Modulating the Single-Molecule Magnet, Magnetocaloric and Luminescent Behavior in Metallacrowns.

The first part of this thesis focuses on the study of single-molecule magnets (SMMs), which have potential uses in high-density magnetic data storage. A new family of [M4Ln2(shi3-)4(Hshi2-)2(H2shi-)2(C5H5N)4(CH3OH)x(H2O)x] complexes (M = GaIII, FeIII; Ln = GdIII, TbIII, DyIII, ErIII, YIII0.9DyIII0.1) were prepared in order to investigate the effect of 3d and 4f magnetic interactions on slow magnetic relaxation behavior. It was found the antiferromagnetic 3d-4f coupling had adverse effects on slow magnetic relaxation. Furthermore, the dynamic magnetic behavior in the Ga4Dy2 analogue was elucidated, with two relaxation processes being attributed to the decoupled and excited ferromagnetic states. The magnetocaloric effect (MCE) is a phenomenon which holds promise for low-temperature refrigeration applications. Iron(III), an inexpensive, isotropic S = 5/2 ion, was selected to develop efficient low-temperature magnetic refrigerants. An investigation of FeIII(X)3[9-MCFeIIIN(shi)-3] compounds (X = acetate or benzoate) revealed that inter- and intramolecular magnetic interactions could be tuned to achieve greater MCE behavior. The acetate complex exhibited a -ΔSm value of -15.4 J kg-1 K-1 (T = 3 K, ΔH = 7 T), which is comparable to higher nuclearity FeIII clusters. Extensive antiferromagnetic intermolecular interactions resulted in a smaller MCE in the benzoate derivative and an analogous FeIII2(isopthalate)3[9-MCFeIIIN(shi)-3]2 dimer compound. These studies show that rational design and control of magnetic interactions may be employed to develop high performance MCE materials. LnIII(benzoate)4[12-MCGaIIIN(shi)-4](pyridinium+) complexes (LnIII = SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, ErIII, TmIII, YbIII) were found to be capable of sensitizing both visible and NIR emitting LnIII ions. Efficient energy transfer from the ligand T1 state to the emitting state on the LnIII led to the observation of remarkable luminescent behavior. In particular, solid state quantum yields for the YbIII and ErIII analogues (5.88% and 4.4·10-2%, respectively) are greater than any reported in the literature. This system presents a highly efficient and modular platform on which to develop practical bio-imaging agents. The work presented in this thesis demonstrates that physical properties can be tuned through systematic ligand and metal substitution in metallacrown coordination complexes. These results have given new insight towards the understanding of single-molecule magnets, MCE materials and luminescent lanthanide complexes.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113333/1/davidyc_1.pd

Design of 2D Porous Coordination Polymers Based on Metallacrown Units

A 12‐metallacrown‐4 (MC) complex was designed and employed as the building block in the synthesis of coordination polymers, one of which is the first permanently porous MC architecture. The connection of the four‐fold symmetric MC subunits by CuII nodes led to the formation of 2D layers of metallacrowns. Channels are present in the crystalline architecture, which exhibits permanent porosity manifested in N2 and CO2 uptake capacity.Permanently porous metallacrowns: Metallacrowns have been exploited for the first time as tailored building blocks for the construction of new (porous) coordination polymers. Metallacrowns are metal‐rich complexes that have exhibited excellent properties in magnetism and luminescence. Benefiting from high‐interest metallacrown building blocks in the synthesis of MOFs can unfold a whole new class of functional materials (see figure).Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137586/1/chem201600562-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137586/2/chem201600562.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137586/3/chem201600562_am.pd

1/N_c Expansion of the Heavy Baryon Isgur-Wise Functions

The 1/N_c expansion of the heavy baryon Isgur-Wise functions is discussed. Because of the contracted SU(2N_f) light quark spin-flavor symmetry, the universality relations among the Isgur-Wise functions of \Lambda_b to \Lambda_c and \Sigma_b^{(*)} to \Sigma_c^{(*)} are valid up to the order of 1/N_c^2.Comment: 7 pages, latex, no figures, to appear in Phys. Rev.

