858 research outputs found
Density functional approach to the band gaps of finite and periodic two-dimensional systems
No full textWe present an approach based on density functional theory for the calculation of fundamental gaps of both finite and periodic two-dimensional (2D) electronic systems. The computational cost of our approach is comparable to that of total energy calculations performed via standard semilocal forms. We achieve this by replacing the 2D local density approximation with a more sophisticated - yet computationally simple - orbital-dependent modeling of the exchange potential within the procedure by Guandalini et al. [Phys. Rev. B 99, 125140 (2019)2469-995010.1103/PhysRevB.99.125140]. We showcase promising results for semiconductor 2D quantum dots and artificial graphene systems, where the band structure can be tuned through, e.g., Kekulé distortion
Density functional approach to the band gaps of finite and periodic two-dimensional systems
No full textWe present an approach based on density functional theory for the calculation of fundamental gaps of both finite and periodic two-dimensional (2D) electronic systems. The computational cost of our approach is comparable to that of total energy calculations performed via standard semilocal forms. We achieve this by replacing the 2D local density approximation with a more sophisticated—yet computationally simple—orbital-dependent modeling of the exchange potential within the procedure by Guandalini et al. [Phys. Rev. B 99, 125140 (2019)]. We showcase promising results for semiconductor 2D quantum dots and artificial graphene systems, where the band structure can be tuned through, e.g., Kekulé distortion
Ipotesi sugli eventi distruttivi rilevati nell’insediamento romano di Montegibbio
No full textPresso la località il Poggio, circa 500 m a N del castello di Montegibbio, in Comune di Sassuolo (Provincia di Modena), la Soprintendenza per i Beni Archeologici dell’Emilia-Romagna ha portato alla luce i resti di una sequenza di insediamenti di età romana (da una villa urbano – rustica del I secolo a. C. sino ad un insediamento del VI secolo d. C.). Una parte delle strutture presentano evidenze di lesioni di rilevante entità, che possono aver portato alla distruzione e al successivo abbandono degli insediamenti stessi. L’edificio più antico rinvenuto negli scavi del 2008, sul quale si focalizza prevalentemente il nostro contributo, aveva un pavimento in opus signinum e un’elevazione in ciottoli e blocchi, talora debolmente arrotondati, e in laterizio.
L’obbiettivo di questo lavoro è di indagare le possibili cause che possono avere provocato le deformazioni rinvenute nelle strutture e ricostruire la sequenza di eventi ambientali che hanno accompagnato la vita e l’abbandono dell’insediamento romano di Montegibbio. Le ipotesi di lavoro che sono state hanno la finalità di rispondere a due domande, ovvero:
• Quali tipologie di eventi possono essere stati responsabili delle deformazioni osservabili sulle strutture? Tali eventi possono essere tanto di origine naturale (dissesto per frana, terremoto, erosione s.l., creep, cedimento e consolidazione dei terreni di fondazione), tanto di origine antropica (cedimento strutturale, asportazioni successive di materiale dovute in particolare alle lavorazioni agricole);
• Quanti eventi si sono eventualmente susseguiti? Si tratta di un solo evento che ha lesionato tutte le strutture o si tratta di una serie di dissesti? E nel secondo caso, i dissesti sono tutti della stessa natura o di natura differente?
