Frustrated collisions and unconventional pairing on a quantum superlattice

We solve the problem of scattering and binding of two spin-1/2 fermions on a one-dimensional superlattice with a period of twice the lattice spacing analytically. We find the exact bound states and the scattering states, consisting of a generalized Bethe ansatz augmented with an extra scattering product due to "asymptotic" degeneracy. If a Bloch band is doubly occupied, the extra wave can be a bound state in the continuum corresponding to a single-particle interband transition. In all other cases, it corresponds to a quasi-momentum changing, frustrated collision.Comment: 4 pages, 2 figure

Accurate photoionisation cross section for He at non-resonant photon energies

The total single-photon ionisation cross section was calculated for helium atoms in their ground state. Using a full configuration-interaction approach the photoionisation cross section was extracted from the complex-scaled resolvent. In the energy range from ionisation threshold to 59\,eV our results agree with an earlier $B$-spline based calculation in which the continuum is box discretised within a relative error of $0.01\%$ in the non-resonant part of the spectrum. Above the \He^{++} threshold our results agree on the other hand very well to a recent Floquet calculation. Thus our calculation confirms the previously reported deviations from the experimental reference data outside the claimed error estimate. In order to extend the calculated spectrum to very high energies, an analytical hydrogenic-type model tail is introduced that should become asymptotically exact for infinite photon energies. Its universality is investigated considering also H$^-$, Li$^+$, and HeH$^+$. With the aid of the tail corrections to the dipole approximation are estimated.Comment: 20 pages, 7 figures, 2 table

Influence of a tight isotropic harmonic trap on photoassociation in ultracold homonuclear alkali gases

The influence of a tight isotropic harmonic trap on photoassociation of two ultracold alkali atoms forming a homonuclear diatomic is investigated using realistic atomic interaction potentials. Confinement of the initial atom pair due to the trap leads to a uniform strong enhancement of the photoassociation rate to most, but also to a strongly suppressed rate for some final states. Thus tighter traps do not necessarily enhance the photoassociation rate. A further massive enhancement of the rate is found for strong interatomic interaction potentials. The details of this interaction play a minor role, except for large repulsive interactions for which a sharp window occurs in the photoassociation spectrum as is known from the trap-free case. A comparison with simplified models describing the atomic interaction like the pseudopotential approximation shows that they often provide reasonable estimates for the trap-induced enhancement of the photoassociation rate even if the predicted rates can be completely erroneous.Comment: 19 pages, 17 figure

The Functional Biology of IL-25

CD4+ T helper (Th) 2 cells secrete interleukin (IL)-4, IL-5 and IL-13 and promote immunity to gastrointestinal helminth infections and chronic inflammation associated with asthma and allergic disorders. However, the innate immune pathways that promote Th2 cell responses remain poorly characterized. The non-hematopoietic cell-derived cytokines thymic stromal lymphopoietin (TSLP), IL-33 and IL-25 (IL-17E) have been implicated in promoting Th2 cell-dependent inflammation at mucosal sites [1-4], but how these cytokines influence innate immune responses are less well defined. Studies in Chapter 2 and 3 examined the cellular mechanisms through which IL-25 promotes Th2 cell responses and demonstrated that IL-25 promotes the accumulation of a previously unrecognized non-B/non-T cell (NBNT) c-kit+ cell population in the gut-associated lymphoid tissue (GALT). Adoptive transfer of IL-25-elicited c-kit+ cells promoted Th2 cytokine responses and conferred protective immunity to helminth infection in normally susceptible Il17e-/- mice. In Chapter 3, characterization of the IL-25-elicited c-kit+ cells revealed these cells to be a lineage negative (Linneg) multi-potent progenitor (MPP) cell population. This cell population, termed MPPtype2 cells, exhibited multi-potent capacity, giving rise to cells of monocyte/macrophage and granulocyte lineages both in vitro and in vivo. These data indicate the IL-25-elicited MPPtype2 cells may contribute to extramedullary hematopoiesis in vivo. The relationships between MPPtype2 cells and other recently identified innate cell populations, including natural helper cells (NHCs), nuocytes, and innate type 2 helper (Ih2) cells were examined in Chapter 4. MPPtype2 cells were found to be phenotypically distinct from nuocytes, NHCs and Ih2 cells. Further, stimulation of IL-25-elicited MPPtype2 cells with TSLP and IL-33 resulted in the differentiation of these cells into a T1/ST2+ IL7Rα+ NHC/nuocyte-like cell population, indicating that MPPtype2 cells could be progenitors of NHC/nuocytes. Combined, the results presented in this thesis demonstrate that IL-25 induces the emergence of a previously unrecognized multi-potent progenitor cell population and suggests that extramedullary hematopoiesis is an evolutionary conserved pathway that promotes Th2 cytokine responses at mucosal sites

Periodontists\u27 Ability to Self-Assess their Knowledge of Periodontics

This study examined periodontists\u27 ability to self-assess their knowledge of periodontics. Self-assessment was measured as the difference between actual knowledge and perceived knowledge of two topics of clinical practice of periodontics: periodontal disease therapy and dental implant therapy. Other variables included were learning needs, motivation to learn, and background characteristics (number of years since graduation from a periodontics training program, classification as Diplomate or non- Diplomate, number of years since achieving Diplomate status, classification as private practitioner, academician, or private practitioner with a part-time academic position, and number of credit hours spent in continuing education per year). A questionnaire was e-mailed to 1,800 periodontists practicing in the USA. Two hundred and nineteen subjects participated in the periodontal disease therapy questionnaire and 200 in the dental implant therapy questionnaire. The results showed a significant difference between actual and perceived knowledge for both topics. Correlation coefficients showed no correlation between participants\u27 actual knowledge and perceived knowledge of periodontal disease therapy and a low to moderate correlation between actual and perceived knowledge of dental implant therapy. Also, the results showed that need and motivation are not related to self-assessment ability, but actual knowledge may be related to moderate-high need and motivation; and, that among the background characteristics, Diplomate status is related to a better ability to self-assess, and fewer years since achieving Diplomate status is related to higher actual knowledge and perceived knowledge. In conclusion, periodontists\u27 ability to selfassess their knowledge of periodontics is at best moderate. The concern that practitioners believe that they have higher knowledge in areas in which objectively measured knowledge is significantly lower continues to be valid

No-go for Partially Massless Spin-2 Yang-Mills

There are various no-go results forbidding self-interactions for a single partially massless spin-2 field. Given the photon-like structure of the linear partially massless field, it is natural to ask whether a multiplet of such fields can interact under an internal Yang-Mills like extension of the partially massless symmetry. We give two arguments that such a partially massless Yang-Mills theory does not exist. The first is that there is no Yang-Mills like non-abelian deformation of the partially massless symmetry, and the second is that cubic vertices with the appropriate structure constants do not exist.Comment: 18 pages. v2 small corrections and ref