Fracture mechanics of laser sintered cracked polyamide for a new method to induce cracks by additive manufacturing

This paper presents an experimental investigation on specimens manufactured by Selective Laser Sintering (SLS), with the purposes of giving designers advice when designing 3D printed parts, and laying the basis for a step forward in the field of fracture mechanics of 3D complex parts. The aim is to investigate the effect of building direction in Polyamide (PA) 3D printed samples and to assess whether a crack can be initiated directly from the sintering process for fracture mechanics study purposes. Six different configurations of Mode I Compact Tension (CT) specimens were manufactured and tested; the experiments were monitored by Digital Image Correlation (DIC) and fractured surfaces were analyzed using microscopy. Results showed that samples with better mechanical performance are those in which all the layers contain a portion of the crack. On the other hand, those with layers parallel to the crack plan offer a preferential pathway for the crack to propagate. DIC and fractography investigations showed that, under certain conditions, small-radius geometries, or too-close surfaces may glue depending on printer resolution. Experiments also showed that SLS is capable of printing specimens with internal cracks that can be used to study fracture mechanics of complex parts or parts with internal cracks

THE EFFECT OF FOUR FLAT PLATE REFLECTORS ON LIGHT ENERGY-HARVESTING SYSTEM CHARACTERISTICS

In this paper, the effect of four flat panel reflectors (bottom, top, left and right side reflectors) on the total light radiation on a small-size photovoltaic cell is analyzed. An analytical model for the determination of the optimum inclination angle of the reflectors with respect to the cell’s horizontal surface is presented. The optimal angle was calculated to be 66°. The calculated value was experimentally verified by measuring the short-circuit current of the cell. It was shown that the increase in the short-circuit current of the cell with reflectors in the optimal position was about 60% for the illumination levels between 10 lx and 1000 lx. The cell with reflectors was used to charge the primary capacitor in the energy harvesting circuitry of the wireless sensor node and it was demonstrated that the time needed for the cell to charge the primary capacitor could be reduced 35-40%. UTICAJ ČETIRI RAVNA REFLEKTORA NA KARAKTERISTIKE SISTEMA KOJI SE AUTONOMNO NAPAJA ENERGIJOM SVETLOSTIU radu je analiziran uticaj četiri ravna reflektora (donji, gornji, levi i desni bočni reflektor) na ukupno svetlosno zračenje koje dospeva na solarnu ćeliju malih dimenzija. Dat je analitički model za određivanje optimalnog nagibnog ugla reflektora u odnosu na horizontalnu ravan u kojoj se nalazi solarna ćelija. Izračunati optimalni ugao iznosi 66°. Izračunata vrednost je eksperimentalno proverena merenjem struje kratkog spoja solarne ćelije i pokazano je da povećanje struje kratkog spoja solarne ćelije sa reflektorima u optimalnom položaju iznosi oko 60% za nivo osvetljenosti između 10 lx i 1000 lx. Solarna ćelija je korišćena za punjenje primarnog kondenzatora samonapajajućeg senzora i pokazano je da vreme potrebno za punjenje primarnog kondenzatora može biti smanjeno od 35% do 40%. HIGHLIGHTSThe effect of four flat panel reflectors on the total light radiation on a small-size photovoltaic cell was analyzed;An analytical model for the determination of an optimum inclination angle of the reflectors with respect to the cell’s surface is presented;The optimal inclination angle of the reflectors was determined to be 66°;The reflectors in the optimal position could increase the cell’s short-circuit current up to 60%;The charging time of the primary capacitor was reduced for 35-40%

Insecticidal Activity of Sage (Salvia Officinalis) Essential Oil to Varroa Destructor (Acari: Varroidae) and Apis Mellifera (Hymenoptera: Apidae)

The need to find alternative systems of the fight against Varroa mite without application of chemicals and provide healthy bee products resulted in investigation of application of different plant essences to arthropod control. In order to perceive the sage essential oil (Salvia officinalis) bioactivity, contact residual toxicity of mites and bees was examined in the laboratory conditions. The chemical composition of essential oil was determined by standard GC and GC/MS methods. Different doses of the sage essential oil dissolved in acetone (0.1–10 μl/Petri dish) were applied in Petri dishes and left to dry for 20 minute at a room temperature. Following this period of time, ten honey bees and five adult female mites were added in each Petri dish and they were all maintained in controlled conditions (T = 30°C, Relative humidity = 60%). Survival of examined honey bees and Varroa mites was recorded two times, after 24 h and 48 h. The most prominent toxic effect on the examined Varroa mites was observed after 24 h and 48 h, with application of 10 μl of sage oil (the average values for dead mite individuals were 3.25 and 3.50, respectively). Recorded biological activities of the oil tested in different doses on both honey bee and Varroa mite revealed opportunity to proceed with further investigation by selecting the most appropriate variants and combinations of the most prominent individual components of the examined sage oil

