89 research outputs found
The effects of foreknowledge and task-set shifting as mirrored in cue- and target-locked event-related potentials
The present study examined the use of foreknowledge in a task-cueing protocol while manipulating sensory updating and executive control in both, informatively and non-informatively pre-cued trials. Foreknowledge, sensory updating (cue switch effects) and task-switching were orthogonally manipulated in order to address the question of whether, and to which extent, the sensory processing of cue changes can partly or totally explain the final task switch costs. Participants responded faster when they could prepare for the upcoming task and if no task-set updating was necessary. Sensory cue switches influenced cue-locked ERPs only when they contained conceptual information about the upcoming task: frontal P2 amplitudes were modulated by task-relevant cue changes, mid-parietal P3 amplitudes by the anticipatory updating of stimulus-response mappings, and P3 peak latencies were modulated by task switching. Task preparation was advantageous for efficient stimulus-response re-mapping at target-onset as mirrored in target N2 amplitudes. However, N2 peak latencies indicate that this process is faster for all repeat trials. The results provide evidence to support a very fast detection of task-relevance in sensory (cue) changes and argue against the view of task repetition benefits as secondary to purely perceptual repetition priming. Advanced preparation may have a stronger influence on behavioral performance and target-locked brain activity than the local effect of repeating or switching the task-set in the current trial
Comparison of Transcritical and Subcritical Heat Pump Systems for Domestic Hot Water Production in Energy Recovery Applications
Water-to-Water heat pump (WtWHP) is an efficient alternative to the current technologies used in Domestic Hot Water (DHW) production. However, this application is characterized by high secondary temperature lifts and irregular demands that define critically its design. In order to maximize the efficiency, transcritical cycles coupled to stratified storage tank has been the preferred solution. Nevertheless, recently subcritical cycles with a subcooling control system has been also considered also as a promising alternative because of the cost with the right desing the efficiencies could be in the range of transcritical system. The objective of this work is to compare the performance of both heat pump systems for DHW production in a heat recovery application where there is no restriction in the low temperature energy source availability. This situation could correspond to a source coming from sewage water or a system of low temperature district heating. The comparison has been made for the optimum configuration of both system which has implied the definition of the proper control strategy, proper sizing of the WtWHP and the tank and incorporation of a primary recovery heat exchanger in order to compare both systems in what is considered as the optimum working conditions. Results show that while both systems are able to operate with similar SCOPs, the CO2 system is more sensitive to water temperature lifts variations and temperature of the heat source than the propane WtWHP resulting in lower performances
Middleware-Controlled Resource consumption for Location Traffic in Cellular Networks
Location is valuable information for services implemented in wireless networks. Location systems often use the infrastructure of cellular networks that have already been deployed. Accordingly, location systems spend resources of the network they use. This paper proposes a middleware to reduce the consumption of network resources and optimize the location traffic that is being carried. This middleware, called MILCO (Middleware for Location Cost Optimization), selects the optimum location technique depending on the request, i.e. the location technique that satisfies the quality of service (QoS) required and minimizes the resource operating expense. In addition, MILCO takes advantage of ongoing and carried location processes to reduce the overall expenditure of resources. Our results show that MILCO can reduce location-process failures and improve latency figures for location provisioning and resource use in cellular networks such as UMTS
Modelling and Simulation of the Impact of Soft Faults in a Reversible Air-to-water Propane Heat Pump
Validação da versão argentina do memory binding test (mbt) para a detecção precoce do transtorno cognitivo leve
Background: “Forgetfulness” is frequent in normal aging and characteristic of the early stages of dementia syndromes. The episodic memory test is central for detecting amnestic mild cognitive impairment (MCI). The Memory Binding Test (MBT) is a simple, easy and brief memory test to detect the early stage of episodic memory impairment. Objective: To validate the Argentine version of the MBT in a Latin American population and to estimate the diagnostic accuracy as a tool for early detection of MCI. Methods: 88 subjects (46 healthy controls and 42 patients with amnestic MCI) matched for age and educational level were evaluated by an extensive neuropsychological battery and the memory binding test. Results: A significantly better performance was detected in the control group; all MBT scales were predictive of MCI diagnosis (p<.01). The MBT showed high sensitivity (69%) and high specificity (88%), with a PPV of 93% and a NPV of 55% for associative paired recall. A statistically significant difference (c2 =14,164, p<.001) was obtained when comparing the area under the curve (AUC) of the MBT (0.88) and the MMSE (0.70). Conclusion: The Argentine version of the MBT correlated significantly with the MMSE and the memory battery and is a useful tool in the detection of MCI. The operating characteristics of the MBT are well suited, surpassing other tests commonly used for detecting MCI.