Spectroscopy of Ultracold LiRb Molecules Using Ionization Detection

We present spectroscopic studies of ultracold LiRb molecules using ionization detection. The molecules are created by cooling and trapping Li and Rb atoms in overlapping magneto-optical traps (MOTs) and using light resonant with a free-bound transition to create weakly bound excited state molecules in a process known as photoassociation (PA). We explore weakly bound vibrational levels of LiRb with PA spectroscopy using ionization detection and, where possible, compare our results with earlier measurements performed in our lab using trap-loss spectroscopy. In addition, we also probe vibrational levels of the ground triplet electronic state and excited electronic states using resonantly enhanced multiphoton ionization (REMPI) spectroscopy. We identify several vibrational levels of the α3Σ+, (3)3ΠΩ and (4)3Σ + states and compare our observations with theoretical calculations. As LiRb is one of the least studied heteronuclear diatomic molecules, these studies are aimed towards exploring the molecular structure. The spectroscopic work is also in line with the long-term project goals of transferring ultracold LiRb molecules into the lowest rotational and vibrational levels of the ground singlet electronic state. Molecules in this rovibronic ground state possess a large electric dipole moment, which is essential for application of ultracold molecules in various quantum computation schemes. The rovibronic ground state will also be an ideal starting point for investigating molecular entangled states

Development of airborne eddy-correlation flux measurement capabilities for reactive oxides of nitrogen

This research is aimed at producing a fundamental new research tool for characterizing the source strength of the most important compound controlling the hemispheric and global scale distribution of tropospheric ozone. Specifically, this effort seeks to demonstrate the proof-of-concept of a new general purpose laser-induced fluorescence based spectrometer for making airborne eddy-correlation flux measurements of nitric oxide (NO) and other reactive nitrogen compounds. The new all solid-state laser technology being used in this advanced sensor will produce a forerunner of the type of sensor technology that should eventually result in highly compact operational systems. The proof-of-concept sensor being developed will have over two orders-of-magnitude greater sensitivity than present-day instruments. In addition, this sensor will offer the possibility of eventual extension to airborne eddy-correlation flux measurements of nitrogen dioxide (NO2) and possibly other compounds, such as ammonia (NH3), peroxyradicals (HO2), nitrateradicals (NO3) and several iodine compounds (e.g., I and IO). Demonstration of the new sensor's ability to measure NO fluxes will occur through a series of laboratory and field tests. This proof-of-concept demonstration will show that not only can airborne fluxes of important ultra-trace compounds be made at the few parts-per-trillion level, but that the high accuracy/precision measurements currently needed for predictive models can also. These measurement capabilities will greatly enhance our current ability to quantify the fluxes of reactive nitrogen into the troposphere and significantly impact upon the accuracy of predictive capabilities to model O3's distribution within the remote troposphere. This development effort also offers a timely approach for producing the reactive nitrogen flux measurement capabilities that will be needed by future research programs such as NASA's planned 1999 Amazon Biogeochemistry and Atmospheric Chemistry Experimental portion of LBA

Doctor of Philosophy

dissertationType I diabetes is caused by selective loss of insulin-producing β-cells. Identifying and activating an endogenous source of new β-cells could be used to replenish those lost in this disease. The nature and existence of an adult pancreatic stem/progenitor cell population, however, is still controversial. Circumstantial evidence indicates that islet cells arise from embryonic ductal cells. In contrast, the majority of adult islet cells appear to regenerate via self-renewal during postnatal expansion and adult homeostasis. That ducts could also give rise to new beta-cells in the adult (neogenesis) was recently suggested in the context of pancreatic ductal ligation (PDL) injury. The Notch signaling pathway inhibits islet development and promotes progenitor cell maintenance during early pancreatic organogenesis, acting primarily through its target gene Hes1. While Hes1 is broadly expressed in the embryonic pancreas, only rare Hes1-expressing cells can be found in the adult organ, among mature ducts and centroacinar cells (CACs), the latter of which have been proposed to represent adult progenitors. This thesis aims to test directly the ability of duct cells to generate islet cells, and to determine the biological function of Hes1+ duct cells. For this, we performed lineage tracing and genetic manipulation using two novel Cre-lines, Muc1IC2, which marks exocrine cells, and Hes1C2, which marks Hes1+ cells. Our work has uncovered three major phases in the development of pancreatic islet cells: (i) initially, new islet cells originate from Notchresponsive exocrine cells, (ii) later in embryogenesis, Notch signaling needs to be downiv regulated in exocrine cells for islet neogenesis to proceed and (iii) from birth onwards, islet cells are maintained by replication of pre-existing cells with no detectable influx from neogenesis. Additionally, our findings demonstrated that early Hes1+ cells represent multipotent progenitors and that their immature state is maintained through active Notch signaling. Interestingly, later in development Notch promotes duct specification of Hes1-expressing bipotent exocrine progenitors. In the mature pancreas, Hes1 expression persists in Notch-sensitive centroacinar cells, which act as facultative exocrine-specific progenitor cells. Thus, the research described in this thesis determines the identity of embryonic and adult pancreatic progenitor cells, and demonstrates that these cells utilize Notch signaling for maintenance of their undifferentiated state

