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Downscaling of microfluidic cell culture and detection devices for electrochemical monitoring has mostly focused on miniaturization of the microfluidic chips which are often designed for specific applications and therefore lack functional flexibility. We present a compact microfluidic cell culture and electrochemical analysis platform with in-built fluid handling and detection, enabling complete cell based assays comprising on-line electrode cleaning, sterilization, surface functionalization, cell seeding, cultivation and electrochemical real-time monitoring of cellular dynamics. To demonstrate the versatility and multifunctionality of the platform, we explored amperometric monitoring of intracellular redox activity in yeast (Saccharomyces cerevisiae) and detection of exocytotically released dopamine from rat pheochromocytoma cells (PC12). Electrochemical impedance spectroscopy was used in both applications for monitoring cell sedimentation and adhesion as well as proliferation in the case of PC12 cells. The influence of flow rate on the signal amplitude in the detection of redox metabolism as well as the effect of mechanical stimulation on dopamine release were demonstrated using the programmable fluid handling capability. The here presented platform is aimed at applications utilizing cell based assays, ranging from e.g. monitoring of drug effects in pharmacological studies, characterization of neural stem cell differentiation, and screening of genetically modified microorganisms to environmental monitoring.
The Arabidopsis Kinome
(2014)
Background
Protein kinases constitute a particularly large protein family in Arabidopsis with important functions in cellular signal transduction networks. At the same time Arabidopsis is a model plant with high frequencies of gene duplications. Here, we have conducted a systematic analysis of the Arabidopsis kinase complement, the kinome, with particular focus on gene duplication events. We matched Arabidopsis proteins to a Hidden-Markov Model of eukaryotic kinases and computed a phylogeny of 942 Arabidopsis protein kinase domains and mapped their origin by gene duplication.
Results
The phylogeny showed two major clades of receptor kinases and soluble kinases, each of which was divided into functional subclades. Based on this phylogeny, association of yet uncharacterized kinases to families was possible which extended functional annotation of unknowns. Classification of gene duplications within these protein kinases revealed that representatives of cytosolic subfamilies showed a tendency to maintain segmentally duplicated genes, while some subfamilies of the receptor kinases were enriched for tandem duplicates. Although functional diversification is observed throughout most subfamilies, some instances of functional conservation among genes transposed from the same ancestor were observed. In general, a significant enrichment of essential genes was found among genes encoding for protein kinases.
Conclusions
The inferred phylogeny allowed classification and annotation of yet uncharacterized kinases. The prediction and analysis of syntenic blocks and duplication events within gene families of interest can be used to link functional biology to insights from an evolutionary viewpoint. The approach undertaken here can be applied to any gene family in any organism with an annotated genome.
Geometric electroelasticity
(2014)
In this work a diffential geometric formulation of the theory of electroelasticity is developed which also includes thermal and magnetic influences. We study the motion of bodies consisting of an elastic material that are deformed by the influence of mechanical forces, heat and an external electromagnetic field. To this end physical balance laws (conservation of mass, balance of momentum, angular momentum and energy) are established. These provide an equation that describes the motion of the body during the deformation. Here the body and the surrounding space are modeled as Riemannian manifolds, and we allow that the body has a lower dimension than the surrounding space. In this way one is not (as usual) restricted to the description of the deformation of three-dimensional bodies in a three-dimensional space, but one can also describe the deformation of membranes and the deformation in a curved space. Moreover, we formulate so-called constitutive relations that encode the properties of the used material. Balance of energy as a scalar law can easily be formulated on a Riemannian manifold. The remaining balance laws are then obtained by demanding that balance of energy is invariant under the action of arbitrary diffeomorphisms on the surrounding space. This generalizes a result by Marsden and Hughes that pertains to bodies that have the same dimension as the surrounding space and does not allow the presence of electromagnetic fields. Usually, in works on electroelasticity the entropy inequality is used to decide which otherwise allowed deformations are physically admissible and which are not. It is alsoemployed to derive restrictions to the possible forms of constitutive relations describing the material. Unfortunately, the opinions on the physically correct statement of the entropy inequality diverge when electromagnetic fields are present. Moreover, it is unclear how to formulate the entropy inequality in the case of a membrane that is subjected to an electromagnetic field. Thus, we show that one can replace the use of the entropy inequality by the demand that for a given process balance of energy is invariant under the action of arbitrary diffeomorphisms on the surrounding space and under linear rescalings of the temperature. On the one hand, this demand also yields the desired restrictions to the form of the constitutive relations. On the other hand, it needs much weaker assumptions than the arguments in physics literature that are employing the entropy inequality. Again, our result generalizes a theorem of Marsden and Hughes. This time, our result is, like theirs, only valid for bodies that have the same dimension as the surrounding space.
Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitation the transient XAS spectrum is consistent with an 8% expansion of the Au–Au bond length and a large increase in disorder associated with melting of the NPs. Recovery of the ground state occurs with a time constant of ∼1.8 ns, arising from thermalisation with the environment. Simulations reveal that the transient spectrum exhibits no signature of charge separation at 100 ps and allows us to estimate an upper limit for the quantum yield (QY) of this process to be <0.1.
Synchronization is a fundamental phenomenon in nature. It can be considered as a general property of self-sustained oscillators to adjust their rhythm in the presence of an interaction.
In this work we investigate complex regimes of synchronization phenomena by means of theoretical analysis, numerical modeling, as well as practical analysis of experimental data.
As a subject of our investigation we consider chimera state, where due to spontaneous symmetry-breaking of an initially homogeneous oscillators lattice split the system into two parts with different dynamics. Chimera state as a new synchronization phenomenon was first found in non-locally coupled oscillators system, and has attracted a lot of attention in the last decade. However, the recent studies indicate that this state is also possible in globally coupled systems. In the first part of this work, we show under which conditions the chimera-like state appears in a system of globally coupled identical oscillators with intrinsic delayed feedback. The results of the research explain how initially monostable oscillators became effectivly bistable in the presence of the coupling and create a mean field that sustain the coexistence of synchronized and desynchronized states. Also we discuss other examples, where chimera-like state appears due to frequency dependence of the phase shift in the bistable system.
In the second part, we make further investigation of this topic by modeling influence of an external periodic force to an oscillator with intrinsic delayed feedback. We made stability analysis of the synchronized state and constructed Arnold tongues. The results explain formation of the chimera-like state and hysteric behavior of the synchronization area. Also, we consider two sets of parameters of the oscillator with symmetric and asymmetric Arnold tongues, that correspond to mono- and bi-stable regimes of the oscillator.
In the third part, we demonstrate the results of the work, which was done in collaboration with our colleagues from Psychology Department of University of Potsdam. The project aimed to study the effect of the cardiac rhythm on human perception of time using synchronization analysis. From our part, we made a statistical analysis of the data obtained from the conducted experiment on free time interval reproduction task. We examined how ones heartbeat influences the time perception and searched for possible phase synchronization between heartbeat cycles and time reproduction responses. The findings support the prediction that cardiac cycles can serve as input signals, and is used for reproduction of time intervals in the range of several seconds.
We present an electrochemical MIP sensor for tamoxifen (TAM)-a nonsteroidal anti-estrogen-which is based on the electropolymerisation of an O-phenylenediamine. resorcinol mixture directly on the electrode surface in the presence of the template molecule. Up to now only. bulk. MIPs for TAM have been described in literature, which are applied for separation in chromatography columns. Electro-polymerisation of the monomers in the presence of TAM generated a film which completely suppressed the reduction of ferricyanide. Removal of the template gave a markedly increased ferricyanide signal, which was again suppressed after rebinding as expected for filling of the cavities by target binding. The decrease of the ferricyanide peak of the MIP electrode depended linearly on the TAM concentration between 1 and 100 nM. The TAM-imprinted electrode showed a 2.3 times higher recognition of the template molecule itself as compared to its metabolite 4-hydroxytamoxifen and no cross-reactivity with the anticancer drug doxorubucin was found. Measurements at + 1.1 V caused a fouling of the electrode surface, whilst pretreatment of TAM with peroxide in presence of HRP generated an oxidation product which was reducible at 0 mV, thus circumventing the polymer formation and electrochemical interferences.
