Kontinuierliche Kreuzkupplungsreaktionen in mikrostrukturierten Systemen

Im Rahmen dieser Arbeit wurden unterschiedliche Palladium-katalysierte Kreuzkupplungsreaktionen untersucht. Ein besonderes Augenmerk wurde dabei auf die Suzuki-Miyaura-Reaktion gelegt. Unter anderem aufgrund der langen Reaktionszeiten und der zweiphasigen Bedingungen ist diese Reaktionsklasse nur sehr schwer als kontinuierlicher Prozess zu etablieren. Vielen dieser Ansätze ist jedoch zu eigen, dass der große Vorteil der Mikroprozesstechnik, eine überlegene Kontrolle von Temperatur und Stofftransport, kaum ausgeschöpft wird. An diesem Punkt setzt diese Arbeit von technischer aus Seite an. Der zweite Schwerpunkt der Arbeit sind die prinzipiellen Untersuchungen an kontinuierlichen Flüssig-Flüssig-Zwei-Phasen-Reaktionen. Im Zuge des DBU-finanzierten Transkat-Projektes wurden hierbei anhand einfacher Veresterungsreaktionen grundlegende Kenntnisse zu Stofftransport, Grenzflächen und Phasentrennung innerhalb mikrostrukturierter Systeme gesammelt. Dank speziell angefertigter Glasmikroreaktoren von der Firma mikroglas chemtech GmbH war eine genaue optische und digitale Charakterisierung der Phasengrenzflächen möglich. Ein wichtiges Ergebnis war darüber hinaus, dass ionische Flüssigkeiten, als eigenständige Phasen verwendet, enorm zum Massentransfer und somit zur Reaktionsgeschwindigkeit beitragen können.

The medical management after surgery for advanced heart failure

The aim of the Research of this Ph D Project is to improve the medical management after surgery for advanced heart failure, both after left ventricular assist devices (LVAD) implantation, and after heart transplantation in the long-term. Regarding heart transplantation (HTx), the Research Project is focused on diagnostics, classification, prevention and treatment of cardiac allograft vasculopathy (CAV), and on treatment of post-HTx cancers; the results are presented in the first part of this Thesis. In particular, the main aspect investigated are the prognostic role of information derived from coronary angiography, coronary tomography and intravascular ultrasound, and the different sensitivity of these techniques in predicting outcomes and in diagnosing CAV. Moreover, the role of mTOR inhibitors on CAV prevention or treatment is investigated, both alone and in combination with different anti-CMV prevention strategies, as well as the impact of mTOR inhibitors on clinical outcomes in the long term. Regarding LVAD, the main focus is on the role of transthoracic echocardiography in the management of patients with a continuous-flow, centrifugal, intrapericardial pump (HVAD, Heartware); this section is reported in the second part of this Thesis. The main aspects investigated are the use of echocardiography in patients with HVAD device and its interaction with the information derived from pump curves' analysis in predicting aortic valve opening status, a surrogate of the condition of support provided by the LVAD.

Synthesen von C-glycosylierten Aminosäuren und Peptiden unter Einsatz speziell konstruierter Mikroreaktoren