Minimally Invasive Accelerated Orthodontic Techniques: A Clinical, Radiological, and Histological Comparison on a Rat Model

Background: Accelerated orthodontics encompasses a group of techniques designed to facilitate the faster movement of teeth. Many techniques developed are designed to cause a controlled injury to the cortex of the bone resulting in a transient osteopenia, also known as the regional acceleratory phenomena (RAP). Little research has been done to compare these techniques and describe their effects on the periodontium. Objective: To clinically, histologically, and radiographically compare several minimally invasive techniques for inducing accelerated orthodontics. Methods: Sixty 8-9-week-old male Sprague Dawley rats were used for this investigation. An orthodontic device consisting of a 50g NiTi closed coil spring was applied to allow for the mesial movement of the upper left first molar. Rats were divided into 4 groups, one control (n=15) and 3 minimally invasive accelerated orthodontic interventions consisting of Piezocision (n=15), Propel (n=15), and pulsed electromagnetic fields (PEMF) (n=15) were included. Five rats from each group were euthanized for histology at 3 time points from baseline at Day 7, Day 21 and Day 49. Histomorphometric and descriptive analysis were performed using axial crosssectional slides of the mid-root region. For clinical analysis, the distance from incisors to test molars were measured with digital calipers at baseline and post-treatment time points. Cone beam computed tomography and micro computed tomography were performed. Results: Bone density was found lower in the Piezocision and Propel groups at day 21, and the periodontium reorganizes by day 49. Piezocision had statistically significant reductions in histologic and radiographic bone density (p\u3c0.05). Conclusion: Decortication techniques, such as Piezocision and Propel, resulted in more osteopenia and tooth movement. Utilization of decortication may facilitate tooth movement through the alveolus to provide an accelerated and safe movement. VI Pulsed electromagnetic fields may demonstrate the potential for regulating bone metabolism without decreases in bone density

Extreme ultraviolet laser excitation of isotopic molecular nitrogen: the dipole-allowed spectrum of ¹⁵N₂ and ¹⁴N¹⁵N

Extreme ultraviolet+ultraviolet (XUV+UV) two-photonionizationspectra of the b ¹Πu(v=0–9), c₃¹Πu(v=0,1), o ¹Πu(v=0,1), c′₄¹Σ⁺u(v=1) and b′¹Σ⁺u(v=1,3–6) states of ¹⁵N₂ were recorded with a resolution of 0.3 cm⁻¹ full-width at half-maximum (FWHM). In addition, the b ¹Πu(v=1,5–7) states of ¹⁴N¹⁵N were investigated with the same laser source. Furthermore, using an ultranarrow bandwidth XUV laser [∼250 MHz (∼0.01 cm⁻¹) FWHM], XUV+UV ionizationspectra of the b ¹Πu(v=0–1,5–7), c₃¹Πu(v=0), o ¹Πu(v=0), c′₄¹Σ⁺u(v=0), and b′¹Σ⁺u(v=1) states of ¹⁵N₂ were recorded in order to better resolve the band-head regions. For ¹⁴N¹⁵N, ultrahigh resolution spectra of the b¹Πu(v=0–1,5–6), c₃¹Πu(v=0), and b′¹Σ⁺u(v=1) states were recorded. Rotational analyses were performed for each band, revealing perturbations arising from the effects of Rydberg-valence interactions in the ¹Πu and ¹Σ⁺u states, and rotational coupling between the ¹Πu and ¹Σ⁺umanifolds. Finally, a comprehensive perturbation model, based on the diabatic-potential representation used previously for ¹⁴N₂, and involving diagonalization of the full interaction matrix for all Rydberg and valence states of ¹Σ⁺u and 1Πu symmetry in the energy window 100 000–110 000 cm⁻¹, was constructed. Term values for ¹⁵N₂ and ¹⁴N¹⁵N computed using this model were found to be in good agreement with experiment.The work was supported by the European Community, under the Access to Research Infrastructures initiative of the Improving Human Potential Program, Contract No. HPRI-CT-1999-00064. K.G.H.B. was supported by the Scientific Visits to Europe Program of the Australian Academy of Science

