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1.
Phys Rev E ; 109(6-1): 064129, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-39021004

RESUMO

We study the performance of a quantum Otto heat engine with two spins coupled by a Heisenberg interaction, taking into account not only the mean values of work and efficiency but also their fluctuations. We first show that, for this system, the output work and its fluctuations are directly related to the magnetization and magnetic susceptibility of the system at equilibrium with either heat bath. We analyze the regions where the work extraction can be done with low relative fluctuation for a given range of temperatures, while still achieving an efficiency higher than that of a single spin system heat engine. In particular, we find that, due to the presence of "idle" levels, an increase in the interspin coupling can either increase or decrease fluctuations, depending on the other parameters. In all cases, however, we find that the relative fluctuations in work or efficiency remain large, implying that this microscopic engine is not very reliable as a source of work.

2.
Phys Rev E ; 105(4-1): 044120, 2022 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-35590646

RESUMO

We study a quantum Otto cycle that uses a 2-qubit working substance whose Hamiltonian does not commute with itself at different times during unitary strokes. We investigate how the cycle responds to the loss of quantum adiabaticity when these strokes are operated with a finite duration. We find that qualitative features such as the possibility of counter-rotating cycles operating as heat engines, or a cycle efficiency that can increase with a decrease in the temperature difference between the baths, are resilient even to highly nonadiabatic strokes. However, cycle efficiency rapidly decreases, although it can still remain above the standard Otto value for small degrees of quantum nonadiabaticity.

3.
Phys Rev E ; 104(5-1): 054128, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34942804

RESUMO

We compare quantum Otto engines based on two different cycle models: a two-bath model, with a standard heat source and sink, and a measurement-based protocol, where the role of heat source is played by a quantum measurement. We furthermore study these cycles using two different "working substances": a single qutrit (spin-1 particle) or a pair of qubits (spin-1/2 particles) interacting via the XXZ Heisenberg interaction. Although both cycle models have the same efficiency when applied on a single-qubit working substance, we find that both can reach higher efficiencies using these more complex working substances by exploiting the existence of "idle" levels, i.e., levels that do not shift while the spins are subjected to a variable magnetic field. Furthermore, with an appropriate choice of measurement, the measurement-based protocol becomes more efficient than the two-bath model.

4.
J Bodyw Mov Ther ; 28: 311-316, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-34776157

RESUMO

BACKGROUND: Joint manipulation is generally used to reduce musculoskeletal pain; however, evidence has emerged challenging the effects associated with the specificity of the manipulated vertebral segment. The aim of this study was to verify immediate hypoalgesic effects between specific and non-specific cervical manipulations in healthy subjects. METHOD: Twenty-one healthy subjects (18-30 years old; 11 males, 10 females) were selected to receive specific cervical manipulation at the C6-7 segment (SCM) and non-specific cervical manipulation (NSCM) in aleatory order. A 48h interval between manipulations was considered. Pressure pain threshold (PPT) was measured pre- and post-manipulation with a digital algometer on the dominant forearm. RESULTS: The SCM produced a significant increase in the PPT (P < 0.001) however no difference was observed in the PPT after the NCSM (P = 0.476). The difference between the two manipulation techniques was 37.26 kPa (95% CI: 14.69 to 59.83, p = 0.002) in favor of the SCM group CONCLUSION: Specific cervical manipulation at the C6-7 segment appears to increase PPT on the forearm compared to non-specific cervical manipulation in healthy subjects.


Assuntos
Manipulação da Coluna , Adolescente , Adulto , Estudos Cross-Over , Feminino , Voluntários Saudáveis , Humanos , Masculino , Cervicalgia , Medição da Dor , Limiar da Dor , Adulto Jovem
5.
Phys Rev E ; 104(4-1): 044133, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34781508

RESUMO

We present a mechanism for efficiency increase in quantum heat engines containing internal energy levels that do not couple to the external work sink. The gain is achieved by using these levels to channel heat in a direction opposite to the one dictated by the second law. No quantum coherence, quantum correlations or ergotropy are required. A similar mechanism allows the engine to run "in reverse" and still produce useful work. We illustrate these ideas using a simple quantum Otto cycle in a coupled-spin system. We find this engine also exhibits other counterintuitive phenomenology. For example, its efficiency may increase as the temperature difference between the heat baths decreases. Conversely, it may cease to operate if the hotter bath becomes too hot or the colder bath too cold.