Die chemische Synthese definierter Glycopeptidstrukturen bildet die Basis einiger vielversprechender Ansätze zur Therapie verschiedener Krankheiten. Die Entwicklung hochaffiner Selektininhibitoren könnte der Behandlung chronischer Entzündungen und zur Unterdrückung der Metastasierung von Tumoren dienen. Vollsynthetische Vakzine auf Basis glycosylierter MUC1-Partialstrukturen sollen das Immunsystem zur Bekämpfung von krankem Gewebe anregen und so perspektivisch eine Impfung gegen Krebs ermöglichen. Da die natürlich vorkommenden O-Glycoside in vivo eine begrenzte Stabilität besitzen, wurde eine Methode entwickelt, welche die modulare Herstellung von stabilen rnC-Glycosylaminosäuren als Mimetika der natürlichen Serin-, Threonin- und Tyrosin-Glycoside ermöglicht. Dazu wurden passend geschützte Kohlenhydrat-Lactone synthetisiert, die in einer mikrowellengestützten Petasis-Olefinierung unter Durchflussbedingungen in die entsprechenden exo-Glycale überführt wurden. Die Reaktionszeit konnte durch diese spezielle Reaktionsführung auf weniger als drei Minuten verringert werden, während konventionell mehrere Stunden benötigt werden. Die C-glycosidische Verknüpfung mit den entsprechenden Aminosäurebausteinen gelang durch eine Hydroborierungs-Suzuki-Kupplungs-Kaskade. Nach umfangreicher Optimierung der Reaktionsparameter ließ sich neben mehreren Monosacchariden auch ein exo-Glycal der Lactose erfolgreich in der Kupplung einsetzen. Nach verschiedenen Schutzgruppenmanipulationen wurden einige der synthetisierten Bausteine zur Synthese C-glycosylierter Partialstrukturen des Mucins MUC1 an der festen Phase herangezogen. In ELISA-Experimenten wurden die C-Glycosylpeptide von an Brustkrebsgewebe bindenden Antikörpern erkannt, die durch Vakzinierung mit ähnlichen Strukturen erhalten worden waren. Zur Synthese zweier Bausteine potenzieller Selektin-Inhibitoren wurde ein Mimetikum des in natürlichen Liganden vorkommenden Tetrasaccharides Sialyl-Lewisx synthetisiert. Bei diesem wurde die terminale Sialinsäure durch (S)-Cyclohexylmilchsäure ersetzt. Die bei der gewählten Syntheseroute notwendige regioselektive Öffnung eines Benzylidenacetals wurde in einem Mikroreaktor durchgeführt, wodurch eine einfache Reaktionsoptimierung mit geringen Substanzmengen möglich war. Die Reaktionszeit liegt mit unter 4 Minuten deutlich unter den üblichen Werten von einer bis mehreren Stunden. In einer Block-Glycosylierung konnte das Pseudotetrasaccharid sowohl an einen C-Lactosyl-Tyrosin-, als auch an einen C-Lactosyl-Serin-Akzeptor angefügt und somit die Synthese der Zielverbindungen abgeschlossen werden. Diese Bausteine können in Zukunft als Bestandteile synthetischer Glycopeptide zum Einsatz kommen, welche Mimetika der natürlichen Selektin-Liganden darstellen sollen.rn

Valorizzazione di acque di vegetazione provenienti da oleifici tramite recupero di polifenoli per adsorbimento

The environmental problems associated to the disposal of the olive oil wastewater (OMW, Olive Mill Wastewaters), and the difficulty in the recycling because of their polyphenolic content, led to propose the separation of their polyphenols. The recovery of polyphenols from olive mill wastewaters (OMWs) provides the double opportunity to obtain high-added value biomolecules and to reduce the phytotoxicity of the effluent. The separation can be obtained by a continuous flow extraction process of adsorption and desorption, this process is characterized by the possibility to recycling the adsorbing phase and the extraction solvent. The present work is part of a project aimed to the development of pilot scale process based on the use of the AMBERLITE XAD16 as adsorption resin. The adsorption stage is preceded by a wastewater filtration pretreatment, and a final desorption process is added to recover the polyphenols using acidified ethanol as the solvent.

Awake tracheal intubation using the Sensascope in 13 patients with an anticipated difficult airway

We present the use of the SensaScope, an S-shaped rigid fibreoptic scope with a flexible distal end, in a series of 13 patients at high risk of, or known to have, a difficult intubation. Patients received conscious sedation with midazolam or fentanyl combined with a remifentanil infusion and topical lidocaine to the oral mucosa and to the trachea via a trans-cricoid injection. Spontaneous ventilation was maintained until confirmation of tracheal intubation. In all cases, tracheal intubation was achieved using the SensaScope. The median (IQR [range]) insertion time (measured from the time the facemask was taken away from the face until an end-expiratory CO(2) reading was visible on the monitor) was 58 s (38-111 [28-300]s). In nine of the 13 cases, advancement of the SensaScope into the trachea was easy. Difficulties included a poor view associated with a bleeding diathesis and saliva, transient loss of spontaneous breathing, and difficulty in advancing the tracheal tube in a patient with unforeseen tracheal narrowing. A poor view in two patients was partially improved by a high continuous flow of oxygen. The SensaScope may be a valuable alternative to other rigid or flexible fibreoptic scopes for awake intubation of spontaneously breathing patients with a predicted difficult airway.