When azobenzene-modified photosensitive polymer films are irradiated with light interference patterns, topographic variations in the film develop that follow the electric field vector distribution resulting in the formation of surface relief grating (SRG). The exact correspondence of the electric field vector orientation in interference pattern in relation to the presence of local topographic minima or maxima of SRG is in general difficult to determine. In my thesis, we have established a systematic procedure to accomplish the correlation between different interference patterns and the topography of SRG. For this, we devise a new setup combining an atomic force microscope and a two-beam interferometer (IIAFM). With this set-up, it is possible to track the topography change in-situ, while at the same time changing polarization and phase of the impinging interference pattern. To validate our results, we have compared two photosensitive materials named in short as PAZO and trimer. This is the first time that an absolute correspondence between the local distribution of electric field vectors of interference pattern and the local topography of the relief grating could be established exhaustively. In addition, using our IIAFM we found that for a certain polarization combination of two orthogonally polarized interfering beams namely SP (↕, ↔) interference pattern, the topography forms SRG with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures below diffraction limit with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We have also probed for the stresses induced during the polymer mass transport by placing an ultra-thin gold film on top (5–30 nm). During irradiation, the metal film not only deforms along with the SRG formation, but ruptures in regular and complex manner. The morphology of the cracks differs strongly depending on the electric field distribution in the interference pattern even when the magnitude and the kinetic of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. The neutron reflectivity measurements of the metal/polymer interface indicate the penetration of metal layer within the polymer resulting in the formation of bonding layer that confirms the transduction of light induced stresses in the polymer layer to a metal film.
The large-scale green synthesis of graphene-type two-dimensional materials is still challenging. Herein, we describe the ionothermal synthesis of carbon-based composites from fructose in the iron-containing ionic liquid 1-butyl-3-methylimidazolium tetrachloridoferrate(III), [Bmim][FeCl4] serving as solvent, catalyst, and template for product formation. The resulting composites consist of oligo-layer graphite nanoflakes and iron carbide particles. The mesoporosity, strong magnetic moment, and high specific surface area of the composites make them attractive for water purification with facile magnetic separation. Moreover, Fe3Cfree graphite can be obtained via acid etching, providing access to fairly large amounts of graphite material. The current approach is versatile and scalable, and thus opens the door to ionothermal synthesis towards the larger-scale synthesis of materials that are, although not made via a sustainable process, useful for water treatment such as the removal of organic molecules.
The synthesis of two novel types of π-expanded coumarins has been developed. Modified Knoevenagel bis-condensation afforded 3,9-dioxa-perylene-2,8-diones. Subsequent oxidative aromatic coupling or light driven electrocyclization reaction led to dibenzo-1,7-dioxacoronene-2,8-dione. Unparalleled synthetic simplicity, straightforward purification and superb optical properties have the potential to bring these perylene and coronene analogs towards various applications.
Graphitic carbon nitride, g-C₃N₄, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C₃N₄ by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H⁺ reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H₂ production O₂ evolution is only possible in the presence of oxidation cocatalysts.
Portal Wissen = Time
(2014)
“What then is time?”, Augustine of Hippo sighs melancholically in Book XI of “Confessions” and continues, “If no one asks me, I know; if I want to explain it to a questioner, I don’t know.” Even today, 1584 years after Augustine, time still appears mysterious. Treatises about the essence of time fill whole libraries – and this magazine.
However, questions of essence are alien to modern sciences. Time is – at least in physics – unproblematic: “Time is defined so that motion looks simple”, briefly and prosaically phrased, waves goodbye to Augustine’s riddle and to the Newtonian concept of absolute time, whose mathematical flow can only be approximately recorded with earthly instruments anyway.
In our everyday language and even in science we still speak of the flow of time but time has not been a natural condition for quite a while now. It is rather a conventional order parameter for change and movement. Processes are arranged by using a class of processes as a counting system in order to compare other processes and to organize them with the help of the temporary categories “before”, “during”, and “after”.
During Galileo’s time one’s own pulse was seen as the time standard for the flight of cannon balls. More sophisticated examination methods later made this seem too impractical. The distance-time diagrams of free-flying cannon balls turned out to be rather imprecise, difficult to replicate, and in no way “simple”. Nowadays, we use cesium atoms. A process is said to take one second when a caesium-133 atom completes 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state. A meter is the length of the path travelled by light in a vacuum in exactly 1/299,792,458 of a second. Fortunately, these data are hard-coded in the Global Positioning System GPS so users do not have to reenter them each time they want to know where they are. In the future, however, they might have to download an app because the time standard has been replaced by sophisticated transitions to ytterbium.
