Diagnosing numerical Cherenkov instabilities in relativistic plasma simulations based on general meshes

Numerical Cherenkov radiation (NCR) or instability is a detrimental effect frequently found in electromagnetic particle-in-cell (EM-PIC) simulations involving relativistic plasma beams. NCR is caused by spurious coupling between electromagnetic-field modes and multiple beam resonances. This coupling may result from the slow down of poorly-resolved waves due to numerical (grid) dispersion and from aliasing mechanisms. NCR has been studied in the past for finite-difference-based EM-PIC algorithms on regular (structured) meshes with rectangular elements. In this work, we extend the analysis of NCR to finite-element-based EM-PIC algorithms implemented on unstructured meshes. The influence of different mesh element shapes and mesh layouts on NCR is studied. Analytic predictions are compared against results from finite-element-based EM-PIC simulations of relativistic plasma beams on various mesh types.Comment: 31 pages, 20 figure

Biosurfactants – potential and applications

Biosurfactants are molecules that exhibit pronounced surface and emulsifying activities, produced by a variety of microorganisms. A host of interesting features of biosurfactants, such as higher biodegradability, lower toxicity, and effectiveness at extremes of temperature, pH and salinity; have led to a wide range of potential applications in the fields of oil recovery, environmental bioremediation, food processing and medicine. In spite of the immense potential of biosurfactants, their use still remains limited, possibly due to their high production and extraction costs, low yields in production processes and lack of information on their toxicity towards human systems [1]. The use and potential commercial application of biosurfactants in the medical field has increased during the past decade [2]. Their antibacterial, antifungal and antiviral activities make them relevant molecules for applications in combating many diseases and as therapeutic agents. In addition their role as anti-adhesive agents against several pathogens indicates their utility as suitable anti-adhesive coating agents for medical insertional materials leading to a reduction of a large number of hospital infections without the use of synthetic drugs and chemicals. The most promising alternative to turn its production competitive for industrial applications is the knowledge of the genes involved in their biosynthesis. Identification and isolation of those genes will allow enhanced production. Furthermore, modification of those genes by genetic engineering will result in the production of novel biosurfactants with specific novel properties. Medicinal and therapeutic perspectives of biosurfactants applications and future research plans will be presented

Infrared spectroscopic studies of novel hydroxybisphosphonates and molecular modelling of their interaction with hydroxyapatite

Bisphosphonates (BPs) are a class of drugs widely used in the treatment of several metabolic bone disorders associated with increased bone resorption, including osteoporosis, Paget’s disease and metastic bone disease [1]. Although BPs can directly inhibit the cellular activity of osteoclasts, their ability to adsorb to bone mineral is also an important factor in determining their potency and duration of action [2]. In this study, we performed a molecular modelling analysis, by molecular mechanics, of the molecular structures of hydroxy(1H-indazol-3-yl)methylenediphosphonic acid (BP1; Figure 1a) and hydroxy(1-methyl-1H-indazol-3-yl)methylenediphosphonic acid (BP2; Figure 1b) and examined their interactions with hydroxyapatite (HA) by energy-minimising 50 different orientations for judiciously selected low energy conformers of each ligand at 10 Å from the mineral surface. We also calculated the vibrational spectra for each BP with semiempirical methods and compared then with FTIR spectra obtained experimentaly. The calculated interaction energies of the studied BPs with HA suggests that BP2 interacts stronger with hydroxyapatite than BP1. These results are in agreement with in vitro and in vivo studies of the 153Sm-BPs complexes. Complex 153Sm-BP2 showed, in vitro, higher HA binding than complex 153Sm-BP1. In vivo studies showed different farmacokinetics parameters with complex 153Sm-BP2 presenting initial higher levels of bone uptake than complex 153Sm-BP1, which concentration is increasing during the 24 h period studied

Biosurfactants production from cheese whey

Biosurfactants are molecules that exhibit pronounced surface and emulsifying activities, produced by a variety of microorganisms. A host of interesting features of biosurfactants, such as higher biodegradability, lower toxicity, and effectiveness at extremes of temperature, pH and salinity; have led to a wide range of potential applications in the fields of oil recovery, environmental bioremediation, food processing and medicine. In spite of the immense potential of biosurfactants, their use still remains limited, mainly due to their high production and extraction costs, low yields in production processes and lack of information on their toxicity towards human systems. However, the use of cheaper substrates and optimal growth and production conditions coupled with novel and efficient multistep downstream processing methods and the use of recombinant and mutant hyper producing microbial strains can make biosurfactant production economically feasible. Often, the amount and type of a raw material can contribute considerably to the production cost; it is estimated that raw materials account for 10 to 30% of the total production costs in most biotechnological processes. Thus, to reduce this cost it is desirable to use low-cost raw materials. One possibility explored extensively is the use of cheap and agro-based raw materials as substrates for biosurfactant production. A variety of cheap raw materials, including plant-derived oils, oil wastes, starchy substances, cheese whey and distillery wastes have been reported to support biosurfactant production. Future biosurfactant research should, therefore, be more focused on the economics of biosurfactant production processes, particularly through the use of alternative low-cost fermentative media. This review looks at the future perspectives of large-scale profitable production of biosurfactants