Spectroscopic Studies on Aluminum Monofluoride

This thesis reports on optical and radio frequency (rf) spectroscopic investigation on the molecule aluminum monofluoride (AlF). The experiments are carried out on a jet-cooled, seeded pulsed molecular beam. The molecules are produced in a laser ablation process. Pulsed dye lasers and excimer lasers are used for optical excitation and ionization. A linear Time-of-flight mass spectrometer is used for ion detection. A detailed characterization of the electronic ground state (X1Σ+) and energetically excited triplet states (a3Π, b3Σ+ and c3Σ+) of AlF is given using Molecular orbital theory. The lifetimes of the b3Σ+ and c3Σ+ states are measured using multiphoton ionization. Rotationally resolved spectra are recorded for the a3Π1 ← X1Σ+, b3Σ+ ← a3Π1 and c3Σ+ ← a3Π1 bands using multiple resonance excitation schemes. Hyperfine resolved spectra are recorded for the b3Σ+, J = 1 ← a3Π1, J = 2 transition. All the spectroscopic studies are carried out between the vibrational ground states of the involved electronic states. Supplementary spectra on vibrational higher states are reported incidentally. A lineshape model, an excitation scheme and a modification of the experimental setup is worked out that enables spectroscopic measurements between the hyperfine levels of the a3Π1,J = 1 state of AlF. The setup includes a self designed and manufactured parallel plates transmission line for the rf-transition. Experiments are carried out with different carrier gases. In the end, a draft for an experimental setup that enables the measurement of spectral lines with sub-natural linewidths is presented.Diese Thesis berichtet über die experminetelle Erforschung des Moleküls Aluminium Monofluorid (AlF) mittels optischer und Hochfrequenz-Spektroskopie. Die Experimente werden an einem gepulsten Molekularstrahl durchgeführt, der durch eine Überschallexpansion erzeugt wird. Die Moleküle werden durch Laserablation hergestellt und optisch mittels Farbstofflasern und Excimer-Lasern angeregt. Der elektronische Grundzustand (X1Σ+) sowie die ersten angeregten Triplettzustände (a3Π, b3Σ+ und c3Σ+) von AlF werden auf der Basis von Molekülorbitaltheorie charakterisiert. Die Lebensdauern der beiden Triplettzustände b3Σ+ und c3Σ+ werden gemessen. Rotationsaufgelöste Spektren der a3Π1 ← X1Σ+, b3Σ+ ← a3Π1 und c3Σ+ ← a3Π1 Banden werden mittels resonanzverstärkter Mehrphotonenionisation aufgenommen. Die Hyperfeinstruktur des b3Σ+, J = 1 ← a3Π1, J = 2 Energeniveaus wird bestimmt. Ein Modell zur Beschreibung der Linienform für einen Übergang innerhalb der Hyperfeinstruktur des a3Π1,J = 1 Energieniveaus wird hergeleitet. Eine Übertragungsleitung wird in den experimentellen Aufbau integriert um mittels Hochfrequenzen einen molekularen Übergang zwischen hyperfeinen Energieniveaus anzuregen. Die Experimente werden mit verschiedenen Gaskompositionen durchgeführt. Zum Schluss wird ein experimenteller Aufbau entwickelt, der die Messung von Absorptionslinen die schmaler sind als die natürliche Linienbreite ermöglicht

Anisotropic massive Brans-Dicke gravity extension of the standard Λ\LambdaCDM model

