Dielectric properties of interfacial water and distribution of ions at the air/water interface

This thesis covers several topics, including (i) the vibrational coupling of the H-O-H bending mode of bulk water, (ii) including the dielectric properties of interfacial water on sub-nanometer length scales, and the influence of interfacial dielectric on the surface water spectrum, and (iii) the distribution of ions at the air/water interface. Here, we employ the heterodyne-detected vibrational sum-frequency generation (HD-SFG) spectroscopy and polarization-resolved pump-probe IR measurement for studying the surface and bulk water, respectively. For bulk water, compared to O-H stretch vibration, information on energy transfer pathways from the H-O-H bending mode is lacking. Here, we reveal that the bend-to-bend coupling is much weaker than the stretch-to-stretch coupling. We find that the intramolecular bend-to-libration energy transfer (≈ 200 fs) takes place much faster than the intermolecular bend-to-bend coupling (≈ 1 ps). For water surface, HD-VSFG allows one to study the microscopic structure and dielectric environment of the interface. This so-called Fresnel factor correction can change the line shapes and absolute amplitudes of SFG spectra substantially. By comparing the experimental and simulated SFG spectra, we resolve the interfacial dielectric function with the angstrom-level depth resolution. Furthermore, we find that the impact of the vibrational coupling of water surface is largely suppressed due to the Fresnel factor. Next, we investigate the microscopic structure of electric double layer (EDL) created by the differential distribution of anions and cations at the interface. We find that small ions will not deplete from water surface but located in a subsurface region leading to a surface stratification

Evolutionary L∞ identification and model reduction for robust control

An evolutionary approach for modern robust control oriented system identification and model reduction in the frequency domain is proposed. The technique provides both an optimized nominal model and a 'worst-case' additive or multiplicative uncertainty bounding function which is compatible with robust control design methodologies. In addition, the evolutionary approach is applicable to both continuous- and discrete-time systems without the need for linear parametrization or a confined problem domain for deterministic convex optimization. The proposed method is validated against a laboratory multiple-input multiple-output (MIMO) test rig and benchmark problems, which show a higher fitting accuracy and provides a tighter L�¢���� error bound than existing methods in the literature do

Fluctuations of Entropy Production in Partially Masked Electric Circuits: Theoretical Analysis

In this work we perform theoretical analysis about a coupled RC circuit with constant driven currents. Starting from stochastic differential equations, where voltages are subject to thermal noises, we derive time-correlation functions, steady-state distributions and transition probabilities of the system. The validity of the fluctuation theorem (FT) is examined for scenarios with complete and incomplete descriptions.Comment: 4 pages, 1 figur

Unique gap structure and symmetry of the charge density wave in single-layer VSe2_2

Single layers of transition metal dichalcogenides (TMDCs) are excellent candidates for electronic applications beyond the graphene platform; many of them exhibit novel properties including charge density waves (CDWs) and magnetic ordering. CDWs in these single layers are generally a planar projection of the corresponding bulk CDWs because of the quasi-two-dimensional nature of TMDCs; a different CDW symmetry is unexpected. We report herein the successful creation of pristine single-layer VSe$_2$, which shows a ($\sqrt7 \times \sqrt3$) CDW in contrast to the (4 $\times$ 4) CDW for the layers in bulk VSe$_2$. Angle-resolved photoemission spectroscopy (ARPES) from the single layer shows a sizable ($\sqrt7 \times \sqrt3$) CDW gap of $\sim$100 meV at the zone boundary, a 220 K CDW transition temperature twice the bulk value, and no ferromagnetic exchange splitting as predicted by theory. This robust CDW with an exotic broken symmetry as the ground state is explained via a first-principles analysis. The results illustrate a unique CDW phenomenon in the two-dimensional limit

On the Antenna Beam Shape Reconstruction Using Planet Transit

The calibration of the in-flight antenna beam shape and possible beamdegradation is one of the most crucial tasks for the upcoming Planck mission. We examine several effects which could significantly influence the in-flight main beam calibration using planet transit: the problems of the variability of the Jupiter's flux, the antenna temperature and passing of the planets through the main beam. We estimate these effects on the antenna beam shape calibration and calculate the limits on the main beam and far sidelobe measurements, using observations of Jupiter and Saturn. We also discuss possible effects of degradation of the mirror surfaces and specify corresponding parameters which can help us to determine these effects.Comment: 10 pages, 8 figure