Topologically protected bound states in photonic parity-time-symmetric crystals.

Parity-time (PT)-symmetric crystals are a class of non-Hermitian systems that allow, for example, the existence of modes with real propagation constants, for self-orthogonality of propagating modes, and for uni-directional invisibility at defects. Photonic PT-symmetric systems that also support topological states could be useful for shaping and routing light waves. However, it is currently debated whether topological interface states can exist at all in PT-symmetric systems. Here, we show theoretically and demonstrate experimentally the existence of such states: states that are localized at the interface between two topologically distinct PT-symmetric photonic lattices. We find analytical closed form solutions of topological PT-symmetric interface states, and observe them through fluorescence microscopy in a passive PT-symmetric dimerized photonic lattice. Our results are relevant towards approaches to localize light on the interface between non-Hermitian crystals.

Photonic coherent state transfer with Hamiltonian dynamics.

We report the observation of near-perfect light wave transfer by emulating quantum state transfer on a lattice with Hamiltonian dynamics, i.e., time-dependent intersite couplings. The structure transferring a single waveguide excitation over 11 sites with a fidelity of 0.93 works for classical light as well as single photons. As our implementation of perfect quantum state transfer uses a photonic setting, we introduce polarization as a new degree of freedom to the transport protocol. We demonstrate rotation operations of up to 40° on polarization during state transfer.

Radiation-loss management in modulated waveguides.

In this work, we discuss the management of radiation loss in photonic waveguides. As an experimental basis, we introduce a new technique of fabricating waveguides with tunable loss, which is particularly useful when implementing non-Hermitian (PT-symmetric) systems. To this end, we employ laser-written waveguides with a transverse sinusoidal modulation, which causes well-controllable radiation losses of almost arbitrary amount. Numerical simulations support our experimental findings. Our study shows that the radiation loss not only depends on the local waveguide curvature but also is influenced by interference effects. As a consequence, the loss is a nonmonotonous function of the bending parameters, such as period length.

Impact of loss on the wave dynamics in photonic waveguide lattices.

We analyze the impact of loss in lattices of coupled optical waveguides and find that, in such a case, the hopping between adjacent waveguides is necessarily complex. This results not only in a transition of the light spreading from ballistic to diffusive, but also in a new kind of diffraction that is caused by loss dispersion. We prove our theoretical results with experimental observations.

GABAergic and glycinergic inhibition modulate monaural auditory response properties in the avian superior olivary nucleus.

The superior olivary nucleus (SON) is the primary source of inhibition in the avian auditory brainstem. While much is known about the role of inhibition at the SON's target nuclei, little is known about how the SON itself processes auditory information or how inhibition modulates these properties. Additionally, the synaptic physiology of inhibitory inputs within the SON has not been described. We investigated these questions using in vivo and in vitro electrophysiological techniques in combination with immunohistochemistry in the chicken, an organism for which the auditory brainstem has otherwise been well characterized. We provide a thorough characterization of monaural response properties in the SON and the influence of inhibitory input in shaping these features. We found that the SON contains a heterogeneous mixture of response patterns to acoustic stimulation and that in most neurons these responses are modulated by both GABAergic and glycinergic inhibitory inputs. Interestingly, many SON neurons tuned to low frequencies have robust phase-locking capability and the precision of this phase locking is enhanced by inhibitory inputs. On the synaptic level, we found that evoked and spontaneous inhibitory postsynaptic currents (IPSCs) within the SON are also mediated by both GABAergic and glycinergic inhibition in all neurons tested. Analysis of spontaneous IPSCs suggests that most SON cells receive a mixture of both purely GABAergic terminals, as well as terminals from which GABA and glycine are coreleased. Evidence for glycinergic signaling within the SON is a novel result that has important implications for understanding inhibitory function in the auditory brainstem.

Primary arteriovenous fistula between the common iliac vessels secondary to aneurysmal disease.

Arteriovenous fistulas between the common iliac vessels are rare; at the present time, only 56 cases have been reported. Forty-seven (83.9%) of these fistulas were secondary to either trauma or surgery for herniated intervertebral disks and nine (16.1%) were caused by aneurysmal disease. Physical examination is very difficult because only 30% of the patients with iliac artery aneurysms have palpable masses before rupture; approximately 60% of the patients already have ruptures at the time of diagnosis. Therefore a high degree of suspicion is necessary and early use of angiography is commendable. Surgical intervention consists of closure of the fistula, resection or ligation of the aneurysm, and restoration of vascular continuity. The survival rate after elective resection is 93%, whereas the operative mortality rate in patients operated on for ruptured iliac artery aneurysms is 52%.

Civilian popliteal artery trauma.

