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Abstract:The Dirac electron tunneling current in an n-p-n bipolar transistor based on armchair graphene nanoribbon (AGNR) has been modeled. The electron wavefunction was derived by employing the relativistic Dirac equation. The transmittance was derived by using the transfer matrix method (TMM). The Landauer formula was used to calculate the Dirac electron tunneling current. The results showed that various variables such as base-emitter voltage, base-collector voltage and the AGNR width affect the Dirac electron tunneling current. It was found that the Dirac electron tunneling current increases with increasing base-emitter and base-collector voltages. Moreover, the increase in the AGNR width results in the increase in the Dirac electron tunneling current.

Nuclear fuel cell calculation is one of the most complicated steps of neutron transport problems in the reactor core. A few numerical methods use neutron flat flux (FF) approximation to solve this problem. In this approach, neutron flux spectrum is assumed constant in each region. The solution of neutron transport equation using collision probability (CP) method based on non flat flux (NFF) approximation by introducing linear spatial distribution function implemented to a simple cylindrical annular cell has been carried out. In this concept, neutron flux spectrum in each region is different each other because of an existing of the spatial function. Numerical calculation of the neutron flux in each region of the cell using NFF approach shows a fairly good agreement compared to those calculated using existing SRAC code and FF approach. Moreover, calculation of the neutron flux in each region of the nuclear fuel cell using NFF approach needs only 6 meshes which give equivalent result when it is calculated using 24 meshes in FF approach. This result indicates that NFF approach is more efficient to be used to calculate the neutron flux in the regions of the cell than FF approach

A method has been developed to measure the swing period of a simple pendulum automatically. The pendulum position is converted into a signal frequency by employing a simple electronic circuit that detects the intensity of infrared light reflected by the pendulum. The signal produced by the electronic circuit is sent to the microphone port and recorded as a 16-bit wave file by common software. The wave file is then processed to obtain the signal period as a function of time by timing all zero crossings. From the obtained signal period as a function of time, an average value of the period is calculated. Using the calculated average period, it was found that the gravitational acceleration is (9.77 ± 0.03) m s −2 . Noting that the G-type La Coste & Romberg G928 gravimeter obtains a gravitational acceleration of 9.78 m s −2 , the present method offers very good accuracy, with a percentage error of about 0.1%.

We have studied tunneling current in a p-n junction based on armchair graphene nanoribbon (AGNR) by using the relativistic Dirac equation and a transfer matrix method (TMM). The electron wave function was derived by solving the relativistic Dirac equation. The TMM, which is a numerical approach, was used to calculate electron transmittance and the tunneling current. The results showed that the tunneling current increases with the bias voltage. On the other hand, the tunneling current increases with the decreases in the electron incidence angle and temperature. Moreover, the increases in the AGNR width and electric field in the p-n junction result in the increase in the tunneling current.