Le problematiche esposte sono state affrontate con un approccio multidisciplinare, che vede l’integrazione di diverse discipline oltre all’Archeologia, tra cui la Geologia e la Geologia Applicata
Zanfrognini e Guandalini: il nodo del 1932-33 e le prospettive della filosofia a Modena nel primo Novecento
No full textL'articolo presenta i risultati di una indagine su materiali di archivio e documentazione dell'epoca per definire i rapporti tra il filosofo Pietro Zanfrognini e lo scrittore ed editore Ugo Guandalini nella genesi della casa editrice Guanda tra il 1932 e il 1933. All'incrocio tra rapporti personali, impostazione del programma editoriale e elaborazione dei rispettivi "Cristianesimo e psicanalisi" (Zanfrognini) e "Adamo" (Guanda), il saggio indaga la relazione tra filosofia religione e psicanalisi, nonché le specifiche intuizioni sull'estetica della pittura, che si vengono così delineando, anche come momento della cultura filosofica a Modena e nell'Italia tra anni Venti e Trenta
Motor responses mediated by orthodromic and antidromic activation of the rostral portion of the cat corpus callosum
No full textThe effects of microstimulation of the rostral portion of the corpus callosum (CC) were examined in seven chronic cats submitted to either unilateral motor cortex ablation (5 preparations) or transection of the rostral two thirds of the CC (2 preparations) in order to identify the routes (ortho- or antidromic) followed by callosal impulses to provoke the motor effects. As in intact animals, motor responses in lesioned preparations consisted of very localized contractions of shoulder, whisker, or eyelid muscles, according to the stimulated sites. Unlike intact animals in which motor responses upon CC microstimulation were bilateral and symmetrical (Spidalieri and Guandalini 1983), in lesioned preparations they appeared contralaterally to the emitting hemisphere, i.e., they were contralateral to the stimulated callosal stump (split-brain preparations) and ipsilateral to the side of the cortical lesion (preparations with unilateral motor cortex ablation), regardless of the current intensity applied (up to a maximum of 50 microA). The unilateral motor responses occurred by the first day after lesion and persisted for the duration of the experiments which lasted to a month or more. Since orthograde degeneration of callosal fibres deprived of their somata has been shown by previous anatomical studies to be complete within 11 days after lesion, these results indicate that selective antidromic activation of callosal fibres is capable of eliciting motor responses. Thresholds for the motor effects in lesioned preparations proved to be from 1.3 to 3.9 (mean, = 2.4 +/- 0.7 SD) times higher than those found before motor cortex ablation. By 18 days after lesion a decrease of threshold currents for the motor responses was observed ranging from 6 to 37% (mean, = 24.2 +/- 13.6 SD), depending on the stimulated sites, relative to values previously found. The shortest train duration and the lowest frequency for minimum threshold were longer (40 vs. 30 ms) and higher (400 vs. 300 Hz), respectively in lesioned preparations than in intact controls. Moreover, a decrease in train duration or frequency provoked larger threshold increases in lesioned preparations than those observed in intact animals. As a whole, these results suggest that in intact animals the motor effects are also mediated by orthodromic callosal volleys
The corticocortical projections of the physiologically defined eye field in the rat medial frontal cortex
No full textThis study investigated in the rat the corticortical projections of the frontal eye fielf (FEF), which is located in the medial frontal cortex. The experiments were carried out on Wistar rats. Seven animals received a single iontophoretic injection of Phaseolus vulgaris leucoagglutinin in an FEF site within the medial frontal cortex where intracortical microstimulation elicited eye movements. In these cases, anterogradely labeled fibers and terminal-like elements were found in both hemispheres. The densest labeling was seen in the injected hemisphere, where labeled fibers prevailed in the visual cortex and their laminar distribution differed between the primary and secondary visual cortices. Dense labeled fibers were also seen in the frontal and retrosplenial cortex, whereas a columnar arrangiament of terminal-like elements was detected in a restricted part of area 1 of the somatosensory cortex. Contralaterally to the injection site, labeled fibers were distributed mainly in the homotopic region. In wo animals, the tracer was injected in a site at the FEF border whose stimulation evoked eye and whisker movements. In these animals, a different distribution of labeling was observed with respect to the other rats in which the tracer was deposited within the FEF, and anterograde labeling was observed in areas 1 and 2 of the parietal cortex of both hemispheres; in addition, no labeling was observed in these cases in the primary visual cortex. These findings suggest that cortical sites confined within the rat FEF are implicated in the control of orienting and exploring behaviors in addition to the control of eye movement
The efferent connections of the pupillary constriction area in the rat medial frontal cortex
