caused by inappropriate pressure being applied by the hand’s fingers. Test was carried out for grasping tasks involving several flexible household objects with a multi-fingered robot hand working in real time. Our approach generates pulses from the deformation detection method and sends an event message to the robot controller when surface deformation is detected. In comparison with other methods, the obtained results reveal that our visual pipeline does not use deformations models of objects and materials, as well as the approach works well both planar and 3D household objects in real time. In addition, our method does not depend on the pose of the robot hand because the location of the reference system is computed from a recognition process of a pattern located place at the robot forearm. The presented experiments demonstrate that the proposed method accomplishes a good monitoring of grasping task with several objects and different grasping configurations in indoor environments.

Evaluation of sampling method effects in 3D non-rigid registration

Since the beginning of 3D computer vision problems, the use of techniques to reduce the data to make it treatable preserving the important aspects of the scene has been necessary. Currently, with the new low-cost RGB-D sensors, which provide a stream of color and 3D data of approximately 30 frames per second, this is getting more relevance. Many applications make use of these sensors and need a preprocessing to downsample the data in order to either reduce the processing time or improve the data (e.g., reducing noise or enhancing the important features). In this paper, we present a comparison of different downsampling techniques which are based on different principles. Concretely, five different downsampling methods are included: a bilinear-based method, a normal-based, a color-based, a combination of the normal and color-based samplings, and a growing neural gas (GNG)-based approach. For the comparison, two different models have been used acquired with the Blensor software. Moreover, to evaluate the effect of the downsampling in a real application, a 3D non-rigid registration is performed with the data sampled. From the experimentation we can conclude that depending on the purpose of the application some kernels of the sampling methods can improve drastically the results. Bilinear- and GNG-based methods provide homogeneous point clouds, but color-based and normal-based provide datasets with higher density of points in areas with specific features. In the non-rigid application, if a color-based sampled point cloud is used, it is possible to properly register two datasets for cases where intensity data are relevant in the model and outperform the results if only a homogeneous sampling is used.