Bound states in the continuum driven by AC fields

We report the formation of bound states in the continuum driven by AC fields. This system consists of a quantum ring connected to two leads. An AC side-gate voltage controls the interference pattern of the electrons passing through the system. We model the system by two sites in parallel connected to two semi-infinite lattices. The energy of these sites change harmonically with time. We obtain the transmission probability and the local density of states at the ring sites as a function of the parameters that define the system. The transmission probability displays a Fano profile when the energy of the incoming electron matches the driving frequency. Correspondingly, the local density of states presents a narrow peak that approaches a Dirac delta function in the weak coupling limit. We attribute these features to the presence of bound states in the continuum.Comment: 5 pages, 3 figure

The Unusual Super-Luminous Supernovae SN 2011kl and ASASSN-15lh

Two recently discovered very luminous supernovae (SNe) present stimulating cases to explore the extents of the available theoretical models. SN 2011kl represents the first detection of a supernova explosion associated with an ultra-long duration gamma ray burst. ASASSN-15lh was even claimed as the most luminous SN ever discovered, challenging the scenarios so far proposed for stellar explosions. Here we use our radiation hydrodynamics code in order to simulate magnetar powered SNe. To avoid explicitly assuming neutron star properties we adopt the magnetar luminosity and spin-down timescale as free parameters of the model. We find that the light curve (LC) of SN 2011kl is consistent with a magnetar power source, as previously proposed, but we note that some amount of 56^Ni (> 0.08 M_sun) is necessary to explain the low contrast between the LC peak and tail. For the case of ASASSN-15lh we find physically plausible magnetar parameters that reproduce the overall shape of the LC provided the progenitor mass is relatively large (a mass of the ejecta approx 6 M_sun). The ejecta hydrodynamics of this event is dominated by the magnetar input, while the effect is more moderate for SN 2011kl. We conclude that a magnetar model may be used for the interpretation of these events and that the hydrodynamic modeling is necessary to derive the properties of powerful magnetars and their progenitors.Comment: Accepted by Astrophysical Journal Letters, 5 pages, 5 figure

Functional MRI of Language Processing and Recovery

__Abstract__ My thesis describe the utility of implementing fMRI to investigate how the language system is reorganized in brain damaged patients. Specifically for aphasia research fMRI allows to show how specific language treatment methods have the potential to enhance language reorganization and therefore optimize language recovery. Chapter 2 provides a brief introduction into the basics of language fMRI and task design for current applications of this technique in both clinical and research practice. I also summarized how different language levels have been explored with a variety of language tasks that have improved the neuroanatomical models of language processing. Chapter 3 explores the cerebro-cerebellar language lateralization pattern in healthy participants and in brain tumors patients with a focus on atypical language representation. Chapter 4 studies the differential auditory processing of spoken and melodically intoned language underlying MIT therapy. Chapter 5 focuses on the neural substrate of phonological and semantic auditory, i.e. receptive, processing in healthy older adults, group who is more applicable to aphasia research. I specifically focused on the functional specialization within the left inferior frontal gyrus (IFG), given its proposed important role for the recovery of language functions in aphasia. Chapter 6 explores the relationship between language lateralization and language recovery, both at the level of language production and comprehension, in 36 patients with mild and severe chronic aphasia after left hemispheric stroke. Chapter 7 investigates whether intensive MIT induces a shift in language lateralization in sub-acute and chronic non-fluent aphasic patients