Subclass-balancing Contrastive Learning for Long-tailed Recognition

Long-tailed recognition with imbalanced class distribution naturally emerges in practical machine learning applications. Existing methods such as data reweighing, resampling, and supervised contrastive learning enforce the class balance with a price of introducing imbalance between instances of head class and tail class, which may ignore the underlying rich semantic substructures of the former and exaggerate the biases in the latter. We overcome these drawbacks by a novel ``subclass-balancing contrastive learning (SBCL)'' approach that clusters each head class into multiple subclasses of similar sizes as the tail classes and enforce representations to capture the two-layer class hierarchy between the original classes and their subclasses. Since the clustering is conducted in the representation space and updated during the course of training, the subclass labels preserve the semantic substructures of head classes. Meanwhile, it does not overemphasize tail class samples, so each individual instance contribute to the representation learning equally. Hence, our method achieves both the instance- and subclass-balance, while the original class labels are also learned through contrastive learning among subclasses from different classes. We evaluate SBCL over a list of long-tailed benchmark datasets and it achieves the state-of-the-art performance. In addition, we present extensive analyses and ablation studies of SBCL to verify its advantages

Effiziente Algorithmen der Positionsbestimmung und positionsbasierte Kontextgewinnung zur Selbstorganisation in drahtlosen Sensornetzwerken

Als zentrales Thema der Arbeit wird die Positionsbestimmung einzelner Knoten innerhalb drahtloser Sensornetzwerke betrachtet. Im zweiten Themenkomplex, der Clusterbildung, wird zum einen ein auf Lokalisierung aufbauendes Verfahren betrachtet. Zum anderen wird ein Algorithmus vorgestellt, welcher nicht auf die Ermittlung konkreter Positionen angewiesen ist. Das im dritten Themenkomplex betrachtete Verfahren zur Erkennung von Fehlern innerhalb drahtloser Sensornetzwerke bietet eine Möglichkeit, um Fehler innerhalb ermittelter Informationen in drahtlosen Sensornetzwerken zu erkennen.As its main topic this thesis deals with positioning of single nodes within wireless sensor networks. Clustering in wireless sensor networks forms the second part of this work. Two newly developed algorithms will be presented. One of them is based on location information. The other uses coarse grained localization technique but without the need for location information. The third topic of this thesis is about an algorithm newly developed to detect erroneous data at a sensor node

The inorganic structural crystallography of antimony trichlorine 1-halonaphthalene molecular complexes

The compounds formed by SbCl₃ and the 1-halonaphthalene in the crystalline state may provide information on some of the factors involved in molecular complex formation. The gradation in both the size and the electronegativity of the naphthalene substituent permits comparisons internally and externally with the parent 2SbCl₃.naphthalene complex. Other molecular complexes are briefly surveyed. (l:l) SbCl₃ l-bromonaphthalene forms triclinic crystals, PT. with a=9.08, b=11.98, c=12.72 Å, ∝=113.1, =93.6, 91.5° V=1268 ų, z=4. Photographic Mo data refined to R=0.14 for 591 reflections. The crystal structure is built up of double lawyers of SbCl₃ molecules alternating in the "c" direction with double layers of 1-bromonaphthalene molecules, tilted 25° to [010] . The SbCl₃ molecules form dimers, further bridged into infinite chains. The Sb atoms are in a distorted pentagonal bipyramid environment, with Å bonded chlorine atom and the aromatic -system in axial positions at 2.38 and 3.32 Å. The lone pair of electrons is stereochemically inactive. (2:l)SbCl₃.l-chloronaphthalene forms monoclinic crystals, Cc, with a=16.059, b=9.525, c=11.674 Å, =98-63°, V=1765 ų, z=4 , Diffractometer Mo data refined to R=0.l25 for 1035 reflections. The structure is built up of double layers of SbCl₃ molecules alternating in the "a" direction with single layers of l-chloronaphthalene molecules, tilted 25° to [00l] . SbCl₃ molecules form dimers, further bridged into infinite chains. Two non-equivalent SbCl₃ molecules are situated near to the l-chloronaphthalene molecule (?3.32 Å) - Sb(l) is close to the ring carrying the chlorine atom whereas ,Sb(2) is close to the other ring on the opposite side. The Sb atom is in-a distorted, pentagonal bipyramid environment, with a bonded chlorine atom and the aromatic -system in axial positions at 2.32 and 3.32 Å respectively. Again the lone pair of electrons is stereochemically inactive. ,(l:l)SbCl₃.1-iodonaphthalene forms triclinic crystals, PI, with a=l3.15, b=7.65, C=15-01 Å, ∝ -104.7°, =102.2°, =108-5°, V=1312 ų,Z-4. Photographic Mo data refined to R=0.20 for 678 reflections having even. With odd serious streaks appear suggesting a partly disordered structure. The crystal structure is built up of double layers of SbCl₃ molecules alternating in the "a" direction with double layers, of l-iodonaphthalene molecules, tilted ~ 25° to [010] . The two SbCl₃ molecules are linked to one another by Sb...Cl bridging, which are Part of an infinite chain. Plane-to-plane molecular stacking of l-C₁₀H₇I is observed. The Sb environment is similar to that in the l-bromonaphthalene compound. It seems that the SbCl₃:l-halonaphthalene complexes may be linked by an electron-donor-acceptor interaction where an electron donation occurs from the . -system to the antimony atom