Baryonium, tetra-quark state and glue-ball in large N_c QCD

From the large-N_c QCD point of view, baryonia, tetra-quark states, hybrids, and glueballs are studied. The existence of these states is argued for. They are constructed from baryons. In N_f=1 large N_c QCD, a baryonium is always identical to a glueball with N_c valence gluons. The ground state 0^{-+} glueball has a mass about 2450 MeV. f_0(1710) is identified as the lowest 0^{++} glueball. The lowest four-quark nonet should be f_0(1370), a_0(1450), K^*_0(1430) and f_0(1500). Combining with the heavy quark effective theory, spectra of heavy baryonia and heavy tetra-quark states are predicted. 1/N_c corrections are discussed.Comment: 16 pages, 3 figure

A Man with Labile Blood Pressure

Ronald Ma and colleagues discuss the differential diagnosis and management of a patient who presented with recurrent episodes of chest discomfort, palpitations, and labile blood pressure

Anomalous Hall effect in ferromagnetic semiconductors

We present a theory of the anomalous Hall effect in ferromagnetic (Mn,III)V semiconductors. Our theory relates the anomalous Hall conductance of a homogeneous ferromagnet to the Berry phase acquired by a quasiparticle wavefunction upon traversing closed paths on the spin-split Fermi surface of a ferromagnetic state. It can be applied equally well to any itinerant electron ferromagnet. The quantitative agreement between our theory and experimental data in both (In,Mn)As and (Ga,Mn)As systems suggests that this disorder independent contribution to the anomalous Hall conductivity dominates in diluted magnetic semiconductors.Comment: 4 pages, 2 figure

Light-Front Approach for Heavy Pentaquark Transitions

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.

Locking bandwidth of two laterally coupled semiconductor lasers subject to optical injection

We report here for the first time (to our knowledge), a new and universal mechanism by which a two-element laser array is locked to external optical injection and admits stably injection-locked states within a nontrivial trapezoidal region. The rate equations for the system are studied both analytically and numerically. We derive a simple mathematical expression for the locking conditions, which reveals that two parallel saddle-node bifurcation branches, not reported for conventional single lasers subject to optical injection, delimit the injection locking range and its width. Important parameters are the linewidth enhancement factor, the laser separation, and the frequency offset between the two laterally-coupled lasers; the influence of these parameters on locking conditions is explored comprehensively. Our analytic approximations are validated numerically by using a path continuation technique as well as direct numerical integration of the rate equations. More importantly, our results are not restricted by waveguiding structures and uncover a generic locking behavior in the lateral arrays in the presence of injection

Quantification of injury burden using multiple data sources: a longitudinal study

Quantification of injury burden is vital for injury prevention, as it provides a guide for setting policies and priorities. This study generated a set of Hong Kong specific disability weights (DWs) derived from patient experiences and hospital records. Patients were recruited from the Accident and Emergency Department (AED) of three major trauma centers in Hong Kong between September 2014 and December 2015 and subsequently interviewed with a focus on health-related quality of life at most three times over a 12-month period. These patient-reported data were then used for estimation of DWs. The burden of injury was determined using the mortality and inpatient data from 2001 to 2012 and then compared with those reported in the UK Burden of Injury (UKBOI) and global burden of diseases (GBD) studies. There were 22,856 mortality cases and 817,953 morbidity cases caused by injuries, in total contributing to 1,027,641 disability-adjusted life years (DALYs) in the 12-year study timeframe. Estimates for DALYs per 100,000 in Hong Kong amounted to 1192, compared with 2924 in UKBOI and 3459 in GBD. Our findings support the use of multiple data sources including patient-reported data and hospital records for estimation of injury burden