Control and synchronization of Chaotic Attitude Control of Satellite with Backstepping controller

A backstepping control system is proposed to control and synchronize the attitude dynamics of a satellite subjected to deterministic external perturbations which induce chaotic motion when no control is affected in this paper. The proposed method is a systematic recursive design approach based on the choice of Lyapunov functions for constructing feedback control laws. The effectiveness of the proposed control scheme is verified by the simulated results.     

Variable Temperature Single Crystal EPR Studies of Cu(II) in Dipotassium Diaquabis(Malonato-<Emphasis Type="Italic">κ</Emphasis><Superscript>2</Superscript><Emphasis Type="Italic">O,O</Emphasis>′) Nickelate Dihydrate: An Example of Contaminated Ground State

Single crystal X-band electron paramagnetic resonance (EPR) studies on divalent copper ions embedded in dipotassium diaquabis(malonato-κ ² O,O′) nickelate dihydrate have been performed at 300, 123 and 77 K to understand the nature of Jahn–Teller distortion in the paramagnetic host lattice. The angular variation of the EPR spectra reveals the presence of two sites, with one site not showing hyperfine resolution even at 77 K. The spin-Hamiltonian parameters of this six-coordinated Cu(II) ion, evaluated from EPR spectra at various temperatures, are:

• 300 K: g ₁₁ = 2.125, g ₂₂ = 2.118, g ₃₃ = 2.290, no copper hyperfine resolution
• 123 K: g ₁₁ = 2.229, g ₂₂ = 2.113, g ₃₃ = 2.319 and A ₁₁ = 5.02, A ₂₂ = 3.82, A ₃₃ = 6.87 mT
• 77 K: g ₁₁ = 2.224, g ₂₂ = 2.114, g ₃₃ = 2.324 and A ₁₁ = 5.32, A ₂₂ = 3.90, A ₃₃ = 7.06 mT

respectively. The low value observed for A ₃₃ at 123 and 77 K has been explained by assuming a ground state \({\text{d}}_{{x^{2} - y^{2} }}\) wave function for Cu(II) ions, contaminated with the excited state \({\text{d}}_{{z^{2} }}\). From the temperature dependence of the EPR spectra, the Cu(II) ions can be considered as a static Jahn–Teller system, with contaminated ground state. The admixture coefficients and bonding parameters have also been calculated by combining EPR and optical data. The EPR spectrum of powder sample confirms single crystal data.

     

Single-Sequence Multi-Slice NMR in Strong Gradient Magnetic Fields

We describe and apply a scheme to obtain nuclear magnetic resonance (NMR) signals from multiple regions in space with a single pulse sequence in systems with strong, usually unavoidable, gradient magnetic fields. This is accomplished with multiple frequency irradiation and reception. Applications described include dual-slice NMR of a fluid to enhance S/N, T ₂ measurements of two different samples, and efficient T ₁ measurement sequence by interleaving shorter delays within a longer delay for different slices.     

Structural,dielectric, and conductivity studies of yttrium-doped LiNiPO<Subscript>4</Subscript> cathode materials

Olivine-structured pure LiNiPO₄ and yttrium-doped LiNiPO₄ have been synthesized by a Pechini-type polymerizable precursor method. Compound formation temperature is confirmed from thermogravimetry to differential thermal analysis. Powder X-ray diffraction pattern confirmed the formation of phase pure LiNiPO₄ compound with an orthorhombic structure with fine crystallite size. Presence of preferred local cation environment is understood from Fourier transform infrared spectroscopy (FTIR) studies. XRD and FTIR studies show that doped yttrium ion entered in the lattice of LiNiPO_4. It has been found that the ionic conductivity of LiNiPO₄ is enhanced by around two orders of magnitude by doping yttrium. Dielectric spectra show the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the sample.     