Second harmonics and compensation effect in ceramic superconductors

A three-dimensional lattice of the Josephson junctions with a finite self-conductance is employed to model the ceramic superconductors. The nonlinear ac susceptibility and the compensation effect are studied by Monte Carlo simulations in this model. The compensation effect is shown to be due to the existence of the chiral glass phase. We demonstrate, in agreement with experiments, that this effect may be present in the ceramic superconductors which show the paramagnetic Meissner effect.Comment: 6 pages, latex, 4 figures, Phys. Rev. B (accepted

Polyphenol Content and Antioxidant Activity of Sour Cherries From Serbia

The aim of this study was to evaluate the content of phenolics: the total phenols (TP), flavonoids (TF), anthocyanins (TA), as well as the total antioxidant\ud capacity (TAC) in three sour cherry cultivars (Prunus cerasus L.) introduced to the southeast Serbia climate conditions. Among the investigated sour cherries,\ud „Oblačinska“ cultivar contained the highest amounts of all groups of phenolics, followed by „Cigančica“ > „Marela“. A significant difference were observed in the phenolic content among different cultivars and growing seasons (p  0.05), and the phenolic compounds were significantly higher in the growing season 2009. The examined cultivars possess a high antioxidant capacity, and all phenolics of highy correlation with TAC. The following compounds were identified and quantified using HPLC-DAD: 4 anthocyanins, the most abundant of which was cyanidin-3-glucoside in “Marela” and “Oblačinska”, and cyanidin-3-glucosylrutinoside in „Cigančica“, and 4 hydroxycinnamic acids, the most abundant of which was neochlorogenic acid in all sour cherry cultivars. The growing and ripening process on the tree of sour cherry cv. „Oblačinska“ was evaluated also. The results showed significant increases in total phenols during the ripening, the total anthocyanins and total antioxidant capacity and 4 quantified anthocyanins, however the neochlorogenic acid decreased during the ripening. The study indicated that the growing and climate conditions in southeast Serbia are convenient for introducing sour cherry cultivars.\u

Multigenic lentiviral vectors for combined and tissue-specific expression of miRNA- and protein-based antiangiogenic factors.

Lentivirus-based gene delivery vectors carrying multiple gene cassettes are powerful tools in gene transfer studies and gene therapy, allowing coexpression of multiple therapeutic factors and, if desired, fluorescent reporters. Current strategies to express transgenes and microRNA (miRNA) clusters from a single vector have certain limitations that affect transgene expression levels and/or vector titers. In this study, we describe a novel vector design that facilitates combined expression of therapeutic RNA- and protein-based antiangiogenic factors as well as a fluorescent reporter from back-to-back RNApolII-driven expression cassettes. This configuration allows effective production of intron-embedded miRNAs that are released upon transduction of target cells. Exploiting such multigenic lentiviral vectors, we demonstrate robust miRNA-directed downregulation of vascular endothelial growth factor (VEGF) expression, leading to reduced angiogenesis, and parallel impairment of angiogenic pathways by codelivering the gene encoding pigment epithelium-derived factor (PEDF). Notably, subretinal injections of lentiviral vectors reveal efficient retinal pigment epithelium-specific gene expression driven by the VMD2 promoter, verifying that multigenic lentiviral vectors can be produced with high titers sufficient for in vivo applications. Altogether, our results suggest the potential applicability of combined miRNA- and protein-encoding lentiviral vectors in antiangiogenic gene therapy, including new combination therapies for amelioration of age-related macular degeneration

Non-Fermi liquid behavior and scaling of low frequency suppression in optical conductivity spectra of CaRuO3_3

Optical conductivity spectra $\sigma_1(\omega)$ of paramagnetic CaRuO$_3$ are investigated at various temperatures. At T=10 K, it shows a non-Fermi liquid behavior of $\sigma_1(\omega)\sim 1/{\omega}^{\frac 12}$, similar to the case of a ferromagnet SrRuO$_3$. As the temperature ($T$) is increased, on the other hand, $\sigma_1(\omega)$ in the low frequency region is progressively suppressed, deviating from the 1/{\omega}^{\frac 12%}-dependence. Interestingly, the suppression of $\sigma_1(\omega)$ is found to scale with $\omega /T$ at all temperatures. The origin of the $$ scaling behavior coupled with the non-Fermi liquid behavior is discussed.Comment: 4 pages, 3 figure

Paramagnetic Meissner Effect in Multiply-Connected Superconductors

We have measured a paramagnetic Meissner effect in Nb-Al2O3-Nb Josephson junction arrays using a scanning SQUID microscope. The arrays exhibit diamagnetism for some cooling fields and paramagnetism for other cooling fields. The measured mean magnetization is always less than 0.3 flux quantum (in terms of flux per unit cell of the array) for the range of cooling fields investigated. We demonstrate that a new model of magnetic screening, valid for multiply-connected superconductors, reproduces all of the essential features of paramagnetism that we observe and that no exotic mechanism, such as d-wave superconductivity, is needed for paramagnetism.Comment: 4 pages, 3 figures, LaTe