For detection and estimation of 2-D frequencies from a 2-D array of data using a subspace decomposition method, one needs to construct a block Hankel matrix. For reliable detection andestimation, the rank of the block Hankel matrix should be made equal to the number of 2-D frequenciesinherent in the data in the absence of noise. In this work, we provide the conditions for achieving the desired rank

The control of the spin-Seebeck current is still a challenging task for the development of spin caloritronic devices. Here, we construct a spin-Seebeck device by inserting a strongly correlated quantum dot (QD) between the metal lead and magnetic insulator. Using the slave-particle approach and non-crossing approximation, we find that the spin-Seebeck effect increases significantly when the energy level of the QD locates near the Fermi level of the metal lead due to the enhancement of spin flipping and occurrences of quantum resonance. Since this can be easily realized by applying a gate voltage in experiments, the spin-Seebeck device proposed here can also work as a thermovoltaic transistor. Moreover, the optimal correlation strength and the energy level position of the QD are discussed to maximize the spin-Seebeck current as required for applications in controllable spin caloritronic devices.

The adoption of geothermal energy in space conditioning of buildings through utilizing ground source heat pump (GSHP, also known as geothermal heat pump) has increased rapidly during the past several decades. However, the impacts of the GSHP utilization on the efficiency of heat pumps and soil temperature distribution remained unclear and needs further investigation. This paper presents a novel model to calculate the soil temperature distribution and the coefficient of performance (COP) of GSHP. Different scenarios were simulated to quantify the impact of different factors on the GSHP performance, including heat balance, daily running mode, and spacing between boreholes. Our results show that GSHP is suitable for buildings with balanced cooling and heating loads. It can keep soil temperature at a relatively constant level for more than 10 years. Long boreholes, additional space between boreholes, intermittent running mode will improve the performance of GSHP, but large initial investment is required. The improper design will make the COP of GSHP even lower than traditional heat pumps. Professional design and maintenance technologies are greatly needed in order to promote this promising technology in the developing world.