We present an explicit detailed theoretical and observational investigation of an anisotropic massive Brans-Dicke (BD) gravity extension of the standard $\Lambda$CDM model, wherein the extension is characterized by two additional degrees of freedom; the BD parameter, $\omega$, and the present day density parameter corresponding to the shear scalar, $\Omega_{\sigma^2,0}$. The BD parameter, determining the deviation from general relativity (GR), by alone characterizes both the dynamics of the effective dark energy (DE) and the redshift dependence of the shear scalar. These two affect each other depending on $\omega$, namely, the shear scalar contributes to the dynamics of the effective DE, and its anisotropic stress --which does not exist in scalar field models of DE within GR-- controls the dynamics of the shear scalar deviating from the usual $\propto(1+z)^6$ form in GR. We mainly confine the current work to non-negative $\omega$ values as it is the right sign --theoretically and observationally-- for investigating the model as a correction to the $\Lambda$CDM. By considering the current cosmological observations, we find that $\omega\gtrsim 250$, $\Omega_{\sigma^2,0}\lesssim 10^{-23}$ and the contribution of the anisotropy of the effective DE to this value is insignificant. We conclude that the simplest anisotropic massive BD gravity extension of the standard $\Lambda$CDM model exhibits no significant deviations from it all the way to the Big Bang Nucleosynthesis. We also point out the interesting features of the model in the case of negative $\omega$ values; for instance, the constraints on $\Omega_{\sigma^2,0}$ could be relaxed considerably, the values of $\omega\sim-1$ (relevant to string theories) predict dramatically different dynamics for the expansion anisotropy.Comment: 27 pages, 6 figures, 1 tabl

One- and two-photon ionization cross sections of the laser excited 6s6p^1P_1 state of barium

Stimulated by a recent measurement of coherent control in photoionization of atomic barium, we have calculated one- and two-photon ionization cross sections of the aligned 6s6p^1P_1 state of barium in the energy range between the 5d_{3/2} and 5d_{5/2} states of Ba^+. We have also measured these photionization spectra in the same energy region, driving the one- or two-photon processes with the second or first harmonic of a tunable dye laser, respectively. Our calculations employ the eigenchannel R-matrix method and multichannel quantum defect theory to calculate the rich array of autoionizing resonances in this energy range. The non-resonant two-photon process is described using lowest-order perturbation theory for the photon-atom interactions, with a discretized intermediate state one-electron continuum. The calculations provide an absolute normalization for the experiment, and they accurately reproduce the rich resonance structures in both the one and two-photon cross sections, and confirm other aspects of experimental observations. These results demonstrate the ability of these computationally inexpensive methods to reproduce the experimental observables in one- and two-photon ionization of heavy alkaline earths, and they lay the groundwork for future studies of the phase-controlled interference between one-photon and two-photon ionization processes.Comment: 10 pages, 9 figures, submitted to Phys.Rev.

Interfacing graphene with peripheral neurons: influence of neurite outgrowth and NGF axonal transport

Graphene displays properties that make it appealing for neuroregenerative medicine, yet the potential of large-scale highly-crystalline graphene as a conductive peripheral neural interface has been scarcely investigated. In particular, pristine graphene offers enhanced electrical properties that can be advantageous for nervous system regeneration applications. In this work, we investigate graphene potential as peripheral nerve interface. First, we perform an unprecedented analysis aimed at revealing how the typical polymeric coatings for neural cultures distribute on graphene at the nanometric scale. Second, we examine the impact of graphene on the culture of two established cellular models for peripheral nervous system: PC12 cell line and primary embryonic rat dorsal root ganglion (DRG) neurons, showing a better and faster axonal elongation using graphene. We then observe that the axon elongation in the first days of culture correlates to an altered nerve growth factor (NGF) axonal transport, with a reduced number of retrogradely moving NGF vesicles in favor of stalled vesicles. We thus hypothesize that the axon elongation observed in the first days of culture could be mediated by this pool of NGF vesicles locally retained in the medial/distal parts of axons. Furthermore, we investigate electrophysiological properties and cytoskeletal structure of peripheral neurons. We observe a reduced neural excitability and altered membrane potential together with a reduced inter-microtubular distance on graphene and correlate these electrophysiological and structural reorganizations of axon physiology to the observed vesicle stalling. Finally, the potential of another 2D material as neural interface, tungsten disulfide, is explored