A skewness-based clustering method

Partitive clustering methods represent one of the earlier and most famous sets of strategy in the field of clustering. The name comes from their main feature: all these methods start from an initial partition and modify it at every step of the process according to a known criterion, until a given convergence rule is satisfied. In other words, as pointed out by Äyrämö and Kärkkäinen (2006), they work essentially as iterative allocation algorithms. In this framework, we do not only focus on “canonical” approaches such as K-means and fuzzy C-means, but discuss some recent symmetrybased partitive clustering methods, mostly developed in the context of computer science and engineering. As it will be shown, these approaches seem to provide encouraging results, especially in the field of image recognition and some related applications, and for this reason, they represent a starting point for our work. In this respect, we are particularly interested in the case of overlapping clusters. As we will clarify, this case may represent a critical aspect for most clustering methods we have considered. In particular, we started our analysis by noting that, in a case of high-dimensional data with overlapping clusters, it may be difficult to choose the component-specific distributions, and no graphical device can help us. So, we decided to investigate non parametric approaches to clustering. In this framework, we focused on the case of clusters with elliptical shapes, and in Gaussian mixtures as a special case. Then, we realized that for elliptical shapes the symmetry could be a “natural” choice. So, we searched for such clustering approaches, and we found the symmetrybased methods cited above. But, surprisingly, none of them was intended to focus on elliptical clusters, since their aim is essentially at handling image recognition of different symmetric shapes. So, we decided to discuss this issue, and to test whether a suitable function of symmetry could improve clustering results in the case of elliptical overlapping clusters. Since we are interested in elliptical shapes, from a clustering point of view, another broad subject that we will discuss is the Gaussian mixture model. In this context, our interest is in the EM-based Mclust algorithm from the R library mclust, see Fraley and Raftery (1999). Thus, our work address both of these topics, partitive clustering methods (with a focus on the symmetry-based approach) and Gaussian model-based clustering. The main reason of such a choice, that is to address two partially different subjects, derives from the essential features of our proposal: a symmetry-based partitive method which is intended to deal with elliptical clusters (with Gaussian being a special case). In this sense, we provide an evaluation of our clustering performances by proposing a comparison with the Gaussian mixture model implemented in the Mclust library, see Fraley and Raftery (1999). This is surely a challenging task, since this method has home-court advantage in the case of Gaussian clusters. In this framework, as pointed out before, we are mainly interested in the case of overlapping clusters. In this sense, a starting point for our work was the assumption that Mclust (also in its “natural” framework, that is Gaussian mixtures) could have problems in centroid estimation when clusters are highly overlapping. Quite obviously, this drawback could be related to its dependency on the mutivariate Gaussian density. So, we searched for a non parametric skewness-based method, which could be appropriate for elliptical distribution (including Gaussian) in the case of overlapping clusters. This was exactly the framework of the proposed Sbam (Skewness-Based Allocation Method) algorithm

The Evolution of Galaxies and Their Environment

The Third Teton Summer School on Astrophysics discussed the formation of galaxies, star formation in galaxies, galaxies and quasars at high red shift, and the intergalactic and intercluster medium and cooling flows. Observation and theoretical research on these topics was presented at the meeting and summaries of the contributed papers are included in this volume

Intelligent control of a ducted fan VTOL UAV with conventional control surfaces

Utilizing UAVs for intelligence, surveillance, and reconnaissance (ISR) is beneficial in both military and civil applications. The best candidates for successful close range ISR missions are small VTOL UAVs with high speed capability. Existing UAVs suffer from the design tradeoffs that are usually required, in order to have both VTOL capability and high speed flight performance. In this thesis, we consider a novel UAV design configuration combining several important design elements from rotorcraft, ducted-fan, tail-sitter, and fixed-wing vehicles. While the UAV configuration is more towards the VTOL type, high speed flight is achieved by performing a transition maneuver from vertical attitude to horizontal attitude. In this unique approach, the crucial characteristics of VTOL and high speed flight are attained in a single UAV design. The capabilities of this vehicle come with challenges of which one of the major ones is the development an effective autonomous controller for the full flight envelope. Ducted-fan type UAVs are unstable platform with highly nonlinear behaviour, and with complex aerodynamic, which lead to inaccuracies in the estimation of the vehicle dynamics. Conventional control approaches have limitations in dealing with all these issues. A promising solution to a ducted-fan flight control problem is to use fuzzy logic control. Unlike conventional control approaches, fuzzy logic has the ability of replicating some of the ways of how humans make decisions. Furthermore, it can handle nonlinear models and it can be developed in a relatively short time, as it does not require the complex mathematics associated with classical control theory. In this study, we explore, develop, and implement an intelligent autonomous fuzzy logic controller for a given ducted-fan UAV through a series of simulations

Reactivity and Coordination Studies of Diphosphacyclobutadiene Sandwich Anions

This thesis reports on the synthesis and characterization of mono-, di-, and oligonuclear cobalt complexes with diphosphacyclobutadiene and diphosphacyclobutene ligands. Chapter 1 reviews the chemistry of transition metal phosphaalkyne and diphosphacyclobutadiene complexes. Besides the synthesis and structural motifs of diphosphacyclobutadiene complexes, this chapter also deals with the coordination properties of such species. In chapters 2 and 3, the functionalization of the diphosphacyclobutadiene ligand is discussed. Chapters 4 and 5 describe coordination studies, which have resulted in the synthesis and characterization of numerous new di- and oligonuclear complexes with diphosphacyclobutadiene ligands. Chapter 6 reports on the thermal properties as well as the potential application of complexes with diphosphacyclobutadienes and other phosphorus containing ligands in atomic layer deposition. The final chapter 7 summarizes the results of this thesis and gives a brief outlook