Nowadays modal logic is one of the important areas of logic, but at the beginning of the emergence of modern logic, there was not much attention to this branch of logic, and even the founders of modern logic, including Russell, had an anti-modal position. One of the factors that led Russell to adopt such a position was the belief that logic is truth functional and extensional, and this is something that the introduction of modality destroys.Of course During the long period of his philosophical work, Russell has taken many and varied positions about modal notions. From the beginning, he did not have an anti-modal position. At first, he considered necessity as a description of an implication, and after some time, he introduced it as a primitive, basic and indefinable concept. Then, in some of his works, following Moore, he considered necessity as a kind of logical priority of propositions, but in the end he took an anti-modal position and tried to completely discard the modal notions. He said that these concepts are properties of propositional functions, not properties of propositions. But Russell has used second-order logic for explaining the modal concepts and explaining the difference between possibility and existence (which declares both of them to be properties of propositional functions), but even with this, he is not able to completely remove the modal notions from language and logic.

The meaning of modality has always been concerned with forces that either determine or condition the human action. The forces that are important for the use of modality are primarily of two kinds. Firstly, the free will of human being, secondly, the power of circumstances. According to Lyons the two main concepts of modality are "necessity" and "possibility". These concepts are dependent on the two forces mentioned above. Necessity and possibility may therefore be divided into other concepts such as intention, determination, persistence, compulsion, duty, hope, prediction, assumption. To express all these ideas, language mainly used modal auxiliaries. According to Palmer there are two basic assumptions concerning modality. The first is that modality may be regarded as a grammatical category just as we view aspect, tense, number, gender, etc. The second is that this category can be identified, described, and compared across different languages. This paper, therefore, concentrates on some major English- German modal auxiliaries through which modality may be expressed and compared. The concept of "wish" is excluded here and it will be dealt with in a separate paper.

Purpose of this review paper is to provide an overview on the application of hyperthermia (HT) [the controlled increased of tumor temperature by 8-3oC] combined with conventional cancer treatment modalities. HT is applied with different methods e.g. superficial-HT, locoregional deep-HT, interstitial-HT, intracavity-HT, and whole body-HT. Studies show that addition of HT to radiotherapy, chemotherapy, or both, will result in better tumor response rate, local control, palliative effects and survival rate, without increasing toxicity, in different tumor sites such as breast cancer, melanoma, head and neck, cervix cancer and glioblastoma. In the recent years, due to the substantial technical improvements in achieving selected increase of temperatures in superficial and deep-seated tumors, thermometry, and treatment planning, HT is becoming more accepted clinically worldwide. HT, as an adjunctive cancer treatment modality, is certainly a promising approach, however, it is not well known yet.

Introduction: PET is a technique for measuring the concentrations of positron-emitting radioisotopes within the body by registering the emitted annihilation radiation. At present, the basic process employed in PET is the annihilation of the emitted positron an electron that results in two almost co-linear gamma-photons travelling in opposite directions, each with 511 keV energy. In the conventional PET decay events are just localized in space and counted, but no other characteristics of the annihilation radiation is explored. Recently it has been shown, that extra information could also be obtained in PET by registering the annihilations into three photons. In spite of the relative rareness of positron annihilation into three photons, it may still be exploited to develop a new imaging modality. Although the rate of 3gamma decays is small, the positioning information conveyed by a single event is much larger than in the case of two gamma, so the total information gained from three gamma may be significant.Methods: Three high resolution detectors arranged in a plane forming angels of about 120o with respect to each other to form a primitive 3-gamma scanner. Each detector generates pulse, which passes to a time pickoff units. Timing signals from the pick-off units are passed to a coincidence unit with timing window of t. If pulses overlap, then logic signal is generated and passed as a trigger to simultaneous sampling analogue-todigital converter (ADC).Results and Conclusion: Three gamma imaging would provide information not only about the local concentration of radionuclide, but also, by virtue of chemical interactions of Positronium, the local chemical environment in tissue. In particular, the concentration of free oxygen could be determined, which would be a significant advantage in oncological applications of PET.