The importance of electron correlation in graphene and hydrogenated graphene

Local density approximation (LDA) and Green function effective Coulomb (GW) calculations are performed to investigate the effect of electronic correlations on the electronic properties of both graphene and graphane. The size of band gap in graphane increases from 3.7 eV in LDA to 4.9 eV in GW approximation. By calculating maximally localized Wannier wave functions, we evaluate the necessary integrals to get the Hubbard U and the exchange J interaction from first principles for both graphene and graphane. Our ab-initio estimates indicate that in the case of graphene, in addition to the hopping amplitude t ～ 2.8 eV giving rise to the Dirac nature of low lying excitations, the Hubbard U value of ～8.7 eV gives rise to a super-exchange strength of J _AFM ～ 3.5 eV. This value dominates over the direct (ferromagnetic) exchange value of J _FM ～ 1.6 eV. This brings substantial Mott-Heisenberg aspects into the problem of graphene. Moreover, similarly large values of the Hubbard and super-exchange strength in graphane suggests that the nature of gap in graphane has substantial Mott character.     

Structural,electronic, optical,elastic and thermal properties of ZnXAs<Subscript>2</Subscript> (X = Si and Ge) chalcopyrite semiconductors

We report first principles calculations of solid state properties of ZnSiAs₂ and ZnGeAs₂ chalcopyrite semiconductors. The structural properties are calculated using a Full Potential Linearized Augmented Plane Wave method (FP-LAPW) of the Density Functional Theory (DFT). A Generalized Gradient Approximation (GGA) scheme proposed by Wu and Cohen (WC) has been chosen to calculate electronic and optical properties. Optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 30 eV. The elastic constants at equilibrium in tetragonal structure are also determined. Temperature effect on the volume, thermal expansion, heat capacity, Debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures and pressures and the silent results were interpreted. Finally using semi-empirical relation, we determined the hardness of the materials which attributed to different covalent bonding strengths.     

Effect of nonlinear gradient terms on pulsating,erupting and creeping solitons

The effect of nonlinear gradient terms on the pulsating, erupting and creeping solitons, respectively, of the cubic–quintic complex Ginzburg–Landau equation is investigated. It is found that the nonlinear gradient terms result in dramatic changes in the soliton behavior. They eliminate the periodicity of the pulsating and erupting solitons and transform them into fixed-shape solitons. This is important for potential use, such as to realize experimentally the undistorted transmission of femtosecond pulses in optical fibers. However, the nonlinear gradient terms cause the creeping soliton to breathe periodically at different frequencies on one side and spread rapidly on the other side. PACS 47.20.Ky; 05.70.Ln; 03.40.Gc; 42.65.Tg     

In situ oxygen plasma cleaning of a PECVD source for hard disk overcoats

Reducing the thickness of the diamond-like carbon protective overcoat to a thickness of about 2–3 nm is one major key to increase the recording density of magnetic disk drives. Plasma-enhanced chemical vapor deposition (PECVD) deposited carbon layers have been shown to be denser and harder than those produced by conventional sputter deposition. One key problem of PECVD deposited carbon is the contamination of the carbon film by particles produced inside the carbon source after long-time operation. This particle production limits the runtime of the source drastically. To avoid this particle generation the source was cleaned by an intermittent in situ oxygen plasma process. The cleaning efficiency was investigated by recording the pressure change inside the source during the cleaning process caused by the CO production. The ratio of the cleaning time and the deposition time shows no significant dependence on the deposition time. An almost linear increase of the ratio with the acetylene flow was observed. This results from a higher deposition rate at higher acetylene flow, leading to a higher contamination inside the source. A strong dependence of the cleaning rate on the oxygen flow in the cleaning process was measured. More oxygen leads to a strong decrease of the needed cleaning time. Adding Ar gas to the oxygen discharge shows no improvement of the needed cleaning time. The cleaning process seems to be dependent only on the amount of reactive oxygen species in the discharge . PACS 62.20.Qp; 52.50.Dg; 52.77.Bm; 52.80.Pi     

Comparison of MINQUE and Simple Estimate of the Error Variance in the General Linear Models

Comparison is made between the MINQUE and simple estimate of the error variance in the normal linear model under the nean square errors criterion,where the model matrix need not have full rank and the dispersion matrix can be singular.Our results show that any one of both estimates cannot be always superior to the other.Some sufficient criteria for any one of them to be better than the other are established.Some interesting relations between these two estimates are also given.