An 18 year experience involved 36 civilian popliteal artery injuries is described. There were no operative or hospital deaths and the amputation rate was 3.6%. Penetrating traumas accounted for 30.6% and blunt traumas for 69.4%. In 20 patients (55.5%) the popliteal artery injury was associated with fracture and/or dislocation of the long bones and/or the knee joint. The average ischaemic time was 7.3 hours and postoperative angiography was performed in 25 patients (69.4%). Surgical reconstruction of the popliteal artery was accomplished by interposition or bypass of autogenous saphenous vein graft in 29 (80.5%), by saphenous vein patch in 5 (13.9%) and by primary end-to-end anastomosis in 1 (2.8%) and by PTFE prosthesis in 1 patient (2.8%). In all cases with bone fracture and/or dislocation bone stabilization was followed by the vascular procedure. The average time of follow-up was 76 months, 28 patients could be evaluated in the postoperative study: in 25 (89.2%) the reconstruction was patent, in 3 (10.8%) occluded. In 13 patients (46.4%) there was a complete success, 7 had a nerve deficit (25.0%), 3 had a claudication (10.7%), in one patient an amputation was necessary (3.6%) and 4 (14.3%) suffered from miscellaneous skeletal problems. Of the 36 patients originally operated, 29 (80.5%) received anticoagulant therapy for at least one year.

[Extrathoracic versus transthoracic methods of surgical correction of stenoses and occlusions of the aortic arch branches: a comparison]. / Extrathorakale versus transthorakale Methoden zur operativen Korrektur von Stenosen und Verschlüssen der Aortenbogenäste: ein Vergleich.

125 reconstructions performed during the years 1968 to 1988 were analysed retrospectively. 81 surgical procedures were extrathoracic (64.8%) and 44 transthoracic (35.2%). The symptoms of the aortic arch branch lesions included subclavian steal syndrome in 67 (53.6%), transient cerebral ischemia in 16 (12.8%), residua of cerebral infarction in 5 (4.0%), monocular ischemic attacks in 16 (12.8%) and ischemic arm symptoms in 27 (21.6%) patients. Surgical repair was achieved by subclavian-carotid transposition in 44 (35.2%), carotid-subclavian bypass in 23 (18.4%), carotid-subclavian transposition in 2 (1.6%), endarterectomy of the subclavian artery in 5 (4.0%), carotid-carotid bypass in 3 (2.4%), subclavian-subclavian bypass in 4 (3.2%), aorto-subclavian bypass in 9 (7.2%), endarterectomy of the left subclavian artery in 18 (14.4%) and reconstruction of the innominate artery in 17 (13.6%) patients. 124 patients had complete remission of symptoms or at least showed marked improvement postoperatively. The overall patency rate of the extra- and transthoracic procedures in 85% at an average follow-up of 115 months. The patency rate in the extrathoracic group is 82% and not significantly lower than in the transthoracic group with a patency rate of 89%.

[Possibilities and limitations of surgical therapy of extracranial vascular occlusion causing stroke (author's transl)]. / Möglichkeiten und Grenzen der gefässchirurgischen Therapie beim extrakraniell bedingten Schlaganfall.

On account of feared postoperative deterioration of the neurological condition and the high mortality, the indication for surgical therapy of a stroke of extracranial origin is often questioned. The mortality rate lies between 6.5% and 42%. Compared with the spontaneous healing process of the apoplectic insult by means of conservative therapy this demonstrates on average a smaller early mortality with a simultaneous higher remission rate of the neurological findings of maximally 70% compared with 48%. 90% of the predominantly arteriosclerotic carotid occlusions occur in the bifurcation area. 40% of the cases undergo additional stenosis or occlusion of the remaining arteries of the brain. Because of the knowledge of the pathogenesis and the pathophysiology of brain oedema on the remaining arteries of the brain. Because of the knowledge of the pathogenesis and the pathophysiology of brain oedema on the one hand, and the periodic relationship of carotid occlusion and incipient thrombosis on the other hand, the 6-hour limit is considered of great significance for operational success. The condition of angiographically-visible intracerebral collateralization and the strict elimination of all patients with unconsciousness or paralysis set forth further important criteria which must be fulfilled before operative procedures are contemplated. The performance of cerebral panangiography gives additional information about stenosis or occlusion of the other arteries. Indications for operation of extracerebral carotid occlusion must be determined individually on the basis of the above-mentioned guidelines.

Mobility transition from ballistic to diffusive transport in non-Hermitian lattices.