6.
J Manipulative Physiol Ther ; 44(3): 244-254, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33879352

RESUMO

OBJECTIVE: The objective of this study was to compare the hypoalgesic effects of isolated or combined use of transcutaneous electrical nerve stimulation (TENS) and cervical joint manipulation (JM) in asymptomatic participants. METHODS: One hundred and forty-four healthy participants aged 18 to 30 years old were randomly assigned to 1 of 4 groups (n = 36 per group): active TENS + active JM, active TENS + placebo JM, placebo TENS + active JM, and placebo TENS + placebo JM. Active or placebo TENS was applied to the dominant forearm. JM was applied to the C6-7 segments. The pressure pain threshold was measured pre- and postintervention and after 20 minutes on the forearm and tibialis anterior of the dominant side. RESULTS: Segmental hypoalgesia was greater in the group active TENS + active JM compared with active TENS + placebo JM (P = .002), placebo TENS + active JM (P < .0001), and placebo TENS + placebo JM (P < .0001). For the extrasegmental hypoalgesia, active TENS + active JM had greater hypoalgesic effect compared with active TENS + placebo JM (P = .033), placebo TENS + active JM (P = .002), and placebo TENS + placebo JM (P < .0001). CONCLUSION: TENS and JM produced hypoalgesia when used alone and, when the treatments were combined, a higher segmental and extrasegmental hypoalgesic effect was obtained in asymptomatic participants.


Assuntos
Vértebras Cervicais/fisiologia , Manipulação da Coluna/métodos , Amplitude de Movimento Articular/fisiologia , Estimulação Elétrica Nervosa Transcutânea/métodos , Adolescente , Adulto , Terapia Combinada , Humanos , Masculino , Manejo da Dor , Medição da Dor/métodos , Limiar da Dor/fisiologia , Adulto Jovem
7.
Sensors (Basel) ; 20(5)2020 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-32121310

RESUMO

Chaotic systems implemented by artificial neural networks are good candidates for data encryption. In this manner, this paper introduces the cryptographic application of the Hopfield and the Hindmarsh-Rose neurons. The contribution is focused on finding suitable coefficient values of the neurons to generate robust random binary sequences that can be used in image encryption. This task is performed by evaluating the bifurcation diagrams from which one chooses appropriate coefficient values of the mathematical models that produce high positive Lyapunov exponent and Kaplan-Yorke dimension values, which are computed using TISEAN. The randomness of both the Hopfield and the Hindmarsh-Rose neurons is evaluated from chaotic time series data by performing National Institute of Standard and Technology (NIST) tests. The implementation of both neurons is done using field-programmable gate arrays whose architectures are used to develop an encryption system for RGB images. The success of the encryption system is confirmed by performing correlation, histogram, variance, entropy, and Number of Pixel Change Rate (NPCR) tests.

8.
Pain Manag ; 8(4): 263-269, 2018 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-29856269

RESUMO

AIM: Transcutaneous electrical nerve stimulation (TENS) and cervical joint manipulation (CJM) are often used for pain treatment. METHODS: A total of 144 healthy subjects will be randomly allocated into four groups: active TENS and CJM, placebos TENS and CJM, placebo TENS and active CJM, active TENS and placebo CJM. TENS will be applied for 20 min followed by CJM. All subjects will be assessed before, during and after interventions, using a digital pressure algometer. DISCUSSION: This is the first study to assess the combined effects of TENS and CJM on pressure pain threshold in healthy individuals. It is possible that both methods combined can enhance the hypoalgesic effect because they activate different analgesic pathways. STUDY REGISTRATION:  NCT03531541 (ClinicalTrials.gov).


Assuntos
Vértebras Cervicais , Manipulações Musculoesqueléticas/métodos , Limiar da Dor/fisiologia , Estimulação Elétrica Nervosa Transcutânea/métodos , Adulto , Terapia Combinada , Voluntários Saudáveis , Humanos , Pressão
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