On a conjecture of Murty and Simon on diameter 2-critical graphs

A graph G is diameter 2-critical if its diameter is two, and the deletion of any edge increases the diameter. Murty and Simon conjectured that the number of edges in a diameter 2-critical graph of order n is at most n²/4 and that the extremal graphs are complete bipartite graphs with equal size partite sets. We use an association with total domination to prove the conjecture for the graphs whose complements have diameter three.     

Bodipy-diacrylate imaging probes for targeted proteins inside live cells

A bodipy probe was developed for site-specific labeling of tagged proteins inside live cells which displays a large spectral change upon covalent coupling to the designed peptide that contains two pairs of Arg-Cys.     

Comparison between heparin-conjugated fibrin and collagen sponge as bone morphogenetic protein-2 carriers for bone regeneration

Bone morphogenetic protein-2 (BMP-2) is used to promote bone regeneration. However, the bone regeneration ability of BMP-2 relies heavily on the delivery vehicle. Previously, we have developed heparin- conjugated fibrin (HCF), a vehicle for long-term delivery of BMP-2 and demonstrated that long-term delivery of BMP-2 enhanced its osteogenic efficacy as compared to short-term delivery at an equivalent dose. The aim of this study was to compare the bone-forming ability of the BMP-2 delivered by HCF to that delivered by clinically utilized BMP-2 delivery vehicle collagen sponge. An in vitro release profile of BMP-2 showed that HCF released 80% of the loaded BMP-2 within 20 days, whereas collagen sponge released the same amount within the first 6 days. Moreover, the BMP-2 released from the HCF showed significantly higher alkaline phosphatase activity than the BMP-2 released from collagen sponge at 2 weeks in vitro. Various doses of BMP-2 were delivered with HCF or collagen sponge to mouse calvarial defects. Eight weeks after the treatment, bone regeneration was evaluated by computed tomography, histology, and histomorphometric analysis. The dose of BMP-2 delivered by HCF to achieve 100% bone formation in the defects was less than half of the BMP-2 dose delivered by collagen sponge to achieve a similar level of bone formation. Additionally, bone regenerated by the HCF-BMP-2 had higher bone density than bone regenerated by the collagen sponge-BMP-2. These data demonstrate that HCF as a BMP-2 delivery vehicle exerts better osteogenic ability of BMP-2 than collagen sponge, a clinically utilized delivery vehicle.     

Ion dose and anneal temperature dependent studies of silicon implanted AlxGa1−xN

Electrical and optical activation studies of Al_xGa_1−xN (x = 0.11 and 0.21) implanted with silicon were made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1 × 10¹⁴ to 1 × 10¹⁵ cm⁻² at room temperature. The implanted samples were subsequently annealed from 1100 to 1300 °C for 20 min in a nitrogen environment. A maximum electrical activation efficiency of 91% was obtained for the Al_0.11Ga_0.89N implanted with the highest dose of 1 × 10¹⁵ cm⁻² even after annealing at 1150 °C. 100% activation efficiencies were successfully obtained for the Al_0.21Ga_0.79N samples after annealing at 1300 °C for both doses of 5 × 10¹⁴ and 1 × 10¹⁵ cm⁻². The mobility of the Si-implanted Al_xGa_1−xN increases with annealing temperature, and the highest mobilities are 109 and 98 cm²/V·s for Al_0.11Ga_0.89N and Al_0.21Ga_0.79N, respectively. The cathodoluminescence (CL) spectra for all the samples exhibited a sharp neutral-donor-bound exciton peak, and the CL intensity increases with annealing temperature, indicating successive improved implantation damage recovery as the annealing temperature is increased. These results provide the optimum annealing conditions for activation of implanted Si ions in Al_xGa_1−xN.     