No full textThis study investigated, in the rat, the efferent projections of the pupillary constriction area, which is located within the medial frontal cortex. In order to identify the location of the pupillary constriction area, in preliminary experiments the medial frontal cortex was microstimulated. Intracortical microstimulation elicited pupillary constriction in a thin strip of cortex the interhemispheric fissure and bordering the frontal eye field and vibrissae area of the somatomotor cortex. Seven animals received a single iontophoretic injection of Phaseolus vulgaris leucoagglutinin in the pupillary constriction area. In these cases, anterogradely labelled fibres and terminal-like elements were found in both hemispheres. The densest labeling was seen in several areas of the injected hemisphere, were labeled fibers prevailed in the secondary visual cortex. Dense labeled fibers were also found in the retrosplenial and cingulate cortex. In the thalamus, labeled fibers were seen in the intralaminar nuclei and posterior nuclear group. In the midbrain and pons, labeled fibers were located in the anterior pretectal area, superior colliculus and in the dorsolateral portion of the central gray. Contralaterally to the injection site, labeled fibers were distributed in the homotopic region. These findings led us to assume that, in the medial frontal cortex of the rat, besides controlling pupillary constriction, the pupillary constriction area may also be involved in controlling orientation and exploring behavior
“Potential carbon efficiency” as a new index to track the performance of biofuels production processes
No full textIn a carbon constrained economy which targets a massive reduction of the CO2 emissions, biogenic carbon is bound to be a scarce resource with high economic value. In such scenario, the carbon efficiency may become the key performance index to represent the revenues of the biomass-to-X conversion plants. In this work, the potential carbon efficiency (PCE) indicator is defined to quantify the achievable carbon efficiency (i.e. the amount of carbon contained in the final product with respect to the available input carbon), of a stream or of a process unit. Compared to the conventional carbon efficiency (CE), that is affected only by the separation/addition of carbon-containing species, the PCE allows quantifying the potential variation of the achievable carbon efficiency in process units where no carbon separation occurs, but where a limiting element is added (e.g. hydrogen through steam addition) or oxygen content is increased (e.g. oxygen injection in a reformer). The difference between the CE and the PCE along a biomass conversion process is typically due to the excess of oxygen atoms in the syngas, which is removed as CO2 in the syngas conditioning unit. Therefore, the difference between CE and PCE shows the potential gain in carbon efficiency that can be obtained by the addition of H2 from an electrolysis process. In this paper, the PCE and the CE have been calculated along the process units of different biomass-to-X plants. The selected case studies allow comparing different gasification technologies (direct gasification, indirect gasification and sorption enhanced gasification) in plants for the production of methanol and synthetic natural gas, showing how CE and PCE are influenced by process units such as the gasification technology, syngas reforming, syngas conditioning and hydrogen addition
Flexible methanol and hydrogen production from biomass gasification with negative emissions
No full textBioenergy plants with carbon capture and storage have been recently receiving attention as negative emission technologies. In this work, a techno-economic analysis of bio-methanol and bio-hydrogen production plants coupled with carbon capture and storage is conducted. The plants include different gasification technologies (direct oxygen-blown gasification and indirect gasification) and different CO2 capture processes (pre-combustion MDEA-based and post-combustion MEA-based CO2 capture) from different streams, to achieve increasing CO2 capture rates at increasing marginal costs. Moreover, an assessment of the economic impact of multi-product plants which flexibly produce methanol and hydrogen is carried out. Overall fuel production efficiencies of between 65.1 and 68.1% have been computed in all cases, showing a little dependency of energy efficiency on the gasification technology and the final product. In methanol production plants, a CO2 capture rate of between 26 and 55%, depending on the gasification technology, can be reached via a pre-combustion capture process at a cost of 41-46 euro per tCO2. In hydrogen production plants, between 64 and 90% capture efficiency can be reached at a cost of 52-56 euro per tCO2. Higher CO2 capture efficiency, resulting in CO2 residual emissions below 2% of the inlet carbon, can be achieved via post-combustion capture with a marginal cost of 98-205 euro per tCO2 and an average cost of 47-77 euro per tCO2. Flexible methanol-H2 production plants result in the highest capex and the highest LCOF. However, when considering the time-dependent H2 market price, the internal rate of return of flexible methanol-H2 plants is slightly higher or slightly lower than that of the corresponding best single-product plant. On the other hand, multi-product flexible plants are never the worst case scenario despite the highest investment costs, thus offering a potential advantage from the financial risk perspective thanks to lower exposure to market price volatility
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