In Vitro Evaluation of Ventricular Cannulation for Rotodynamic Cardiac Assist Devices

The influence of positioning and geometry of ventricular cannulas for contemporary continuous flow Left Ventricular Assist Devices (LVADs) was evaluated in a non-beating isolated heart preparation with borescopic visualization. Preload and LVAD flow were varied to evaluate degrees of ventricular decompression up to the point of ventricular collapse. The performance of a flanged cannula was compared to a conventional bevel-tipped cannula: quantitatively by the maximal flow attainable, and qualitatively by visualization of fluid tracer particles within the ventricular chamber. Three forms of ventricular suck-down occurred: concentric collapse, gradual entrainment and instantaneous entrainment. In some circumstances, unstable oscillations of the ventricle were observed prior to complete collapse. Under conditions of low preload, the flanged cannula demonstrated less positional sensitivity, provided greater flow, and exhibited fewer areas of stagnation than the beveled cannula. These observations warrant further consideration of a flanged ventricular cannula to mitigate complications encountered with conventional cannulae.

A refined TALDICE-1a age scale from 55 to 112 ka before present for the Talos Dome ice core based on high-resolution methane measurements

A precise synchronization of different climate records is indispensable for a correct dynamical interpretation of paleoclimatic data. A chronology for the TALDICE ice core from the Ross Sea sector of East Antarctica has recently been presented based on methane synchronization with Greenland and the EDC ice cores and δ18Oice synchronization with EDC in the bottom part (TALDICE-1). Using new high-resolution methane data obtained with a continuous flow analysis technique, we present a refined age scale for the age interval from 55–112 thousand years (ka) before present, where TALDICE is synchronized with EDC. New and more precise tie points reduce the uncertainties of the age scale from up to 1900 yr in TALDICE-1 to below 1100 yr over most of the refined interval and shift the Talos Dome dating to significantly younger ages during the onset of Marine Isotope Stage 3. Thus, discussions of climate dynamics at sub-millennial time scales are now possible back to 110 ka, in particular during the inception of the last ice age. Calcium data of EDC and TALDICE are compared to show the impact of the refinement to the synchronization of the two ice cores not only for the gas but also for the ice age scale.

Water isotopic ratios from a continuously melted ice core sample

A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of δ18O and δD on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub μl amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a~home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW–SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1‰ and 0.5‰ for δ18O and δD, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of δ18O and δD, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the field during the 2010 season as part of the NEEM deep ice core drilling project in North Greenland.

In vitro hemodynamic evaluation of ventricular suction conditions of the EVAHEART ventricular assist pump

Purpose: Mismatches between pump output and venous return in a continuous-flow ventricular assist device may elicit episodes of ventricular suction. This research describes a series of in vitro experiments to characterize the operating conditions under which the EVAHEART centrifugal blood pump (Sun Medical Technology Research Corp., Nagano, Japan) can be operated with minimal concern regarding left ventricular (LV) suction. Methods: The pump was interposed into a pneumatically driven pulsatile mock circulatory system (MCS) in the ventricular apex to aorta configuration. Under varying conditions of preload, afterload, and systolic pressure, the speed of the pump was increased step-wise until suction was observed. Identification of suction was based on pump inlet pressure. Results: In the case of reduced LV systolic pressure, reduced preload (=10 mmHg), and afterload (=60 mmHg), suction was observed for speeds =2,200 rpm. However, suction did not occur at any speed (up to a maximum speed of 2,400 rpm) when preload was kept within 10-14 mmHg and afterload =80 mmHg. Although in vitro experiments cannot replace in vivo models, the results indicated that ventricular suction can be avoided if sufficient preload and afterload are maintained. Conclusion: Conditions of hypovolemia and/or hypotension may increase the risk of suction at the highest speeds, irrespective of the native ventricular systolic pressure. However, in vitro guidelines are not directly transferrable to the clinical situation; therefore, patient-specific evaluation is recommended, which can be aided by ultrasonography at various points in the course of support.

