The graphs which are cospectral with the generalized pineapple graph

Let $p, k, q$ be positive integers with $p\geqslant 4,$ $p-2 \geqslant k$ and let $K_{p,k}^{q}$ be the generalized pineapple graph which is obtained by joining independent set of $q$ vertices with $k$ vertices of a complete graph $K_{p}.$ In this paper, we determine all graphs which are cospectral with $K_{p,k}^{q}.$

Search for Osme Bonds With π Systems as Electron Donors

The Osme bond is defined as pairing a Group 8 metal atom as an electron acceptor in a noncovalent interaction with a nucleophile. DFT calculations with the ωB97XD functional consider MO4 (M = Ru, Os) as the Lewis acid, paired with a series of π electron donors C2H2 , C2H4 , C6H6 , C4H5N, C4H4O, and C4H4S. The calculations establish interaction energies in the range between 9.5 and 26.4 kJ/mol. Os engages in stronger interactions than does Ru, and those involving more extensive π-systems within the aromatic rings form stronger bonds than do the smaller ethylene and acetylene. Extensive analysis questions the existence of a true Osme bond, as the bonding chiefly involves interactions with the three O atoms of MO4 that lie closest to the π-system, via π(C-C)→σ*(M-O) transfers. These interactions are supplemented by back donation from M-O bonds to the π*(CC) antibonding orbitals of the π-systems. Dispersion makes a large contribution to these interactions, higher than electrostatics and much greater than induction

Instability of the Octarepeat Region of the Human Prion Protein Gene

Prion diseases are a family of unique fatal transmissible neurodegenerative diseases that affect humans and many animals. Sporadic Creutzfeldt-Jakob disease (sCJD) is the most common prion disease in humans, accounting for 85–90% of all human prion cases, and exhibits a high degree of diversity in phenotypes. The etiology of sCJD remains to be elucidated. The human prion protein gene has an octapeptide repeat region (octarepeats) that normally contains 5 repeats of 24–27 bp (1 nonapeptide and 4 octapeptide coding sequences). An increase of the octarepeat numbers to six or more or a decrease of the octarepeat number to three is linked to genetic prion diseases with heterogeneous phenotypes in humans. Here we report that the human octarepeat region is prone to either contraction or expansion when subjected to PCR amplification in vitro using Taq or Pwo polymerase and when replicated in wild type E. coli cells. Octarepeat insertion mutants were even less stable, and the mutation rate for the wild type octarepeats was much higher when replicated in DNA mismatch repair-deficient E.coli cells. All observed octarepeat mutants resulting from DNA replication in E.coli were contained in head-to-head plasmid dimers and DNA mfold analysis (http://mfold.rna.albany.edu/?q=mfold/DNA-Folding-Form) indicates that both DNA strands of the octarepeat region would likely form multiple stable hairpin structures, suggesting that the octarepeat sequence may form stable hairpin structures during DNA replication or repair to cause octarepeat instability. These results provide the first evidence supporting a somatic octarepeat mutation-based model for human sCJD etiology: 1) the instability of the octarepeat region leads to accumulation of somatic octarepeat mutations in brain cells during development and aging, 2) this instability is augmented by compromised DNA mismatch repair in aged cells, and 3) eventually some of the octarepeat mutation-containing brain cells start spontaneous de novo prion formation and replication to initiate sCJD

Carbene Triel Bonds Between TrR3 (Tr=B, Al) and N-Heterocyclic Carbenes

The carbene triel bond is predicted and characterized by theoretical calculations. The C lone pair of N‐heterocyclic carbenes (NHCs) is allowed to interact with the central triel atom of TrR3 (Tr = B and Al; R = H, F, Cl, and Br). The ensuing bond is very strong, with an interaction energy of nearly 90 kcal/mol. Replacement of the C lone pair by that of either N or Si weakens the binding. The bond is strengthened by electron‐withdrawing substituents on the triel atom, and the reverse occurs with substitution on the NHC. However, these effects do not strictly follow the typical pattern of F \u3e Cl \u3e Br. The TrR3 molecule suffers a good deal of geometric deformation, requiring on the order of 30 kcal/mol, in forming the complex. The R(C···Tr) bond is quite short, for example, 1.6 Å for Tr = B, and shows other indications of at least a partially covalent bond, such as a high electron density at the bond critical point and a good deal of intermolecular charge transfer