The conventional character of the time concept should not tempt us to believe that everything is somehow relative and, as a result, arbitrary. The relation of one’s own pulse to an atomic clock is absolute and as real as the relation of an hourglass to the path of the sun. The exact sciences are relational sciences. They are not about the thing-initself as Newton and Kant dreamt, but rather about relations as Leibniz and, later, Mach pointed out.
It is not surprising that the physical time standard turned out to be rather impractical for other scientists. The psychology of time perception tells us – and you will all agree – that the perceived age is quite different from the physical age. The older we get the shorter the years seem. If we simply assume that perceived duration is inversely related to physical age and that a 20-year old also perceives a physical year as a psychological one, we come to the surprising discovery that at 90 years we are 90 years old. With an assumed life expectancy of 90 years, 67% (or 82%) of your felt lifetime is behind you at the age of 20 (or 40) physical years.
Before we start to wallow in melancholy in the face of the “relativity of time”, let me again quote Augustine. “But at any rate this much I dare affirm I know: that if nothing passed there would be no past time; if nothing were approaching, there would be no future time; if nothing were, there would be no present time.” Well, – or as Bob Dylan sings “The times they are a-changin”.
I wish you an exciting time reading this issue.
Prof. Martin Wilkens
Professor of Quantum Optics
Rezensiertes Werk:
George, Rosemary Marangoly, Indian English and the Fiction of National Literature - Cambridge: Cambridge University Press, 2013. - Hb. viii, 285 pp. - (Zeitschrift für Anglistik und Amerikanistik ; 62(4)) ISBN 978-1-107-04000-7.
Magnetite is an iron oxide, which is ubiquitous in rocks and is usually deposited as small nanoparticulate matter among other rock material. It differs from most other iron oxides because it contains divalent and trivalent iron. Consequently, it has a special crystal structure and unique magnetic properties. These properties are used for paleoclimatic reconstructions where naturally occurring magnetite helps understanding former geological ages. Further on, magnetic properties are used in bio- and nanotechnological applications –synthetic magnetite serves as a contrast agent in MRI, is exploited in biosensing, hyperthermia or is used in storage media.
Magnetic properties are strongly size-dependent and achieving size control under preferably mild synthesis conditions is of interest in order to obtain particles with required properties. By using a custom-made setup, it was possible to synthesize stable single domain magnetite nanoparticles with the co-precipitation method. Furthermore, it was shown that magnetite formation is temperature-dependent, resulting in larger particles at higher temperatures. However, mechanistic approaches about the details are incomplete.
Formation of magnetite from solution was shown to occur from nanoparticulate matter rather than solvated ions. The theoretical framework of such processes has only started to be described, partly due to the lack of kinetic or thermodynamic data. Synthesis of magnetite nanoparticles at different temperatures was performed and the Arrhenius plot was used determine an activation energy for crystal growth of 28.4 kJ mol-1, which led to the conclusion that nanoparticle diffusion is the rate-determining step.
Furthermore, a study of the alteration of magnetite particles of different sizes as a function of their storage conditions is presented. The magnetic properties depend not only on particle size but also depend on the structure of the oxide, because magnetite oxidizes to maghemite under environmental conditions. The dynamics of this process have not been well described. Smaller nanoparticles are shown to oxidize more rapidly than larger ones and the lower the storage temperature, the lower the measured oxidation. In addition, the magnetic properties of the altered particles are not decreased dramatically, thus suggesting that this alteration will not impact the use of such nanoparticles as medical carriers.
Finally, the effect of biological additives on magnetite formation was investigated. Magnetotactic bacteria¬¬ are able to synthesize and align magnetite nanoparticles of well-defined size and morphology due to the involvement of special proteins with specific binding properties. Based on this model of morphology control, phage display experiments were performed to determine peptide sequences that preferably bind to (111)-magnetite faces. The aim was to control the shape of magnetite nanoparticles during the formation. Magnetotactic bacteria are also able to control the intracellular redox potential with proteins called magnetochromes. MamP is such a protein and its oxidizing nature was studied in vitro via biomimetic magnetite formation experiments based on ferrous ions. Magnetite and further trivalent oxides were found.