A TWO-STAGE MICROBIAL FUEL CELL SYSTEM TO CONVERT SOLID ORGANIC WASTE TO ELECTRICITY

Microbial fuel cell (MFC) research has focused mostly on producing electricity using soluble organic and inorganic substrates. This study focused on converting solid organic waste into electricity using a two-stage MFC process. In the first stage, a hydrolysis reactor produced soluble organic substrates from solid organic waste. The soluble substrates from the hydrolysis reactor were pumped to the second stage reactor: a continuous-flow, air-cathode MFC. Maximum power output (Pmax) of the MFC was 296 mW/m3 at a current density of 25.4 mA/m2 while being fed only leachate from the first stage reactor. Addition of phosphate buffer increased Pmax to 1,470 mW/m3 (89.4 mA/m2), although this result could not be duplicated with repeated polarization testing. The minimum internal resistance achieved was 77 Omega with leachate feed and 17 Omega with phosphate buffer. The low coulombic efficiency (

ACETYL RADICAL IN TOBACCO SMOKE: DETECTION, QUANTIFICATION AND SIMULATION

Free radicals are present in cigarette smoke and can have a negative effect on human health by attacking lipids, nucleic acids, proteins and other biologically important species. However, because of the complexity of the tobacco smoke system and the dynamic nature of radicals, little is known about the identity of the radicals, and debate continues on the mechanisms by which those radicals are produced. In this study, acetyl radicals were trapped from the gas phase using 3-amino-2, 2, 5, 5- tetramethyl-proxyl (3AP) on solid support to form stable 3AP adducts for later analysis by high performance liquid chromatography (HPLC), mass spectrometry/tandem mass spectrometry (MS-MS/MS) and liquid chromatography- mass spectrometry (LC-MS). Simulations of acetyl radical generation were performed using Matlab and the Master Chemical Mechanism (MCM) programs. A range of 10- 150 nmol/cigarette of acetyl radical was measured from gas phase tobacco smoke of both commerial and research cigarettes under several different smoking conditions. More radicals were detected from the puff smoking method compared to continuous flow sampling. Approximately twice as many acetyl radicals were trapped when a GF/F particle filter was placed before the trapping zone. Computational simulations show that NO/NO2 reacts with isoprene, initiating chain reactions to produce a hydroxyl radical, which abstracts hydrogen from acetaldehyde to generate acetyl radical. With initial concentrations of NO, acetaldehyde, and isoprene in a real-world cigarette smoke scenario, these mechanisms can account for the full amount of acetyl radical detected experimentally. This study contributes to the overall understanding of the free radical generation in gas phase cigarette smoke.

TANK SIZING AND OPTIMIZING LOOP PLACEMENT IN A BRANCHED WATER DISTRIBUTION SYSTEM

More than eighteen percent of the world’s population lives without reliable access to clean water, forced to walk long distances to get small amounts of contaminated surface water. Carrying heavy loads of water long distances and ingesting contaminated water can lead to long-term health problems and even death. These problems affect the most vulnerable populations, women, children, and the elderly, more than anyone else. Water access is one of the most pressing issues in development today. Boajibu, a small village in Sierra Leone, where the author served in Peace Corps for two years, lacks access to clean water. Construction of a water distribution system was halted when a civil war broke out in 1992 and has not been continued since. The community currently relies on hand-dug and borehole wells that can become dirty during the dry season, which forces people to drink contaminated water or to travel a far distance to collect clean water. This report is intended to provide a design the system as it was meant to be built. The water system design was completed based on the taps present, interviews with local community leaders, local surveying, and points taken with a GPS. The design is a gravity-fed branched water system, supplied by a natural spring on a hill adjacent to Boajibu. The system’s source is a natural spring on a hill above Boajibu, but the flow rate of the spring is unknown. There has to be enough flow from the spring over a 24-hour period to meet the demands of the users on a daily basis, or what is called providing continuous flow. If the spring has less than this amount of flow, the system must provide intermittent flow, flow that is restricted to a few hours a day. A minimum flow rate of 2.1 liters per second was found to be necessary to provide continuous flow to the users of Boajibu. If this flow is not met, intermittent flow can be provided to the users. In order to aid the construction of a distribution system in the absence of someone with formal engineering training, a table was created detailing water storage tank sizing based on possible source flow rates. A builder can interpolate using the source flow rate found to get the tank size from the table. However, any flow rate below 2.1 liters per second cannot be used in the table. In this case, the builder should size the tank such that it can take in the water that will be supplied overnight, as all the water will be drained during the day because the users will demand more than the spring can supply through the night. In the developing world, there is often a problem collecting enough money to fund large infrastructure projects, such as a water distribution system. Often there is only enough money to add only one or two loops to a water distribution system. It is helpful to know where these one or two loops can be most effectively placed in the system. Various possible loops were designated for the Boajibu water distribution system and the Adaptive Greedy Heuristic Loop Addition Selection Algorithm (AGHLASA) was used to rank the effectiveness of the possible loops to construct. Loop 1 which was furthest upstream was selected because it benefitted the most people for the least cost. While loops which were further downstream were found to be less effective because they would benefit fewer people. Further studies should be conducted on the water use habits of the people of Boajibu to more accurately predict the demands that will be placed on the system. Further population surveying should also be conducted to predict population change over time so that the appropriate capacity can be built into the system to accommodate future growth. The flow at the spring should be measured using a V-notch weir and the system adjusted accordingly. Future studies can be completed adjusting the loop ranking method so that two users who may be using the water system for different lengths of time are not counted the same and vulnerable users are weighted more heavily than more robust users.

