Performance of cognitive stop-and-wait hybrid automatic repeat request in the face of imperfect sensing

The cognitive radio (CR) paradigm has the potential of improving the exploitation of the electromagnetic spectrum by detecting instantaneously unoccupied spectrum slots allocated to primary users (PUs). In order to support the process of spectrum reuse, we consider a CR scheme, which senses and opportunistically accesses a PU's spectrum for communication between a pair of nodes relying on the stop-and-wait hybrid automatic repeat request (SW-HARQ) protocol. This arrangement is represented by the cognitive SW-HARQ (CSW-HARQ), where the availability/unavailability of the PU's channel is modeled as a two-state Markov chain having OFF and ON states, respectively. Once the cognitive user (CU) finds that the PU's channel is available (i.e., in the OFF state), the CU transmits data over the PU channel's spectrum, while relying on the principles of SW-HARQ. We investigate both the throughput and the delay of CSW-HARQ, with a special emphasis on the impact of the various system parameters involved in the scenarios of both perfect and imperfect spectrum sensing. Furthermore, we analyze both the throughput as well as the average packet delay and end-to-end packet delay of the CSW-HARQ system. We propose a pair of analytical approaches: 1) the probability-based and 2) the discrete time Markov chain-based. Closed-form expressions are derived for both the throughput and the delay under the perfect and imperfect sensing environments that are validated by simulation. We demonstrate that the activity of PUs, the transmission reliability of the CU, and the sensing environment have a significant impact on both the throughput and the delay of the CR system

Impact of Training and Development on Organization Performance with Mediating Role of Intention to Quit as Human Resource Quality Cost

The study is focused on the analysis of the impact of the training and development efforts in the  Small  and Medium  Enterprises  of  Pakistan  on  the  intention  of  employees  to  leave  the organization  considering  it  as  an  expense  and  the  wastage  of  time  and  resources  by  the organization.  The  study  will  also  evaluate  the  ultimate  impact  of  the  intentions  of  the employees  on  the  performance  of  the  organization.  The salary  based  employees  of  the organizations  having  5 –  250  employees  have  been  selected  on  the  basis  of  stratified sampling  technique  for  the  data  collection  purposes.  Out  of 600  questionnaires  distributed, 290  were  returned  and  278  were  used  for  the  study.  The relationship of training and development and organization performance has been found to be positively mediated by the intention of employees to quit the organizations. The positive relationship might exist due to the  number  of  other  factors  like  inflation,  less  job  opportunities  existing  in  the  Pakistani context. The study will be highly significant for the practitioners in the SMEs, shifting their focus towards the increased training and development efforts

Chloramphenicol enhances Photosystem II photodamage in intact cells of the cyanobacterium Synechocystis PCC 6803.

The effect of chloramphenicol, an often used protein synthesis inhibitor, in photosynthetic systems was studied on the rate of Photosystem II (PSII) photodamage in the cyanobacterium Synechocystis PCC 6803. Light-induced loss of PSII activity was compared in the presence of chloramphenicol and another protein synthesis inhibitor, lincomycin, by measuring the rate of oxygen evolution in Synechocystis 6803 cells. Our data show that the rate of PSII photodamage was significantly enhanced by chloramphenicol, at the usually applied 200 μg mL-1 concentration, relative to that obtained in the presence of lincomycin. Chloramphenicol-induced enhancement of photodamage has been observed earlier in isolated PSII membrane particles, and has been assigned to the damaging effect of chloramphenicol-mediated superoxide production (Rehman et al. 2016, Front Plant Sci 7:479). This effect points to the involvement of superoxide as damaging agent in the presence of chloramphenicol also in Synechocystis cells. The chloramphenicol-induced enhancement of photodamage was observed not only in wild-type Synechocystis 6803, which contains both Photosystem I (PSI) and PSII, but also in a PSI-less mutant which contains only PSII. Importantly, the rate of PSII photodamage was also enhanced by the absence of PSI when compared to that in the wild-type strain under all conditions studied here, i.e., without addition and in the presence of protein synthesis inhibitors. We conclude that chloramphenicol enhances photodamage mostly by its interaction with PSII, leading probably to superoxide production. The presence of PSI is also an important regulatory factor of PSII photodamage most likely via decreasing excitation pressure on PSII

Numerical modelling of the effects of change in river channel morphology on flooding frequency in the Dijle valley, Belgium, using TELEMAC-2D modelling system

Hydrodynamic

Hydro-morphodynamic modelling of the Dijle Valley [Belgium] under land-use/land-cover changes

Hydrodynamic

The stress-induced SCP/HLIP family of small light-harvesting-like proteins (ScpABCDE) protects Photosystem II from photoinhibitory damages in the cyanobacterium Synechocystis sp. PCC 6803.

Small CAB-like proteins (SCPs) are single-helix light-harvesting-like proteins found in all organisms performing oxygenic photosynthesis. We investigated the effect of growth in moderate salt stress on these stress-induced proteins in the cyanobacterium Synechocystis sp. PCC 6803 depleted of Photosystem I (PSI), which expresses SCPs constitutively, and compared these cells with a PSI-less/ScpABCDE- mutant. SCPs, by stabilizing chlorophyll-binding proteins and Photosystem II (PSII) assembly, protect PSII from photoinhibitory damages, and in their absence electrons accumulate and will lead to ROS formation. The presence of 0.2 M NaCl in the growth medium increased the respiratory activity and other PSII electron sinks in the PSI-less/ScpABCDE- strain. We postulate that this salt-induced effect consumes the excess of PSII-generated electrons, reduces the pressure of the electron transport chain, and thereby prevents 1O2 production

Singlet oxygen damages the function of Photosystem II in isolated thylakoids and in the green alga Chlorella sorokiniana

Singlet oxygen (O-1(2)) is an important damaging agent, which is produced during illumination by the interaction of the triplet excited state pigment molecules with molecular oxygen. In cells of photosynthetic organisms O-1(2) is formed primarily in chlorophyll containing complexes, and damages pigments, lipids, proteins and other cellular constituents in their environment. A useful approach to study the physiological role of O-1(2) is the utilization of external photosensitizers. In the present study, we employed a multiwell plate-based screening method in combination with chlorophyll fluorescence imaging to characterize the effect of externally produced O-1(2) on the photosynthetic activity of isolated thylakoid membranes and intact Chlorella sorokiniana cells. The results show that the external O-1(2) produced by the photosensitization reactions of Rose Bengal damages Photosystem II both in isolated thylakoid membranes and in intact cells in a concentration dependent manner indicating that O-1(2) plays a significant role in photodamage of Photosystem II