Within all physical disciplines, it is accepted that wave transport is predetermined by the existence of disorder. In this vein, it is known that ballistic transport is possible only when a structure is ordered, and that disorder is crucial for diffusion or (Anderson-)localization to occur. As this commonly accepted picture is based on the very foundations of quantum mechanics where Hermiticity of the Hamiltonian is naturally assumed, the question arises whether these concepts of transport hold true within the more general context of non-Hermitian systems. Here we demonstrate theoretically and experimentally that in ordered time-independent -symmetric systems, which are symmetric under space-time reflection, wave transport can undergo a sudden change from ballistic to diffusive after a specific point in time. This transition as well as the diffusive transport in general is impossible in Hermitian systems in the absence of disorder. In contrast, we find that this transition depends only on the degree of dissipation.

Analysing the robustness of cellular rhythms.

Autonomous oscillations at the cellular level are important for various timing and signalling functions. The rhythms depend on environmental influences in a specific manner. In particular, the period of some rhythms has been shown to be very robust to certain environmental factors whereas other rhythms show a high sensitivity towards these factors. It is discussed that the robustness of the systems towards environmental changes results from underlying design principles. However, a comparison of robustness properties of different rhythms is lacking. Here we analyse the sensitivity of the oscillatory period with respect to parameter variations in models describing oscillations in calcium signalling, glycolysis and the circadian system. By comparing models for the same and different rhythms it is shown that the sensitivity depends on the oscillatory mechanism rather than the details of the model description. In particular, we find models of calcium oscillations to be very sensitive, those for glycolytic oscillations intermediately sensitive and models for circadian rhythms very robust. The results are discussed with respect to the temperature dependency of the rhythms. The question of what impact design principles have on the robustness of an oscillator, is addressed more explicitly by a direct comparison of systems with positive and negative feedback regulation for various reaction chain lengths. We find that the systems with negative feedback are more robust than corresponding systems with positive feedback. An increase in the length of the reaction chain under regulation leads to a decrease in sensitivity.

Direct subclavian-carotid anastomosis for the subclavian steal syndrome.

Between 1984 and 1986, 38 patients--25 males and 13 females--underwent treatment for proximal subclavian arteriosclerotic lesions. All of these patients presented with symptoms of the subclavian steal syndrome and 13 (34.2%) had additional claudication of the arm. Preoperative angiography showed distal filling of the subclavian artery via retrograde flow in the vertebral artery. 31 patients (81.5%) had total occlusion of the proximal subclavian artery and 7 (18.5%) presented with severe stenosis. 34 of these lesions were on the left (89.5%) and 4 on the right side (10.5%). Complete cerebral angiography was performed in each patient with emphasis on visualisation of the carotid bifurcation and selective opacification of the aortic arch vessels if indicated. Doppler ultrasound flow measurement in the vertebral artery yielded the basic data which were then used for comparative postoperative evaluation. The operation was performed under general anaesthesia and heparinisation. A shunt was not required while performing the direct end-to-side anastomosis between the transected subclavian and the common carotid artery. Arteriosclerotic plaques in the distal stump of the transected subclavian artery and occasionally the origin of the vertebral artery were dealt with by simple eversion endarterectomy. There was no operative mortality; the postoperative complication rate was 13.1% including palsy of the recurrent nerve in 3 patients, a lymphatic cyst of the neck in one patient and bleeding requiring re-exploration in another. Occlusion of the reconstructed artery or neurologic deficit did not occur. Post operatively all patients were treated with platelet inhibitors. The average follow-up period was 13 months, when the reconstructed arteries were found to be patent in 37 patients (97.4%).(ABSTRACT TRUNCATED AT 250 WORDS)

Carotid occlusion caused by seat belt trauma.

Surgical reconstruction should be considered in patients showing episodes of transient cerebral ischaemia or progressive neurological deterioration secondary to carotid arterial injuries proved by arteriography. Even complete thrombosis of the internal carotid artery may be managed successfully, if thrombectomy and intimal repair are undertaken within some hours after the onset of neurological symptoms. Unger reported a mortality rate of 21% following carotid arterial trauma, 34% of the patients improved if they underwent surgical repair, whereas only 14% of the patients improved if they had ligation or were not treated surgically. Statistical data have shown that both shock and coma are bad prognostic omens and patients presenting with these signs have less than a 50% chance leaving the hospital alive and well, even if they receive optimum emergency management. Although coma has been suggested as a contraindication to carotid repair, review of the literature has shown the data to be too limited to warrant such a conclusion.

[Operative therapy of the pilonidal sinus; 115 controlled patients (author's transl)]. / Beitrag zur operativen Therapie des Sakraldermoids. Bericht über 115 kontrollierte Patienten.

The operative results of 115 patients with pilonidal sinus are described. The patients were controlled in 1977, 2 to 11 years after surgery. Only small, non-infected pilonidal sinuses should be radically excised followed by primary suture and Redon-drainage. For extended sinuses and for recurrences the best results are obtained when the wound is left open or marsupialisation is applied. Pilonidal sinus-abscesses should be incised. This simple procedure resulted in primary healing in 23% of our patients.