Italia: La chiusura della Casa dell’Emigrante come spunto riflessione sui rientri degli emigrati italiani

In the literature on migration, as well as in social policies regarding this phenomenon, the situation of returning emigrants receives scant attention. This essay establishes an intricate connection between attitudes and policies that prevail in a country regarding emigration and those concerning immigration. The case of Italy provides a prime example for this as it once was a classical country of emigration, only to turn, in recent decades, into a country that appears highly attractive (and relatively accessible) to immigrants. The essay traces the pervasive ambiguity that characterizes this country’s attitudes towards emigration from the beginning of mass emigration shortly after the unification of Italy in 1868 to the emigration policies of the fascist regime of Mussolini and the post-World War II waves of emigration right through to the corresponding ambiguity concerning the status of immigrants in contemporary society, including the indifferent treatment of returning Italian emigrants who constitute a considerable numerical phenomenon. These reflections take their origin from the impending closure of a reception centre in Lazio, the Casa dell’Emigrante near Sant’Elia Fiumerapido, Province of Frosinone, ostensibly for financial reasons. This centre had been the only one of its kind in the whole of Italy dealing officially with the needs of repatriated Italians. It had assisted returning emigrants both with practical matters, such as negotiating the labyrinth of Italian bureaucracy , and with psychological implications of a return, which are often considerable given the time lag of experiences with current social realities and the frequently unrealistic expectations associated with the return. Questions of identity become highly acute in those circumstances. The threatened closure of the centre illustrates the unwillingness of the state to face up to the factual prevalence of migratory experiences in the country as a whole and as a core element of national history, experiences of migration in both directions. The statistics speak for themselves: of the 4.660.427 persons who left Italy between 1880 and 1950, 2.322.451 have returned, almost exactly 50%. To those have to be added 3.628.430 returnees of the 5.109.860 emigrants who left Italy between the end of World War II and 1976 for Europe alone. Attitudes towards people leaving changed ostensibly over time. In the first two decades after Unification parliament on the one hand wanted to show some concern over the fate of its citizens, not wanting to abandon those newly created citizens entirely to their own destiny, while on the other portraying their decisions to emigrate as expressions of individual liberty and responsibility and not necessitated by want and poverty. Emigrants had to prove, paradoxically that they had the requisite means to emigrate when in fact poverty was largely driving them to emigrate. To admit that publicly would have amounted to admission of economic and political failure made evident through emigration. In contrast to that Mussolini’s emigration policies not only enforced large population movements within the territory of Italy to balance unemployment between regions and particularly between North and South, but also declared it citizen’s duty to be ready to move also to the colonies, thereby ‘turning emigration as a sign of social crisis into a sign of national strength and the success of the country’s political agenda’ (Gaspari 2001, p. 34). The duplicity continued even after World War II when secret deals were done with the USA to allow a continuous flow of Italian immigrants and EU membership obviously further facilitated the departure of unemployed, impoverished Italians. With the growing prosperity of Italy the reversal of the direction of migration became more obvious. On the basis of empirical research conducted by one of the author on returning emigrants four types of motives for returning can be distinguished: 1. Return as a result of failure – particularly the emigrants who left during the 1950-1970 period usually had no linguistic preparation, and in any case the gap between the spoken and the written language is enormous with the latter often being insurmountable. This gives rise to nostalgic sentiments which motivates a return into an environment where language is familiar 2. Return as a means of preserving an identity – the life of emigrants often takes place within ghetto-like conditions where familiarity is being reproduced but under restricted conditions and hence not entirely authentic. The necessity for saving money permits only a partial entry into the host society and at the same time any accumulating savings add to the desire to return home where life can be lived fully again – or so it seems. 3. Return of investment – the impossibility to become fully part of another society often motivates migrants to accumulate not so much material wealth but new experiences and competences which they then aim to reinvest in their home country. 4. Return to retire – for many emigrants returning home becomes acute once they leave a productive occupation and feelings of estrangement build up, in conjunction with the efforts of having invested in building a house back home. All those motives are associated with a variety of difficulties on the actual return home because, above all, time in relation to the country of origin has been suspended for the emigrant and the encounter with the reality of that country reveals constant discrepancies and requires constant readjustment. This is where the need for assistance to returning emigrants arises. The fact that such an important centre of assistance has been closed is further confirmation of the still prevailing politics of ambiguity which nominally demand integration from nationals and non-nationals alike but deny the means of achieving this. Citizenship is not a natural result of nationality but requires the means for active participation in society. Furthermore, the experiences of returning immigrants provide important cues for the double ambivalence in which immigrants to Italy live between the demands made on them to integrate, the simultaneous threats of repatriation and the alienation from the immigrants’ home country which grows inexorably during the absence. The state can only regain its credibility by putting an end to this ambiguity and provide to returning emigrants, and immigrants alike, the means of reconstructing strong communal identities.