Effect of Carbon Hybridization in C—F Bond as an Electron Donor in Triel Bonds

The ability of the F atom of HC≡CF, H2C=CHF and H3CCH2F to serve as an electron donor to the triel (Tr) atom of TrR3 in the context of a triel bond is assessed by ab initio calculations. The triel bond formed by Csp3—F is strongest, as high as 30 kcal/mol, followed by Csp2—F, and then by Csp—F whose triel bonds can be as small as 1 kcal/mol. The noncovalent bond strength diminishes in the order Tr = Al \u3e Ga \u3e B, consistent with the intensity of the π-hole above the Tr atom in the monomer. The triel bond strength of the Al and Ga complexes increases along with the electronegativity of the R substituent but is largest for R=H when Tr=B. Electrostatics play the largest role in the stronger triel bonds, but dispersion makes an outsized contribution for the weakest such bonds

On-Farm-Produced Organic Amendments on Maintaining and Enhancing Soil Fertility and Nitrogen Availability in Organic or Low Input Agriculture

Maintaining and enhancing soil fertility are key issues for sustainability in an agricultural system with organic or low input methods. On-farm–produced green manure as a source of soil organic matter (SOM) plays a critical role in long-term productivity. But producing green manure requires land and water; thus, increasing biodiversity, such as by intercropping with green manure crops, could be an approach to enhance the efficiency of renewable resources especially in developing countries. This article discusses soil fertility and its maintenance and enhancement with leguminous intercropping from four points of view: soil fertility and organic matter function, leguminous green manure, intercropping principles, and soil conservation. Important contributions of leguminous intercropping include SOM enhancement and fertility building, biological nitrogen (N) and other plant nutrition availability. Under a well-designed and managed system, competition between the target and intercropping crops can be reduced. The plant uptake efficiency of biologically fixed N is estimated to be double that of industrial N fertilizers. After N-rich plant residues are incorporated into soil, the carbon (C):nitrogen ratio of added straw decreases. Another high mitigation potential of legume intercropping lies in soil conservation by preventing soil and water erosion. Many opportunities exist to introduce legumes in short-term rotation, intercropping, living mulch, and cover crops in an organically managed farm system. Worldwide, long-term soil fertility enhancement remains a challenge due to the current world population and agricultural practices. Cropping system including legumes is a step in the right direction to meeting the needs of food security and sustainability

CUPre: Cross-domain Unsupervised Pre-training for Few-Shot Cell Segmentation

While pre-training on object detection tasks, such as Common Objects in Contexts (COCO) [1], could significantly boost the performance of cell segmentation, it still consumes on massive fine-annotated cell images [2] with bounding boxes, masks, and cell types for every cell in every image, to fine-tune the pre-trained model. To lower the cost of annotation, this work considers the problem of pre-training DNN models for few-shot cell segmentation, where massive unlabeled cell images are available but only a small proportion is annotated. Hereby, we propose Cross-domain Unsupervised Pre-training, namely CUPre, transferring the capability of object detection and instance segmentation for common visual objects (learned from COCO) to the visual domain of cells using unlabeled images. Given a standard COCO pre-trained network with backbone, neck, and head modules, CUPre adopts an alternate multi-task pre-training (AMT2) procedure with two sub-tasks -- in every iteration of pre-training, AMT2 first trains the backbone with cell images from multiple cell datasets via unsupervised momentum contrastive learning (MoCo) [3], and then trains the whole model with vanilla COCO datasets via instance segmentation. After pre-training, CUPre fine-tunes the whole model on the cell segmentation task using a few annotated images. We carry out extensive experiments to evaluate CUPre using LIVECell [2] and BBBC038 [4] datasets in few-shot instance segmentation settings. The experiment shows that CUPre can outperform existing pre-training methods, achieving the highest average precision (AP) for few-shot cell segmentation and detection