On Two Complementary Types of Total Time Derivative in Classical Field Theories and Maxwell's Equations

Close insight into mathematical and conceptual structure of classical field theories shows serious inconsistencies in their common basis. In other words, we claim in this work to have come across two severe mathematical blunders in the very foundations of theoretical hydrodynamics. One of the defects concerns the traditional treatment of time derivatives in Eulerian hydrodynamic description. The other one resides in the conventional demonstration of the so-called Convection Theorem. Both approaches are thought to be necessary for cross-verification of the standard differential form of continuity equation. Any revision of these fundamental results might have important implications for all classical field theories. Rigorous reconsideration of time derivatives in Eulerian description shows that it evokes Minkowski metric for any flow field domain without any previous postulation. Mathematical approach is developed within the framework of congruences for general 4-dimensional differentiable manifold and the final result is formulated in form of a theorem. A modified version of the Convection Theorem provides a necessary cross-verification for a reconsidered differential form of continuity equation. Although the approach is developed for one-component (scalar) flow field, it can be easily generalized to any tensor field. Some possible implications for classical electrodynamics are also explored.Comment: no figure

A Hybrid Laser Ultrasonic Based Systemf ro Composite Molding

Conventional piezoelectric based ultrasonic systems have been extensively employed for material characterization. These systems however, have been challenged by the recent need to rapidly scan large areas of new materials such as composites having complex geometry. A promising candidate addressing this issue is laser ultrasonics. Though laser ultrasonics is not new and has generated considerable research interest in the past two decades, its industrial acceptance has been limited. Among its many benefits, laser ultrasonics promise the flexibility of a couplant free inspection system. Pulsed lasers, in particular, offer energy concentration at high repetition rates which can be readily directed at any location on the specimen for interrogation purposes. The detection of laser ultrasound is usually done through Michaelson or Fabry-Perot type interferometric systems. Though these detection systems have the advantage of couplant free detection, they constitute a major component of system cost owing to the precision required. The sensitivity of such systems are also not satisfactory

Acoustic Tomographic Reconstruction of Fiber Angle in Orthotropic Composite Materials

Composite materials are complex structures widely utilized in modern industry. Numerous nondestructive testing techniques are used to examine these composites for manufacturing flaws, including ultrasonic testing. Normally the reinforcing fibers in a composite material are aligned in a prescribed fashion, from a simple unidirectional composite to a complex composite laminate lay-up. Defects caused by manufacturing or in-service use can result in buckling or warping of the fibers. This is an important concern when dealing with thick composites

A Preliminary List of the Flora of the Perkiomen Region

41 page annotated list of vascular plants collected by the authors in and around the Perkiomen Creek in Montgomery County, Pennsylvania. About the year 1915 Dr. Kline, Brendle and Mumbauer began to make weekly collecting trips. This preliminary catalogue rests mostly upon the work done on these trips. [from the Foreword]https://digitalcommons.ursinus.edu/faculty_books/1011/thumbnail.jp

Ultrasonic Evaluation of Adhesive Bond Strength Using Spectroscopic Techniques

In this program statistical analysis of ultrasonically determined parameters was used to identify the features of acoustic wave propagation in adhesively bonded structures which could be used to determine adhesive bond strength. The parameters associated with the interaction of ultrasonic waves with the adhesive-aluminum interfaces and adhesive interlayer which were investigated included bondline transit time, amplitude ratios of reflections from the various interfaces, frequency dependent attenuation and spectral resonance characteristics. Aluminum specimens with both etched and as-received surface preparation were studied. The capabilities of the Fokker bondtester for adhesive strength determination were also assessed. Adaptive learning techniques were used to statistically examine correlation between the observed acoustic properties and shear strength for 394 specimens

The role of intermolecular coupling in the photophysics of disordered organic semiconductors: Aggregate emission in regioregular polythiophene

We address the role of excitonic coulping on the nature of photoexcitations in the conjugated polymer regioregular poly(3-hexylthiophene). By means of temperature-dependent absorption and photoluminescence spectroscopy, we show that optical emission is overwhelmingly dominated by weakly coupled H-aggregates. The relative absorbance of the 0-0 and 0-1 vibronic peaks provides a powerfully simple means to extract the magnitude of the intermolecular coupling energy, approximately 5 and 30 meV for films spun from isodurene and chloroform solutions respectively.Comment: 10 pages, 4 figures, published in Phys. Rev. Let

Effect of well-width on the electro-optical properties of a quantum well

We record photoreflectance from Ge/GeSi modulation doped quantum wells possessing $10^4$ V/cm perpendicular electric fields. Qualitatively very different spectra are obtained from samples of well-width 100 \AA and 250 \AA. Comparing the wavefunctions calculated from an $8 \times 8$ \textbf{k.p} theory, we find that while they remain confined in the narrower 100 \AA QW, the electric field causes them to tunnel into the forbidden gap in the 250 \AA\ well. This implies that the samples should show a transition from the quantum confined Franz-Keldysh effect to the bulk-like Franz-Keldysh effect. Close to the band-edge where Franz-Keldysh effects are important, simulated photoreflectance spectra reproduce the essential features of the experiment, without any adjustable parameters.Comment: 8 pages, 8 figures. Submitted to Phys. Rev.

The significance of non-sustained hypotension in emergency department patients with sepsis

Objective Few studies have documented the incidence and significance of non-sustained hypotension in emergency department (ED) patients with sepsis. We hypothesized that ED non-sustained hypotension increases risk of in-hospital mortality in patients with sepsis. Methods Secondary analysis of a prospective cohort study. ED patients aged >17 years admitted to the hospital with explicitly defined sepsis were prospectively identified. Inclusion criteria Evidence of systemic inflammation (>1 criteria) and suspicion for infection. Patients with overt shock were excluded. The primary outcome was in-hospital mortality. Results Seven hundred patients with sepsis were enrolled, including 150 (21%) with non-sustained hypotension. The primary outcome of in-hospital mortality was present in 10% (15/150) of patients with non-sustained hypotension compared with 3.6% (20/550) of patients with no hypotension. The presence of non-sustained hypotension resulted in three times the risk of mortality than no hypotension (risk ratio = 2.8, 95% CI 1.5–5.2). Patients with a lowest systolic blood pressure <80 mmHg had a threefold increase in mortality rate compared with patients with a lowest systolic blood pressure ≥80 mmHg (5 vs. 16%). In logistic regression analysis, non-sustained hypotension was an independent predictor of in-hospital mortality. Conclusion Non-sustained hypotension in the ED confers a significantly increased risk of death during hospitalization in patients admitted with sepsis. These data should impart reluctance to dismiss non-sustained hypotension, including a single measurement, as not clinically significant or meaningful