A robust reference signal generator for synchronized ventricular assist devices

Ventricular assist devices (VADs) are blood pumps that offer an option to support the circulation of patients with severe heart failure. Since a failing heart has a remaining pump function, its interaction with the VAD influences the hemodynamics. Ideally, the heart's action is taken into account for actuating the device such that the device is synchronized to the natural cardiac cycle. To realize this in practice, a reliable real-time algorithm for the automatic synchronization of the VAD to the heart rate is required. This paper defines the tasks such an algorithm needs to fulfill: the automatic detection of irregular heart beats and the feedback control of the phase shift between the systolic phases of the heart and the assist device. We demonstrate a possible solution to these problems and analyze its performance in two steps. First, the algorithm is tested using the MIT-BIH arrhythmia database. Second, the algorithm is implemented in a controller for a pulsatile and a continuous-flow VAD. These devices are connected to a hybrid mock circulation where three test scenarios are evaluated. The proposed algorithm ensures a reliable synchronization of the VAD to the heart cycle, while being insensitive to irregularities in the heart rate.

ON THE EXISTENCE OF SHOCKS IN IRRADIATED EXOPLANETARY ATMOSPHERES

Supersonic flows are expected to exist in the atmospheres of irradiated exoplanets, but the question of whether shocks develop lingers. Specifically, it reduces to whether continuous flow in a closed loop may become supersonic and if some portions of the supersonic flow steepen into shocks. We first demonstrate that continuous, supersonic flow may exist in two flavors: isentropic and non-isentropic, with shocks being included in the latter class of solutions. Supersonic flow is a necessary but insufficient condition for shocks to develop. The development of a shock requires the characteristics of neighboring points in a flow to intersect. We demonstrate that the intersection of characteristics may be quantified via the knowledge of the Mach number. Finally, we examine three-dimensional simulations of hot Jovian atmospheres and demonstrate that shock formation is expected to occur mostly on the dayside hemisphere, upstream of the substellar point, because the enhanced temperatures near the substellar point provide a natural pressure barrier for the returning flow. Understanding the role of shocks in irradiated exoplanetary atmospheres is relevant to correctly modeling observables such as the peak offsets of infrared phase curves.