Low temperature characterization of the photocurrent produced by two-photon transitions in a quantum dot intermediate band solar cell

Conceived to exceed the conversion efficiency of conventional photovoltaic devices, the intermediate band solar cell bases its operation on exploiting, besides the usual band-to-band optical transitions, the absorption of two sub-bandgap photons. For the present, the only technology used to implement an intermediate band in real devices has been the growth of an InAs/GaAs quantum dot superlattice. In practice, the obtained material shows two limitations: the narrow energy gap between conduction and intermediate band and the appearance of growth defects due to the lattice stress. The consequences are the presence of non-radiative recombination mechanisms and the thermal escape of electrons from the intermediate to the conduction band, hindering the splitting of the quasi-Fermi levels associated with the intermediate and conduction bands and the observation of photocurrent associated with the two-photon absorption. By reducing the temperature at which the devices are characterised we have suppressed the parasitic thermal mechanisms and have succeeded in measuring the photocurrent caused by the absorption of two below bandgap photons. In this work, the characterization of this photocurrent at low temperature is presented and discussed

WATER LOSS IN SMALL SETTLEMENTS / VANDENS NUOSTOLIAI MAŽOSE GYVENVIETĖSE

The main performance indicators of a water supply system include the quality and safety of water, continuous work, relevant pressure and small water loss. The majority of foreign and local projects on reducing water loss have been carried out in the water supply systems of metropolitans; however, the specificity of small settlements differs from that of big cities. Differences can be observed not only in the development of infrastructure and technical indicators but also in the features of water consumption. The article presents the analysis of water loss formation and describes reduction measures in a small settlement. The conducted research defines that water loss in big cities is much smaller than that in small settlements. The major part of water used in small settlements is applied for agrarian purposes rather than for domestic needs. It has been found that water is employed for the irrigation of plants and livestock watering, which often is not accounted. Research also shows that slight (<0.2 m³/h) physical water loss (holes in the network) that occur in small settlements may compose up to 30% of all water supplied to the water network. Santrauka Pagrindiniai vandens tiekimo sistemos efektyvumo rodikliai yra šie: vandens saugumas ir kokybė, nepertraukiamas darbas, tinkamas slėgis ir maži vandens nuostoliai. Absoliuti dauguma užsienio ir šalies vandens nuostolių mažinimo projektų buvo atlikta didmiesčių vandentiekiuose, tačiau mažų gyvenviečių specifika gerokai skiriasi nuo didžiųjų miestų. Skiriasi ne tik infrastruktūros lygis, techniniai rodikliai, bet ir vandens vartojimo ypatumai. Straipsnyje analizuojami vandens nuostolių susidarymas ir galimi mažinimo būdai mažose gyvenvietėse. Nustatyta, kad rajono centruose susidarantys vandens nuostoliai yra gerokai mažesni nei mažose gyvenvietėse. Didžioji dalis gyvenvietėse vartojamo vandens skirta augalams laistyti ir gyvuliams girdyti, o ne gyventojų buitiniams poreikiams tenkinti. Nustatyta, kad vanduo, naudojamas laistyti ir gyvuliams girdyti, dažnai nėra įtraukiamas į apskaitą. Nustatyta, kad mažų gyvenviečių vandentiekio tinkle susidarantys maži (<0,2 m³/h) fiziniai nuostoliai (pvz., dėl skylių tinkle), gali sudaryti daugiau nei 30 % viso į tinklą tiekiamo vandens kiekio. Reikšminiai žodžiai: vandens nuostoliai; vandens vartojimas; vandens apskaita

Determining spatial memory span: the role of movement time and articulation rate.

In studies of verbal memory span individual differences in speech rate have been found to predict the number of items that can be recalled in order. This is thought to happen because overt speech rate is related to the rate of internal verbal rehearsal. For spatial span there may also be an internal rehearsal system linked to overt responding, and if there is a strong analogy to be drawn between the verbal and spatial domains, then movement time between spatial targets should predict the number of spatial locations that can be recalled. In the first study reported, none of the six measures of movement time did predict spatial span, but, as expected, speech rate predicted verbal span. In addition, speech rate predicted spatial span. In a second study the use of articulatory suppression during span presentation showed that verbal span dropped, but was still predicted by speech rate. Spatial span was again predicted by the time it took to say digits rather than the time it took to make movements to spatial targets. There would not seem to be any simple analogy between the limitations on verbal span and those on spatial span. In addition, the relationship between speech rate and sequential memory performance may be more complex than previous studies have suggested

The Complexity of Checking Consistency of Pedigree Information and Related Problems

Consistency checking is a fundamental computational problem in genetics