This work helps understanding basic mechanisms of magnetite formation and gives insight into non-classical crystal growth. In addition, it is shown that alteration of magnetite nanoparticles is mainly based on oxidation to maghemite and does not significantly influence the magnetic properties. Finally, biomimetic experiments help understanding the role of MamP within the bacteria and furthermore, a first step was performed to achieve morphology control in magnetite formation via co-precipitation.
New porous materials based on covalently connected monomers are presented. The key step of the synthesis is an acetalisation reaction. In previous years we used acetalisation reactions extensively to build up various molecular rods. Based on this approach, investigations towards porous polymeric materials were conducted by us. Here we wish to present the results of these studies in the synthesis of 1D polyacetals and porous 3D polyacetals. By scrambling experiments with 1D acetals we could prove that exchange reactions occur between different building blocks (evidenced by MALDI-TOF mass spectrometry). Based on these results we synthesized porous 3D polyacetals under the same mild conditions.
Stress drop is a key factor in earthquake mechanics and engineering seismology. However, stress drop calculations based on fault slip can be significantly biased, particularly due to subjectively determined smoothing conditions in the traditional least-square slip inversion. In this study, we introduce a mechanically constrained Bayesian approach to simultaneously invert for fault slip and stress drop based on geodetic measurements. A Gaussian distribution for stress drop is implemented in the inversion as a prior. We have done several synthetic tests to evaluate the stability and reliability of the inversion approach, considering different fault discretization, fault geometries, utilized datasets, and variability of the slip direction, respectively. We finally apply the approach to the 2010 M8.8 Maule earthquake and invert for the coseismic slip and stress drop simultaneously. Two fault geometries from the literature are tested. Our results indicate that the derived slip models based on both fault geometries are similar, showing major slip north of the hypocenter and relatively weak slip in the south, as indicated in the slip models of other studies. The derived mean stress drop is 5-6 MPa, which is close to the stress drop of similar to 7 MPa that was independently determined according to force balance in this region Luttrell et al. (J Geophys Res, 2011). These findings indicate that stress drop values can be consistently extracted from geodetic data.
In a recent paper, the Lefschetz number for endomorphisms (modulo trace class operators) of sequences of trace class curvature was introduced. We show that this is a well defined, canonical extension of the classical Lefschetz number and establish the homotopy invariance of this number. Moreover, we apply the results to show that the Lefschetz fixed point formula holds for geometric quasiendomorphisms of elliptic quasicomplexes.
Background Transcatheter aortic-valve implantation (TAVI) is an established alternative therapy in patients with severe aortic stenosis and a high surgical risk. Despite a rapid growth in its use, very few data exist about the efficacy of cardiac rehabilitation (CR) in these patients. We assessed the hypothesis that patients after TAVI benefit from CR, compared to patients after surgical aortic-valve replacement (sAVR).
Methods From September 2009 to August 2011, 442 consecutive patients after TAVI (n=76) or sAVR (n=366) were referred to a 3-week CR. Data regarding patient characteristics as well as changes of functional (6-min walk test. 6-MWT), bicycle exercise test), and emotional status (Hospital Anxiety and Depression Scale) were retrospectively evaluated and compared between groups after propensity score adjustment.
Results Patients after TAVI were significantly older (p<0.001), more female (p<0.001), and had more often coronary artery disease (p=0.027), renal failure (p=0.012) and a pacemaker (p=0.032). During CR, distance in 6-MWT (both groups p0.001) and exercise capacity (sAVR p0.001, TAVI p0.05) significantly increased in both groups. Only patients after sAVR demonstrated a significant reduction in anxiety and depression (p0.001). After propensity scores adjustment, changes were not significantly different between sAVR and TAVI, with the exception of 6-MWT (p=0.004).
Conclusions Patients after TAVI benefit from cardiac rehabilitation despite their older age and comorbidities. CR is a helpful tool to maintain independency for daily life activities and participation in socio-cultural life.
Background: Chronic kidney disease (CKD) is a frequent comorbidity among elderly patients and those with cardiovascular disease. CKD carries prognostic relevance. We aimed to describe patient characteristics, risk factor management and control status of patients in cardiac rehabilitation (CR), differentiated by presence or absence of CKD.
Design and methods: Data from 92,071 inpatients with adequate information to calculate glomerular filtration rate (GFR) based on the Cockcroft-Gault formula were analyzed at the beginning and the end of a 3-week CR stay. CKD was defined as estimated GFR <60 ml/min/1.73 m(2).
