Quadruple bonding between iron and boron in the BFe(CO)3- complex.

While main group elements have four valence orbitals accessible for bonding, quadruple bonding to main group elements is extremely rare. Here we report that main group element boron is able to form quadruple bonding interactions with iron in the BFe(CO)3- anion complex, which has been revealed by quantum chemical investigation and identified by mass-selected infrared photodissociation spectroscopy in the gas phase. The complex is characterized to have a B-Fe(CO)3- structure of C3v symmetry and features a B-Fe bond distance that is much shorter than that expected for a triple bond. Various chemical bonding analyses indicate that the complex involves unprecedented B≣Fe quadruple bonding interactions. Besides the common one electron-sharing σ bond and two Fe→B dative π bonds, there is an additional weak B→Fe dative σ bonding interaction. This finding of the new quadruple bonding indicates that there might exist a wide range of boron-metal complexes that contain such high multiplicity of chemical bonds

Seed removal on loess slopes in relation to runoff and sediment yield

Overland flow and sediment transport can carry away seeds at the soil surface and in the soil, cause a secondary seed dispersal event, lead to seed redistribution, and influence the spatial distribution of seedling renewal, which plays an important role in vegetation restoration and succession. The objectives of this study were to investigate the process of seed loss on loess slopes and its relationship to the yield of runoff and sediment, the effects of rainfall intensity, slope gradient and seed morphology on seed removal. Rainfall simulation experiments were carried out in 1 m(2) plots on 10 degrees, 15 degrees, 20 degrees and 25 degrees loess slopes for a 60-minute duration with intensities of 50 mm/h, 100 mm/h and 150 mm/h, respectively. A mixture of 75 seeds from 16 species on the Chinese hilly-gullied Loess Plateau had been placed in these plots, and we measured the number of seeds lost, the distance seeds displaced, the runoff rate and amount, and soil loss rate and amount. Results showed that the accumulated seed loss rates in the rainfall process were closely related to the corresponding sediment yield, and even more closely related to the runoff amount. The seed removal obviously increased with rainfall intensity but did not obviously change with slope gradient, and results varied among species. At 50 mm/h rainfall, there was almost no seed loss on the four slopes, but 30-45% of the seeds moved from their original position. However, 79.5% and 86.4% of the seeds were eroded at 100 mm/h and 150 mm/h, respectively. Of these, 46.9% and 20.4% of the seeds were displaced, and 32.6% and 66.0% of the seeds were lost. Total seed removal was also affected by the seed amount and position on slopes, species composition of the seeds, and slope length. It was suggested that seed removal during water erosion events can affect seed redistribution and, consequently, species composition and vegetation spatial distribution. (C) 2010 Elsevier B.V. All rights reserved

A Balanced Filtering Directional Coupler with Wide Common-Mode Suppression Based on Slotline Structure

In this paper, a balanced-to-balanced filtering directional coupler (FDC) that can realize a 3 dB coupling degree directional coupler with high isolation and directivity is proposed. The design of the proposed FDC is primarily based on microstrip/slotline transition structures, resonance structures, and odd–even mode phase velocity compensation structures. A U-type microstrip feed line integrated with a stepped-impedance slotline resonator is adopted at the input and output ports, which makes the differential-mode (DM) responses independent of the common-mode (CM) ones, and brings superior DM transmission and CM suppression. In addition, by loading the microstrip stub-loaded resonators (SLRs), a DM passband with sharp filtering performance is realized, and transmission zeros (TZs) can be added into the design, which makes it more selective. Moreover, phase compensating slotlines are added into the coupling structure to enhance the isolation. In order to verify the feasibility of the proposed design method, an FDC prototype circuit was made and tested. The simulation results are in good agreement with the measured results. The designed coupler’s DM operating band covers 2.65 GHz to 3 GHz (FBW = 12.4%), and the insertion and return losses are 4.6 dB and 20 dB, respectively. The isolation degree is better than 15 dB, and the CM suppression is more than 55 dB. The total coupler size is about 67.7 mm × 63.8 mm. The designed balanced-to-balanced FDC can be widely used in S-band wireless communication systems