Fully-connected networks with local connections

Fully-connected mesh networks with local connections are described. Each connector links only nearest neighbors of the node lattice and carries enough passive pass-through vias to provide direct one-to-one links between all the nodes. If the nodes form a one-dimensional ring, then each connector must contain at least N(N−1)/2 physical channels. However, if the nodes are arranged in a d-dimensional hyper-torus, the number of channels per connector drops to N(N ^1/d −1)/2, which scales much more favorably at large N. Such arrangements can provide fully-meshed connectivity when parts of the network are physically inaccessible or when the network needs to be scaled up in a modular fashion.     

Minimum Cost Homomorphism Dichotomy for Oriented Cycles

For digraphs D and H, a mapping f : V(D) → V(H) is a homomorphism of D to H if uv ∈ A(D) implies f(u) f(v) ∈ A(H). If, moreover, each vertex u ∈ V(D) is associated with costs c _i (u), i ∈ V(H), then the cost of the homomorphism f is ∑ _{u ∈V(D)} c _f(u)(u). For each fixed digraph H, we have the minimum cost homomorphism problem for H (abbreviated MinHOM(H)). The problem is to decide, for an input graph D with costs c _i (u), u ∈ V(D), i ∈ V(H), whether there exists a homomorphism of D to H and, if one exists, to find one of minimum cost. We obtain a dichotomy classification for the time complexity of MinHOM(H) when H is an oriented cycle. We conjecture a dichotomy classification for all digraphs with possible loops.     

Selective adhesion of intestinal epithelial cells on patterned films with amine functionalities formed by plasma enhanced chemical vapor deposition

Control of cell adhesion to surfaces is important to develop analytical tools in the areas of biomedical engineering. To control cell adhesiveness of the surface, we constructed a variety of plasma polymerized hexamethyldisiloxane (PPHMDSO) thin films deposited at the plasma power range of 10-100 W by plasma enhanced chemical vapor deposition (PECVD). The PPHMDSO film that was formed at 10 W was revealed to be resistant to cell adhesion. The resistance to cell adhesion is closely related to physicochemical properties of the film. Atomic force microscopic data show an increase in surface roughness from 0.52 nm to 0.74 nm with increasing plasma power. From Fourier transform infrared (FT-IR) absorption spectroscopy data, it was also determined that the methyl (-CH₃) peak intensity increases with increasing plasma power, whereas the hydroxyl (-OH) peak decreases. X-ray photoelectron spectroscopy data reveal an increase in C-O bonding with increasing plasma power. These results suggest that C-O bonding and hydroxyl (-OH) and methyl (-CH₃) functional groups play a critical part in cell adhesion. Furthermore, to enhance a diversity of film surface, we accumulated the patterned plasma polymerized ethylenediamine (PPEDA) thin film on the top of the PPHMDSO thin film. The PPEDA film is established to be strongly cell-adherent. This patterned two-layer film stacking method can be used to form the selectively limited cell-adhesive PPEDA spots over the adhesion-resistant surface.     

A Fluorogenic Probe for Cell Surface Phosphatidylserine Using an Intramolecular Indicator Displacement Sensing Mechanism

The detection of externalized phosphatidylserine (PS) on the cell surface is commonly used to distinguish between living, apoptotic, and necrotic cells. The tools of choice for many researchers to study apoptosis are annexin V‐fluorophore conjugates. However, the use of this 35 kDa protein is associated with several drawbacks, including temperature sensitivity, Ca²⁺ dependence, and slow binding kinetics. Herein, a fluorogenic probe for cell surface PS, P‐IID , is described, which operates by an intramolecular indicator displacement (IID) mechanism. An intramolecularly bound coumarin indicator is released in the presence of cell surface PS, leading to a fluorescence “turn‐on” response. P‐IID demonstrates superior performance when compared to annexin V, for both fluorescence imaging and flow cytometry. This allows P‐IID to be used in time‐lapse imaging of apoptosis using confocal laser scanning microscopy and demonstrates the utility of the IID mechanism in live cells.