Results: Compared with non-CKD patients, CKD patients were significantly older (72.0 versus 58.0 years) and more often had diabetes mellitus, arterial hypertension, and atherothrombotic manifestations (previous stroke, peripheral arterial disease), but fewer were current or previous smokers had a CHD family history. Exercise capacity was much lower in CKD (59 vs. 92Watts). Fewer patients with CKD were treated with percutaneous coronary intervention (PCI), but more had coronary artery bypass graft (CABG) surgery. Patients with CKD compared with non-CKD less frequently received statins, acetylsalicylic acid (ASA), clopidogrel, beta blockers, and angiotensin converting enzyme (ACE) inhibitors, and more frequently received angiotensin receptor blockers, insulin and oral anticoagulants. In CKD, mean low density lipoprotein cholesterol (LDL-C), total cholesterol, and high density lipoprotein cholesterol (HDL-C) were slightly higher at baseline, while triglycerides were substantially lower. This lipid pattern did not change at the discharge visit, but overall control rates for all described parameters (with the exception of HDL-C) were improved substantially. At discharge, systolic blood pressure (BP) was higher in CKD (124 versus 121 mmHg) and diastolic BP was lower (72 versus 74 mmHg). At discharge, 68.7% of CKD versus 71.9% of non-CKD patients had LDL-C <100 mg/dl. Physical fitness on exercise testing improved substantially in both groups. When the Modification of Diet in Renal Disease (MDRD) formula was used for CKD classification, there was no clinically relevant change in these results.
Conclusion: Within a short period of 3-4 weeks, CR led to substantial improvements in key risk factors such as lipid profile, blood pressure, and physical fitness for all patients, even if CKD was present.
The International Project for the Evaluation of Educational Achievement (IEA) was formed in the 1950s (Postlethwaite, 1967). Since that time, the IEA has conducted many studies in the area of mathematics, such as the First International Mathematics Study (FIMS) in 1964, the Second International Mathematics Study (SIMS) in 1980-1982, and a series of studies beginning with the Third International Mathematics and Science Study (TIMSS) which has been conducted every 4 years since 1995. According to Stigler et al. (1999), in the FIMS and the SIMS, U.S. students achieved low scores in comparison with students in other countries (p. 1). The TIMSS 1995 “Videotape Classroom Study” was therefore a complement to the earlier studies conducted to learn “more about the instructional and cultural processes that are associated with achievement” (Stigler et al., 1999, p. 1). The TIMSS Videotape Classroom Study is known today as the TIMSS Video Study. From the findings of the TIMSS 1995 Video Study, Stigler and Hiebert (1999) likened teaching to “mountain ranges poking above the surface of the water,” whereby they implied that we might see the mountaintops, but we do not see the hidden parts underneath these mountain ranges (pp. 73-78). By watching the videotaped lessons from Germany, Japan, and the United States again and again, they discovered that “the systems of teaching within each country look similar from lesson to lesson. At least, there are certain recurring features [or patterns] that typify many of the lessons within a country and distinguish the lessons among countries” (pp. 77-78). They also discovered that “teaching is a cultural activity,” so the systems of teaching “must be understood in relation to the cultural beliefs and assumptions that surround them” (pp. 85, 88). From this viewpoint, one of the purposes of this dissertation was to study some cultural aspects of mathematics teaching and relate the results to mathematics teaching and learning in Vietnam. Another research purpose was to carry out a video study in Vietnam to find out the characteristics of Vietnamese mathematics teaching and compare these characteristics with those of other countries. In particular, this dissertation carried out the following research tasks: - Studying the characteristics of teaching and learning in different cultures and relating the results to mathematics teaching and learning in Vietnam - Introducing the TIMSS, the TIMSS Video Study and the advantages of using video study in investigating mathematics teaching and learning - Carrying out the video study in Vietnam to identify the image, scripts and patterns, and the lesson signature of eighth-grade mathematics teaching in Vietnam - Comparing some aspects of mathematics teaching in Vietnam and other countries and identifying the similarities and differences across countries - Studying the demands and challenges of innovating mathematics teaching methods in Vietnam – lessons from the video studies Hopefully, this dissertation will be a useful reference material for pre-service teachers at education universities to understand the nature of teaching and develop their teaching career.