“Esquecimento” Ă© queixa frequente no envelhecimento normal e tambĂ©m ocorre nos primeiros estágios de sĂndromes demenciais. Testes de memĂłria episĂłdica sĂŁo fundamentais para detectar comprometimento cognitivo amnĂ©stico (CCL). O teste de MemĂłria Associativa (Memory Binding Test-MBT) Ă© um teste fácil e breve para detectar a fase inicial de perda de memĂłria episĂłdica. Objetivo: Validar a versĂŁo argentina do MBT e estimar a sua acurácia como instrumento diagnĂłstico para a detecção precoce do CCL. MĂ©todos: 88 indivĂduos (46 controles saudáveis e 42 pacientes com CCL amnĂ©stico), emparelhados por idade e nĂvel educacional, foram avaliados com extensa bateria neuropsicolĂłgica e o MBT. Resultados: Um desempenho significativamente melhor foi detectada no grupo controle; todas as escalas do MBT foram preditivas do diagnĂłstico de CCL (p<0,01). O MBT apresentou alta sensibilidade (69%) e alta especificidade (88%), com valor preditivo (VP) positivo de 93% e e VP negativo de 55% para a recordação dos itens associados (associative paired recall). Diferença estatisticamente significativa (c2 =14,164, p<0,001) foi obtida quando foram comparadas as áreas sob as curvas (AUC) do MBT (0,88) e o Mini-Exame do Estado Mental (MEEM) (0,70). ConclusĂŁo: A versĂŁo argentina do MBT correlacionou-se significativamente com o MEEM e com a bateria de memĂłria e Ă© uma ferramenta Ăştil na detecção de CCL. As caracterĂsticas operacionais do MBT sĂŁo bem adequadas, superando outros testes usualmente utilizados para a detecção de CCL.Fil: Román, Fabián. Gobierno de la Ciudad de Buenos Aires. Hospital "Dr. Abel Zubizarreta"; Argentina. Universidad de la Costa.; ColombiaFil: Iturry, MĂłnica Liliana. Gobierno de la Ciudad de Buenos Aires. Hospital "Dr. Abel Zubizarreta". Servicio de NeurologĂa. Laboratorio de InvestigaciĂłn de la Memoria; ArgentinaFil: Rojas, ZenĂłn Galeno. Gobierno de la Ciudad de Buenos Aires. Hospital "Dr. Abel Zubizarreta". Servicio de NeurologĂa. Laboratorio de InvestigaciĂłn de la Memoria; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Barcelo, Ernesto. Universidad de la Costa.; ColombiaFil: Buschke, Herman. Albert Einstein College of Medicine; Estados UnidosFil: Allegri, Ricardo Francisco. Universidad de la Costa.; Colombia. FundaciĂłn para la Lucha contra las Enfermedades NeurolĂłgicas de la Infancia; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
Fundamental limitations on "warp drive" spacetimes
"Warp drive" spacetimes are useful as "gedanken-experiments" that force us to
confront the foundations of general relativity, and among other things, to
precisely formulate the notion of "superluminal" communication. We verify the
non-perturbative violation of the classical energy conditions of the Alcubierre
and Natario warp drive spacetimes and apply linearized gravity to the
weak-field warp drive, testing the energy conditions to first and second order
of the non-relativistic warp-bubble velocity. We are primarily interested in a
secondary feature of the warp drive that has not previously been remarked upon,
if it could be built, the warp drive would be an example of a "reaction-less
drive". For both the Alcubierre and Natario warp drives we find that the
occurrence of significant energy condition violations is not just a high-speed
effect, but that the violations persist even at arbitrarily low speeds.
An interesting feature of this construction is that it is now meaningful to
place a finite mass spaceship at the center of the warp bubble, and compare the
warp field energy with the mass-energy of the spaceship. There is no hope of
doing this in Alcubierre's original version of the warp-field, since by
definition the point in the center of the warp bubble moves on a geodesic and
is "massless". That is, in Alcubierre's original formalism and in the Natario
formalism the spaceship is always treated as a test particle, while in the
linearized theory we can treat the spaceship as a finite mass object. For both
the Alcubierre and Natario warp drives we find that even at low speeds the net
(negative) energy stored in the warp fields must be a significant fraction of
the mass of the spaceship.Comment: 18 pages, Revtex4. V2: one reference added, some clarifying comments
and discussion, no physics changes, accepted for publication in Classical and
Quantum Gravit
Usefulness of discriminability and response bias indices for the evaluation of recognition memory in mild cognitive impairment and Alzheimer disease
Background: Most studies examining episodic memory in Alzheimer disease (AD) have focused on patients' impaired ability to remember information. This approach provides only a partial picture of memory deficits since other factors involved are not considered. Objective: To evaluate the recognition memory performance by using a yes/no procedure to examine the effect of discriminability and response bias measures in amnestic mild cognitive impairment (a-MCI), AD dementia, and normal-aging subjects. Methods: We included 43 controls and 45 a-MCI and 51 mild AD dementia patients. Based on the proportions of correct responses (hits) and false alarms from the Rey Auditory Verbal Learning Test (RAVLT), discriminability (d′) and response bias (C) indices from signal detection theory (SDT) were calculated. Results: Results showed significant group differences for d′ (F (2) = 83.26, p < 0.001), and C (F (2) = 6.05, p = 0.00). The best predictors of group membership were delayed recall and d′ scores. The d′ measure correctly classified subjects with 82.98% sensitivity and 91.11% specificity. Conclusions: a-MCI and AD dementia subjects exhibit less discrimination accuracy and more liberal response bias than controls. Furthermore, combined indices of delayed recall and discriminability from the RAVLT are effective in defining early AD. SDT may help enhance diagnostic specificity
Energy conditions, traversable wormholes and dust shells
Firstly, we review the pointwise and averaged energy conditions, the quantum
inequality and the notion of the ``volume integral quantifier'', which provides
a measure of the ``total amount'' of energy condition violating matter.
Secondly, we present a specific metric of a spherically symmetric traversable
wormhole in the presence of a generic cosmological constant, verifying that the
null and the averaged null energy conditions are violated, as was to be
expected. Thirdly, a pressureless dust shell is constructed around the interior
wormhole spacetime by matching the latter geometry to a unique vacuum exterior
solution. In order to further minimize the usage of exotic matter, we then find
regions where the surface energy density is positive, thereby satisfying all of
the energy conditions at the junction surface. An equation governing the
behavior of the radial pressure across the junction surface is also deduced.
Lastly, taking advantage of the construction, specific dimensions of the
wormhole, namely, the throat radius and the junction interface radius, and
estimates of the total traversal time and maximum velocity of an observer
journeying through the wormhole, are also found by imposing the traversability
conditions.Comment: 11 pages, 3 figures, Revtex
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