Abstract: In a power supply network network of a printed circuit board, a through hole network for power supply electrically connected to main power supply pads connected with power supply cables is electrically and substantially independent of an internal network comprising networks of power supply layers on the like and a through hold network for load. Thereby, each of source currents supplied from the power supply cables reaches the through hole network for each load, once, via the through hold network for power supply and horizontal buses, therefore the dispersion in the drop of voltage across the main power supply pads and each of the loads is effectively decreased.

Abstract: A fire retardent for woody materials, which is an aqueous solution comprising 100 parts by weight as solids content of a water-soluble 3-(dialkylphosphonopropionamide) represented by the following general formula ##STR1## wherein each of R.sub.1 and R.sub.2 represents an alkyl group having 1 to 3 carbon atoms, and R.sub.3 represents a hyrogen atom or a methyl group, and at least 100 parts by weight as solids of a water-soluble melamine resin as essential ingredients and having a pH of not more than 3.

Abstract: In a cooling structure for electronic apparatus in which cards consisting of electronic components mounted on circuit boards are arranged in parallel on a motherboard. A pressure adjustment device with holes is arranged in a cooling air flow passage of each card. The area of the holes is selected in relation to the pressure loss characteristics of the related card based upon average air-flow sectional area.

Abstract: A bi-directional capacitor microphone is formed of first and second transducer sections, each section comprising a diaphragm and a back plate facing the diaphragm and separated therefrom. The diaphragm of the first transducer section includes an electret and the back plate of the second transducer section includes another electret. The back plates of the first and second transducer sections are disposed in a back-to-back configuration and are electrically coupled to each other and to one output. The diaphragms of the first and second transducer sections are connected to each other and to another output, so that an output signal appears between the outputs. Preferably, both electrets are selected to have a negative polarity. The bi-directional microphone so constructed exhibits superior response for lower audio frequencies.